epoll: use epoll_pwait2() if available

[libevent] / buffer.c

/*
 * Copyright (c) 2002-2007 Niels Provos <provos@citi.umich.edu>
 * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "event2/event-config.h"
#include "evconfig-private.h"

#ifdef _WIN32
#include <winsock2.h>
#include <windows.h>
#include <io.h>
#endif

#include <sys/types.h>

#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#ifdef EVENT__HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif

#ifdef EVENT__HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif

#ifdef EVENT__HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif

#ifdef EVENT__HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif

#ifdef EVENT__HAVE_SYS_SENDFILE_H
#include <sys/sendfile.h>
#endif
#ifdef EVENT__HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif


#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef EVENT__HAVE_STDARG_H
#include <stdarg.h>
#endif
#ifdef EVENT__HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <limits.h>

#include "event2/event.h"
#include "event2/buffer.h"
#include "event2/buffer_compat.h"
#include "event2/bufferevent.h"
#include "event2/bufferevent_compat.h"
#include "event2/bufferevent_struct.h"
#include "event2/thread.h"
#include "log-internal.h"
#include "mm-internal.h"
#include "util-internal.h"
#include "evthread-internal.h"
#include "evbuffer-internal.h"
#include "bufferevent-internal.h"
#include "event-internal.h"

/* some systems do not have MAP_FAILED */
#ifndef MAP_FAILED
#define MAP_FAILED      ((void *)-1)
#endif

/* send file support */
#if defined(EVENT__HAVE_SYS_SENDFILE_H) && defined(EVENT__HAVE_SENDFILE) && defined(__linux__)
#define USE_SENDFILE            1
#define SENDFILE_IS_LINUX       1
#elif defined(EVENT__HAVE_SENDFILE) && defined(__FreeBSD__)
#define USE_SENDFILE            1
#define SENDFILE_IS_FREEBSD     1
#elif defined(EVENT__HAVE_SENDFILE) && defined(__APPLE__)
#define USE_SENDFILE            1
#define SENDFILE_IS_MACOSX      1
#elif defined(EVENT__HAVE_SENDFILE) && defined(__sun__) && defined(__svr4__)
#define USE_SENDFILE            1
#define SENDFILE_IS_SOLARIS     1
#endif

/* Mask of user-selectable callback flags. */
#define EVBUFFER_CB_USER_FLAGS      0xffff
/* Mask of all internal-use-only flags. */
#define EVBUFFER_CB_INTERNAL_FLAGS  0xffff0000

/* Flag set if the callback is using the cb_obsolete function pointer  */
#define EVBUFFER_CB_OBSOLETE           0x00040000

/* evbuffer_chain support */
#define CHAIN_SPACE_PTR(ch) ((ch)->buffer + (ch)->misalign + (ch)->off)
#define CHAIN_SPACE_LEN(ch) ((ch)->flags & EVBUFFER_IMMUTABLE ? \
            0 : (ch)->buffer_len - ((ch)->misalign + (ch)->off))

#define CHAIN_PINNED(ch)  (((ch)->flags & EVBUFFER_MEM_PINNED_ANY) != 0)
#define CHAIN_PINNED_R(ch)  (((ch)->flags & EVBUFFER_MEM_PINNED_R) != 0)

/* evbuffer_ptr support */
#define PTR_NOT_FOUND(ptr) do {                 \
        (ptr)->pos = -1;                                        \
        (ptr)->internal_.chain = NULL;          \
        (ptr)->internal_.pos_in_chain = 0;      \
} while (0)

#define EVBUFFER_MAX_READ_DEFAULT       4096

static void evbuffer_chain_align(struct evbuffer_chain *chain);
static int evbuffer_chain_should_realign(struct evbuffer_chain *chain,
    size_t datalen);
static void evbuffer_deferred_callback(struct event_callback *cb, void *arg);
static int evbuffer_ptr_memcmp(const struct evbuffer *buf,
    const struct evbuffer_ptr *pos, const char *mem, size_t len);
static struct evbuffer_chain *evbuffer_expand_singlechain(struct evbuffer *buf,
    size_t datlen);
static int evbuffer_ptr_subtract(struct evbuffer *buf, struct evbuffer_ptr *pos,
    size_t howfar);
static int evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg);
static inline void evbuffer_chain_incref(struct evbuffer_chain *chain);

static struct evbuffer_chain *
evbuffer_chain_new(size_t size)
{
        struct evbuffer_chain *chain;
        size_t to_alloc;

        if (size > EVBUFFER_CHAIN_MAX - EVBUFFER_CHAIN_SIZE)
                return (NULL);

        to_alloc = size + EVBUFFER_CHAIN_SIZE;

        /* we get everything in one chunk */
        if ((chain = mm_malloc(to_alloc)) == NULL)
                return (NULL);

        memset(chain, 0, EVBUFFER_CHAIN_SIZE);

        chain->buffer_len = to_alloc - EVBUFFER_CHAIN_SIZE;

        /* this way we can manipulate the buffer to different addresses,
         * which is required for mmap for example.
         */
        chain->buffer = EVBUFFER_CHAIN_EXTRA(unsigned char, chain);

        chain->refcnt = 1;

        return (chain);
}

static struct evbuffer_chain *
evbuffer_chain_new_membuf(size_t size)
{
        size_t to_alloc;

        if (size > EVBUFFER_CHAIN_MAX - EVBUFFER_CHAIN_SIZE)
                return (NULL);

        size += EVBUFFER_CHAIN_SIZE;

        /* get the next largest memory that can hold the buffer */
        if (size < EVBUFFER_CHAIN_MAX / 2) {
                to_alloc = MIN_BUFFER_SIZE;
                while (to_alloc < size) {
                        to_alloc <<= 1;
                }
        } else {
                to_alloc = size;
        }

        return evbuffer_chain_new(to_alloc - EVBUFFER_CHAIN_SIZE);
}

static inline void
evbuffer_chain_free(struct evbuffer_chain *chain)
{
        EVUTIL_ASSERT(chain->refcnt > 0);
        if (--chain->refcnt > 0) {
                /* chain is still referenced by other chains */
                return;
        }

        if (CHAIN_PINNED(chain)) {
                /* will get freed once no longer dangling */
                chain->refcnt++;
                chain->flags |= EVBUFFER_DANGLING;
                return;
        }

        /* safe to release chain, it's either a referencing
         * chain or all references to it have been freed */
        if (chain->flags & EVBUFFER_REFERENCE) {
                struct evbuffer_chain_reference *info =
                    EVBUFFER_CHAIN_EXTRA(
                            struct evbuffer_chain_reference,
                            chain);
                if (info->cleanupfn)
                        (*info->cleanupfn)(chain->buffer,
                            chain->buffer_len,
                            info->extra);
        }
        if (chain->flags & EVBUFFER_FILESEGMENT) {
                struct evbuffer_chain_file_segment *info =
                    EVBUFFER_CHAIN_EXTRA(
                            struct evbuffer_chain_file_segment,
                            chain);
                if (info->segment) {
#ifdef _WIN32
                        if (info->segment->is_mapping)
                                UnmapViewOfFile(chain->buffer);
#endif
                        evbuffer_file_segment_free(info->segment);
                }
        }
        if (chain->flags & EVBUFFER_MULTICAST) {
                struct evbuffer_multicast_parent *info =
                    EVBUFFER_CHAIN_EXTRA(
                            struct evbuffer_multicast_parent,
                            chain);
                /* referencing chain is being freed, decrease
                 * refcounts of source chain and associated
                 * evbuffer (which get freed once both reach
                 * zero) */
                EVUTIL_ASSERT(info->source != NULL);
                EVUTIL_ASSERT(info->parent != NULL);
                EVBUFFER_LOCK(info->source);
                evbuffer_chain_free(info->parent);
                evbuffer_decref_and_unlock_(info->source);
        }

        mm_free(chain);
}

static void
evbuffer_free_all_chains(struct evbuffer_chain *chain)
{
        struct evbuffer_chain *next;
        for (; chain; chain = next) {
                next = chain->next;
                evbuffer_chain_free(chain);
        }
}

#ifndef NDEBUG
static int
evbuffer_chains_all_empty(struct evbuffer_chain *chain)
{
        for (; chain; chain = chain->next) {
                if (chain->off)
                        return 0;
        }
        return 1;
}
#else
/* The definition is needed for EVUTIL_ASSERT, which uses sizeof to avoid
"unused variable" warnings. */
static inline int evbuffer_chains_all_empty(struct evbuffer_chain *chain) {
        return 1;
}
#endif

/* Free all trailing chains in 'buf' that are neither pinned nor empty, prior
 * to replacing them all with a new chain.  Return a pointer to the place
 * where the new chain will go.
 *
 * Internal; requires lock.  The caller must fix up buf->last and buf->first
 * as needed; they might have been freed.
 */
static struct evbuffer_chain **
evbuffer_free_trailing_empty_chains(struct evbuffer *buf)
{
        struct evbuffer_chain **ch = buf->last_with_datap;
        /* Find the first victim chain.  It might be *last_with_datap */
        while ((*ch) && ((*ch)->off != 0 || CHAIN_PINNED(*ch)))
                ch = &(*ch)->next;
        if (*ch) {
                EVUTIL_ASSERT(evbuffer_chains_all_empty(*ch));
                evbuffer_free_all_chains(*ch);
                *ch = NULL;
        }
        return ch;
}

/* Add a single chain 'chain' to the end of 'buf', freeing trailing empty
 * chains as necessary.  Requires lock.  Does not schedule callbacks.
 */
static void
evbuffer_chain_insert(struct evbuffer *buf,
    struct evbuffer_chain *chain)
{
        ASSERT_EVBUFFER_LOCKED(buf);
        if (*buf->last_with_datap == NULL) {
                /* There are no chains data on the buffer at all. */
                EVUTIL_ASSERT(buf->last_with_datap == &buf->first);
                EVUTIL_ASSERT(buf->first == NULL);
                buf->first = buf->last = chain;
        } else {
                struct evbuffer_chain **chp;
                chp = evbuffer_free_trailing_empty_chains(buf);
                *chp = chain;
                if (chain->off)
                        buf->last_with_datap = chp;
                buf->last = chain;
        }
        buf->total_len += chain->off;
}

static inline struct evbuffer_chain *
evbuffer_chain_insert_new(struct evbuffer *buf, size_t datlen)
{
        struct evbuffer_chain *chain;
        if ((chain = evbuffer_chain_new_membuf(datlen)) == NULL)
                return NULL;
        evbuffer_chain_insert(buf, chain);
        return chain;
}

void
evbuffer_chain_pin_(struct evbuffer_chain *chain, unsigned flag)
{
        EVUTIL_ASSERT((chain->flags & flag) == 0);
        chain->flags |= flag;
}

void
evbuffer_chain_unpin_(struct evbuffer_chain *chain, unsigned flag)
{
        EVUTIL_ASSERT((chain->flags & flag) != 0);
        chain->flags &= ~flag;
        if (chain->flags & EVBUFFER_DANGLING)
                evbuffer_chain_free(chain);
}

static inline void
evbuffer_chain_incref(struct evbuffer_chain *chain)
{
    ++chain->refcnt;
}

struct evbuffer *
evbuffer_new(void)
{
        struct evbuffer *buffer;

        buffer = mm_calloc(1, sizeof(struct evbuffer));
        if (buffer == NULL)
                return (NULL);

        LIST_INIT(&buffer->callbacks);
        buffer->refcnt = 1;
        buffer->last_with_datap = &buffer->first;
        buffer->max_read = EVBUFFER_MAX_READ_DEFAULT;

        return (buffer);
}

int
evbuffer_set_flags(struct evbuffer *buf, ev_uint64_t flags)
{
        EVBUFFER_LOCK(buf);
        buf->flags |= (ev_uint32_t)flags;
        EVBUFFER_UNLOCK(buf);
        return 0;
}

int
evbuffer_clear_flags(struct evbuffer *buf, ev_uint64_t flags)
{
        EVBUFFER_LOCK(buf);
        buf->flags &= ~(ev_uint32_t)flags;
        EVBUFFER_UNLOCK(buf);
        return 0;
}

void
evbuffer_incref_(struct evbuffer *buf)
{
        EVBUFFER_LOCK(buf);
        ++buf->refcnt;
        EVBUFFER_UNLOCK(buf);
}

void
evbuffer_incref_and_lock_(struct evbuffer *buf)
{
        EVBUFFER_LOCK(buf);
        ++buf->refcnt;
}

int
evbuffer_defer_callbacks(struct evbuffer *buffer, struct event_base *base)
{
        EVBUFFER_LOCK(buffer);
        buffer->cb_queue = base;
        buffer->deferred_cbs = 1;
        event_deferred_cb_init_(&buffer->deferred,
            event_base_get_npriorities(base) / 2,
            evbuffer_deferred_callback, buffer);
        EVBUFFER_UNLOCK(buffer);
        return 0;
}

int
evbuffer_enable_locking(struct evbuffer *buf, void *lock)
{
#ifdef EVENT__DISABLE_THREAD_SUPPORT
        return -1;
#else
        if (buf->lock)
                return -1;

        if (!lock) {
                EVTHREAD_ALLOC_LOCK(lock, EVTHREAD_LOCKTYPE_RECURSIVE);
                if (!lock)
                        return -1;
                buf->lock = lock;
                buf->own_lock = 1;
        } else {
                buf->lock = lock;
                buf->own_lock = 0;
        }

        return 0;
#endif
}

void
evbuffer_set_parent_(struct evbuffer *buf, struct bufferevent *bev)
{
        EVBUFFER_LOCK(buf);
        buf->parent = bev;
        EVBUFFER_UNLOCK(buf);
}

static void
evbuffer_run_callbacks(struct evbuffer *buffer, int running_deferred)
{
        struct evbuffer_cb_entry *cbent, *next;
        struct evbuffer_cb_info info;
        size_t new_size;
        ev_uint32_t mask, masked_val;
        int clear = 1;

        if (running_deferred) {
                mask = EVBUFFER_CB_NODEFER|EVBUFFER_CB_ENABLED;
                masked_val = EVBUFFER_CB_ENABLED;
        } else if (buffer->deferred_cbs) {
                mask = EVBUFFER_CB_NODEFER|EVBUFFER_CB_ENABLED;
                masked_val = EVBUFFER_CB_NODEFER|EVBUFFER_CB_ENABLED;
                /* Don't zero-out n_add/n_del, since the deferred callbacks
                   will want to see them. */
                clear = 0;
        } else {
                mask = EVBUFFER_CB_ENABLED;
                masked_val = EVBUFFER_CB_ENABLED;
        }

