Adding FIFO audio output. This is pretty much identical to the old one,

ChangeLog

 ver 0.14.0 (????/??/??)
-* New null audio output plugin
+* New null audio output
 * Zeroconf support using Bonjour
 * New zeroconf_enabled option so that Zeroconf support can be disabled
 * Enable the AAC input plugin if support for it has been compiled in
@@ -8,6 +8,7 @@ ver 0.14.0 (????/??/??)
 * Fix a bug where closing an ALSA dmix device could cause MPD to hang
 * Make the shout output block while trying to connect instead of failing
 * New timeout parameter for shout outputs to define a connection timeout
+* New FIFO audio output
 
 ver 0.13.0 (2007/5/28)
 * New JACK audio output

configure.ac

@@ -69,6 +69,7 @@ AC_ARG_ENABLE(oss,[  --disable-oss           disable OSS support (default: enabl
 AC_ARG_ENABLE(alsa,[  --disable-alsa          disable ALSA support (default: enable)],[enable_alsa=$enableval],[enable_alsa=yes])
 AC_ARG_ENABLE(jack,[  --disable-jack          disable jack support (default: enable)],[enable_jack=$enableval],[enable_jack=yes])
 AC_ARG_ENABLE(pulse,[  --disable-pulse         disable support for the PulseAudio sound server (default: enable)],[enable_pulse=$enableval],[enable_pulse=yes])
+AC_ARG_ENABLE(fifo,[  --disable-fifo          disable support for writing audio to a FIFO (default: enable)],[enable_fifo=$enableval],[enable_fifo=yes])
 AC_ARG_ENABLE(mvp,[  --enable-mvp            enable support for Hauppauge Media MVP (default: disable)],[enable_mvp=$enableval],[enable_mvp=no])
 AC_ARG_ENABLE(oggvorbis,[  --disable-oggvorbis     disable Ogg Vorbis support (default: enable)],[enable_oggvorbis=$enableval],enable_oggvorbis=yes)
 AC_ARG_ENABLE(oggflac,[  --disable-oggflac       disable OggFLAC support (default: enable)],[enable_oggflac=$enableval],enable_oggflac=yes)
@@ -197,6 +198,12 @@ if test x$enable_lsr = xyes; then
 	                  [enable_lsr=no;AC_MSG_WARN([libsamplerate not found -- disabling])])
 fi
 
+if test x$enable_fifo = xyes; then
+	AC_CHECK_FUNC([mkfifo],
+	              [enable_fifo=yes;AC_DEFINE([HAVE_FIFO], 1, [Define to enable support for writing audio to a FIFO])],
+	              [enable_fifo=no;AC_MSG_WARN([mkfifo not found -- disabling support for writing audio to a FIFO])])
+fi
+
 if test x$enable_mvp = xyes; then
    AC_DEFINE(HAVE_MVP,1,[Define to enable Hauppauge Media MVP support])
 fi
@@ -664,6 +671,12 @@ else
 	echo " PulseAudio support ............disabled"
 fi
 
+if test x$enable_fifo = xyes; then
+	echo " FIFO support ..................enabled"
+else
+	echo " FIFO support ..................disabled"
+fi
+
 if test x$enable_mvp = xyes; then
 	echo " Media MVP support .............enabled"
 else
@@ -685,6 +698,7 @@ if test x$enable_ao = xno &&
    test x$enable_osx = xno &&
    test x$enable_pulse = xno &&
    test x$enable_jack = xno &&
+   test x$enable_fifo = xno &&
    test x$enable_mvp = xno; then
 	AC_MSG_ERROR([No Audio Output types configured!])
 fi

doc/mpd.conf.5

@@ -335,6 +335,17 @@ default is "".
 This specifies how many bytes to write to the audio device at once.  This
 parameter is to work around a bug in older versions of libao on sound cards
 with very small buffers.  The default is 1024.
+.SH REQUIRED FIFO OUTPUT PARAMETERS
+.TP
+.B path <path>
+This specifies the path of the FIFO to output to.  Must be an absolute path.
+If the path does not exist it will be created when mpd is started, and removed
+when mpd is stopped.  The FIFO will be created with the same user and group as
+mpd is running as.  Default permissions can be modified by using the builtin
+shell command "umask".  If a FIFO already exists at the specified path it will
+be reused, and will \fBnot\fP be removed when mpd is stopped.  You can use the
+"mkfifo" command to create this, and then you may modify the permissions to
+your liking.
 .SH REQUIRED SHOUT OUTPUT PARAMETERS
 .TP
 .B name <name>

