Example: preflight-service (Rust)

Location: examples/rust/src/bin/preflight_service.rs

Run:

cd examples/rust
cargo run --bin preflight_service

What it demonstrates

A custodian or relayer service in Rust that:

1. Fetches the live registry via HTTP (ureq) using get_cells to discover the current outpoint
2. Parses the BLKL v2 payload with parse_registry_payload
3. Checks three candidate transactions with check_transaction
4. Accepts clean candidates, rejects blacklisted ones, and rejects missing-dep transactions (fail-closed)

Outputs:

candidate-payment: accepted for signing
blacklisted-payment: rejected — BlacklistedLockArgs (code -11)
missing-registry-dep: rejected — MissingRegistryCellDep (code -8)

If the live registry has no active entries, the blacklisted-payment branch is reported as unavailable rather than fabricated.

SDK patterns

• Manual get_cells RPC call to discover registry outpoint (no findRegistryCell in Rust SDK — implement using the indexer directly)
• parse_registry_payload to parse the fetched cell data bytes
• check_transaction with now_secs for time-based entry evaluation

Production note

This example uses a local path dependency (../../sdk/rust). In a real project, use the published crate:

[dependencies]
ckb-transaction-firewall-sdk = "0.3"

See Rust SDK API for full type signatures and Pre-flight check in Rust for the complete how-to.