        ASSERT_EVBUFFER_LOCKED(buffer);

        if (LIST_EMPTY(&buffer->callbacks)) {
                buffer->n_add_for_cb = buffer->n_del_for_cb = 0;
                return;
        }
        if (buffer->n_add_for_cb == 0 && buffer->n_del_for_cb == 0)
                return;

        new_size = buffer->total_len;
        info.orig_size = new_size + buffer->n_del_for_cb - buffer->n_add_for_cb;
        info.n_added = buffer->n_add_for_cb;
        info.n_deleted = buffer->n_del_for_cb;
        if (clear) {
                buffer->n_add_for_cb = 0;
                buffer->n_del_for_cb = 0;
        }
        for (cbent = LIST_FIRST(&buffer->callbacks);
             cbent != LIST_END(&buffer->callbacks);
             cbent = next) {
                /* Get the 'next' pointer now in case this callback decides
                 * to remove itself or something. */
                next = LIST_NEXT(cbent, next);

                if ((cbent->flags & mask) != masked_val)
                        continue;

                if ((cbent->flags & EVBUFFER_CB_OBSOLETE))
                        cbent->cb.cb_obsolete(buffer,
                            info.orig_size, new_size, cbent->cbarg);
                else
                        cbent->cb.cb_func(buffer, &info, cbent->cbarg);
        }
}

void
evbuffer_invoke_callbacks_(struct evbuffer *buffer)
{
        if (LIST_EMPTY(&buffer->callbacks)) {
                buffer->n_add_for_cb = buffer->n_del_for_cb = 0;
                return;
        }

        if (buffer->deferred_cbs) {
                if (event_deferred_cb_schedule_(buffer->cb_queue, &buffer->deferred)) {
                        evbuffer_incref_and_lock_(buffer);
                        if (buffer->parent)
                                bufferevent_incref_(buffer->parent);
                        EVBUFFER_UNLOCK(buffer);
                }
        }

        evbuffer_run_callbacks(buffer, 0);
}

static void
evbuffer_deferred_callback(struct event_callback *cb, void *arg)
{
        struct bufferevent *parent = NULL;
        struct evbuffer *buffer = arg;

        /* XXXX It would be better to run these callbacks without holding the
         * lock */
        EVBUFFER_LOCK(buffer);
        parent = buffer->parent;
        evbuffer_run_callbacks(buffer, 1);
        evbuffer_decref_and_unlock_(buffer);
        if (parent)
                bufferevent_decref_(parent);
}

static void
evbuffer_remove_all_callbacks(struct evbuffer *buffer)
{
        struct evbuffer_cb_entry *cbent;

        while ((cbent = LIST_FIRST(&buffer->callbacks))) {
                LIST_REMOVE(cbent, next);
                mm_free(cbent);
        }
}

void
evbuffer_decref_and_unlock_(struct evbuffer *buffer)
{
        struct evbuffer_chain *chain, *next;
        ASSERT_EVBUFFER_LOCKED(buffer);

        EVUTIL_ASSERT(buffer->refcnt > 0);

        if (--buffer->refcnt > 0) {
                EVBUFFER_UNLOCK(buffer);
                return;
        }

        for (chain = buffer->first; chain != NULL; chain = next) {
                next = chain->next;
                evbuffer_chain_free(chain);
        }
        evbuffer_remove_all_callbacks(buffer);
        if (buffer->deferred_cbs)
                event_deferred_cb_cancel_(buffer->cb_queue, &buffer->deferred);

        EVBUFFER_UNLOCK(buffer);
        if (buffer->own_lock)
                EVTHREAD_FREE_LOCK(buffer->lock, EVTHREAD_LOCKTYPE_RECURSIVE);
        mm_free(buffer);
}

void
evbuffer_free(struct evbuffer *buffer)
{
        EVBUFFER_LOCK(buffer);
        evbuffer_decref_and_unlock_(buffer);
}

int evbuffer_set_max_read(struct evbuffer *buf, size_t max)
{
        if (max > INT_MAX) {
                return -1;
        }

        EVBUFFER_LOCK(buf);
        buf->max_read = max;
        EVBUFFER_UNLOCK(buf);
        return 0;
}
size_t evbuffer_get_max_read(struct evbuffer *buf)
{
        size_t result;
        EVBUFFER_LOCK(buf);
        result = buf->max_read;
        EVBUFFER_UNLOCK(buf);
        return result;
}

void
evbuffer_lock(struct evbuffer *buf)
{
        EVBUFFER_LOCK(buf);
}

void
evbuffer_unlock(struct evbuffer *buf)
{
        EVBUFFER_UNLOCK(buf);
}

size_t
evbuffer_get_length(const struct evbuffer *buffer)
{
        size_t result;
        EVBUFFER_LOCK(buffer);
        result = buffer->total_len;
        EVBUFFER_UNLOCK(buffer);
        return result;
}

size_t
evbuffer_get_contiguous_space(const struct evbuffer *buf)
{
        struct evbuffer_chain *chain;
        size_t result;

        EVBUFFER_LOCK(buf);
        chain = buf->first;
        result = (chain != NULL ? chain->off : 0);
        EVBUFFER_UNLOCK(buf);

        return result;
}

size_t
evbuffer_add_iovec(struct evbuffer * buf, struct evbuffer_iovec * vec, int n_vec) {
        int n;
        size_t res;
        size_t to_alloc;

        EVBUFFER_LOCK(buf);

        res = to_alloc = 0;

        for (n = 0; n < n_vec; n++) {
                to_alloc += vec[n].iov_len;
        }

        if (evbuffer_expand_fast_(buf, to_alloc, 2) < 0) {
                goto done;
        }

        for (n = 0; n < n_vec; n++) {
                /* XXX each 'add' call here does a bunch of setup that's
                 * obviated by evbuffer_expand_fast_, and some cleanup that we
                 * would like to do only once.  Instead we should just extract
                 * the part of the code that's needed. */

                if (evbuffer_add(buf, vec[n].iov_base, vec[n].iov_len) < 0) {
                        goto done;
                }

                res += vec[n].iov_len;
        }

done:
    EVBUFFER_UNLOCK(buf);
    return res;
}

int
evbuffer_reserve_space(struct evbuffer *buf, ev_ssize_t size,
    struct evbuffer_iovec *vec, int n_vecs)
{
        struct evbuffer_chain *chain, **chainp;
        int n = -1;

        EVBUFFER_LOCK(buf);
        if (buf->freeze_end)
                goto done;
        if (n_vecs < 1)
                goto done;
        if (n_vecs == 1) {
                if ((chain = evbuffer_expand_singlechain(buf, size)) == NULL)
                        goto done;

                vec[0].iov_base = (void *)CHAIN_SPACE_PTR(chain);
                vec[0].iov_len = (size_t)CHAIN_SPACE_LEN(chain);
                EVUTIL_ASSERT(size<0 || (size_t)vec[0].iov_len >= (size_t)size);
                n = 1;
        } else {
                if (evbuffer_expand_fast_(buf, size, n_vecs)<0)
                        goto done;
                n = evbuffer_read_setup_vecs_(buf, size, vec, n_vecs,
                                &chainp, 0);
        }

done:
        EVBUFFER_UNLOCK(buf);
        return n;

}

static int
advance_last_with_data(struct evbuffer *buf)
{
        int n = 0;
        struct evbuffer_chain **chainp = buf->last_with_datap;

        ASSERT_EVBUFFER_LOCKED(buf);

        if (!*chainp)
                return 0;

        while ((*chainp)->next) {
                chainp = &(*chainp)->next;
                if ((*chainp)->off)
                        buf->last_with_datap = chainp;
                ++n;
        }
        return n;
}

int
evbuffer_commit_space(struct evbuffer *buf,
    struct evbuffer_iovec *vec, int n_vecs)
{
        struct evbuffer_chain *chain, **firstchainp, **chainp;
        int result = -1;
        size_t added = 0;
        int i;

        EVBUFFER_LOCK(buf);

        if (buf->freeze_end)
                goto done;
        if (n_vecs == 0) {
                result = 0;
                goto done;
        } else if (n_vecs == 1 &&
            (buf->last && vec[0].iov_base == (void *)CHAIN_SPACE_PTR(buf->last))) {
                /* The user only got or used one chain; it might not
                 * be the first one with space in it. */
                if ((size_t)vec[0].iov_len > (size_t)CHAIN_SPACE_LEN(buf->last))
                        goto done;
                buf->last->off += vec[0].iov_len;
                added = vec[0].iov_len;
                if (added)
                        advance_last_with_data(buf);
                goto okay;
        }

        /* Advance 'firstchain' to the first chain with space in it. */
        firstchainp = buf->last_with_datap;
        if (!*firstchainp)
                goto done;
        if (CHAIN_SPACE_LEN(*firstchainp) == 0) {
                firstchainp = &(*firstchainp)->next;
        }

        chain = *firstchainp;
        /* pass 1: make sure that the pointers and lengths of vecs[] are in
         * bounds before we try to commit anything. */
        for (i=0; i<n_vecs; ++i) {
                if (!chain)
                        goto done;
                if (vec[i].iov_base != (void *)CHAIN_SPACE_PTR(chain) ||
                    (size_t)vec[i].iov_len > CHAIN_SPACE_LEN(chain))
                        goto done;
                chain = chain->next;
        }
        /* pass 2: actually adjust all the chains. */
        chainp = firstchainp;
        for (i=0; i<n_vecs; ++i) {
                (*chainp)->off += vec[i].iov_len;
                added += vec[i].iov_len;
                if (vec[i].iov_len) {
                        buf->last_with_datap = chainp;
                }
                chainp = &(*chainp)->next;
        }

okay:
        buf->total_len += added;
        buf->n_add_for_cb += added;
        result = 0;
        evbuffer_invoke_callbacks_(buf);

done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

static inline int
HAS_PINNED_R(struct evbuffer *buf)
{
        return (buf->last && CHAIN_PINNED_R(buf->last));
}

static inline void
ZERO_CHAIN(struct evbuffer *dst)
{
        ASSERT_EVBUFFER_LOCKED(dst);
        dst->first = NULL;
        dst->last = NULL;
        dst->last_with_datap = &(dst)->first;
        dst->total_len = 0;
}

/* Prepares the contents of src to be moved to another buffer by removing
 * read-pinned chains. The first pinned chain is saved in first, and the
 * last in last. If src has no read-pinned chains, first and last are set
 * to NULL. */
static int
PRESERVE_PINNED(struct evbuffer *src, struct evbuffer_chain **first,
                struct evbuffer_chain **last)
{
        struct evbuffer_chain *chain, **pinned;

        ASSERT_EVBUFFER_LOCKED(src);

        if (!HAS_PINNED_R(src)) {
                *first = *last = NULL;
                return 0;
        }

        pinned = src->last_with_datap;
        if (!CHAIN_PINNED_R(*pinned))
                pinned = &(*pinned)->next;
        EVUTIL_ASSERT(CHAIN_PINNED_R(*pinned));
        chain = *first = *pinned;
        *last = src->last;

        /* If there's data in the first pinned chain, we need to allocate
         * a new chain and copy the data over. */
        if (chain->off) {
                struct evbuffer_chain *tmp;

