starter.c

#include "hookapi.h"

// TODO: Parameterize this so that you can specify the minimum allowed payment when deploying the hook.
const int64_t MINIMUM_AMOUNT_IN_DROPS = 100000; // 0.1 XRP

int64_t hook(uint32_t reserved ) {

    GUARD(1);   // every hook needs to import guard function and use it at least once

    unsigned char amount_buffer[48];
    int64_t amount_len = otxn_field(SBUF(amount_buffer), sfAmount);

    // Any IOU payments will be accepted.
    if (amount_len != 8)
        accept(SBUF("Minimum_payment: IOUs are always allowed. Passing"), 0);

    if (AMOUNT_TO_DROPS(amount_buffer) < MINIMUM_AMOUNT_IN_DROPS)
        rollback(SBUF("Minimum_payment: Rejecting incoming XRP transaction, amount is below the specified minimal amount."), 5);
    
    // If we're here, it's an valid transaction.
    accept(SBUF("Minimum_payment: Valid payment. Passing"), 0);
    return 0;
}