[pulseaudio-discuss] [PATCH 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 holding a reference
to the input memblock to keep it around until the next
pa_resampler_run() call, in case the resampler doesn't
consume all of the input. The leftover data is concatenated
to the new input in the add_leftover() function that is
called before resampling, after format conversion and
channel remapping.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=47156
---
 src/pulsecore/resampler.c |   85 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 76 insertions(+), 9 deletions(-)

diff --git a/src/pulsecore/resampler.c b/src/pulsecore/resampler.c
index 5f791da..ca77f88 100644
--- a/src/pulsecore/resampler.c
+++ b/src/pulsecore/resampler.c
@@ -56,8 +56,9 @@ struct pa_resampler {
     size_t i_fz, o_fz, w_sz;
     pa_mempool *mempool;
 
-    pa_memchunk buf1, buf2, buf4, buf5;
-    unsigned buf1_samples, buf2_samples, buf4_samples, buf5_samples;
+    pa_memchunk buf1, buf2, buf3, buf4, buf5;
+    unsigned buf1_samples, buf2_samples, buf3_samples, buf4_samples, buf5_samples;
+    pa_memchunk leftover;
 
     pa_sample_format_t work_format;
 
@@ -338,10 +339,14 @@ void pa_resampler_free(pa_resampler *r) {
         pa_memblock_unref(r->buf1.memblock);
     if (r->buf2.memblock)
         pa_memblock_unref(r->buf2.memblock);
+    if (r->buf3.memblock)
+        pa_memblock_unref(r->buf3.memblock);
     if (r->buf4.memblock)
         pa_memblock_unref(r->buf4.memblock);
     if (r->buf5.memblock)
         pa_memblock_unref(r->buf5.memblock);
+    if (r->leftover.memblock)
+        pa_memblock_unref(r->leftover.memblock);
 
     pa_xfree(r);
 }
@@ -373,17 +378,24 @@ 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.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) {
@@ -407,7 +419,7 @@ 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.length / r->o_fz) * r->i_ss.rate) / ss.rate) * r->i_fz;
 }
 
 void pa_resampler_reset(pa_resampler *r) {
@@ -415,6 +427,11 @@ void pa_resampler_reset(pa_resampler *r) {
 
     if (r->impl_reset)
         r->impl_reset(r);
+
+    if (r->leftover.memblock) {
+        pa_memblock_unref(r->leftover.memblock);
+        pa_memchunk_reset(&r->leftover);
+    }
 }
 
 pa_resample_method_t pa_resampler_get_method(pa_resampler *r) {
@@ -1136,6 +1153,50 @@ static pa_memchunk *remap_channels(pa_resampler *r, pa_memchunk *input) {
     return &r->buf2;
 }
 
+static pa_memchunk *add_leftover(pa_resampler *r, pa_memchunk *input) {
+    unsigned out_n_samples;
+    void *src;
+    void *dst;
+
+    pa_assert(r);
+    pa_assert(input);
+
+    /* Concatenate leftover and input and place the result in buf3. */
+
+    if (r->leftover.length <= 0)
+        return input;
+
+    r->buf3.index = 0;
+    r->buf3.length = r->leftover.length + input->length;
+
+    out_n_samples = (unsigned) (r->buf3.length / r->w_sz);
+
+    if (!r->buf3.memblock || r->buf3_samples < out_n_samples) {
+        if (r->buf3.memblock)
+            pa_memblock_unref(r->buf3.memblock);
+
+        r->buf3_samples = out_n_samples;
+        r->buf3.memblock = pa_memblock_new(r->mempool, r->buf3.length);
+    }
+
+    src = (uint8_t *) pa_memblock_acquire(r->leftover.memblock) + r->leftover.index;
+    dst = pa_memblock_acquire(r->buf3.memblock);
+    memcpy(dst, src, r->leftover.length);
+
+    src = (uint8_t *) pa_memblock_acquire(input->memblock) + input->index;
+    dst = (uint8_t *) dst + r->leftover.length;
+    memcpy(dst, src, input->length);
+
+    pa_memblock_release(r->leftover.memblock);
+    pa_memblock_release(input->memblock);
+    pa_memblock_release(r->buf3.memblock);
+
+    pa_memblock_unref(r->leftover.memblock);
+    pa_memchunk_reset(&r->leftover);
+
+    return &r->buf3;
+}
+
 static pa_memchunk *resample(pa_resampler *r, pa_memchunk *input) {
     unsigned in_n_frames, in_n_samples;
     unsigned out_n_frames, out_n_samples;
@@ -1221,6 +1282,7 @@ 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) {
@@ -1258,12 +1320,17 @@ 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);
 
     pa_memblock_release(input->memblock);
     pa_memblock_release(output->memblock);
 
     *out_n_frames = (unsigned) data.output_frames_gen;
+
+    if (data.input_frames_used < in_n_frames) {
+        r->leftover.index = input->index + data.input_frames_used * r->o_fz;
+        r->leftover.length = (in_n_frames - data.input_frames_used) * r->o_fz;
+        r->leftover.memblock = pa_memblock_ref(input->memblock);
+    }
 }
 
 static void libsamplerate_update_rates(pa_resampler *r) {
-- 
1.7.10