In rtcConnection.HandlePacket the backend->client reader goroutine was
spawned unconditionally on every inbound client packet, which leaked
goroutines under steady-state WHEP load (STUN keepalives + RTCP feedback).
Guard the spawn with sync.Once so it runs exactly once per connection.
In SRTConnection.handleHandshake apply the same sync.Once guard so a
client retry of handshake 2 (because our handshake 3 was dropped) does
not race a second reader on backendUDP.Read.
In both Run loops, hoist the 4096-byte receive buffer out of the read
loop; callers consume the slice synchronously and the kernel copies on
Write/sendto, so no caller retains the slice past the call. To keep this
safe for SRT, clone ExtraData in SRTHandshakePacket.UnmarshalBinary so
decoded handshakes do not alias the reused receive buffer.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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