Regarding the behavior of trust lines | XRPL Development in JavaScript - Level 3

Next, we will explain the behavior of trust lines when making an offer.

Let’s try a scenario where Bob sells B.EUR issued by Issuer B and buys A.USD issued by Issuer A, and this B.EUR eventually is delivered to Daniel.

Prerequisites

Charlie needs to make a payment to Daniel, who wants to receive B.EUR. However, at this point, Charlie does not hold B.EUR and only has XRP and A.USD issued by Issuer A. Therefore, Charlie considers whether he can exchange his A.USD.

1. Bob will create an offer to sell B.EUR issued by Issuer B and buy A.USD issued by Issuer A to provide liquidity.
2. Charlie will initiate the process to send A.USD as B.EUR to Daniel.

Creating the Script

1. Use the existing createOffers.js to create an offer from Bob.

   import { Client, xrpToDrops } from 'xrpl';
   import { wallets } from './wallets.js';
   import { createOffer } from './utils/createOffer.js';
   
   const client = new Client('wss://s.altnet.rippletest.net:51233'); // Using Testnet
   
   async function main() {
       try {
           await client.connect();
   
           const { issuerA, issuerB, alice, bob, charlie, daniel } = wallets;
   
           // await createOffer(
           //   client,
           //   alice,
           //   { currency: 'USD', issuer: issuerA.address, value: '100' },
           //   { currency: 'EUR', issuer: issuerB.address, value: '100' }
           // );
   
           await createOffer(
               client,
               bob,
               { currency: 'EUR', issuer: issuerB.address, value: '100' },
               { currency: 'USD', issuer: issuerA.address, value: '100' }
           );
       } catch (error) {
           console.error(`Error in offer creation: ${error}`);
       } finally {
           await client.disconnect();
       }
   }
   
   main();

2. Use the existing crossCurrencyPayment.js to make a payment from Charlie.

   crossCurrencyPayment.js

   import xrpl from 'xrpl';
   import { wallets } from './wallets.js';
   import { sendPayment } from './utils/payment.js';
   
   const client = new xrpl.Client('wss://s.altnet.rippletest.net:51233');
   
   const main = async () => {
       await client.connect();
   
       const { issuerA, issuerB, alice, bob, charlie, daniel } = wallets;
   
       // await sendPayment(
       //   client,
       //   daniel,
       //   { currency: 'USD', issuer: issuerA.address, value: '100' }, // Currency Charlie wants to receive: A.USD
       //   charlie.address,
       //   {
       //     sendMax: { currency: 'EUR', issuer: issuerB.address, value: '100' }, // Currency Daniel wants to pay: B.EUR
       //   }
       // );
   
       // Payment from Charlie to Daniel
       await sendPayment(
           client,
           charlie,
           { currency: 'EUR', issuer: issuerB.address, value: '100' }, // Currency Daniel wants to receive: B.EUR
           daniel.address,
           {
               sendMax: { currency: 'USD', issuer: issuerA.address, value: '100' }, // Currency Charlie wants to pay: A.USD
           }
       );
   
       await client.disconnect();
   };
   
   main().catch(console.error);

Running the Script

1. Run the following commands in the command line to execute the script.

   node createOffers.js
   node crossCurrencyPayment.js

2. If the following log appears as a result of crossCurrencyPayment.js, it is successful.

   Payment sent from rnP7Q6LaejYi7oaN4qJHkKhnESZYAyVQwh to rf6R7pFgytT9JKjMVjKqeTv6MeDTrbNw3: {
       id: 14,
       result: {
           Account: 'rnP7Q6LaejYi7oaN4qJHkKhnESZYAyVQwh', // Charlie
           Amount: {
               currency: 'EUR',
               issuer: 'rstM9rxhKo4N4WEaQgQmQSPQRgZqkhHkaU', // issuerB
               value: '100'
           },
           DeliverMax: {
               currency: 'EUR',
               issuer: 'rstM9rxhKo4N4WEaQgQmQSPQRgZqkhHkaU',
               value: '100'
           },
           Destination: 'rf6R7pFgytT9JKjMVjKqeTv6MeDTrbNw3', // Daniel
           Fee: '12',
           Flags: 0,
           LastLedgerSequence: 1085862,
           SendMax: {
               currency: 'USD',
               issuer: 'rfkJ7Uz6NrNV1FdbmKB5wepoim51KFpYQp', // issuerA
               value: '100' // Max amount
           },
           Sequence: 1046427,
           SigningPubKey: 'ED88C6BDCFE0FB8612FCE299211DDAB0E6E6498EEAD14D07673D7C2C0778361766',
           TransactionType: 'Payment',
           TxnSignature: 'CE013A27741315A5DE67B811DF4AA793F3CBF24AA80D0EED9A1148B790A6A9713B1DE457BF3F3EECC5C155A8CA81D9536F7C151239DF6BEBA13BFCA057255E02',
           ctid: 'C010919400000001',
           date: 770335361,
           hash: '95CE240790C3B1AA5C59CB1C1A4747B42901B06F3F4217C5BFC3E4F07D372E07',
           inLedger: 1085844,
           ledger_index: 1085844,
           meta: {
               AffectedNodes: [Array],
               TransactionIndex: 0,
               TransactionResult: 'tesSUCCESS', // Success
               delivered_amount: [Object]
           },
           validated: true
       },
       type: 'response'
   }

   At this point, please check the explorer to confirm the following:

   1. Bob’s balance of B.EUR decreased to 900, and his balance of A.USD increased to 100.
   2. Charlie’s balance of A.USD increased to 1,000 (returned to the initial state).
   3. Daniel’s balance of B.EUR increased to 1,000 (returned to the initial state).

About Trust Lines

Bob is able to hold A.USD even though he did not explicitly set a trust line for it.

This is the behavior triggered by the OfferCreate transaction, and you can interpret it as “placing an order for A.USD = trusting A.USD”.

In the next chapter, we will explain cross-currency payment patterns and more.