Add embedded smoldot light-client transport to the provider node#297
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ilchu wants to merge 5 commits into
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Add embedded smoldot light-client transport to the provider node#297ilchu wants to merge 5 commits into
ilchu wants to merge 5 commits into
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The provider can now follow the chain without any operated RPC
infrastructure: --chain-transport light boots an embedded smoldot
instance that warp-syncs the relay chain and derives parachain
finality from it. The RPC transport remains the default; the switch
is config-level because all chain access already flows through the
chain_connection seam introduced with the event-driven coordinators.
- ChainTransport::Light { relay_spec, para_spec } with SpecSource
being either a vetted spec file (production: trust-preserving) or
fetched from a node's RPC at startup (dev convenience for zombienet,
which regenerates genesis every run; logged loudly as trust-defeating).
- ChainHandle keeps the LightClient alive; the follower's stall
watchdog rebuilding the connection therefore boots a fresh smoldot,
recovering even from a wedged smoldot background task (the silent-
hang failure mode tracked upstream as subxt#1536).
- The first finalized block after a (re)connect gets a 300s budget
(warp sync + peer discovery) before the 60s stall watchdog applies.
- scripts/test-light-client.sh: manual e2e against a running zombienet.
It synthesizes the light-client parachain spec from zombienet's
network directory - convert-to-raw genesis (smoldot cannot execute
runtimeGenesis), inject the collator's boot nodes, and align
relay_chain with the relay spec's exact id (smoldot matches
parachain to relay by exact id; omni-node tolerates the westend-local
vs westend_local_testnet mismatch, smoldot does not).
Verified live: the provider ran with --chain-transport light against
a local zombienet, synced the relay + parachain via smoldot, followed
finalized blocks, and served its on-chain registration on /info.
282 provider-node tests pass; clippy clean.
The merge from the base branch brought mock-connection tests that built ChainHandle with struct-literal syntax; the _light keep-alive field added on this branch is private outside chain_connection, so the RPC arm and those tests now construct handles via from_api.
Enabling subxt's light-client feature put smoldot and smoldot-light into cargo-deny's feature-resolved graph for the first time, and their GPL-3.0-or-later WITH Classpath-exception-2.0 expression was not in the allow list. Allowed via exceptions scoped to those two crates - compatible with the GPL-3.0-only provider node, and the exception only grants additional linking permissions - rather than allowing the expression workspace-wide. Also covers the Light transport's failure paths for the patch gate: missing spec file, invalid spec contents rejected by smoldot, and an unreachable spec-fetch node.
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Implements the embedded smoldot light-client transport from #222: with
--chain-transport light, the provider node follows the chain through an embedded smoldot instance that syncs the relay chain and derives parachain finality from it — no operated RPC infrastructure required. The RPC transport remains the default; flipping the default is a deliberate follow-up decision after soak time, per the investigation's sequencing.This PR is small by design: all chain access already flows through the
chain_connectionseam and the single-follower architecture from #291, so the transport is a construction-site change plus spec handling.What's in it
ChainTransport::Light { relay_spec, para_spec }inchain_connection, each spec aSpecSource: a vetted spec file (the trust-preserving production path; for Paseo the relay spec comes frompaseo-network/paseo-chain-specs) or fetched from a node's RPC at startup (dev convenience for zombienet, which regenerates genesis every run — logged loudly as trust-defeating, since it reintroduces exactly the node trust the light client exists to remove).ChainHandlekeeps theLightClientinstance alive; the follower's stall watchdog rebuilding the connection therefore boots a fresh smoldot, so the recovery path covers even a wedged smoldot background task (the silent-hang failure mode tracked upstream as Light Client: subxt API will do nothing after smoldot thread panic. subxt#1536), not just a dropped subscription.--chain-transport {rpc|light},--relay-chain-spec,--para-chain-spec,--relay-rpc(relay-spec fetch fallback);--chain-rpckeeps double duty as the RPC endpoint and the para-spec fetch source. Resolution logic is unit-tested, including the error when the light transport has no relay-spec source.scripts/test-light-client.sh: manual e2e against a running zombienet. It synthesizes the light-client para spec from zombienet's network directory, encoding three non-obvious requirements: smoldot needs raw genesis storage (zombienet's collator spec isruntimeGenesis, so the script runschain-spec-builder convert-to-rawon it, preserving the genesis hash), the advertised boot nodes live only in the non-raw variant and get injected, and the para spec'srelay_chainid must exactly match the relay spec's id (omni-node tolerateswestend-localvswestend_local_testnet; smoldot does not). The same three facts will drive the real Paseo chain-spec packaging for the default flip.Verification
283 provider-node tests pass; clippy clean. Live on this exact HEAD (i.e. including the event-driven follower and static-bindings event decoding from #291 running over the light transport):
scripts/test-light-client.shagainst a local zombienet — embedded smoldot synced the relay and parachain, followed finalized blocks, and/infoserved the provider's on-chain registration read through it.Relates to #222. Stacked on #291.