Add BEP 11 PEX and a growable shared peer pool to the swarm#12
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The swarm statically partitioned the initial peer list across workers at Start, so a worker that lost its peers couldn't get others' and PEX peers had nowhere to go. Replace that with a shared, growable pool and wire in BEP 11 peer exchange. Protocol (peer.go): - Advertise ut_pex (local id 2) alongside ut_metadata in the BEP 10 extended handshake. - parsePexPeers validates against PeerMessageLimits, then unpacks added (compact v4) and added6 (compact v6) via the existing unpackPeers, and drops unconnectable entries (port 0 / unspecified IP) at the boundary. - PeerConn buffers harvested peers (handlePexMessage / DrainPexPeers). Swarm (swarm.go): - peerChan (buffered) + mutex-guarded knownAddrs replace the static split; AddPeers dedups and pushes non-blocking. - Workers acquire a connection from the pool BEFORE pulling work, so a worker waiting on a peer can't strand a piece marked in-progress. - inFlight (atomic) is incremented at the pull, before dialing, so the new exhaustion supervisor can't mistake an in-flight connect for a dead swarm; it cancels only after the pool is empty, inFlight==0, and pieces remain, sustained across a short grace window. - The unbuffered-resultChan / drain / close-after-WaitGroup shutdown is preserved verbatim. Wiring (downloader.go): downloadPiece harvests ut_pex messages; the worker drains them into the pool after each piece. connectToAny is replaced by a single-addr dialAndHandshake. Tested unit (dead-peer skip, PEX discovery e2e, exhaustion, no-leak) under -race, and end-to-end against a real Transmission seeder (5 MiB / 20 pieces, checksum verified) — during which Transmission's ut_pex was harvested and used, validating the path against a real client.
iksnerd
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Jun 21, 2026
Add BEP 11 PEX and a growable shared peer pool to the swarm
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What
Replaces the swarm's static peer-list partitioning with a shared, growable peer pool and wires in BEP 11 peer exchange (ut_pex). PEX discovers peers during a download; the old
Start()split the initial list across workers with no way to add peers mid-flight, so PEX peers had nowhere to go — doing both together also closes the deferred static-partitioning reliability gap.Changes
Protocol (
peer.go)ut_pex(local id 2) alongsideut_metadatain the BEP 10 extended handshake.parsePexPeers: validates againstPeerMessageLimits, unpacksadded(compact v4) +added6(compact v6) via the existingunpackPeers, and drops unconnectable entries (port 0 / unspecified IP) at the trust boundary.PeerConnbuffers harvested peers (handlePexMessage/DrainPexPeers).Swarm (
swarm.go)peerChan(buffered) + mutex-guardedknownAddrsreplace the static split;AddPeersdedups + non-blocking push.inFlight(atomic) is incremented at the pull, before dialing, so the new exhaustion supervisor can't mistake an in-flight connect for a dead swarm. It cancels only after the pool is empty,inFlight==0, and pieces remain — sustained across a short grace window.resultChan/ drain / close-after-WaitGroupshutdown is preserved verbatim.Wiring (
downloader.go)downloadPieceharvestsut_pexmessages; the worker drains them into the pool after each piece.connectToAny→ single-addrdialAndHandshake.Testing
-race): dead-peer skip, PEX discovery end-to-end, peer-supply exhaustion, no goroutine leak, plus the parser/handshake/drain tests.transmission-daemonseeder (5 MiB / 20 pieces) — checksum verified. Transmission'sut_pexwas harvested and used mid-download, validating the PEX path against a real client. This run also surfaced (and fixed) Transmission advertising an unconnectable port-0 peer.🤖 Generated with Claude Code