src/Makefile.am

@@ -2,14 +2,15 @@ bin_PROGRAMS = mpd
 SUBDIRS = $(MP4FF_SUBDIR)
 
 mpd_audioOutputs = \
+	audioOutputs/audioOutput_shout.c \
 	audioOutputs/audioOutput_null.c \
+	audioOutputs/audioOutput_fifo.c \
 	audioOutputs/audioOutput_alsa.c \
 	audioOutputs/audioOutput_ao.c \
 	audioOutputs/audioOutput_oss.c \
 	audioOutputs/audioOutput_osx.c \
 	audioOutputs/audioOutput_pulse.c \
 	audioOutputs/audioOutput_mvp.c \
-	audioOutputs/audioOutput_shout.c \
 	audioOutputs/audioOutput_jack.c
 
 mpd_inputPlugins = \

src/audio.c

@@ -94,6 +94,7 @@ void loadAudioDrivers(void)
 	initAudioOutputPlugins();
 	loadAudioOutputPlugin(&shoutPlugin);
 	loadAudioOutputPlugin(&nullPlugin);
+	loadAudioOutputPlugin(&fifoPlugin);
 	loadAudioOutputPlugin(&alsaPlugin);
 	loadAudioOutputPlugin(&aoPlugin);
 	loadAudioOutputPlugin(&ossPlugin);

src/audioOutput.h

@@ -107,6 +107,7 @@ void printAllOutputPluginTypes(FILE * fp);
 
 extern AudioOutputPlugin shoutPlugin;
 extern AudioOutputPlugin nullPlugin;
+extern AudioOutputPlugin fifoPlugin;
 extern AudioOutputPlugin alsaPlugin;
 extern AudioOutputPlugin aoPlugin;
 extern AudioOutputPlugin ossPlugin;

