Building Atomic Cross-Border Settlement on Stellar
Building Atomic Cross-Border Settlement on Stellar: The AnchorFX Story A technical deep-dive into Soroban escrow contracts, FX oracles, and mainnet deployment — from testnet prototype to production. se The Problem Cross-border payments still take 3-5 days and cost 6.5% on average. Correspondent banking chains are slow, opaque, and expensive. The $800B remittance market has no atomic settlement layer. Stellar was purpose-built for this. 5-second finality. Built-in DEX. Path payments at the protocol level. And now, with Soroban smart contracts, programmable settlement. AnchorFX is an open-source protocol that combines these primitives into trustless, atomic FX settlement between regulated financial anchors. Two Soroban contracts — an Escrow Factory and an FX Rate Oracle — communicate via cross-contract calls to lock, rate, and settle funds in a single atomic flow. Architecture Sender → [Escrow Contract] → Receiver │ [Oracle Contract] │ FX Rate Data Contract 1: Escrow Factory (995 lines, 23 tests) The escrow contract is a multi-escrow factory with per-escrow storage. Each escrow goes through a defined lifecycle: Created — Sender locks tokens with a timeout and settlement conditions CounterpartyApproved — Receiver signs off on the terms Settled — Admin releases funds at the locked FX rate Refunded — Sender reclaims after timeout expires Cancelled — Admin cancels (circuit breaker) pub fn create_escrow ( env : Env , sender : Address , receiver : Address , token : Address , amount : i128 , timeout_blocks : u32 , corridor : u32 , ) -> u64 { sender .require_auth (); // Read oracle rate at creation time — locks the rate let oracle_addr = env .storage () .instance () .get ( & ORACLE_KEY ) .unwrap (); let rate : u64 = env .invoke_contract ( & oracle_addr , & symbol_short! ( "get_rate" ), ... ); // Store escrow with locked rate // ... } Key security decisions: Per-escrow storage — O(1) reads, independent TTL per escrow Checks-effects-interactions — state saved before token trans