                EVUTIL_ASSERT(pinned == src->last_with_datap);
                tmp = evbuffer_chain_new_membuf(chain->off);
                if (!tmp)
                        return -1;
                memcpy(tmp->buffer, chain->buffer + chain->misalign,
                        chain->off);
                tmp->off = chain->off;
                *src->last_with_datap = tmp;
                src->last = tmp;
                chain->misalign += chain->off;
                chain->off = 0;
        } else {
                src->last = *src->last_with_datap;
                *pinned = NULL;
        }

        return 0;
}

static inline void
RESTORE_PINNED(struct evbuffer *src, struct evbuffer_chain *pinned,
                struct evbuffer_chain *last)
{
        ASSERT_EVBUFFER_LOCKED(src);

        if (!pinned) {
                ZERO_CHAIN(src);
                return;
        }

        src->first = pinned;
        src->last = last;
        src->last_with_datap = &src->first;
        src->total_len = 0;
}

static inline void
COPY_CHAIN(struct evbuffer *dst, struct evbuffer *src)
{
        ASSERT_EVBUFFER_LOCKED(dst);
        ASSERT_EVBUFFER_LOCKED(src);
        dst->first = src->first;
        if (src->last_with_datap == &src->first)
                dst->last_with_datap = &dst->first;
        else
                dst->last_with_datap = src->last_with_datap;
        dst->last = src->last;
        dst->total_len = src->total_len;
}

static void
APPEND_CHAIN(struct evbuffer *dst, struct evbuffer *src)
{
        struct evbuffer_chain **chp;

        ASSERT_EVBUFFER_LOCKED(dst);
        ASSERT_EVBUFFER_LOCKED(src);

        chp = evbuffer_free_trailing_empty_chains(dst);
        *chp = src->first;

        if (src->last_with_datap == &src->first)
                dst->last_with_datap = chp;
        else
                dst->last_with_datap = src->last_with_datap;
        dst->last = src->last;
        dst->total_len += src->total_len;
}

static inline void
APPEND_CHAIN_MULTICAST(struct evbuffer *dst, struct evbuffer *src)
{
        struct evbuffer_chain *tmp;
        struct evbuffer_chain *chain = src->first;
        struct evbuffer_multicast_parent *extra;

        ASSERT_EVBUFFER_LOCKED(dst);
        ASSERT_EVBUFFER_LOCKED(src);

        for (; chain; chain = chain->next) {
                if (!chain->off || chain->flags & EVBUFFER_DANGLING) {
                        /* skip empty chains */
                        continue;
                }

                tmp = evbuffer_chain_new(sizeof(struct evbuffer_multicast_parent));
                if (!tmp) {
                        event_warn("%s: out of memory", __func__);
                        return;
                }
                extra = EVBUFFER_CHAIN_EXTRA(struct evbuffer_multicast_parent, tmp);
                /* reference evbuffer containing source chain so it
                 * doesn't get released while the chain is still
                 * being referenced to */
                evbuffer_incref_(src);
                extra->source = src;
                /* reference source chain which now becomes immutable */
                evbuffer_chain_incref(chain);
                extra->parent = chain;
                chain->flags |= EVBUFFER_IMMUTABLE;
                tmp->buffer_len = chain->buffer_len;
                tmp->misalign = chain->misalign;
                tmp->off = chain->off;
                tmp->flags |= EVBUFFER_MULTICAST|EVBUFFER_IMMUTABLE;
                tmp->buffer = chain->buffer;
                evbuffer_chain_insert(dst, tmp);
        }
}

static void
PREPEND_CHAIN(struct evbuffer *dst, struct evbuffer *src)
{
        ASSERT_EVBUFFER_LOCKED(dst);
        ASSERT_EVBUFFER_LOCKED(src);
        src->last->next = dst->first;
        dst->first = src->first;
        dst->total_len += src->total_len;
        if (*dst->last_with_datap == NULL) {
                if (src->last_with_datap == &(src)->first)
                        dst->last_with_datap = &dst->first;
                else
                        dst->last_with_datap = src->last_with_datap;
        } else if (dst->last_with_datap == &dst->first) {
                dst->last_with_datap = &src->last->next;
        }
}

int
evbuffer_add_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
        struct evbuffer_chain *pinned, *last;
        size_t in_total_len, out_total_len;
        int result = 0;

        EVBUFFER_LOCK2(inbuf, outbuf);
        in_total_len = inbuf->total_len;
        out_total_len = outbuf->total_len;

        if (in_total_len == 0 || outbuf == inbuf)
                goto done;

        if (outbuf->freeze_end || inbuf->freeze_start) {
                result = -1;
                goto done;
        }

        if (PRESERVE_PINNED(inbuf, &pinned, &last) < 0) {
                result = -1;
                goto done;
        }

        if (out_total_len == 0) {
                /* There might be an empty chain at the start of outbuf; free
                 * it. */
                evbuffer_free_all_chains(outbuf->first);
                COPY_CHAIN(outbuf, inbuf);
        } else {
                APPEND_CHAIN(outbuf, inbuf);
        }

        RESTORE_PINNED(inbuf, pinned, last);

        inbuf->n_del_for_cb += in_total_len;
        outbuf->n_add_for_cb += in_total_len;

        evbuffer_invoke_callbacks_(inbuf);
        evbuffer_invoke_callbacks_(outbuf);

done:
        EVBUFFER_UNLOCK2(inbuf, outbuf);
        return result;
}

int
evbuffer_add_buffer_reference(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
        size_t in_total_len, out_total_len;
        struct evbuffer_chain *chain;
        int result = 0;

        EVBUFFER_LOCK2(inbuf, outbuf);
        in_total_len = inbuf->total_len;
        out_total_len = outbuf->total_len;
        chain = inbuf->first;

        if (in_total_len == 0)
                goto done;

        if (outbuf->freeze_end || outbuf == inbuf) {
                result = -1;
                goto done;
        }

        for (; chain; chain = chain->next) {
                if ((chain->flags & (EVBUFFER_FILESEGMENT|EVBUFFER_SENDFILE|EVBUFFER_MULTICAST)) != 0) {
                        /* chain type can not be referenced */
                        result = -1;
                        goto done;
                }
        }

        if (out_total_len == 0) {
                /* There might be an empty chain at the start of outbuf; free
                 * it. */
                evbuffer_free_all_chains(outbuf->first);
        }
        APPEND_CHAIN_MULTICAST(outbuf, inbuf);

        outbuf->n_add_for_cb += in_total_len;
        evbuffer_invoke_callbacks_(outbuf);

done:
        EVBUFFER_UNLOCK2(inbuf, outbuf);
        return result;
}

int
evbuffer_prepend_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
        struct evbuffer_chain *pinned, *last;
        size_t in_total_len, out_total_len;
        int result = 0;

        EVBUFFER_LOCK2(inbuf, outbuf);

        in_total_len = inbuf->total_len;
        out_total_len = outbuf->total_len;

        if (!in_total_len || inbuf == outbuf)
                goto done;

        if (outbuf->freeze_start || inbuf->freeze_start) {
                result = -1;
                goto done;
        }

        if (PRESERVE_PINNED(inbuf, &pinned, &last) < 0) {
                result = -1;
                goto done;
        }

        if (out_total_len == 0) {
                /* There might be an empty chain at the start of outbuf; free
                 * it. */
                evbuffer_free_all_chains(outbuf->first);
                COPY_CHAIN(outbuf, inbuf);
        } else {
                PREPEND_CHAIN(outbuf, inbuf);
        }

        RESTORE_PINNED(inbuf, pinned, last);

        inbuf->n_del_for_cb += in_total_len;
        outbuf->n_add_for_cb += in_total_len;

        evbuffer_invoke_callbacks_(inbuf);
        evbuffer_invoke_callbacks_(outbuf);
done:
        EVBUFFER_UNLOCK2(inbuf, outbuf);
        return result;
}

int
evbuffer_drain(struct evbuffer *buf, size_t len)
{
        struct evbuffer_chain *chain, *next;
        size_t remaining, old_len;
        int result = 0;

        EVBUFFER_LOCK(buf);
        old_len = buf->total_len;

        if (old_len == 0)
                goto done;

        if (buf->freeze_start) {
                result = -1;
                goto done;
        }

        if (len >= old_len && !HAS_PINNED_R(buf)) {
                len = old_len;
                for (chain = buf->first; chain != NULL; chain = next) {
                        next = chain->next;
                        evbuffer_chain_free(chain);
                }

                ZERO_CHAIN(buf);
        } else {
                if (len >= old_len)
                        len = old_len;

                buf->total_len -= len;
                remaining = len;
                for (chain = buf->first;
                     remaining >= chain->off;
                     chain = next) {
                        next = chain->next;
                        remaining -= chain->off;

                        if (chain == *buf->last_with_datap) {
                                buf->last_with_datap = &buf->first;
                        }
                        if (&chain->next == buf->last_with_datap)
                                buf->last_with_datap = &buf->first;

                        if (CHAIN_PINNED_R(chain)) {
                                EVUTIL_ASSERT(remaining == 0);
                                chain->misalign += chain->off;
                                chain->off = 0;
                                break;
                        } else
                                evbuffer_chain_free(chain);
                }

                buf->first = chain;
                EVUTIL_ASSERT(remaining <= chain->off);
                chain->misalign += remaining;
                chain->off -= remaining;
        }

        buf->n_del_for_cb += len;
        /* Tell someone about changes in this buffer */
        evbuffer_invoke_callbacks_(buf);

done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

/* Reads data from an event buffer and drains the bytes read */
int
evbuffer_remove(struct evbuffer *buf, void *data_out, size_t datlen)
{
        ev_ssize_t n;
        EVBUFFER_LOCK(buf);
        n = evbuffer_copyout_from(buf, NULL, data_out, datlen);
        if (n > 0) {
                if (evbuffer_drain(buf, n)<0)
                        n = -1;
        }
        EVBUFFER_UNLOCK(buf);
        return (int)n;
}

ev_ssize_t
evbuffer_copyout(struct evbuffer *buf, void *data_out, size_t datlen)
{
        return evbuffer_copyout_from(buf, NULL, data_out, datlen);
}

ev_ssize_t
evbuffer_copyout_from(struct evbuffer *buf, const struct evbuffer_ptr *pos,
    void *data_out, size_t datlen)
{
        /*XXX fails badly on sendfile case. */
        struct evbuffer_chain *chain;
        char *data = data_out;
        size_t nread;
        ev_ssize_t result = 0;
        size_t pos_in_chain;

        EVBUFFER_LOCK(buf);

        if (pos) {
                if (datlen > (size_t)(EV_SSIZE_MAX - pos->pos)) {
                        result = -1;
                        goto done;
                }
                chain = pos->internal_.chain;
                pos_in_chain = pos->internal_.pos_in_chain;
                if (datlen + pos->pos > buf->total_len)
                        datlen = buf->total_len - pos->pos;
        } else {
                chain = buf->first;
                pos_in_chain = 0;
                if (datlen > buf->total_len)
                        datlen = buf->total_len;
        }


        if (datlen == 0)
                goto done;

        if (buf->freeze_start) {
                result = -1;
                goto done;
        }

        nread = datlen;

        while (datlen && datlen >= chain->off - pos_in_chain) {
                size_t copylen = chain->off - pos_in_chain;
                memcpy(data,
                    chain->buffer + chain->misalign + pos_in_chain,
                    copylen);
                data += copylen;
                datlen -= copylen;

                chain = chain->next;
                pos_in_chain = 0;
                EVUTIL_ASSERT(chain || datlen==0);
        }

        if (datlen) {
                EVUTIL_ASSERT(chain);
                EVUTIL_ASSERT(datlen+pos_in_chain <= chain->off);

                memcpy(data, chain->buffer + chain->misalign + pos_in_chain,
                    datlen);
        }

        result = nread;
done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

/* reads data from the src buffer to the dst buffer, avoids memcpy as
 * possible. */
/*  XXXX should return ev_ssize_t */
int
evbuffer_remove_buffer(struct evbuffer *src, struct evbuffer *dst,
    size_t datlen)
{
        /*XXX We should have an option to force this to be zero-copy.*/

        /*XXX can fail badly on sendfile case. */
        struct evbuffer_chain *chain, *previous;
        size_t nread = 0;
        int result;

        EVBUFFER_LOCK2(src, dst);

        chain = previous = src->first;

        if (datlen == 0 || dst == src) {
                result = 0;
                goto done;
        }

        if (dst->freeze_end || src->freeze_start) {
                result = -1;
                goto done;
        }

        /* short-cut if there is no more data buffered */
        if (datlen >= src->total_len) {
                datlen = src->total_len;
                evbuffer_add_buffer(dst, src);
                result = (int)datlen; /*XXXX should return ev_ssize_t*/
                goto done;
        }

        /* removes chains if possible */
        while (chain->off <= datlen) {
                /* We can't remove the last with data from src unless we
                 * remove all chains, in which case we would have done the if
                 * block above */
                EVUTIL_ASSERT(chain != *src->last_with_datap);
                nread += chain->off;
                datlen -= chain->off;
                previous = chain;
                if (src->last_with_datap == &chain->next)
                        src->last_with_datap = &src->first;
                chain = chain->next;
        }

        if (chain != src->first) {
                /* we can remove the chain */
                struct evbuffer_chain **chp;
                chp = evbuffer_free_trailing_empty_chains(dst);

                if (dst->first == NULL) {
                        dst->first = src->first;
                } else {
                        *chp = src->first;
                }
                dst->last = previous;
                previous->next = NULL;
                src->first = chain;
                advance_last_with_data(dst);

                dst->total_len += nread;
                dst->n_add_for_cb += nread;
        }

        /* we know that there is more data in the src buffer than
         * we want to read, so we manually drain the chain */
        evbuffer_add(dst, chain->buffer + chain->misalign, datlen);
        chain->misalign += datlen;
        chain->off -= datlen;
        nread += datlen;

