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* fix: don't undercount data channel bitrate over idle gaps
BitrateCalculator divided drained bytes by wall-clock time, including
idle gaps between sparse writes. A fast channel fed sparsely (e.g. 1 KB
every second, acked in a few ms) therefore reported its low offered load
(~8 kbps) instead of its drain capacity (~800 kbps). In the unreliable
writer that shrinks targetLatencyLimit and drops bursts on a channel
that is actually keeping up.
Measure the rate over backlogged ("busy") time only, so idle time no
longer dilutes the estimate. Backlog is detected from the buffer
occupancy just before a write (bufferedAmount - bytesWritten): since no
bytes are added between writes the buffer only drains, so a non-zero
pre-write level means it never emptied and the interval was genuinely
busy. Gating on the post-write buffered amount would be wrong -- it
always includes the just-enqueued (not yet SACKed) bytes and is ~never
zero, collapsing the estimate back to wall-clock. When no backlog is
ever observed the calculator reports no estimate (ok=false) instead of a
confidently-low number.
Introduce BitrateMode:
- BusyOnly (writer default): busy denominator, all drained bytes counted.
- ExcludeIdleDrain: also drops bytes drained across non-backlogged
intervals for a clean drain-capacity estimate free of idle
contamination.
- WallClock: elapsed-time denominator, all bytes; for the test-client
reader which has no send buffer to observe.
Call sites keep the conservative behaviour (writers BusyOnly, reader
WallClock). Tests exercise both writer modes and the mixed idle-then-
backlog window where they diverge.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
* Trim comments in data channel bitrate calculator
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
* Make BitrateMode.String a method on the enum
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>