fix: broadcast all SRT control packets to all connections

[datagutt]

Summary

• Broadcasts all SRT control packets (ACKs, NAKs, ACKACK, KEEPALIVE, etc.) to all connections instead of only sending non-ACK packets to the last active connection
• Previously, NAKs were sent only to last_address() which could be a dead connection, causing retransmission failures

Problem

When a connection dies or becomes unhealthy:

1. last_address() might still point to the dead connection
2. NAKs sent to that connection would be lost
3. The sender never receives the NAK and doesn't retransmit
4. Packet loss goes unrecovered

Solution

Broadcast all SRT control packets to all connections in the group, matching the existing behavior for ACKs. This ensures NAKs reach the sender through at least one healthy connection.

Safety

• SRT sender already handles duplicate NAKs safely (marks packet as handled after first NAK)
• SRT handles duplicate handshakes via state guards (m_bConnecting flag)
• ACKs already use this broadcast pattern successfully

Summary by CodeRabbit

• Bug Fixes
  • Control packet broadcasting now includes negative acknowledgements (NAKs) alongside ACKs so all active group connections receive critical control packets.
  • Transmission error messages standardized to "Failed to send SRT packet" for clearer diagnostics.
  • Packet distribution logic refined for more consistent handling of control packets across connection groups.

[coderabbitai]

Walkthrough

ACKs and NAKs are now treated as broadcast-worthy and sent to all connections in a group; other control packets continue to be sent to the group's last_address(). A new helper is_srt_nak was added to classify NAK packets; logging text and explanatory comments were updated.

Changes

Cohort / File(s)	Summary
SRT Control Packet Handling src/protocol/srt_handler.cpp	Broadcast logic extended so ACKs and NAKs are sent to all connections (is_srt_ack(...) or NAK). Non-ACK control packets still target group->last_address(). Updated failure log message to "Failed to send SRT packet" and added comments about ACK/NAK broadcast rationale.
SRT Packet Type Helpers src/common.c, src/common.h	Added is_srt_nak(void *pkt, int n) declaration and implementation to detect NAK packet types, mirroring the existing ACK helper. No other public signatures changed.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 I sniff the bytes and hop along,

ACKs and NAKs join the hopping throng,
Sent to all, no message slips,
I tap my paw and fix the rips,
Hoppy packets, all day long! 🥕

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: broadcast all SRT control packets to all connections' directly matches the PR's main objective and accurately summarizes the core change.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/send-control-packets-to-all-connections

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