        /* You might think we would want to increment dst->n_add_for_cb
         * here too.  But evbuffer_add above already took care of that.
         */
        src->total_len -= nread;
        src->n_del_for_cb += nread;

        if (nread) {
                evbuffer_invoke_callbacks_(dst);
                evbuffer_invoke_callbacks_(src);
        }
        result = (int)nread;/*XXXX should change return type */

done:
        EVBUFFER_UNLOCK2(src, dst);
        return result;
}

unsigned char *
evbuffer_pullup(struct evbuffer *buf, ev_ssize_t size)
{
        struct evbuffer_chain *chain, *next, *tmp, *last_with_data;
        unsigned char *buffer, *result = NULL;
        ev_ssize_t remaining;
        int removed_last_with_data = 0;
        int removed_last_with_datap = 0;

        EVBUFFER_LOCK(buf);

        chain = buf->first;

        if (size < 0)
                size = buf->total_len;
        /* if size > buf->total_len, we cannot guarantee to the user that she
         * is going to have a long enough buffer afterwards; so we return
         * NULL */
        if (size == 0 || (size_t)size > buf->total_len)
                goto done;

        /* No need to pull up anything; the first size bytes are
         * already here. */
        if (chain->off >= (size_t)size) {
                result = chain->buffer + chain->misalign;
                goto done;
        }

        /* Make sure that none of the chains we need to copy from is pinned. */
        remaining = size - chain->off;
        EVUTIL_ASSERT(remaining >= 0);
        for (tmp=chain->next; tmp; tmp=tmp->next) {
                if (CHAIN_PINNED(tmp))
                        goto done;
                if (tmp->off >= (size_t)remaining)
                        break;
                remaining -= tmp->off;
        }

        if (CHAIN_PINNED(chain)) {
                size_t old_off = chain->off;
                if (CHAIN_SPACE_LEN(chain) < size - chain->off) {
                        /* not enough room at end of chunk. */
                        goto done;
                }
                buffer = CHAIN_SPACE_PTR(chain);
                tmp = chain;
                tmp->off = size;
                size -= old_off;
                chain = chain->next;
        } else if (chain->buffer_len - chain->misalign >= (size_t)size) {
                /* already have enough space in the first chain */
                size_t old_off = chain->off;
                buffer = chain->buffer + chain->misalign + chain->off;
                tmp = chain;
                tmp->off = size;
                size -= old_off;
                chain = chain->next;
        } else {
                if ((tmp = evbuffer_chain_new_membuf(size)) == NULL) {
                        event_warn("%s: out of memory", __func__);
                        goto done;
                }
                buffer = tmp->buffer;
                tmp->off = size;
                buf->first = tmp;
        }

        /* TODO(niels): deal with buffers that point to NULL like sendfile */

        /* Copy and free every chunk that will be entirely pulled into tmp */
        last_with_data = *buf->last_with_datap;
        for (; chain != NULL && (size_t)size >= chain->off; chain = next) {
                next = chain->next;

                if (chain->buffer) {
                        memcpy(buffer, chain->buffer + chain->misalign, chain->off);
                        size -= chain->off;
                        buffer += chain->off;
                }
                if (chain == last_with_data)
                        removed_last_with_data = 1;
                if (&chain->next == buf->last_with_datap)
                        removed_last_with_datap = 1;

                evbuffer_chain_free(chain);
        }

        if (chain != NULL) {
                memcpy(buffer, chain->buffer + chain->misalign, size);
                chain->misalign += size;
                chain->off -= size;
        } else {
                buf->last = tmp;
        }

        tmp->next = chain;

        if (removed_last_with_data) {
                buf->last_with_datap = &buf->first;
        } else if (removed_last_with_datap) {
                if (buf->first->next && buf->first->next->off)
                        buf->last_with_datap = &buf->first->next;
                else
                        buf->last_with_datap = &buf->first;
        }

        result = (tmp->buffer + tmp->misalign);

done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

/*
 * Reads a line terminated by either '\r\n', '\n\r' or '\r' or '\n'.
 * The returned buffer needs to be freed by the called.
 */
char *
evbuffer_readline(struct evbuffer *buffer)
{
        return evbuffer_readln(buffer, NULL, EVBUFFER_EOL_ANY);
}

static inline ev_ssize_t
evbuffer_strchr(struct evbuffer_ptr *it, const char chr)
{
        struct evbuffer_chain *chain = it->internal_.chain;
        size_t i = it->internal_.pos_in_chain;
        while (chain != NULL) {
                char *buffer = (char *)chain->buffer + chain->misalign;
                char *cp = memchr(buffer+i, chr, chain->off-i);
                if (cp) {
                        it->internal_.chain = chain;
                        it->internal_.pos_in_chain = cp - buffer;
                        it->pos += (cp - buffer - i);
                        return it->pos;
                }
                it->pos += chain->off - i;
                i = 0;
                chain = chain->next;
        }

        return (-1);
}

static inline char *
find_eol_char(char *s, size_t len)
{
#define CHUNK_SZ 128
        /* Lots of benchmarking found this approach to be faster in practice
         * than doing two memchrs over the whole buffer, doin a memchr on each
         * char of the buffer, or trying to emulate memchr by hand. */
        char *s_end, *cr, *lf;
        s_end = s+len;
        while (s < s_end) {
                size_t chunk = (s + CHUNK_SZ < s_end) ? CHUNK_SZ : (s_end - s);
                cr = memchr(s, '\r', chunk);
                lf = memchr(s, '\n', chunk);
                if (cr) {
                        if (lf && lf < cr)
                                return lf;
                        return cr;
                } else if (lf) {
                        return lf;
                }
                s += CHUNK_SZ;
        }

        return NULL;
#undef CHUNK_SZ
}

static ev_ssize_t
evbuffer_find_eol_char(struct evbuffer_ptr *it)
{
        struct evbuffer_chain *chain = it->internal_.chain;
        size_t i = it->internal_.pos_in_chain;
        while (chain != NULL) {
                char *buffer = (char *)chain->buffer + chain->misalign;
                char *cp = find_eol_char(buffer+i, chain->off-i);
                if (cp) {
                        it->internal_.chain = chain;
                        it->internal_.pos_in_chain = cp - buffer;
                        it->pos += (cp - buffer) - i;
                        return it->pos;
                }
                it->pos += chain->off - i;
                i = 0;
                chain = chain->next;
        }

        return (-1);
}

static inline size_t
evbuffer_strspn(
        struct evbuffer_ptr *ptr, const char *chrset)
{
        size_t count = 0;
        struct evbuffer_chain *chain = ptr->internal_.chain;
        size_t i = ptr->internal_.pos_in_chain;

        if (!chain)
                return 0;

        while (1) {
                char *buffer = (char *)chain->buffer + chain->misalign;
                for (; i < chain->off; ++i) {
                        const char *p = chrset;
                        while (*p) {
                                if (buffer[i] == *p++)
                                        goto next;
                        }
                        ptr->internal_.chain = chain;
                        ptr->internal_.pos_in_chain = i;
                        ptr->pos += count;
                        return count;
                next:
                        ++count;
                }
                i = 0;

                if (! chain->next) {
                        ptr->internal_.chain = chain;
                        ptr->internal_.pos_in_chain = i;
                        ptr->pos += count;
                        return count;
                }

                chain = chain->next;
        }
}


static inline int
evbuffer_getchr(struct evbuffer_ptr *it)
{
        struct evbuffer_chain *chain = it->internal_.chain;
        size_t off = it->internal_.pos_in_chain;

        if (chain == NULL)
                return -1;

        return (unsigned char)chain->buffer[chain->misalign + off];
}

struct evbuffer_ptr
evbuffer_search_eol(struct evbuffer *buffer,
    struct evbuffer_ptr *start, size_t *eol_len_out,
    enum evbuffer_eol_style eol_style)
{
        struct evbuffer_ptr it, it2;
        size_t extra_drain = 0;
        int ok = 0;

        /* Avoid locking in trivial edge cases */
        if (start && start->internal_.chain == NULL) {
                PTR_NOT_FOUND(&it);
                if (eol_len_out)
                        *eol_len_out = extra_drain;
                return it;
        }

        EVBUFFER_LOCK(buffer);

        if (start) {
                memcpy(&it, start, sizeof(it));
        } else {
                it.pos = 0;
                it.internal_.chain = buffer->first;
                it.internal_.pos_in_chain = 0;
        }

        /* the eol_style determines our first stop character and how many
         * characters we are going to drain afterwards. */
        switch (eol_style) {
        case EVBUFFER_EOL_ANY:
                if (evbuffer_find_eol_char(&it) < 0)
                        goto done;
                memcpy(&it2, &it, sizeof(it));
                extra_drain = evbuffer_strspn(&it2, "\r\n");
                break;
        case EVBUFFER_EOL_CRLF_STRICT: {
                it = evbuffer_search(buffer, "\r\n", 2, &it);
                if (it.pos < 0)
                        goto done;
                extra_drain = 2;
                break;
        }
        case EVBUFFER_EOL_CRLF: {
                ev_ssize_t start_pos = it.pos;
                /* Look for a LF ... */
                if (evbuffer_strchr(&it, '\n') < 0)
                        goto done;
                extra_drain = 1;
                /* ... optionally preceded by a CR. */
                if (it.pos == start_pos)
                        break; /* If the first character is \n, don't back up */
                /* This potentially does an extra linear walk over the first
                 * few chains.  Probably, that's not too expensive unless you
                 * have a really pathological setup. */
                memcpy(&it2, &it, sizeof(it));
                if (evbuffer_ptr_subtract(buffer, &it2, 1)<0)
                        break;
                if (evbuffer_getchr(&it2) == '\r') {
                        memcpy(&it, &it2, sizeof(it));
                        extra_drain = 2;
                }
                break;
        }
        case EVBUFFER_EOL_LF:
                if (evbuffer_strchr(&it, '\n') < 0)
                        goto done;
                extra_drain = 1;
                break;
        case EVBUFFER_EOL_NUL:
                if (evbuffer_strchr(&it, '\0') < 0)
                        goto done;
                extra_drain = 1;
                break;
        default:
                goto done;
        }

        ok = 1;
done:
        EVBUFFER_UNLOCK(buffer);

        if (!ok)
                PTR_NOT_FOUND(&it);
        if (eol_len_out)
                *eol_len_out = extra_drain;

        return it;
}

char *
evbuffer_readln(struct evbuffer *buffer, size_t *n_read_out,
                enum evbuffer_eol_style eol_style)
{
        struct evbuffer_ptr it;
        char *line;
        size_t n_to_copy=0, extra_drain=0;
        char *result = NULL;

        EVBUFFER_LOCK(buffer);

        if (buffer->freeze_start) {
                goto done;
        }

        it = evbuffer_search_eol(buffer, NULL, &extra_drain, eol_style);
        if (it.pos < 0)
                goto done;
        n_to_copy = it.pos;

        if ((line = mm_malloc(n_to_copy+1)) == NULL) {
                event_warn("%s: out of memory", __func__);
                goto done;
        }

        evbuffer_remove(buffer, line, n_to_copy);
        line[n_to_copy] = '\0';

        evbuffer_drain(buffer, extra_drain);
        result = line;
done:
        EVBUFFER_UNLOCK(buffer);

        if (n_read_out)
                *n_read_out = result ? n_to_copy : 0;

        return result;
}

#define EVBUFFER_CHAIN_MAX_AUTO_SIZE 4096

/* Adds data to an event buffer */

int
evbuffer_add(struct evbuffer *buf, const void *data_in, size_t datlen)
{
        struct evbuffer_chain *chain, *tmp;
        const unsigned char *data = data_in;
        size_t remain, to_alloc;
        int result = -1;

        EVBUFFER_LOCK(buf);

        if (buf->freeze_end) {
                goto done;
        }
        /* Prevent buf->total_len overflow */
        if (datlen > EV_SIZE_MAX - buf->total_len) {
                goto done;
        }

        if (*buf->last_with_datap == NULL) {
                chain = buf->last;
        } else {
                chain = *buf->last_with_datap;
        }

        /* If there are no chains allocated for this buffer, allocate one
         * big enough to hold all the data. */
        if (chain == NULL) {
                chain = evbuffer_chain_insert_new(buf, datlen);
                if (!chain)
                        goto done;
        }

        if ((chain->flags & EVBUFFER_IMMUTABLE) == 0) {
                /* Always true for mutable buffers */
                EVUTIL_ASSERT(chain->misalign >= 0 &&
                    (ev_uint64_t)chain->misalign <= EVBUFFER_CHAIN_MAX);
                remain = chain->buffer_len - (size_t)chain->misalign - chain->off;
                if (remain >= datlen) {
                        /* there's enough space to hold all the data in the
                         * current last chain */
                        memcpy(chain->buffer + chain->misalign + chain->off,
                            data, datlen);
                        chain->off += datlen;
                        buf->total_len += datlen;
                        buf->n_add_for_cb += datlen;
                        goto out;
                } else if (!CHAIN_PINNED(chain) &&
                    evbuffer_chain_should_realign(chain, datlen)) {
                        /* we can fit the data into the misalignment */
                        evbuffer_chain_align(chain);

