AmB2BMedia::writeStream: guard zero sample rate to prevent SIGFPE crash

[hecko]

Bug

AudioStreamData::writeStream (core/AmB2BMedia.cpp) does:

int sample_rate = stream->getSampleRate();
int got = 0;
if (in) got = in->get(ts, buffer, sample_rate, f_size);
...
  got = src_stream->get(ts, buffer, sample_rate, f_size);
...
  return stream->put(ts, buffer, sample_rate, got);

getSampleRate() returns 0 when the stream format is not yet set (or a zero-clock-rate codec was negotiated). sample_rate is then used as the divisor deeper in the AmAudio chain — e.g. AmBufferedAudio::get:

size_t nget = PCM16_S2B(nb_samples * getSampleRate() / output_sample_rate);

With output_sample_rate == 0 this is an integer divide-by-zero → SIGFPE, whole process crash. It is reachable on the B2B/SBC media path whenever a leg with a custom input (announcement / hold music / playback = an AmBufferedAudio) is attached to a stream whose sample rate is still 0.

Fix

Return early when sample_rate == 0, before any get()/put() call. This mirrors the identical guard already merged for AmSession::writeStreams (#542); this parallel B2B path was left unpatched.

int sample_rate = stream->getSampleRate();
if (sample_rate == 0) return 0;

Validation

• Confirmed the buggy path is present in current master and that the divide sink (AmBufferedAudio::get, core/AmBufferedAudio.cpp:90) performs integer division by output_sample_rate.
• Confirmed AmSession::writeStreams already carries the equivalent guard (with the same SIGFPE comment), so this only closes the remaining sibling gap.

Acknowledgement

Backport of the fix from the yeti-switch/sems fork, commit dc7aa5563d705eb7be1ee46706a9eda18fbbeb88 ("AmSession,AmB2BMedia::writeStreams: return 0 on zero output_sample_rate"). Thanks to the yeti-switch maintainers.

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[Copilot]

Pull request overview

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Adds a safeguard in the B2B media send path to prevent a divide-by-zero (SIGFPE) crash when the stream sample rate is still unset (0).

Changes:

• Early-return from AudioStreamData::writeStream when stream->getSampleRate() returns 0
• Documents why the guard is needed and aligns behavior with AmSession::writeStreams

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