[pulseaudio-discuss] [PATCH v2 3/3] resampler: Add support for resamplers that consume less data than asked.

[Tanu Kaskinen]

libsamplerate_resample() assumed that src_process() would
always consume the whole input buffer. That was an invalid
assumption leading to crashes.

This patch adds a leftover memchunk for storing any
non-consumed input. When pa_resampler_run() is called next
time, the leftover is prepended to the new input.

Changes in v2:
 - If add_leftover() is called with zero-length input while
   the leftover length is non-zero, we don't try to acquire
   the input memblock.
 - Instead of taking a reference to the original input in
   libsamplerate_resample(), we copy the leftover data to a
   new memblock. This is done, because otherwise, if the
   input is one of the internal buffers, the data can get
   overwritten before reading it in add_leftover().
 - Store add_leftover_buf size in bytes instead of samples
   (more convenient, but less consistent with other code).

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=47156
---
 src/pulsecore/resampler.c |   94 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 87 insertions(+), 7 deletions(-)

diff --git a/src/pulsecore/resampler.c b/src/pulsecore/resampler.c
index 258d1fe..ef014f8 100644
--- a/src/pulsecore/resampler.c
+++ b/src/pulsecore/resampler.c
@@ -58,12 +58,16 @@ struct pa_resampler {
 
     pa_memchunk to_work_format_buf;
     pa_memchunk remap_buf;
+    pa_memchunk add_leftover_buf; /* For concatenating leftover with input. */
     pa_memchunk resample_buf;
     pa_memchunk from_work_format_buf;
+    pa_memchunk leftover_buf; /* For storing the leftover data. */
     unsigned to_work_format_buf_samples;
     unsigned remap_buf_samples;
+    unsigned add_leftover_buf_bytes;
     unsigned resample_buf_samples;
     unsigned from_work_format_buf_samples;
+    unsigned leftover_buf_bytes;
 
     pa_sample_format_t work_format;
 
@@ -344,10 +348,14 @@ void pa_resampler_free(pa_resampler *r) {
         pa_memblock_unref(r->to_work_format_buf.memblock);
     if (r->remap_buf.memblock)
         pa_memblock_unref(r->remap_buf.memblock);
+    if (r->add_leftover_buf.memblock)
+        pa_memblock_unref(r->add_leftover_buf.memblock);
     if (r->resample_buf.memblock)
         pa_memblock_unref(r->resample_buf.memblock);
     if (r->from_work_format_buf.memblock)
         pa_memblock_unref(r->from_work_format_buf.memblock);
+    if (r->leftover_buf.memblock)
+        pa_memblock_unref(r->leftover_buf.memblock);
 
     pa_xfree(r);
 }
@@ -379,17 +387,24 @@ void pa_resampler_set_output_rate(pa_resampler *r, uint32_t rate) {
 size_t pa_resampler_request(pa_resampler *r, size_t out_length) {
     pa_assert(r);
 
-    /* Let's round up here */
-
+    /* Let's round up here to make it more likely that the caller will get at
+     * least out_length amount of data from pa_resampler_run().
+     *
+     * We don't take the leftover into account here. If we did, then it might
+     * be in theory possible that this function would return 0 and
+     * pa_resampler_run() would also return 0. That could lead to infinite
+     * loops. When the leftover is ignored here, such loops would eventually
+     * terminate, because the leftover would grow each round, finally
+     * surpassing the minimum input threshold of the resampler. */
     return (((((out_length + r->o_fz-1) / r->o_fz) * r->i_ss.rate) + r->o_ss.rate-1) / r->o_ss.rate) * r->i_fz;
 }
 
 size_t pa_resampler_result(pa_resampler *r, size_t in_length) {
     pa_assert(r);
 
-    /* Let's round up here */
-
-    return (((((in_length + r->i_fz-1) / r->i_fz) * r->o_ss.rate) + r->i_ss.rate-1) / r->i_ss.rate) * r->o_fz;
+    /* Let's round up here to ensure that the caller will always allocate big
+     * enough output buffer. */
+    return (((((in_length + r->i_fz-1) / r->i_fz + r->leftover_buf.length / r->o_fz) * r->o_ss.rate) + r->i_ss.rate-1) / r->i_ss.rate) * r->o_fz;
 }
 
 size_t pa_resampler_max_block_size(pa_resampler *r) {
@@ -413,7 +428,7 @@ size_t pa_resampler_max_block_size(pa_resampler *r) {
 
     fs = pa_frame_size(&ss);
 