                        memcpy(chain->buffer + chain->off, data, datlen);
                        chain->off += datlen;
                        buf->total_len += datlen;
                        buf->n_add_for_cb += datlen;
                        goto out;
                }
        } else {
                /* we cannot write any data to the last chain */
                remain = 0;
        }

        /* we need to add another chain */
        to_alloc = chain->buffer_len;
        if (to_alloc <= EVBUFFER_CHAIN_MAX_AUTO_SIZE/2)
                to_alloc <<= 1;
        if (datlen > to_alloc)
                to_alloc = datlen;
        tmp = evbuffer_chain_new_membuf(to_alloc);
        if (tmp == NULL)
                goto done;

        if (remain) {
                memcpy(chain->buffer + chain->misalign + chain->off,
                    data, remain);
                chain->off += remain;
                buf->total_len += remain;
                buf->n_add_for_cb += remain;
        }

        data += remain;
        datlen -= remain;

        memcpy(tmp->buffer, data, datlen);
        tmp->off = datlen;
        evbuffer_chain_insert(buf, tmp);
        buf->n_add_for_cb += datlen;

out:
        evbuffer_invoke_callbacks_(buf);
        result = 0;
done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

int
evbuffer_prepend(struct evbuffer *buf, const void *data, size_t datlen)
{
        struct evbuffer_chain *chain, *tmp;
        int result = -1;

        EVBUFFER_LOCK(buf);

        if (datlen == 0) {
                result = 0;
                goto done;
        }
        if (buf->freeze_start) {
                goto done;
        }
        if (datlen > EV_SIZE_MAX - buf->total_len) {
                goto done;
        }

        chain = buf->first;

        if (chain == NULL) {
                chain = evbuffer_chain_insert_new(buf, datlen);
                if (!chain)
                        goto done;
        }

        /* we cannot touch immutable buffers */
        if ((chain->flags & EVBUFFER_IMMUTABLE) == 0) {
                /* Always true for mutable buffers */
                EVUTIL_ASSERT(chain->misalign >= 0 &&
                    (ev_uint64_t)chain->misalign <= EVBUFFER_CHAIN_MAX);

                /* If this chain is empty, we can treat it as
                 * 'empty at the beginning' rather than 'empty at the end' */
                if (chain->off == 0)
                        chain->misalign = chain->buffer_len;

                if ((size_t)chain->misalign >= datlen) {
                        /* we have enough space to fit everything */
                        memcpy(chain->buffer + chain->misalign - datlen,
                            data, datlen);
                        chain->off += datlen;
                        chain->misalign -= datlen;
                        buf->total_len += datlen;
                        buf->n_add_for_cb += datlen;
                        goto out;
                } else if (chain->misalign) {
                        /* we can only fit some of the data. */
                        memcpy(chain->buffer,
                            (char*)data + datlen - chain->misalign,
                            (size_t)chain->misalign);
                        chain->off += (size_t)chain->misalign;
                        buf->total_len += (size_t)chain->misalign;
                        buf->n_add_for_cb += (size_t)chain->misalign;
                        datlen -= (size_t)chain->misalign;
                        chain->misalign = 0;
                }
        }

        /* we need to add another chain */
        if ((tmp = evbuffer_chain_new_membuf(datlen)) == NULL)
                goto done;
        buf->first = tmp;
        if (buf->last_with_datap == &buf->first && chain->off)
                buf->last_with_datap = &tmp->next;

        tmp->next = chain;

        tmp->off = datlen;
        EVUTIL_ASSERT(datlen <= tmp->buffer_len);
        tmp->misalign = tmp->buffer_len - datlen;

        memcpy(tmp->buffer + tmp->misalign, data, datlen);
        buf->total_len += datlen;
        buf->n_add_for_cb += datlen;

out:
        evbuffer_invoke_callbacks_(buf);
        result = 0;
done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

/** Helper: realigns the memory in chain->buffer so that misalign is 0. */
static void
evbuffer_chain_align(struct evbuffer_chain *chain)
{
        EVUTIL_ASSERT(!(chain->flags & EVBUFFER_IMMUTABLE));
        EVUTIL_ASSERT(!(chain->flags & EVBUFFER_MEM_PINNED_ANY));
        memmove(chain->buffer, chain->buffer + chain->misalign, chain->off);
        chain->misalign = 0;
}

#define MAX_TO_COPY_IN_EXPAND 4096
#define MAX_TO_REALIGN_IN_EXPAND 2048

/** Helper: return true iff we should realign chain to fit datalen bytes of
    data in it. */
static int
evbuffer_chain_should_realign(struct evbuffer_chain *chain,
    size_t datlen)
{
        return chain->buffer_len - chain->off >= datlen &&
            (chain->off < chain->buffer_len / 2) &&
            (chain->off <= MAX_TO_REALIGN_IN_EXPAND);
}

/* Expands the available space in the event buffer to at least datlen, all in
 * a single chunk.  Return that chunk. */
static struct evbuffer_chain *
evbuffer_expand_singlechain(struct evbuffer *buf, size_t datlen)
{
        struct evbuffer_chain *chain, **chainp;
        struct evbuffer_chain *result = NULL;
        ASSERT_EVBUFFER_LOCKED(buf);

        chainp = buf->last_with_datap;

        /* XXX If *chainp is no longer writeable, but has enough space in its
         * misalign, this might be a bad idea: we could still use *chainp, not
         * (*chainp)->next. */
        if (*chainp && CHAIN_SPACE_LEN(*chainp) == 0)
                chainp = &(*chainp)->next;

        /* 'chain' now points to the first chain with writable space (if any)
         * We will either use it, realign it, replace it, or resize it. */
        chain = *chainp;

        if (chain == NULL ||
            (chain->flags & (EVBUFFER_IMMUTABLE|EVBUFFER_MEM_PINNED_ANY))) {
                /* We can't use the last_with_data chain at all.  Just add a
                 * new one that's big enough. */
                goto insert_new;
        }

        /* If we can fit all the data, then we don't have to do anything */
        if (CHAIN_SPACE_LEN(chain) >= datlen) {
                result = chain;
                goto ok;
        }

        /* If the chain is completely empty, just replace it by adding a new
         * empty chain. */
        if (chain->off == 0) {
                goto insert_new;
        }

        /* If the misalignment plus the remaining space fulfills our data
         * needs, we could just force an alignment to happen.  Afterwards, we
         * have enough space.  But only do this if we're saving a lot of space
         * and not moving too much data.  Otherwise the space savings are
         * probably offset by the time lost in copying.
         */
        if (evbuffer_chain_should_realign(chain, datlen)) {
                evbuffer_chain_align(chain);
                result = chain;
                goto ok;
        }

        /* At this point, we can either resize the last chunk with space in
         * it, use the next chunk after it, or   If we add a new chunk, we waste
         * CHAIN_SPACE_LEN(chain) bytes in the former last chunk.  If we
         * resize, we have to copy chain->off bytes.
         */

        /* Would expanding this chunk be affordable and worthwhile? */
        if (CHAIN_SPACE_LEN(chain) < chain->buffer_len / 8 ||
            chain->off > MAX_TO_COPY_IN_EXPAND ||
                datlen >= (EVBUFFER_CHAIN_MAX - chain->off)) {
                /* It's not worth resizing this chain. Can the next one be
                 * used? */
                if (chain->next && CHAIN_SPACE_LEN(chain->next) >= datlen) {
                        /* Yes, we can just use the next chain (which should
                         * be empty. */
                        result = chain->next;
                        goto ok;
                } else {
                        /* No; append a new chain (which will free all
                         * terminal empty chains.) */
                        goto insert_new;
                }
        } else {
                /* Okay, we're going to try to resize this chain: Not doing so
                 * would waste at least 1/8 of its current allocation, and we
                 * can do so without having to copy more than
                 * MAX_TO_COPY_IN_EXPAND bytes. */
                /* figure out how much space we need */
                size_t length = chain->off + datlen;
                struct evbuffer_chain *tmp = evbuffer_chain_new_membuf(length);
                if (tmp == NULL)
                        goto err;

                /* copy the data over that we had so far */
                tmp->off = chain->off;
                memcpy(tmp->buffer, chain->buffer + chain->misalign,
                    chain->off);
                /* fix up the list */
                EVUTIL_ASSERT(*chainp == chain);
                result = *chainp = tmp;

                if (buf->last == chain)
                        buf->last = tmp;

                tmp->next = chain->next;
                evbuffer_chain_free(chain);
                goto ok;
        }

insert_new:
        result = evbuffer_chain_insert_new(buf, datlen);
        if (!result)
                goto err;
ok:
        EVUTIL_ASSERT(result);
        EVUTIL_ASSERT(CHAIN_SPACE_LEN(result) >= datlen);
err:
        return result;
}

/* Make sure that datlen bytes are available for writing in the last n
 * chains.  Never copies or moves data. */
int
evbuffer_expand_fast_(struct evbuffer *buf, size_t datlen, int n)
{
        struct evbuffer_chain *chain = buf->last, *tmp, *next;
        size_t avail;
        int used;

        ASSERT_EVBUFFER_LOCKED(buf);
        EVUTIL_ASSERT(n >= 2);

        if (chain == NULL || (chain->flags & EVBUFFER_IMMUTABLE)) {
                /* There is no last chunk, or we can't touch the last chunk.
                 * Just add a new chunk. */
                chain = evbuffer_chain_insert_new(buf, datlen);
                if (chain == NULL)
                        return (-1);
                else
                        return (0);
        }

        used = 0; /* number of chains we're using space in. */
        avail = 0; /* how much space they have. */
        /* How many bytes can we stick at the end of buffer as it is?  Iterate
         * over the chains at the end of the buffer, tring to see how much
         * space we have in the first n. */
        for (chain = *buf->last_with_datap; chain; chain = chain->next) {
                if (chain->off) {
                        size_t space = (size_t) CHAIN_SPACE_LEN(chain);
                        EVUTIL_ASSERT(chain == *buf->last_with_datap);
                        if (space) {
                                avail += space;
                                ++used;
                        }
                } else {
                        /* No data in chain; realign it. */
                        chain->misalign = 0;
                        avail += chain->buffer_len;
                        ++used;
                }
                if (avail >= datlen) {
                        /* There is already enough space.  Just return */
                        return (0);
                }
                if (used == n)
                        break;
        }

        /* There wasn't enough space in the first n chains with space in
         * them. Either add a new chain with enough space, or replace all
         * empty chains with one that has enough space, depending on n. */
        if (used < n) {
                /* The loop ran off the end of the chains before it hit n
                 * chains; we can add another. */
                EVUTIL_ASSERT(chain == NULL);

                tmp = evbuffer_chain_new_membuf(datlen - avail);
                if (tmp == NULL)
                        return (-1);

                buf->last->next = tmp;
                buf->last = tmp;
                /* (we would only set last_with_data if we added the first
                 * chain. But if the buffer had no chains, we would have
                 * just allocated a new chain earlier) */
                return (0);
        } else {
                /* Nuke _all_ the empty chains. */
                int rmv_all = 0; /* True iff we removed last_with_data. */
                chain = *buf->last_with_datap;
                if (!chain->off) {
                        EVUTIL_ASSERT(chain == buf->first);
                        rmv_all = 1;
                        avail = 0;
                } else {
                        /* can't overflow, since only mutable chains have
                         * huge misaligns. */
                        avail = (size_t) CHAIN_SPACE_LEN(chain);
                        chain = chain->next;
                }


                for (; chain; chain = next) {
                        next = chain->next;
                        EVUTIL_ASSERT(chain->off == 0);
                        evbuffer_chain_free(chain);
                }
                EVUTIL_ASSERT(datlen >= avail);
                tmp = evbuffer_chain_new_membuf(datlen - avail);
                if (tmp == NULL) {
                        if (rmv_all) {
                                ZERO_CHAIN(buf);
                        } else {
                                buf->last = *buf->last_with_datap;
                                (*buf->last_with_datap)->next = NULL;
                        }
                        return (-1);
                }

                if (rmv_all) {
                        buf->first = buf->last = tmp;
                        buf->last_with_datap = &buf->first;
                } else {
                        (*buf->last_with_datap)->next = tmp;
                        buf->last = tmp;
                }
                return (0);
        }
}

int
evbuffer_expand(struct evbuffer *buf, size_t datlen)
{
        struct evbuffer_chain *chain;

        EVBUFFER_LOCK(buf);
        chain = evbuffer_expand_singlechain(buf, datlen);
        EVBUFFER_UNLOCK(buf);
        return chain ? 0 : -1;
}

/*
 * Reads data from a file descriptor into a buffer.
 */

#if defined(EVENT__HAVE_SYS_UIO_H) || defined(_WIN32)
#define USE_IOVEC_IMPL
#endif

#ifdef USE_IOVEC_IMPL

#ifdef EVENT__HAVE_SYS_UIO_H
/* number of iovec we use for writev, fragmentation is going to determine
 * how much we end up writing */

#define DEFAULT_WRITE_IOVEC 128

#if defined(UIO_MAXIOV) && UIO_MAXIOV < DEFAULT_WRITE_IOVEC
#define NUM_WRITE_IOVEC UIO_MAXIOV
#elif defined(IOV_MAX) && IOV_MAX < DEFAULT_WRITE_IOVEC
#define NUM_WRITE_IOVEC IOV_MAX
#else
#define NUM_WRITE_IOVEC DEFAULT_WRITE_IOVEC
#endif

#define IOV_TYPE struct iovec
#define IOV_PTR_FIELD iov_base
#define IOV_LEN_FIELD iov_len
#define IOV_LEN_TYPE size_t
#else
#define NUM_WRITE_IOVEC 16
#define IOV_TYPE WSABUF
#define IOV_PTR_FIELD buf
#define IOV_LEN_FIELD len
#define IOV_LEN_TYPE unsigned long
#endif
#endif
#define NUM_READ_IOVEC 4

/** Helper function to figure out which space to use for reading data into
    an evbuffer.  Internal use only.

