Improvments to the mempool transaction subscription.

backend/src/api/websocket-handler.ts

@@ -2,7 +2,7 @@ const config = require('../../mempool-config.json');
 
 import * as WebSocket from 'ws';
 import * as fs from 'fs';
-import { Block, TransactionExtended, Statistic } from '../interfaces';
+import { Block, TransactionExtended, Statistic, WebsocketResponse } from '../interfaces';
 import blocks from './blocks';
 import memPool from './mempool';
 import mempoolBlocks from './mempool-blocks';
@@ -36,7 +36,8 @@ class WebsocketHandler {
     this.wss.on('connection', (client: WebSocket) => {
       client.on('message', (message: any) => {
         try {
-          const parsedMessage = JSON.parse(message);
+          const parsedMessage: WebsocketResponse = JSON.parse(message);
+          const response = {};
 
           if (parsedMessage.action === 'want') {
             client['want-blocks'] = parsedMessage.data.indexOf('blocks') > -1;
@@ -48,6 +49,15 @@ class WebsocketHandler {
           if (parsedMessage && parsedMessage['track-tx']) {
             if (/^[a-fA-F0-9]{64}$/.test(parsedMessage['track-tx'])) {
               client['track-tx'] = parsedMessage['track-tx'];
+              // Client is telling the transaction wasn't found but it might have appeared before we had the time to start watching for it
+              if (parsedMessage['watch-mempool']) {
+                const tx = memPool.getMempool()[client['track-tx']];
+                if (tx) {
+                  response['tx'] = tx;
+                } else {
+                  client['track-mempool-tx'] = parsedMessage['track-tx'];
+                }
+              }
             } else {
               client['track-tx'] = null;
             }
@@ -78,7 +88,11 @@ class WebsocketHandler {
           }
 
           if (parsedMessage.action === 'ping') {
-            client.send(JSON.stringify({'pong': true}));
+            response['pong'] = true;
+          }
+
+          if (Object.keys(response).length) {
+            client.send(JSON.stringify(response));
           }
         } catch (e) {
           console.log(e);
@@ -133,10 +147,11 @@ class WebsocketHandler {
         response['mempool-blocks'] = mBlocks;
       }
 
-      if (client['track-tx']) {
-        const tx = newTransactions.find((t) => t.txid === client['track-tx']);
+      if (client['track-mempool-tx']) {
+        const tx = newTransactions.find((t) => t.txid === client['track-mempool-tx']);
         if (tx) {
           response['tx'] = tx;
+          client['track-mempool-tx'] = null;
         }
       }