From: Nick Mathewson <nickm@torproject.org>
Date: Fri, 26 Mar 2010 18:51:39 +0000 (-0400)
Subject: Make evbuffer_prepend handle empty buffers better
X-Git-Tag: release-2.0.5-beta~70
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=c87272b7b91b4f443092eb2a81f03c83457ab03a;p=libevent

Make evbuffer_prepend handle empty buffers better

If the first chunk of a buffer is empty, and we're told to prepend to
the buffer, we should be willing to use the entire first chunk.
Instead, we were dependent on the value of chunk->misalign.
---

diff --git a/buffer.c b/buffer.c
index 06974bad..5cbd10b1 100644
--- a/buffer.c
+++ b/buffer.c
@@ -1398,8 +1398,13 @@ evbuffer_prepend(struct evbuffer *buf, const void *data, size_t datlen)
 
 	/* we cannot touch immutable buffers */
 	if ((chain->flags & EVBUFFER_IMMUTABLE) == 0) {
+		/* 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 */
+			/* we have enough space to fit everything */
 			memcpy(chain->buffer + chain->misalign - datlen,
 			    data, datlen);
 			chain->off += datlen;
@@ -1408,6 +1413,7 @@ evbuffer_prepend(struct evbuffer *buf, const void *data, size_t 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,
 			    chain->misalign);