Smart Contract ↔ Backend Integration

ABI Encoding/Decoding from Go:

import "github.com/ethereum/go-ethereum/accounts/abi"

// Parse contract ABI
parsedABI, _ := abi.JSON(strings.NewReader(contractABIJson))
// Encode function call
data, _ := parsedABI.Pack("settle", paymentId, amount)
// Decode return values / event data
results, _ := parsedABI.Unpack("getBalance", returnData)

go-ethereum Bindings: Use abigen to generate type-safe Go bindings from Solidity ABI.

abigen --abi Settlement.abi --pkg settlement --out settlement.go

This generates a Go struct with methods mirroring every contract function. Compile-time type safety, auto-completion, and no manual ABI packing.

Event Log Parsing:

// Subscribe to events
query := ethereum.FilterQuery{
    Addresses: []common.Address{contractAddr},
    Topics:    [][]common.Hash{{settledEventSig}},
}
logs, _ := client.FilterLogs(ctx, query)

for _, log := range logs {
    event, _ := parsedABI.Unpack("PaymentSettled", log.Data)
    // event contains decoded paymentId, amount, timestamp
    // log.Topics[1] contains indexed paymentId
}

Safe Transaction Submission from Backend:

1. Build the inner transaction (target, value, data)
Calculate Safe transaction hash (EIP-712 typed data)
Collect M-of-N signatures (backend HSM + co-signers)
Submit to Safe Transaction Service API
Or call execTransaction() directly if threshold met

For Gnosis Pay: the backend uses the Safe Roles Module for scoped delegation (EURe only, issuer Safe only, daily limit) and Gelato Relay for gasless execution — no per-tx user signature needed for card settlements.