shairport-sync/audio_pipe.c

/*
 * pipe output driver. This file is part of Shairport.
 * Copyright (c) James Laird 2013
 * All rights reserved.
 *
 * Modifications for audio synchronisation
 * and related work, copyright (c) Mike Brady 2014
 * All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#include "audio.h"
#include "common.h"
#include <errno.h>
#include <fcntl.h>
#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

static int fd = -1;

char *pipename = NULL;
int warned = 0;

static void start(__attribute__((unused)) int sample_rate,
                  __attribute__((unused)) int sample_format) {
  
  
  // this will leave fd as -1 if a reader hasn't been attached to the pipe
  // we check that it's not a "real" error though. From the "man 2 open" page:
  // "ENXIO  O_NONBLOCK | O_WRONLY is set, the named file is a FIFO, and no process has the FIFO open for reading."
  fd = open(pipename, O_WRONLY | O_NONBLOCK);
  if ((fd == -1) && (errno != ENXIO) && (warned == 0)) {
    char errorstring[1024];
    strerror_r(errno, (char *)errorstring, sizeof(errorstring));
    debug(1, "pipe: start -- error %d (\"%s\") opening the pipe named \"%s\".", errno, (char*)errorstring, pipename);
    warn("Error %d opening the pipe named \"%s\".", errno, pipename);
    warned = 1;
  }
}

static int play(void *buf, int samples) {
  // if the file is not open, try to open it.
  char errorstring[1024];
  if (fd == -1) {
    fd = open(pipename, O_WRONLY | O_NONBLOCK);
  }
  // if it's got a reader, write to it.
  if (fd > 0) {
    int rc = non_blocking_write(fd, buf, samples * 4);
    if ((rc < 0) && (warned == 0)) {
      strerror_r(errno, (char *)errorstring, 1024);
      warn("Error %d writing to the pipe named \"%s\": \"%s\".", errno, pipename, errorstring);
      warned = 1;
    }
  } else if ((fd == -1) && (errno != ENXIO) && (warned == 0)) {
    strerror_r(errno, (char *)errorstring, 1024);
    warn("Error %d opening the pipe named \"%s\": \"%s\".", errno, pipename, errorstring);
    warned = 1;
  }
  return warned;
}

static void stop(void) {
  // Don't close the pipe just because a play session has stopped.
  //  if (fd > 0)
  //    close(fd);
}

static int init(int argc, char **argv) {
  debug(1, "pipe init");
  //  const char *str;
  //  int value;
  //  double dvalue;

  // set up default values first

  config.audio_backend_buffer_desired_length = 1.0;
  config.audio_backend_latency_offset = 0;

  // do the "general" audio  options. Note, these options are in the "general" stanza!
  parse_general_audio_options();

  if (config.cfg != NULL) {
    /* Get the Output Pipename. */
    const char *str;
    if (config_lookup_string(config.cfg, "pipe.name", &str)) {
      pipename = (char *)str;
    }

    if ((pipename) && (strcasecmp(pipename, "STDOUT") == 0))
      die("Can't use \"pipe\" backend for STDOUT. Use the \"stdout\" backend instead.");
  }

  if ((pipename == NULL) && (argc != 1))
    die("bad or missing argument(s) to pipe");

  if (argc == 1)
    pipename = strdup(argv[0]);

  // here, create the pipe
  if (mkfifo(pipename, 0644) && errno != EEXIST)
    die("Could not create output pipe \"%s\"", pipename);

  debug(1, "Pipename is \"%s\"", pipename);

  return 0;
}

static void deinit(void) {
  if (fd > 0)
    close(fd);
}

static void help(void) { printf("    specify the pathname of the pipe to write to.\n"); }

audio_output audio_pipe = {.name = "pipe",
                           .help = &help,
                           .init = &init,
                           .deinit = &deinit,
                           .prepare = NULL,
                           .start = &start,
                           .stop = &stop,
                           .is_running = NULL,
                           .flush = NULL,
                           .delay = NULL,
                           .play = &play,
                           .volume = NULL,
                           .parameters = NULL,
                           .mute = NULL};