-    return (((block_size_max/fs - EXTRA_FRAMES)*r->i_ss.rate)/ss.rate)*r->i_fz;
+    return (((block_size_max / fs - EXTRA_FRAMES - r->leftover_buf.length / r->o_fz) * r->i_ss.rate) / ss.rate) * r->i_fz;
 }
 
 void pa_resampler_reset(pa_resampler *r) {
@@ -421,6 +436,11 @@ void pa_resampler_reset(pa_resampler *r) {
 
     if (r->impl_reset)
         r->impl_reset(r);
+
+    if (r->leftover_buf.memblock) {
+        pa_memblock_unref(r->leftover_buf.memblock);
+        r->leftover_buf.length = 0;
+    }
 }
 
 pa_resample_method_t pa_resampler_get_method(pa_resampler *r) {
@@ -1143,6 +1163,48 @@ static pa_memchunk *remap_channels(pa_resampler *r, pa_memchunk *input) {
     return &r->remap_buf;
 }
 
+static pa_memchunk *add_leftover(pa_resampler *r, pa_memchunk *input) {
+    void *src;
+    void *dst;
+
+    pa_assert(r);
+    pa_assert(input);
+
+    /* Concatenate leftover and input and place the result in
+     * add_leftover_buf. */
+
+    if (r->leftover_buf.length <= 0)
+        return input;
+
+    r->add_leftover_buf.length = r->leftover_buf.length + input->length;
+
+    if (!r->add_leftover_buf.memblock || r->add_leftover_buf_bytes < r->add_leftover_buf.length) {
+        if (r->add_leftover_buf.memblock)
+            pa_memblock_unref(r->add_leftover_buf.memblock);
+
+        r->add_leftover_buf_bytes = r->add_leftover_buf.length;
+        r->add_leftover_buf.memblock = pa_memblock_new(r->mempool, r->add_leftover_buf.length);
+    }
+
+    src = (uint8_t *) pa_memblock_acquire(r->leftover_buf.memblock);
+    dst = pa_memblock_acquire(r->add_leftover_buf.memblock);
+    memcpy(dst, src, r->leftover_buf.length);
+    pa_memblock_release(r->leftover_buf.memblock);
+
+    if (input->length > 0) {
+        src = (uint8_t *) pa_memblock_acquire(input->memblock) + input->index;
+        dst = (uint8_t *) dst + r->leftover_buf.length;
+        memcpy(dst, src, input->length);
+        pa_memblock_release(input->memblock);
+    }
+
+    pa_memblock_release(r->add_leftover_buf.memblock);
+
+    r->leftover_buf.length = 0;
+
+    return &r->add_leftover_buf;
+}
+
 static pa_memchunk *resample(pa_resampler *r, pa_memchunk *input) {
     unsigned in_n_frames, in_n_samples;
     unsigned out_n_frames, out_n_samples;
@@ -1229,6 +1291,7 @@ void pa_resampler_run(pa_resampler *r, const pa_memchunk *in, pa_memchunk *out)
     buf = (pa_memchunk*) in;
     buf = convert_to_work_format(r, buf);
     buf = remap_channels(r, buf);
+    buf = add_leftover(r, buf);
     buf = resample(r, buf);
 
     if (buf->length) {
@@ -1266,7 +1329,24 @@ static void libsamplerate_resample(pa_resampler *r, const pa_memchunk *input, un
     data.end_of_input = 0;
 
     pa_assert_se(src_process(r->src.state, &data) == 0);
-    pa_assert((unsigned) data.input_frames_used == in_n_frames);
+
+    if (data.input_frames_used < in_n_frames) {
+        void *dst;
+
+        r->leftover_buf.length = (in_n_frames - data.input_frames_used) * r->w_sz * r->o_ss.channels;
+
+        if (!r->leftover_buf.memblock || r->leftover_buf_bytes < r->leftover_buf.length) {
+            if (r->leftover_buf.memblock)
+                pa_memblock_unref(r->leftover_buf.memblock);
+
+            r->leftover_buf_bytes = r->leftover_buf.length;
+            r->leftover_buf.memblock = pa_memblock_new(r->mempool, r->leftover_buf.length);
+        }
+
+        dst = pa_memblock_acquire(r->leftover_buf.memblock);
+        memcpy(dst, data.data_in + data.input_frames_used * r->o_ss.channels, r->leftover_buf.length);
+        pa_memblock_release(r->leftover_buf.memblock);
+    }
 
     pa_memblock_release(input->memblock);
     pa_memblock_release(output->memblock);
-- 
1.7.10