    @param buf The buffer to read into
    @param howmuch How much we want to read.
    @param vecs An array of two or more iovecs or WSABUFs.
    @param n_vecs_avail The length of vecs
    @param chainp A pointer to a variable to hold the first chain we're
      reading into.
    @param exact Boolean: if true, we do not provide more than 'howmuch'
      space in the vectors, even if more space is available.
    @return The number of buffers we're using.
 */
int
evbuffer_read_setup_vecs_(struct evbuffer *buf, ev_ssize_t howmuch,
    struct evbuffer_iovec *vecs, int n_vecs_avail,
    struct evbuffer_chain ***chainp, int exact)
{
        struct evbuffer_chain *chain;
        struct evbuffer_chain **firstchainp;
        size_t so_far;
        int i;
        ASSERT_EVBUFFER_LOCKED(buf);

        if (howmuch < 0)
                return -1;

        so_far = 0;
        /* Let firstchain be the first chain with any space on it */
        firstchainp = buf->last_with_datap;
        EVUTIL_ASSERT(*firstchainp);
        if (CHAIN_SPACE_LEN(*firstchainp) == 0) {
                firstchainp = &(*firstchainp)->next;
        }

        chain = *firstchainp;
        EVUTIL_ASSERT(chain);
        for (i = 0; i < n_vecs_avail && so_far < (size_t)howmuch; ++i) {
                size_t avail = (size_t) CHAIN_SPACE_LEN(chain);
                if (avail > (howmuch - so_far) && exact)
                        avail = howmuch - so_far;
                vecs[i].iov_base = (void *)CHAIN_SPACE_PTR(chain);
                vecs[i].iov_len = avail;
                so_far += avail;
                chain = chain->next;
        }

        *chainp = firstchainp;
        return i;
}

static int
get_n_bytes_readable_on_socket(evutil_socket_t fd)
{
#if defined(FIONREAD) && defined(_WIN32)
        unsigned long lng = EVBUFFER_MAX_READ_DEFAULT;
        if (ioctlsocket(fd, FIONREAD, &lng) < 0)
                return -1;
        /* Can overflow, but mostly harmlessly. XXXX */
        return (int)lng;
#elif defined(FIONREAD)
        int n = EVBUFFER_MAX_READ_DEFAULT;
        if (ioctl(fd, FIONREAD, &n) < 0)
                return -1;
        return n;
#else
        return EVBUFFER_MAX_READ_DEFAULT;
#endif
}

/* TODO(niels): should this function return ev_ssize_t and take ev_ssize_t
 * as howmuch? */
int
evbuffer_read(struct evbuffer *buf, evutil_socket_t fd, int howmuch)
{
        struct evbuffer_chain **chainp;
        int n;
        int result;

#ifdef USE_IOVEC_IMPL
        int nvecs, i, remaining;
#else
        struct evbuffer_chain *chain;
        unsigned char *p;
#endif

        EVBUFFER_LOCK(buf);

        if (buf->freeze_end) {
                result = -1;
                goto done;
        }

        n = get_n_bytes_readable_on_socket(fd);
        if (n <= 0 || n > (int)buf->max_read)
                n = (int)buf->max_read;
        if (howmuch < 0 || howmuch > n)
                howmuch = n;

#ifdef USE_IOVEC_IMPL
        /* Since we can use iovecs, we're willing to use the last
         * NUM_READ_IOVEC chains. */
        if (evbuffer_expand_fast_(buf, howmuch, NUM_READ_IOVEC) == -1) {
                result = -1;
                goto done;
        } else {
                IOV_TYPE vecs[NUM_READ_IOVEC];
#ifdef EVBUFFER_IOVEC_IS_NATIVE_
                nvecs = evbuffer_read_setup_vecs_(buf, howmuch, vecs,
                    NUM_READ_IOVEC, &chainp, 1);
#else
                /* We aren't using the native struct iovec.  Therefore,
                   we are on win32. */
                struct evbuffer_iovec ev_vecs[NUM_READ_IOVEC];
                nvecs = evbuffer_read_setup_vecs_(buf, howmuch, ev_vecs, 2,
                    &chainp, 1);

                for (i=0; i < nvecs; ++i)
                        WSABUF_FROM_EVBUFFER_IOV(&vecs[i], &ev_vecs[i]);
#endif

#ifdef _WIN32
                {
                        DWORD bytesRead;
                        DWORD flags=0;
                        if (WSARecv(fd, vecs, nvecs, &bytesRead, &flags, NULL, NULL)) {
                                /* The read failed. It might be a close,
                                 * or it might be an error. */
                                if (WSAGetLastError() == WSAECONNABORTED)
                                        n = 0;
                                else
                                        n = -1;
                        } else
                                n = bytesRead;
                }
#else
                n = readv(fd, vecs, nvecs);
#endif
        }

#else /*!USE_IOVEC_IMPL*/
        /* If we don't have FIONREAD, we might waste some space here */
        /* XXX we _will_ waste some space here if there is any space left
         * over on buf->last. */
        if ((chain = evbuffer_expand_singlechain(buf, howmuch)) == NULL) {
                result = -1;
                goto done;
        }

        /* We can append new data at this point */
        p = chain->buffer + chain->misalign + chain->off;

#ifndef _WIN32
        n = read(fd, p, howmuch);
#else
        n = recv(fd, p, howmuch, 0);
#endif
#endif /* USE_IOVEC_IMPL */

        if (n == -1) {
                result = -1;
                goto done;
        }
        if (n == 0) {
                result = 0;
                goto done;
        }

#ifdef USE_IOVEC_IMPL
        remaining = n;
        for (i=0; i < nvecs; ++i) {
                /* can't overflow, since only mutable chains have
                 * huge misaligns. */
                size_t space = (size_t) CHAIN_SPACE_LEN(*chainp);
                /* XXXX This is a kludge that can waste space in perverse
                 * situations. */
                if (space > EVBUFFER_CHAIN_MAX)
                        space = EVBUFFER_CHAIN_MAX;
                if ((ev_ssize_t)space < remaining) {
                        (*chainp)->off += space;
                        remaining -= (int)space;
                } else {
                        (*chainp)->off += remaining;
                        buf->last_with_datap = chainp;
                        break;
                }
                chainp = &(*chainp)->next;
        }
#else
        chain->off += n;
        advance_last_with_data(buf);
#endif
        buf->total_len += n;
        buf->n_add_for_cb += n;

        /* Tell someone about changes in this buffer */
        evbuffer_invoke_callbacks_(buf);
        result = n;
done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

#ifdef USE_IOVEC_IMPL
static inline int
evbuffer_write_iovec(struct evbuffer *buffer, evutil_socket_t fd,
    ev_ssize_t howmuch)
{
        IOV_TYPE iov[NUM_WRITE_IOVEC];
        struct evbuffer_chain *chain = buffer->first;
        int n, i = 0;

        if (howmuch < 0)
                return -1;

        ASSERT_EVBUFFER_LOCKED(buffer);
        /* XXX make this top out at some maximal data length?  if the
         * buffer has (say) 1MB in it, split over 128 chains, there's
         * no way it all gets written in one go. */
        while (chain != NULL && i < NUM_WRITE_IOVEC && howmuch) {
#ifdef USE_SENDFILE
                /* we cannot write the file info via writev */
                if (chain->flags & EVBUFFER_SENDFILE)
                        break;
#endif
                iov[i].IOV_PTR_FIELD = (void *) (chain->buffer + chain->misalign);
                if ((size_t)howmuch >= chain->off) {
                        /* XXXcould be problematic when windows supports mmap*/
                        iov[i++].IOV_LEN_FIELD = (IOV_LEN_TYPE)chain->off;
                        howmuch -= chain->off;
                } else {
                        /* XXXcould be problematic when windows supports mmap*/
                        iov[i++].IOV_LEN_FIELD = (IOV_LEN_TYPE)howmuch;
                        break;
                }
                chain = chain->next;
        }
        if (! i)
                return 0;

#ifdef _WIN32
        {
                DWORD bytesSent;
                if (WSASend(fd, iov, i, &bytesSent, 0, NULL, NULL))
                        n = -1;
                else
                        n = bytesSent;
        }
#else
        n = writev(fd, iov, i);
#endif
        return (n);
}
#endif

#ifdef USE_SENDFILE
static inline int
evbuffer_write_sendfile(struct evbuffer *buffer, evutil_socket_t dest_fd,
    ev_ssize_t howmuch)
{
        struct evbuffer_chain *chain = buffer->first;
        struct evbuffer_chain_file_segment *info =
            EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_file_segment,
                chain);
        const int source_fd = info->segment->fd;
#if defined(SENDFILE_IS_MACOSX) || defined(SENDFILE_IS_FREEBSD)
        int res;
        ev_off_t len = chain->off;
#elif defined(SENDFILE_IS_LINUX) || defined(SENDFILE_IS_SOLARIS)
        ev_ssize_t res;
        off_t offset = chain->misalign;
#endif

        ASSERT_EVBUFFER_LOCKED(buffer);

#if defined(SENDFILE_IS_MACOSX)
        res = sendfile(source_fd, dest_fd, chain->misalign, &len, NULL, 0);
        if (res == -1 && !EVUTIL_ERR_RW_RETRIABLE(errno))
                return (-1);

        return (len);
#elif defined(SENDFILE_IS_FREEBSD)
        res = sendfile(source_fd, dest_fd, chain->misalign, chain->off, NULL, &len, 0);
        if (res == -1 && !EVUTIL_ERR_RW_RETRIABLE(errno))
                return (-1);

        return (len);
#elif defined(SENDFILE_IS_LINUX)
        res = sendfile(dest_fd, source_fd, &offset, chain->off);
        if (res == -1 && EVUTIL_ERR_RW_RETRIABLE(errno)) {
                /* if this is EAGAIN or EINTR return 0; otherwise, -1 */
                return (0);
        }
        return (res);
#elif defined(SENDFILE_IS_SOLARIS)
        {
                const off_t offset_orig = offset;
                res = sendfile(dest_fd, source_fd, &offset, chain->off);
                if (res == -1 && EVUTIL_ERR_RW_RETRIABLE(errno)) {
                        if (offset - offset_orig)
                                return offset - offset_orig;
                        /* if this is EAGAIN or EINTR and no bytes were
                         * written, return 0 */
                        return (0);
                }
                return (res);
        }
#endif
}
#endif

int
evbuffer_write_atmost(struct evbuffer *buffer, evutil_socket_t fd,
    ev_ssize_t howmuch)
{
        int n = -1;

        EVBUFFER_LOCK(buffer);

        if (buffer->freeze_start) {
                goto done;
        }

        if (howmuch < 0 || (size_t)howmuch > buffer->total_len)
                howmuch = buffer->total_len;

        if (howmuch > 0) {
#ifdef USE_SENDFILE
                struct evbuffer_chain *chain = buffer->first;
                if (chain != NULL && (chain->flags & EVBUFFER_SENDFILE))
                        n = evbuffer_write_sendfile(buffer, fd, howmuch);
                else {
#endif
#ifdef USE_IOVEC_IMPL
                n = evbuffer_write_iovec(buffer, fd, howmuch);
#elif defined(_WIN32)
                /* XXX(nickm) Don't disable this code until we know if
                 * the WSARecv code above works. */
                void *p = evbuffer_pullup(buffer, howmuch);
                EVUTIL_ASSERT(p || !howmuch);
                n = send(fd, p, howmuch, 0);
#else
                void *p = evbuffer_pullup(buffer, howmuch);
                EVUTIL_ASSERT(p || !howmuch);
                n = write(fd, p, howmuch);
#endif
#ifdef USE_SENDFILE
                }
#endif
        }

        if (n > 0)
                evbuffer_drain(buffer, n);

done:
        EVBUFFER_UNLOCK(buffer);
        return (n);
}

int
evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd)
{
        return evbuffer_write_atmost(buffer, fd, -1);
}

unsigned char *
evbuffer_find(struct evbuffer *buffer, const unsigned char *what, size_t len)
{
        unsigned char *search;
        struct evbuffer_ptr ptr;

        EVBUFFER_LOCK(buffer);

        ptr = evbuffer_search(buffer, (const char *)what, len, NULL);
        if (ptr.pos < 0) {
                search = NULL;
        } else {
                search = evbuffer_pullup(buffer, ptr.pos + len);
                if (search)
                        search += ptr.pos;
        }
        EVBUFFER_UNLOCK(buffer);
        return search;
}

