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pacat: Write to stream only in frame-sized chunks

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Current pacat code reads whatever available from STDIN and writes
it directly to the playback stream. A minimal buffer is created
for each read operation; no further reads are then allowed unless
earlier read buffer has been fully consumed by a stream write.

While quite simple, this model breaks upon the new requirements of
writing only frame-aligned data to the stream (commits #1 and #2).
The kernel read syscall can return a length much smaller than the
frame-aligned size requested, leading to invalid unaligned writes.

This can easily be reproduced by choosing a starved STDIN backend:

  pacat /dev/random    pa_stream_write() failed: EINVAL
  echo 1234 | pacat    pa_stream_write() failed: EINVAL

or by playing an incomplete WAV file in raw, non-paplay, mode.

So guard against such incomplete kernel reads by writing only in
frame-aligned sizes, while caching any trailing partial frame for
subsequent writes.

Other operation modes are not affected. Non-raw paplay playback is
handled by libsndfile, ensuring complete reads, and recording mode
just writes to the STDOUT fd without any special needs.

CommitReference #1: 22827a5e1e
CommitReference #2: 150ace90f3
BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=98475
BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=77595

Suggested-by: David Henningsson <diwic@ubuntu.com>
Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
This commit is contained in:
Ahmed S. Darwish 2016-12-20 09:07:31 +00:00 • committed by Tanu Kaskinen
parent 65958ca833
commit f7b8df50c7
1 changed files with 53 additions and 45 deletions
Download patch file Download diff file Expand all files Collapse all files

98
src/utils/pacat.c
View file

@ -56,6 +56,23 @@ static pa_context *context = NULL;
static pa_stream *stream = NULL;
static pa_mainloop_api *mainloop_api = NULL;
/* Playback Mode (raw):
*
* We can only write audio to the PA stream in multiples of the stream's
* sample-spec frame size. Meanwhile, the STDIN read(2) system call can return
* a length much smaller than the frame-aligned size requested - leading to
* invalid writes. This can be reproduced by choosing a starved STDIN backend
* (e.g. "pacat /dev/random", "echo 1234 | pacat"), or an incomplete WAV file
* in raw non-paplay mode.
*
* Solve this by writing only frame-aligned sizes, while caching the resulting
* trailing partial frames here. This partial frame is then directly written
* in the next stream write iteration. Rinse and repeat.
*/
static void *partialframe_buf = NULL;
static size_t partialframe_len = 0;
/* Recording Mode buffers */
static void *buffer = NULL;
static size_t buffer_length = 0, buffer_index = 0;
@ -153,34 +170,6 @@ static void start_drain(void) {
quit(0);
}
/* Write some data to the stream */
static void do_stream_write(size_t length) {
size_t l;
pa_assert(length);
if (!buffer || !buffer_length)
return;
l = length;
if (l > buffer_length)
l = buffer_length;
if (pa_stream_write(stream, (uint8_t*) buffer + buffer_index, l, NULL, 0, PA_SEEK_RELATIVE) < 0) {
pa_log(_("pa_stream_write() failed: %s"), pa_strerror(pa_context_errno(context)));
quit(1);
return;
}
buffer_length -= l;
buffer_index += l;
if (!buffer_length) {
pa_xfree(buffer);
buffer = NULL;
buffer_index = buffer_length = 0;
}
}
/* This is called whenever new data may be written to the stream */
static void stream_write_callback(pa_stream *s, size_t length, void *userdata) {
pa_assert(s);
@ -192,11 +181,6 @@ static void stream_write_callback(pa_stream *s, size_t length, void *userdata) {
if (stdio_event)
mainloop_api->io_enable(stdio_event, PA_IO_EVENT_INPUT);
if (!buffer)
return;
do_stream_write(length);
} else {
sf_count_t bytes;
void *data;
@ -540,25 +524,34 @@ fail:
/* New data on STDIN **/
static void stdin_callback(pa_mainloop_api*a, pa_io_event *e, int fd, pa_io_event_flags_t f, void *userdata) {
size_t l, w = 0;
ssize_t r;
bool stream_not_ready;
uint8_t *buf = NULL;
size_t writable, towrite, r;
pa_assert(a == mainloop_api);
pa_assert(e);
pa_assert(stdio_event == e);
stream_not_ready = !stream || pa_stream_get_state(stream) != PA_STREAM_READY ||
!(l = w = pa_stream_writable_size(stream));
/* Stream not ready? */
if (!stream || pa_stream_get_state(stream) != PA_STREAM_READY ||
!(writable = pa_stream_writable_size(stream))) {
if (buffer || stream_not_ready) {
mainloop_api->io_enable(stdio_event, PA_IO_EVENT_NULL);
return;
}
buffer = pa_xmalloc(l);
if (pa_stream_begin_write(stream, (void **)&buf, &writable) < 0) {
pa_log(_("pa_stream_begin_write() failed: %s"), pa_strerror(pa_context_errno(context)));
quit(1);
return;
}
if ((r = pa_read(fd, buffer, l, userdata)) <= 0) {
/* Partial frame cached from a previous write iteration? */
if (partialframe_len) {
pa_assert(partialframe_len < pa_frame_size(&sample_spec));
memcpy(buf, partialframe_buf, partialframe_len);
}
if ((r = pa_read(fd, buf + partialframe_len, writable - partialframe_len, userdata)) <= 0) {
if (r == 0) {
if (verbose)
pa_log(_("Got EOF."));
@ -574,12 +567,23 @@ static void stdin_callback(pa_mainloop_api*a, pa_io_event *e, int fd, pa_io_even
stdio_event = NULL;
return;
}
r += partialframe_len;
buffer_length = (uint32_t) r;
buffer_index = 0;
/* Cache any trailing partial frames for the next write */
towrite = pa_frame_align(r, &sample_spec);
partialframe_len = r - towrite;
if (w)
do_stream_write(w);
if (partialframe_len)
memcpy(partialframe_buf, buf + towrite, partialframe_len);
if (towrite) {
if (pa_stream_write(stream, buf, towrite, NULL, 0, PA_SEEK_RELATIVE) < 0) {
pa_log(_("pa_stream_write() failed: %s"), pa_strerror(pa_context_errno(context)));
quit(1);
return;
}
} else
pa_stream_cancel_write(stream);
}
/* Some data may be written to STDOUT */
@ -1148,6 +1152,9 @@ int main(int argc, char *argv[]) {
}
}
if (raw && mode == PLAYBACK)
partialframe_buf = pa_xmalloc(pa_frame_size(&sample_spec));
/* Set up a new main loop */
if (!(m = pa_mainloop_new())) {
pa_log(_("pa_mainloop_new() failed."));
@ -1229,6 +1236,7 @@ quit:
pa_xfree(silence_buffer);
pa_xfree(buffer);
pa_xfree(partialframe_buf);
pa_xfree(server);
pa_xfree(device);