Add example of reliable transaction submission (#1059)

snippets/src/reliableTransactionSubmission.ts

@@ -0,0 +1,200 @@
+import {
+  RippleAPI,
+  AccountInfoResponse, 
+  LedgerClosedEvent
+} from '../../dist/npm'
+import https = require('https')
+
+/**
+ * When implementing Reliable Transaction Submission, there are many potential solutions, each with different trade-offs. The main decision points are:
+ * 1) Transaction preparation:
+ *    - How do we decide which account sequence and LastLedgerSequence numbers to use?
+ *      (To prevent unintentional duplicate transactions, an {account, account_sequence} pair can be used as a transaction's idempotency key)
+ *    - How do we decide how much to pay for the transaction fee? (If our transactions have been failing due to low fee, we should consider increasing this value)
+ * 2) Transaction status retrieval. Options include:
+ *    - Poll for transaction status:
+ *      - On a regular interval (e.g. every 3-5 seconds), or
+ *      - When a new validated ledger is detected
+ *      + (To accommodate an edge case in transaction retrieval, check the sending account's Sequence number to confirm that it has the expected value;
+ *         alternatively, wait until a few additional ledgers have been validated before deciding that a transaction has definitively not been included in a validated ledger)
+ *    - Listen for transaction status: scan all validated transactions to see if our transactions are among them
+ * 3) What do we do when a transaction fails? It is possible to implement retry logic, but caution is advised. Note that there are a few ways for a transaction to fail:
+ *    A) `tec`: The transaction was included in a ledger but only claimed the transaction fee
+ *    B) `tesSUCCESS` but unexpected result: The transaction was successful but did not have the expected result. This generally does not occur for XRP-to-XRP payments
+ *    C) The transaction was not, and never will be, included in a validated ledger [3C]
+ * 
+ * References:
+ * - https://xrpl.org/reliable-transaction-submission.html
+ * - https://xrpl.org/send-xrp.html
+ * - https://xrpl.org/look-up-transaction-results.html
+ * - https://xrpl.org/get-started-with-rippleapi-for-javascript.html
+ * - https://xrpl.org/monitor-incoming-payments-with-websocket.html
+ * 
+ * For the implementation in this example, we have made the following decisions:
+ * 1) The script will choose the account sequence and LastLedgerSequence numbers automatically. We allow ripple-lib to choose the fee.
+ *    Payments are defined upfront, and idempotency is not needed. If the script is run a second time, duplicate payments will result.
+ * 2) We will listen for notification that a new validated ledger has been found, and poll for transaction status at that time.
+ *    Futhermore, as a precaution, we will wait until the server is 3 ledgers past the transaction's LastLedgerSequence
+ *    (with the transaction nowhere to be seen) before deciding that it has definitively failed per [3C]
+ * 3) Transactions will not be automatically retried. Transactions are limited to XRP-to-XRP payments and cannot "succeed" in an unexpected way.
+ */
+reliableTransactionSubmissionExample()
+
+async function reliableTransactionSubmissionExample() {
+  /**
+   * Array of payments to execute.
+   * 
+   * For brevity, these are XRP-to-XRP payments, taking a source, destination, and an amount in drops.
+   * 
+   * The script will attempt to make all of these payments as quickly as possible, and report the final status of each. Transactions that fail are NOT retried.
