Before this change, calculate_packet_hash() (SHA-256 + hex + upper) was called
3 times per forwarded packet and 4 times per dropped packet:
__call__ → pkt_hash_full = packet.calculate_packet_hash() #1
→ flood/direct_forward → is_duplicate → calculate_packet_hash() #2
→ flood/direct_forward → mark_seen → calculate_packet_hash() #3
(drop) → _get_drop_reason → is_duplicate → calculate_packet_hash() #4
pkt_hash_full was computed in __call__ but never threaded down into
process_packet, flood_forward, direct_forward, is_duplicate, or _get_drop_reason.
Each method recomputed it independently.
Fix: add optional packet_hash: Optional[str] = None to is_duplicate,
_get_drop_reason, flood_forward, direct_forward, and process_packet. Pass
pkt_hash_full from __call__ through the chain. Each method uses the provided
hash or falls back to computing it — preserving backward compatibility for
external callers (TraceHelper, etc.) that have no pre-computed hash.
Result: 1 SHA-256 computation per packet in the hot path regardless of whether
the packet is forwarded or dropped.
Also adds explicit INVARIANT docstrings to flood_forward, direct_forward, and
is_duplicate documenting that these methods must remain synchronous (no await).
The is_duplicate + mark_seen pair is atomic within the asyncio event loop; adding
an await between them would allow two concurrent tasks to both pass the duplicate
check for the same packet — forwarding it twice.
Docs: docs/pr_hash_once.md — problem analysis, call-chain diagram, per-method
diffs, quantification (~3-8 µs saved per packet), test plan (including hash-count
assertion), and proof that passing the original's hash to the deep-copied packet
is correct.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit sets up the initial project structure for the PyMC Repeater Daemon.
It includes base configuration files, dependency definitions, and scaffolding
for the main daemon service responsible for handling PyMC repeating operations.
