feat(#91): ChainExchange client — gateway-free header-chain fetch#110
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feat(#91): ChainExchange client — gateway-free header-chain fetch#110Reiers wants to merge 1 commit into
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…r libp2p Adds the requesting half of /fil/chain/xchg/0.0.1 (the responder landed in #17). A bridge-off Lantern (#76, --no-fallback-rpc) can now backfill a gossip head+N gap by pulling the whole verified header chain from a real Filecoin peer in ONE request, with zero upstream RPC (no Glif, no gateway). This is Stage A of the snapshot-free full-node epic (#87). net/chainxchg/client.go - Client.FetchTipsetChain(head, length): headers-only request, walks parent-ward newest->oldest. Handwritten CBOR both directions (same zero-dependency policy as the responder), cross-checked against Lotus chain/exchange cbor_gen layout. - Trust model: every header CID-verified; level 0 must equal the requested head set, each deeper level must equal the previous level's Parents, heights strictly decreasing. Caller derives head from already-verified data (a gossip block's Parents / the quorum anchor), so a malicious peer can only refuse, never splice. - Partial (101) responses accepted; NotFound (201)/GoAway (202) fail that peer and rotate to the next. Bounded response read (32 MiB), peer cap, trusted-floor-first peer ordering, observable ClientStats. net/blockingest/blockingest.go - ChainFetcher interface + SetChainFetcher: in parent-walk (bridge-off) mode the ingestor prefers ONE ChainExchange request over the per-CID bitswap walk, falling back to the walk on error (or surfacing the error when there is no per-CID source). net/chainxchg/client_test.go - Two-host libp2p harness: happy path, partial, NotFound, spliced-chain rejection, no-peers. Full suite green, build+vet+fmt clean. Stacks on feat/108-no-fallback-rpc (#76 scaffolding). Server-side chain serving remains a separate follow-up.
This was referenced Jul 2, 2026
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Closes the client half of #91 (Stage A of #87). The responder side landed in #17; this adds the requester so a bridge-off Lantern (#76, `--no-fallback-rpc`) can backfill a gossip head+N gap by pulling the whole CID-verified header chain from a real Filecoin peer in ONE request — zero upstream RPC (no Glif, no gateway).
What's in
net/chainxchg/client.go—Client.FetchTipsetChain(head, length), headers-only, parent-ward. Handwritten CBOR both directions (zero-dep, cross-checked vs Lotuschain/exchangecbor_gen). Trust model: every header CID-verified, level 0 == requested head set, each deeper level == previous level'sParents, heights strictly decreasing → a bad peer can only refuse, never splice. Partial(101) accepted; NotFound(201)/GoAway(202) rotate to next peer. Bounded 32 MiB read, peer cap, trusted-floor-first ordering,ClientStats.net/blockingest/blockingest.go—ChainFetcherinterface +SetChainFetcher; parent-walk (bridge-off) mode prefers one ChainExchange request over the per-CID bitswap walk, falling back on error.net/chainxchg/client_test.go— two-host libp2p harness: happy path, partial, NotFound, spliced-chain rejection, no-peers.Evidence
go build ./...OKgo vet ./net/chainxchg/ ./net/blockingest/cleangofmt -lcleango test -count=1 ./net/chainxchg/ ./net/blockingest/→ both okScope / follow-ups
SetChainFetcheron the ingestor + use it for the anchor seed, which also finishes Boot anchor Glif-independence under --no-fallback-rpc (#76 follow-up) #109) is the next commit.feat/108-no-fallback-rpc([Tracking] Lantern bridge-off parity for stock Curio (maxboom / PR #1311) #76 scaffolding); rebase tomainonce feat(#76): --no-fallback-rpc for a provably Glif-free standalone daemon #108 lands.