feat(api): fast-sync CAS content gateway over HTTP (#115)#123
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Option B of the fast-sync overlay (epic #111), reframed for web/browser wallets that cannot speak Bitcoin P2P. An optional, IPFS-free, self-verifying content endpoint. - internal/api/resolution.go: GET /fastsync/cas/<cid> backed by a CASGateway (the node's CAS satisfies it). CORS-open (the data is public + self-verifying, so there is nothing to protect), OPTIONS preflight, GET-only, 404 on not-found via cas.ErrNotFound, immutable Cache-Control (content-addressed). Bounded to 4 MiB. Mounted only when WithCASGateway is set (like /stats). - internal/config + cmd/ion-node: --serve-fast-sync enables the gateway on `serve`. A client MUST verify sha256/multihash(body) == the CID, so this is a trustless IPFS replacement, not a trusted source. The /fastsync/anchors endpoint needs the bundle store moved into the concurrent-safe main store first (serve and start are separate processes; the #113 bbolt store takes a single-process lock) — that lands next. Shares the eventual transport-agnostic serving core with Option C (#122, native P2P). Test: TestFastSyncCASGateway — present cid 200 + CORS + body; missing 404; OPTIONS 204; POST 405; route absent without a gateway. go test -race ./... green. Co-authored-by: Liran Cohen <liranlasvegas@gmail.com> Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Summary
Option B of the fast-sync overlay (epic #111), reframed for web/browser wallets that can't speak Bitcoin P2P: an optional, IPFS-free, self-verifying content endpoint.
GET /fastsync/cas/<cid>— backed by aCASGateway(the node's CAS). CORS-open (the data is public and content-addressed, nothing to protect), OPTIONS preflight, GET-only,404on not-found, immutableCache-Control(content is immutable by CID), bounded to 4 MiB.WithCASGatewayis set (like/stats); enabled by--serve-fast-syncon theservecommand.A client MUST verify
multihash(body) == cid, so this is a trustless IPFS replacement — the node serving it doesn't have to be trusted. It's also the cure for the IPFS-unpinning availability gap we observed live (pendingRetryable).Why CAS first / what's next
serveandstartrun as separate processes. The/fastsync/anchorsendpoint reads the bundle store, which is bbolt (single-process lock) from #113 — so it needs the bundle store moved into the concurrent-safe main store first. That's the next slice. CAS-by-CID needs only the filesystem CAS + cas client, so it ships cleanly now and delivers the primary web-wallet value immediately.Both endpoints will share the transport-agnostic serving core with Option C (#122, native P2P via vendored btcd wire).
Tests
TestFastSyncCASGateway: present CID → 200 + CORS + body; missing → 404; OPTIONS → 204; POST → 405; route absent without a gateway.go test -race ./...green (28 packages).Post-Deploy Monitoring & Validation
--serve-fast-sync,servelogs the gateway endpoint at startup.GET /fastsync/cas/<cid>returns content the node holds in its CAS cache. Web wallets get an IPFS-free, CORS-open content source.servenode runs with--serve-fast-sync.Part of #111. Advances #115 (CAS slice; anchors endpoint to follow).
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