/* Subract <b>howfar</b> from the position of <b>pos</b> within
 * <b>buf</b>. Returns 0 on success, -1 on failure.
 *
 * This isn't exposed yet, because of potential inefficiency issues.
 * Maybe it should be. */
static int
evbuffer_ptr_subtract(struct evbuffer *buf, struct evbuffer_ptr *pos,
    size_t howfar)
{
        if (pos->pos < 0)
                return -1;
        if (howfar > (size_t)pos->pos)
                return -1;
        if (pos->internal_.chain && howfar <= pos->internal_.pos_in_chain) {
                pos->internal_.pos_in_chain -= howfar;
                pos->pos -= howfar;
                return 0;
        } else {
                const size_t newpos = pos->pos - howfar;
                /* Here's the inefficient part: it walks over the
                 * chains until we hit newpos. */
                return evbuffer_ptr_set(buf, pos, newpos, EVBUFFER_PTR_SET);
        }
}

int
evbuffer_ptr_set(struct evbuffer *buf, struct evbuffer_ptr *pos,
    size_t position, enum evbuffer_ptr_how how)
{
        size_t left = position;
        struct evbuffer_chain *chain = NULL;
        int result = 0;

        EVBUFFER_LOCK(buf);

        switch (how) {
        case EVBUFFER_PTR_SET:
                chain = buf->first;
                pos->pos = position;
                position = 0;
                break;
        case EVBUFFER_PTR_ADD:
                /* this avoids iterating over all previous chains if
                   we just want to advance the position */
                if (pos->pos < 0 || EV_SIZE_MAX - position < (size_t)pos->pos) {
                        EVBUFFER_UNLOCK(buf);
                        return -1;
                }
                chain = pos->internal_.chain;
                pos->pos += position;
                position = pos->internal_.pos_in_chain;
                break;
        }

        EVUTIL_ASSERT(EV_SIZE_MAX - left >= position);
        while (chain && position + left >= chain->off) {
                left -= chain->off - position;
                chain = chain->next;
                position = 0;
        }
        if (chain) {
                pos->internal_.chain = chain;
                pos->internal_.pos_in_chain = position + left;
        } else if (left == 0) {
                /* The first byte in the (nonexistent) chain after the last chain */
                pos->internal_.chain = NULL;
                pos->internal_.pos_in_chain = 0;
        } else {
                PTR_NOT_FOUND(pos);
                result = -1;
        }

        EVBUFFER_UNLOCK(buf);

        return result;
}

/**
   Compare the bytes in buf at position pos to the len bytes in mem.  Return
   less than 0, 0, or greater than 0 as memcmp.
 */
static int
evbuffer_ptr_memcmp(const struct evbuffer *buf, const struct evbuffer_ptr *pos,
    const char *mem, size_t len)
{
        struct evbuffer_chain *chain;
        size_t position;
        int r;

        ASSERT_EVBUFFER_LOCKED(buf);

        if (pos->pos < 0 ||
            EV_SIZE_MAX - len < (size_t)pos->pos ||
            pos->pos + len > buf->total_len)
                return -1;

        chain = pos->internal_.chain;
        position = pos->internal_.pos_in_chain;
        while (len && chain) {
                size_t n_comparable;
                if (len + position > chain->off)
                        n_comparable = chain->off - position;
                else
                        n_comparable = len;
                r = memcmp(chain->buffer + chain->misalign + position, mem,
                    n_comparable);
                if (r)
                        return r;
                mem += n_comparable;
                len -= n_comparable;
                position = 0;
                chain = chain->next;
        }

        return 0;
}

struct evbuffer_ptr
evbuffer_search(struct evbuffer *buffer, const char *what, size_t len, const struct evbuffer_ptr *start)
{
        return evbuffer_search_range(buffer, what, len, start, NULL);
}

struct evbuffer_ptr
evbuffer_search_range(struct evbuffer *buffer, const char *what, size_t len, const struct evbuffer_ptr *start, const struct evbuffer_ptr *end)
{
        struct evbuffer_ptr pos;
        struct evbuffer_chain *chain, *last_chain = NULL;
        const unsigned char *p;
        char first;

        EVBUFFER_LOCK(buffer);

        if (start) {
                memcpy(&pos, start, sizeof(pos));
                chain = pos.internal_.chain;
        } else {
                pos.pos = 0;
                chain = pos.internal_.chain = buffer->first;
                pos.internal_.pos_in_chain = 0;
        }

        if (end)
                last_chain = end->internal_.chain;

        if (!len || len > EV_SSIZE_MAX)
                goto done;

        first = what[0];

        while (chain) {
                const unsigned char *start_at =
                    chain->buffer + chain->misalign +
                    pos.internal_.pos_in_chain;
                p = memchr(start_at, first,
                    chain->off - pos.internal_.pos_in_chain);
                if (p) {
                        pos.pos += p - start_at;
                        pos.internal_.pos_in_chain += p - start_at;
                        if (!evbuffer_ptr_memcmp(buffer, &pos, what, len)) {
                                if (end && pos.pos + (ev_ssize_t)len > end->pos)
                                        goto not_found;
                                else
                                        goto done;
                        }
                        ++pos.pos;
                        ++pos.internal_.pos_in_chain;
                        if (pos.internal_.pos_in_chain == chain->off) {
                                chain = pos.internal_.chain = chain->next;
                                pos.internal_.pos_in_chain = 0;
                        }
                } else {
                        if (chain == last_chain)
                                goto not_found;
                        pos.pos += chain->off - pos.internal_.pos_in_chain;
                        chain = pos.internal_.chain = chain->next;
                        pos.internal_.pos_in_chain = 0;
                }
        }

not_found:
        PTR_NOT_FOUND(&pos);
done:
        EVBUFFER_UNLOCK(buffer);
        return pos;
}

int
evbuffer_peek(struct evbuffer *buffer, ev_ssize_t len,
    struct evbuffer_ptr *start_at,
    struct evbuffer_iovec *vec, int n_vec)
{
        struct evbuffer_chain *chain;
        int idx = 0;
        ev_ssize_t len_so_far = 0;

        /* Avoid locking in trivial edge cases */
        if (start_at && start_at->internal_.chain == NULL)
                return 0;

        EVBUFFER_LOCK(buffer);

        if (start_at) {
                chain = start_at->internal_.chain;
                len_so_far = chain->off
                    - start_at->internal_.pos_in_chain;
                idx = 1;
                if (n_vec > 0) {
                        vec[0].iov_base = (void *)(chain->buffer + chain->misalign
                            + start_at->internal_.pos_in_chain);
                        vec[0].iov_len = len_so_far;
                }
                chain = chain->next;
        } else {
                chain = buffer->first;
        }

        if (n_vec == 0 && len < 0) {
                /* If no vectors are provided and they asked for "everything",
                 * pretend they asked for the actual available amount. */
                len = buffer->total_len;
                if (start_at) {
                        len -= start_at->pos;
                }
        }

        while (chain) {
                if (len >= 0 && len_so_far >= len)
                        break;
                if (idx<n_vec) {
                        vec[idx].iov_base = (void *)(chain->buffer + chain->misalign);
                        vec[idx].iov_len = chain->off;
                } else if (len<0) {
                        break;
                }
                ++idx;
                len_so_far += chain->off;
                chain = chain->next;
        }

        EVBUFFER_UNLOCK(buffer);

        return idx;
}


int
evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap)
{
        char *buffer;
        size_t space;
        int sz, result = -1;
        va_list aq;
        struct evbuffer_chain *chain;


        EVBUFFER_LOCK(buf);

        if (buf->freeze_end) {
                goto done;
        }

        /* make sure that at least some space is available */
        if ((chain = evbuffer_expand_singlechain(buf, 64)) == NULL)
                goto done;

        for (;;) {
#if 0
                size_t used = chain->misalign + chain->off;
                buffer = (char *)chain->buffer + chain->misalign + chain->off;
                EVUTIL_ASSERT(chain->buffer_len >= used);
                space = chain->buffer_len - used;
#endif
                buffer = (char*) CHAIN_SPACE_PTR(chain);
                space = (size_t) CHAIN_SPACE_LEN(chain);

#ifndef va_copy
#define va_copy(dst, src)       memcpy(&(dst), &(src), sizeof(va_list))
#endif
                va_copy(aq, ap);

                sz = evutil_vsnprintf(buffer, space, fmt, aq);

                va_end(aq);

                if (sz < 0)
                        goto done;
                if (INT_MAX >= EVBUFFER_CHAIN_MAX &&
                    (size_t)sz >= EVBUFFER_CHAIN_MAX)
                        goto done;
                if ((size_t)sz < space) {
                        chain->off += sz;
                        buf->total_len += sz;
                        buf->n_add_for_cb += sz;

                        advance_last_with_data(buf);
                        evbuffer_invoke_callbacks_(buf);
                        result = sz;
                        goto done;
                }
                if ((chain = evbuffer_expand_singlechain(buf, sz + 1)) == NULL)
                        goto done;
        }
        /* NOTREACHED */

done:
        EVBUFFER_UNLOCK(buf);
        return result;
}

int
evbuffer_add_printf(struct evbuffer *buf, const char *fmt, ...)
{
        int res = -1;
        va_list ap;

        va_start(ap, fmt);
        res = evbuffer_add_vprintf(buf, fmt, ap);
        va_end(ap);

        return (res);
}

int
evbuffer_add_reference(struct evbuffer *outbuf,
    const void *data, size_t datlen,
    evbuffer_ref_cleanup_cb cleanupfn, void *extra)
{
        struct evbuffer_chain *chain;
        struct evbuffer_chain_reference *info;
        int result = -1;

        chain = evbuffer_chain_new(sizeof(struct evbuffer_chain_reference));
        if (!chain)
                return (-1);
        chain->flags |= EVBUFFER_REFERENCE | EVBUFFER_IMMUTABLE;
        chain->buffer = (unsigned char *)data;
        chain->buffer_len = datlen;
        chain->off = datlen;

        info = EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_reference, chain);
        info->cleanupfn = cleanupfn;
        info->extra = extra;

        EVBUFFER_LOCK(outbuf);
        if (outbuf->freeze_end) {
                /* don't call chain_free; we do not want to actually invoke
                 * the cleanup function */
                mm_free(chain);
                goto done;
        }
        evbuffer_chain_insert(outbuf, chain);
        outbuf->n_add_for_cb += datlen;

        evbuffer_invoke_callbacks_(outbuf);

        result = 0;
done:
        EVBUFFER_UNLOCK(outbuf);

        return result;
}

/* TODO(niels): we may want to add to automagically convert to mmap, in
 * case evbuffer_remove() or evbuffer_pullup() are being used.
 */
struct evbuffer_file_segment *
evbuffer_file_segment_new(
        int fd, ev_off_t offset, ev_off_t length, unsigned flags)
{
        struct evbuffer_file_segment *seg =
            mm_calloc(sizeof(struct evbuffer_file_segment), 1);
        if (!seg)
                return NULL;
        seg->refcnt = 1;
        seg->fd = fd;
        seg->flags = flags;
        seg->file_offset = offset;
        seg->cleanup_cb = NULL;
        seg->cleanup_cb_arg = NULL;
#ifdef _WIN32
#ifndef lseek
#define lseek _lseeki64
#endif
#ifndef fstat
#define fstat _fstat
#endif
#ifndef stat
#define stat _stat
#endif
#endif
        if (length == -1) {
                struct stat st;
                if (fstat(fd, &st) < 0)
                        goto err;
                length = st.st_size;
        }
        seg->length = length;

        if (offset < 0 || length < 0 ||
            ((ev_uint64_t)length > EVBUFFER_CHAIN_MAX) ||
            (ev_uint64_t)offset > (ev_uint64_t)(EVBUFFER_CHAIN_MAX - length))
                goto err;

#if defined(USE_SENDFILE)
        if (!(flags & EVBUF_FS_DISABLE_SENDFILE)) {
                seg->can_sendfile = 1;
                goto done;
        }
#endif

        if (evbuffer_file_segment_materialize(seg)<0)
                goto err;

#if defined(USE_SENDFILE)
done:
#endif
        if (!(flags & EVBUF_FS_DISABLE_LOCKING)) {
                EVTHREAD_ALLOC_LOCK(seg->lock, 0);
        }
        return seg;
err:
        mm_free(seg);
        return NULL;
}

#ifdef EVENT__HAVE_MMAP
static long
get_page_size(void)
{
#ifdef SC_PAGE_SIZE
        return sysconf(SC_PAGE_SIZE);
#elif defined(_SC_PAGE_SIZE)
        return sysconf(_SC_PAGE_SIZE);
#else
        return 1;
#endif
}
#endif

/* DOCDOC */
/* Requires lock */
static int
evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg)
{
        const unsigned flags = seg->flags;
        const int fd = seg->fd;
        const ev_off_t length = seg->length;
        const ev_off_t offset = seg->file_offset;

        if (seg->contents || seg->is_mapping)
                return 0; /* already materialized */