+   */
+  const payments = []
+  
+  const sourceAccount = (await generateTestnetAccount()).account
+  console.log(`Generated new Testnet account: ${sourceAccount.classicAddress}/${sourceAccount.secret}`)
+  // Send amounts from 1 drop to 10 drops
+  for (let i = 1; i <= 10; i++) {
+    payments.push({
+      source: sourceAccount,
+      destination: 'rhsoCozhUxwcyQgzFi1FVRoMVQgk7cZd4L', // Random Testnet destination
+      amount_drops: i.toString(),
+    })
+  }
+  const results = await performPayments(payments)
+  console.log(JSON.stringify(results, null, 2))
+  process.exit(0)
+}
+
+async function performPayments(payments) {
+  const finalResults = []
+  const txFinalizedPromises = []
+  const api = new RippleAPI({server: 'wss://s.altnet.rippletest.net:51233'})
+  await api.connect()
+
+  for (let i = 0; i < payments.length; i++) {
+    const payment = payments[i]
+    const account_info: AccountInfoResponse = await api.request('account_info', {
+      account: payment.source.classicAddress,
+      ledger_index: 'current'})
+    const sequence = account_info.account_data.Sequence
+    const preparedPayment = await api.preparePayment(payment.source.classicAddress, {
+      source: {
+        address: payment.source.classicAddress,
+        amount: {
+          value: payment.amount_drops,
+          currency: 'drops'
+        }
+      },
+      destination: {
+        address: payment.destination,
+        minAmount: {
+          value: payment.amount_drops,
+          currency: 'drops'
+        }
+      }
+    }, {
+      sequence
+    })
+    const signed = api.sign(preparedPayment.txJSON, payment.source.secret)
+    finalResults.push({
+      id: signed.id
+    })
+    const result = await api.submit(signed.signedTransaction)
+
+    // Most of the time we'll get 'tesSUCCESS' or (after many submissions) 'terQUEUED'
+    console.log(`tx ${i} - tentative: ${result.resultCode}`)
+
+    const txFinalizedPromise = new Promise((resolve) => {
+      const ledgerClosedCallback = async (event: LedgerClosedEvent) => {
+        let status
+        try {
+          status = await api.getTransaction(signed.id)
+        } catch (e) {
+          // Typical error when the tx hasn't been validated yet:
+          if (e.name !== 'MissingLedgerHistoryError') {
+            console.log(e)
+          }
+
+          if (event.ledger_index > preparedPayment.instructions.maxLedgerVersion + 3) {
+            // Assumptions:
+            // - We are still connected to the same rippled server
+            // - No ledger gaps occurred
+            // - All ledgers between the time we submitted the tx and now have been checked for the tx
+            status = {
+              finalResult: 'Transaction was not, and never will be, included in a validated ledger'
+            }
+          } else {
+            // Check again later:
+            api.connection.once('ledgerClosed', ledgerClosedCallback)
+            return
+          }
+        }
+
+        for (let j = 0; j < finalResults.length; j++) {
+          if (finalResults[j].id === signed.id) {
+            finalResults[j].result = status.address ? {
+              source: status.address,
+              destination: status.specification.destination.address,
+              deliveredAmount: status.outcome.deliveredAmount,
+              result: status.outcome.result,
+              timestamp: status.outcome.timestamp,
+              ledgerVersion: status.outcome.ledgerVersion
+            } : status
+            process.stdout.write('.')
+            return resolve()
+          }
+        }
+      }
+      api.connection.once('ledgerClosed', ledgerClosedCallback)
+    })
+    txFinalizedPromises.push(txFinalizedPromise)
+  }
+  await Promise.all(txFinalizedPromises)
+  return finalResults
+}
+
+/**
+ * Generate a new Testnet account by requesting one from the faucet
+ */
+async function generateTestnetAccount(): Promise<{
+  account: {
+    xAddress: string,
+    classicAddress, string,
+    secret: string
+  },
+  balance: number
+ }> {
+  const options = {
+    hostname: 'faucet.altnet.rippletest.net',
+    port: 443,
+    path: '/accounts',
+    method: 'POST'
+  }
+  return new Promise((resolve, reject) => {
+    const request = https.request(options, response => {
+      const chunks = []
+      response.on('data', d => {
+        chunks.push(d)
+      })
+      response.on('end', () => {
+        const body = Buffer.concat(chunks).toString()
+
+        // "application/json; charset=utf-8"
+        if (response.headers['content-type'].startsWith('application/json')) {
+          resolve(JSON.parse(body))
+        } else {
+          reject({
+            statusCode: response.statusCode,
+            contentType: response.headers['content-type'],
+            body
+          })
+        }
+      })
+    })
+    request.on('error', error => {
+      console.error(error)
+      reject(error)
+    })
+    request.end()
+  })
+}