granicus.if.org Git - strace/blob - stage_output.c

   1 /*
   2  * Copyright (c) 2017 Intel Corporation
   3  * Copyright (c) 2019 Paul Chaignon <paul.chaignon@gmail.com>
   4  * All rights reserved.
   5  *
   6  * SPDX-License-Identifier: LGPL-2.1-or-later
   7  */
   8
   9 /*
  10  * open_memstream returns a FILE stream that allows writing to a
  11  * dynamically growing buffer, that can be either copied to
  12  * tcp->outf (syscall successful) or dropped (syscall failed)
  13  */
  14
  15 #include "defs.h"
  16
  17 struct staged_output_data {
  18         char *memfptr;
  19         size_t memfloc;
  20         FILE *real_outf;        /* Backup for real outf while staging */
  21 };
  22
  23 FILE *
  24 strace_open_memstream(struct tcb *tcp)
  25 {
  26         FILE *fp = NULL;
  27
  28 #if HAVE_OPEN_MEMSTREAM
  29         tcp->staged_output_data = xmalloc(sizeof(*tcp->staged_output_data));
  30         fp = open_memstream(&tcp->staged_output_data->memfptr,
  31                             &tcp->staged_output_data->memfloc);
  32         if (!fp)
  33                 perror_msg_and_die("open_memstream");
  34         /*
  35          * Call to fflush required to update tcp->memfptr,
  36          * see open_memstream man page.
  37          */
  38         fflush(fp);
  39
  40         /* Store the FILE pointer for later restauration. */
  41         tcp->staged_output_data->real_outf = tcp->outf;
  42         tcp->outf = fp;
  43 #endif
  44
  45         return fp;
  46 }
  47
  48 void
  49 strace_close_memstream(struct tcb *tcp, bool publish)
  50 {
  51 #if HAVE_OPEN_MEMSTREAM
  52         if (!tcp->staged_output_data) {
  53                 debug_msg("memstream already closed");
  54                 return;
  55         }
  56
  57         if (fclose(tcp->outf))
  58                 perror_msg("fclose(tcp->outf)");
  59
  60         tcp->outf = tcp->staged_output_data->real_outf;
  61         if (tcp->staged_output_data->memfptr) {
  62                 if (publish)
  63                         fputs_unlocked(tcp->staged_output_data->memfptr,
  64                                        tcp->outf);
  65                 else
  66                         debug_msg("syscall output dropped: %s",
  67                                   tcp->staged_output_data->memfptr);
  68
  69                 free(tcp->staged_output_data->memfptr);
  70                 tcp->staged_output_data->memfptr = NULL;
  71         }
  72         free(tcp->staged_output_data);
  73         tcp->staged_output_data = NULL;
  74 #endif
  75 }