#if defined(EVENT__HAVE_MMAP)
        if (!(flags & EVBUF_FS_DISABLE_MMAP)) {
                off_t offset_rounded = 0, offset_leftover = 0;
                void *mapped;
                if (offset) {
                        /* mmap implementations don't generally like us
                         * to have an offset that isn't a round  */
                        long page_size = get_page_size();
                        if (page_size == -1)
                                goto err;
                        offset_leftover = offset % page_size;
                        offset_rounded = offset - offset_leftover;
                }
#if defined(EVENT__HAVE_MMAP64)
                mapped = mmap64(NULL, length + offset_leftover,
#else
                mapped = mmap(NULL, length + offset_leftover,
#endif
                    PROT_READ,
#ifdef MAP_NOCACHE
                    MAP_NOCACHE | /* ??? */
#endif
#ifdef MAP_FILE
                    MAP_FILE |
#endif
                    MAP_PRIVATE,
                    fd, offset_rounded);
                if (mapped == MAP_FAILED) {
                        event_warn("%s: mmap(%d, %d, %zu) failed",
                            __func__, fd, 0, (size_t)(offset + length));
                } else {
                        seg->mapping = mapped;
                        seg->contents = (char*)mapped+offset_leftover;
                        seg->mmap_offset = 0;
                        seg->is_mapping = 1;
                        goto done;
                }
        }
#endif
#ifdef _WIN32
        if (!(flags & EVBUF_FS_DISABLE_MMAP)) {
                intptr_t h = _get_osfhandle(fd);
                HANDLE m;
                ev_uint64_t total_size = length+offset;
                if ((HANDLE)h == INVALID_HANDLE_VALUE)
                        goto err;
                m = CreateFileMapping((HANDLE)h, NULL, PAGE_READONLY,
                    (total_size >> 32), total_size & 0xfffffffful,
                    NULL);
                if (m != INVALID_HANDLE_VALUE) { /* Does h leak? */
                        seg->mapping_handle = m;
                        seg->mmap_offset = offset;
                        seg->is_mapping = 1;
                        goto done;
                }
        }
#endif
        {
                ev_off_t start_pos = lseek(fd, 0, SEEK_CUR), pos;
                ev_off_t read_so_far = 0;
                char *mem;
                int e;
                ev_ssize_t n = 0;
                if (!(mem = mm_malloc(length)))
                        goto err;
                if (start_pos < 0) {
                        mm_free(mem);
                        goto err;
                }
                if (lseek(fd, offset, SEEK_SET) < 0) {
                        mm_free(mem);
                        goto err;
                }
                while (read_so_far < length) {
                        n = read(fd, mem+read_so_far, length-read_so_far);
                        if (n <= 0)
                                break;
                        read_so_far += n;
                }

                e = errno;
                pos = lseek(fd, start_pos, SEEK_SET);
                if (n < 0 || (n == 0 && length > read_so_far)) {
                        mm_free(mem);
                        errno = e;
                        goto err;
                } else if (pos < 0) {
                        mm_free(mem);
                        goto err;
                }

                seg->contents = mem;
        }

done:
        return 0;
err:
        return -1;
}

void evbuffer_file_segment_add_cleanup_cb(struct evbuffer_file_segment *seg,
        evbuffer_file_segment_cleanup_cb cb, void* arg)
{
        EVUTIL_ASSERT(seg->refcnt > 0);
        seg->cleanup_cb = cb;
        seg->cleanup_cb_arg = arg;
}

void
evbuffer_file_segment_free(struct evbuffer_file_segment *seg)
{
        int refcnt;
        EVLOCK_LOCK(seg->lock, 0);
        refcnt = --seg->refcnt;
        EVLOCK_UNLOCK(seg->lock, 0);
        if (refcnt > 0)
                return;
        EVUTIL_ASSERT(refcnt == 0);

        if (seg->is_mapping) {
#ifdef _WIN32
                CloseHandle(seg->mapping_handle);
#elif defined (EVENT__HAVE_MMAP)
                off_t offset_leftover;
                offset_leftover = seg->file_offset % get_page_size();
                if (munmap(seg->mapping, seg->length + offset_leftover) == -1)
                        event_warn("%s: munmap failed", __func__);
#endif
        } else if (seg->contents) {
                mm_free(seg->contents);
        }

        if ((seg->flags & EVBUF_FS_CLOSE_ON_FREE) && seg->fd >= 0) {
                close(seg->fd);
        }
        
        if (seg->cleanup_cb) {
                (*seg->cleanup_cb)((struct evbuffer_file_segment const*)seg, 
                    seg->flags, seg->cleanup_cb_arg);
                seg->cleanup_cb = NULL;
                seg->cleanup_cb_arg = NULL;
        }

        EVTHREAD_FREE_LOCK(seg->lock, 0);
        mm_free(seg);
}

int
evbuffer_add_file_segment(struct evbuffer *buf,
    struct evbuffer_file_segment *seg, ev_off_t offset, ev_off_t length)
{
        struct evbuffer_chain *chain;
        struct evbuffer_chain_file_segment *extra;
        int can_use_sendfile = 0;

        EVBUFFER_LOCK(buf);
        EVLOCK_LOCK(seg->lock, 0);
        if (buf->flags & EVBUFFER_FLAG_DRAINS_TO_FD) {
                can_use_sendfile = 1;
        } else {
                if (evbuffer_file_segment_materialize(seg)<0) {
                        EVLOCK_UNLOCK(seg->lock, 0);
                        EVBUFFER_UNLOCK(buf);
                        return -1;
                }
        }
        EVLOCK_UNLOCK(seg->lock, 0);

        if (buf->freeze_end)
                goto err;

        if (length < 0) {
                if (offset > seg->length)
                        goto err;
                length = seg->length - offset;
        }

        /* Can we actually add this? */
        if (offset+length > seg->length)
                goto err;

        chain = evbuffer_chain_new(sizeof(struct evbuffer_chain_file_segment));
        if (!chain)
                goto err;
        extra = EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_file_segment, chain);

        chain->flags |= EVBUFFER_IMMUTABLE|EVBUFFER_FILESEGMENT;
        if (can_use_sendfile && seg->can_sendfile) {
                chain->flags |= EVBUFFER_SENDFILE;
                chain->misalign = seg->file_offset + offset;
                chain->off = length;
                chain->buffer_len = chain->misalign + length;
        } else if (seg->is_mapping) {
#ifdef _WIN32
                ev_uint64_t total_offset = seg->mmap_offset+offset;
                ev_uint64_t offset_rounded=0, offset_remaining=0;
                LPVOID data;
                if (total_offset) {
                        SYSTEM_INFO si;
                        memset(&si, 0, sizeof(si)); /* cargo cult */
                        GetSystemInfo(&si);
                        offset_remaining = total_offset % si.dwAllocationGranularity;
                        offset_rounded = total_offset - offset_remaining;
                }
                data = MapViewOfFile(
                        seg->mapping_handle,
                        FILE_MAP_READ,
                        offset_rounded >> 32,
                        offset_rounded & 0xfffffffful,
                        length + offset_remaining);
                if (data == NULL) {
                        mm_free(chain);
                        goto err;
                }
                chain->buffer = (unsigned char*) data;
                chain->buffer_len = length+offset_remaining;
                chain->misalign = offset_remaining;
                chain->off = length;
#else
                chain->buffer = (unsigned char*)(seg->contents + offset);
                chain->buffer_len = length;
                chain->off = length;
#endif
        } else {
                chain->buffer = (unsigned char*)(seg->contents + offset);
                chain->buffer_len = length;
                chain->off = length;
        }

        EVLOCK_LOCK(seg->lock, 0);
        ++seg->refcnt;
        EVLOCK_UNLOCK(seg->lock, 0);
        extra->segment = seg;
        buf->n_add_for_cb += length;
        evbuffer_chain_insert(buf, chain);

        evbuffer_invoke_callbacks_(buf);

        EVBUFFER_UNLOCK(buf);

        return 0;
err:
        EVBUFFER_UNLOCK(buf);
        evbuffer_file_segment_free(seg); /* Lowers the refcount */
        return -1;
}

int
evbuffer_add_file(struct evbuffer *buf, int fd, ev_off_t offset, ev_off_t length)
{
        struct evbuffer_file_segment *seg;
        unsigned flags = EVBUF_FS_CLOSE_ON_FREE;
        int r;

        seg = evbuffer_file_segment_new(fd, offset, length, flags);
        if (!seg)
                return -1;
        r = evbuffer_add_file_segment(buf, seg, 0, length);
        if (r == 0)
                evbuffer_file_segment_free(seg);
        return r;
}

int
evbuffer_setcb(struct evbuffer *buffer, evbuffer_cb cb, void *cbarg)
{
        EVBUFFER_LOCK(buffer);

        if (!LIST_EMPTY(&buffer->callbacks))
                evbuffer_remove_all_callbacks(buffer);

        if (cb) {
                struct evbuffer_cb_entry *ent =
                    evbuffer_add_cb(buffer, NULL, cbarg);
                if (!ent) {
                        EVBUFFER_UNLOCK(buffer);
                        return -1;
                }
                ent->cb.cb_obsolete = cb;
                ent->flags |= EVBUFFER_CB_OBSOLETE;
        }
        EVBUFFER_UNLOCK(buffer);
        return 0;
}

struct evbuffer_cb_entry *
evbuffer_add_cb(struct evbuffer *buffer, evbuffer_cb_func cb, void *cbarg)
{
        struct evbuffer_cb_entry *e;
        if (! (e = mm_calloc(1, sizeof(struct evbuffer_cb_entry))))
                return NULL;
        EVBUFFER_LOCK(buffer);
        e->cb.cb_func = cb;
        e->cbarg = cbarg;
        e->flags = EVBUFFER_CB_ENABLED;
        LIST_INSERT_HEAD(&buffer->callbacks, e, next);
        EVBUFFER_UNLOCK(buffer);
        return e;
}

int
evbuffer_remove_cb_entry(struct evbuffer *buffer,
                         struct evbuffer_cb_entry *ent)
{
        EVBUFFER_LOCK(buffer);
        LIST_REMOVE(ent, next);
        EVBUFFER_UNLOCK(buffer);
        mm_free(ent);
        return 0;
}

int
evbuffer_remove_cb(struct evbuffer *buffer, evbuffer_cb_func cb, void *cbarg)
{
        struct evbuffer_cb_entry *cbent;
        int result = -1;
        EVBUFFER_LOCK(buffer);
        LIST_FOREACH(cbent, &buffer->callbacks, next) {
                if (cb == cbent->cb.cb_func && cbarg == cbent->cbarg) {
                        result = evbuffer_remove_cb_entry(buffer, cbent);
                        goto done;
                }
        }
done:
        EVBUFFER_UNLOCK(buffer);
        return result;
}

int
evbuffer_cb_set_flags(struct evbuffer *buffer,
                      struct evbuffer_cb_entry *cb, ev_uint32_t flags)
{
        /* the user isn't allowed to mess with these. */
        flags &= ~EVBUFFER_CB_INTERNAL_FLAGS;
        EVBUFFER_LOCK(buffer);
        cb->flags |= flags;
        EVBUFFER_UNLOCK(buffer);
        return 0;
}

int
evbuffer_cb_clear_flags(struct evbuffer *buffer,
                      struct evbuffer_cb_entry *cb, ev_uint32_t flags)
{
        /* the user isn't allowed to mess with these. */
        flags &= ~EVBUFFER_CB_INTERNAL_FLAGS;
        EVBUFFER_LOCK(buffer);
        cb->flags &= ~flags;
        EVBUFFER_UNLOCK(buffer);
        return 0;
}

int
evbuffer_freeze(struct evbuffer *buffer, int start)
{
        EVBUFFER_LOCK(buffer);
        if (start)
                buffer->freeze_start = 1;
        else
                buffer->freeze_end = 1;
        EVBUFFER_UNLOCK(buffer);
        return 0;
}

int
evbuffer_unfreeze(struct evbuffer *buffer, int start)
{
        EVBUFFER_LOCK(buffer);
        if (start)
                buffer->freeze_start = 0;
        else
                buffer->freeze_end = 0;
        EVBUFFER_UNLOCK(buffer);
        return 0;
}

#if 0
void
evbuffer_cb_suspend(struct evbuffer *buffer, struct evbuffer_cb_entry *cb)
{
        if (!(cb->flags & EVBUFFER_CB_SUSPENDED)) {
                cb->size_before_suspend = evbuffer_get_length(buffer);
                cb->flags |= EVBUFFER_CB_SUSPENDED;
        }
}

void
evbuffer_cb_unsuspend(struct evbuffer *buffer, struct evbuffer_cb_entry *cb)
{
        if ((cb->flags & EVBUFFER_CB_SUSPENDED)) {
                unsigned call = (cb->flags & EVBUFFER_CB_CALL_ON_UNSUSPEND);
                size_t sz = cb->size_before_suspend;
                cb->flags &= ~(EVBUFFER_CB_SUSPENDED|
                               EVBUFFER_CB_CALL_ON_UNSUSPEND);
                cb->size_before_suspend = 0;
                if (call && (cb->flags & EVBUFFER_CB_ENABLED)) {
                        cb->cb(buffer, sz, evbuffer_get_length(buffer), cb->cbarg);
                }
        }
}
#endif

int
evbuffer_get_callbacks_(struct evbuffer *buffer, struct event_callback **cbs,
    int max_cbs)
{
        int r = 0;
        EVBUFFER_LOCK(buffer);
        if (buffer->deferred_cbs) {
                if (max_cbs < 1) {
                        r = -1;
                        goto done;
                }
                cbs[0] = &buffer->deferred;
                r = 1;
        }
done:
        EVBUFFER_UNLOCK(buffer);
        return r;
}