src/audioOutputs/audioOutput_fifo.c

+/* the Music Player Daemon (MPD)
+ * Copyright (C) 2003-2007 by Warren Dukes (warren.dukes@gmail.com)
+ * This project's homepage is: http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "../audioOutput.h"
+
+#include <stdlib.h>
+
+#ifdef HAVE_FIFO
+
+#include "../log.h"
+#include "../conf.h"
+#include "../utils.h"
+#include "../timer.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#define FIFO_BUFFER_SIZE 65536 /* pipe capacity on Linux >= 2.6.11 */
+
+typedef struct _FifoData {
+	char *path;
+	int input;
+	int output;
+	int created;
+	Timer *timer;
+} FifoData;
+
+static FifoData *newFifoData()
+{
+	FifoData *ret;
+
+	ret = xmalloc(sizeof(FifoData));
+
+	ret->path = NULL;
+	ret->input = -1;
+	ret->output = -1;
+	ret->created = 0;
+	ret->timer = NULL;
+	
+	return ret;
+}
+
+static void freeFifoData(FifoData *fd)
+{
+	if (fd->path)
+		free(fd->path);
+
+	if (fd->timer)
+		timer_free(fd->timer);
+
+	free(fd);
+}
+
+static void removeFifo(FifoData *fd)
+{
+	DEBUG("Removing FIFO \"%s\"\n", fd->path);
+
+	if (unlink(fd->path) < 0) {
+		ERROR("Could not remove FIFO \"%s\": %s\n",
+		      fd->path, strerror(errno));
+		return;
+	}
+
+	fd->created = 0;
+}
+
+static void closeFifo(FifoData *fd)
+{
+	struct stat st;
+
+	if (fd->input >= 0) {
+		close(fd->input);
+		fd->input = -1;
+	}
+
+	if (fd->output >= 0) {
+		close(fd->output);
+		fd->output = -1;
+	}
+
+	if (fd->created && (stat(fd->path, &st) == 0))
+		removeFifo(fd);
+}
+
+static int makeFifo(FifoData *fd)
+{
+	if (mkfifo(fd->path, 0666) < 0) {
+		ERROR("Couldn't create FIFO \"%s\": %s\n",
+		      fd->path, strerror(errno));
+		return -1;
+	}
+
+	fd->created = 1;
+
+	return 0;
+}
+
+static int checkFifo(FifoData *fd)
+{
+	struct stat st;
+
+	if (stat(fd->path, &st) < 0) {
+		if (errno == ENOENT) {
+			/* Path doesn't exist */
+			return makeFifo(fd);
+		}
+
+		ERROR("Failed to stat FIFO \"%s\": %s\n",
+		      fd->path, strerror(errno));
+		return -1;
+	}
+
+	if (!S_ISFIFO(st.st_mode)) {
+		ERROR("\"%s\" already exists, but is not a FIFO\n", fd->path);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int openFifo(FifoData *fd)
+{
+	if (checkFifo(fd) < 0)
+		return -1;
+
+	fd->input = open(fd->path, O_RDONLY|O_NONBLOCK);
+	if (fd->input < 0) {
+		ERROR("Could not open FIFO \"%s\" for reading: %s\n",
+		      fd->path, strerror(errno));
+		closeFifo(fd);
+		return -1;
+	}
+
+	fd->output = open(fd->path, O_WRONLY|O_NONBLOCK);
+	if (fd->output < 0) {
+		ERROR("Could not open FIFO \"%s\" for writing: %s\n",
+		      fd->path, strerror(errno));
+		closeFifo(fd);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int fifo_initDriver(AudioOutput *audioOutput, ConfigParam *param)
+{
+	FifoData *fd;
+	BlockParam *path = NULL;
+
+	if (param)
+		path = getBlockParam(param, "path");
+
+	if (!path) {
+		FATAL("No \"path\" parameter specified for fifo output "
+		      "defined at line %i\n", param->line);
+	}
+
+	if (path->value[0] != '/') {
+		FATAL("\"path\" parameter for fifo output is not an absolute "
+		      "path at line %i\n", param->line);
+	}
+
+	fd = newFifoData();
+	fd->path = xstrdup(path->value);
+	audioOutput->data = fd;
+
+	if (openFifo(fd) < 0) {
+		freeFifoData(fd);
+		return -1;
+	}
+
+	return 0;
+}
+
+static void fifo_finishDriver(AudioOutput *audioOutput)
+{
+	FifoData *fd = (FifoData *)audioOutput->data;
+
+	closeFifo(fd);
+	freeFifoData(fd);
+}
+
+static int fifo_openDevice(AudioOutput *audioOutput)
+{
+	FifoData *fd = (FifoData *)audioOutput->data;
+
+	if (fd->timer)
+		timer_free(fd->timer);
+
+	fd->timer = timer_new(&audioOutput->outAudioFormat);
+
+	audioOutput->open = 1;
+
+	return 0;
+}
+
+static void fifo_closeDevice(AudioOutput *audioOutput)
+{
+	FifoData *fd = (FifoData *)audioOutput->data;
+
+	if (fd->timer) {
+		timer_free(fd->timer);
+		fd->timer = NULL;
+	}
+
+	audioOutput->open = 0;
+}
+
+static void fifo_dropBufferedAudio(AudioOutput *audioOutput)
+{
+	FifoData *fd = (FifoData *)audioOutput->data;
+	char buf[FIFO_BUFFER_SIZE];
+	int bytes = 1;
+
+	timer_reset(fd->timer);
+
+	while (bytes > 0 && errno != EINTR)
+		bytes = read(fd->input, buf, FIFO_BUFFER_SIZE);
+
+	if (bytes < 0 && errno != EAGAIN) {
+		WARNING("Flush of FIFO \"%s\" failed: %s\n",
+		        fd->path, strerror(errno));
+	}
+}
+
+static int fifo_playAudio(AudioOutput *audioOutput, char *playChunk, int size)
+{
+	FifoData *fd = (FifoData *)audioOutput->data;
+	int offset = 0;
+	int bytes;
+
+	if (!fd->timer->started)
+		timer_start(fd->timer);
+	else
+		timer_sync(fd->timer);
+
+	timer_add(fd->timer, size);
+
+	while (size) {
+		bytes = write(fd->output, playChunk + offset, size);
+		if (bytes < 0) {
+			switch (errno) {
+			case EAGAIN:
+				/* The pipe is full, so empty it */
+				fifo_dropBufferedAudio(audioOutput);
+				continue;
+			case EINTR:
+				continue;
+			}
+
+			ERROR("Closing FIFO output \"%s\" due to write error: "
+			      "%s\n", fd->path, strerror(errno));
+			fifo_closeDevice(audioOutput);
+			return -1;
+		}
+
+		size -= bytes;
+		offset += bytes;
+	}
+
+	return 0;
+}
+
+AudioOutputPlugin fifoPlugin = {
+	"fifo",
+	NULL, /* testDefaultDeviceFunc */
+	fifo_initDriver,
+	fifo_finishDriver,
+	fifo_openDevice,
+	fifo_playAudio,
+	fifo_dropBufferedAudio,
+	fifo_closeDevice,
+	NULL, /* sendMetadataFunc */
+};
+
+#else /* HAVE_FIFO */
+
+DISABLED_AUDIO_OUTPUT_PLUGIN(fifoPlugin)
+
+#endif /* !HAVE_FIFO */