1  /*
       2   * Copyright (c) 2017 Intel Corporation
       3   * Copyright (c) 2019 Paul Chaignon <paul.chaignon@gmail.com>
       4   * Copyright (c) 2019-2023 The strace developers.
       5   * All rights reserved.
       6   *
       7   * SPDX-License-Identifier: LGPL-2.1-or-later
       8   */
       9  
      10  /*
      11   * open_memstream returns a FILE stream that allows writing to a
      12   * dynamically growing buffer, that can be either copied to
      13   * tcp->outf (syscall successful) or dropped (syscall failed)
      14   */
      15  
      16  #include "defs.h"
      17  
      18  struct staged_output_data {
      19  	char *memfptr;
      20  	size_t memfloc;
      21  	FILE *real_outf;	/* Backup for real outf while staging */
      22  };
      23  
      24  FILE *
      25  strace_open_memstream(struct tcb *tcp)
      26  {
      27  	FILE *fp = NULL;
      28  
      29  #ifdef HAVE_OPEN_MEMSTREAM
      30  	tcp->staged_output_data = xmalloc(sizeof(*tcp->staged_output_data));
      31  	fp = open_memstream(&tcp->staged_output_data->memfptr,
      32  			    &tcp->staged_output_data->memfloc);
      33  	if (!fp)
      34  		perror_msg_and_die("open_memstream");
      35  	/*
      36  	 * Call to fflush required to update tcp->memfptr,
      37  	 * see open_memstream man page.
      38  	 */
      39  	fflush(fp);
      40  
      41  	/* Store the FILE pointer for later restoration. */
      42  	tcp->staged_output_data->real_outf = tcp->outf;
      43  	tcp->outf = fp;
      44  #endif
      45  
      46  	return fp;
      47  }
      48  
      49  void
      50  strace_close_memstream(struct tcb *tcp, bool publish)
      51  {
      52  #ifdef HAVE_OPEN_MEMSTREAM
      53  	if (!tcp->staged_output_data) {
      54  		debug_msg("memstream already closed");
      55  		return;
      56  	}
      57  
      58  	if (fclose(tcp->outf))
      59  		perror_msg("fclose(tcp->outf)");
      60  
      61  	tcp->outf = tcp->staged_output_data->real_outf;
      62  	if (tcp->staged_output_data->memfptr) {
      63  		if (publish)
      64  			fputs_unlocked(tcp->staged_output_data->memfptr,
      65  				       tcp->outf);
      66  		else
      67  			debug_msg("syscall output dropped: %s",
      68  				  tcp->staged_output_data->memfptr);
      69  
      70  		free(tcp->staged_output_data->memfptr);
      71  		tcp->staged_output_data->memfptr = NULL;
      72  	}
      73  	free(tcp->staged_output_data);
      74  	tcp->staged_output_data = NULL;
      75  #endif
      76  }