Websocket subscription for fallback server health status

backend/src/api/bitcoin/bitcoin-api-abstract-factory.ts

@@ -29,6 +29,7 @@ export interface AbstractBitcoinApi {
   $getOutSpendsByOutpoint(outpoints: { txid: string, vout: number }[]): Promise<IEsploraApi.Outspend[]>;
 
   startHealthChecks(): void;
+  getHealthStatus(): HealthCheckHost[];
 }
 export interface BitcoinRpcCredentials {
   host: string;
@@ -38,3 +39,14 @@ export interface BitcoinRpcCredentials {
   timeout: number;
   cookie?: string;
 }
+
+export interface HealthCheckHost {
+  host: string;
+  active: boolean;
+  rtt: number;
+  latestHeight: number;
+  socket: boolean;
+  outOfSync: boolean;
+  unreachable: boolean;
+  checked: boolean;
+}

backend/src/api/bitcoin/bitcoin-api.ts

@@ -1,5 +1,5 @@
 import * as bitcoinjs from 'bitcoinjs-lib';
-import { AbstractBitcoinApi } from './bitcoin-api-abstract-factory';
+import { AbstractBitcoinApi, HealthCheckHost } from './bitcoin-api-abstract-factory';
 import { IBitcoinApi } from './bitcoin-api.interface';
 import { IEsploraApi } from './esplora-api.interface';
 import blocks from '../blocks';
@@ -382,6 +382,10 @@ class BitcoinApi implements AbstractBitcoinApi {
   }
 
   public startHealthChecks(): void {};
+
+  public getHealthStatus() {
+    return [];
+  }
 }
 
 export default BitcoinApi;

backend/src/api/bitcoin/esplora-api.ts

@@ -1,7 +1,7 @@
 import config from '../../config';
-import axios, { AxiosResponse } from 'axios';
+import axios from 'axios';
 import http from 'http';
-import { AbstractBitcoinApi } from './bitcoin-api-abstract-factory';
+import { AbstractBitcoinApi, HealthCheckHost } from './bitcoin-api-abstract-factory';
 import { IEsploraApi } from './esplora-api.interface';
 import logger from '../../logger';
 import { Common } from '../common';
@@ -157,7 +157,7 @@ class FailoverRouter {
   }
 
   // sort hosts by connection quality, and update default fallback
-  private sortHosts(): FailoverHost[] {
+  public sortHosts(): FailoverHost[] {
     // sort by connection quality
     return this.hosts.slice().sort((a, b) => {
       if ((a.unreachable || a.outOfSync) === (b.unreachable || b.outOfSync)) {
@@ -342,6 +342,19 @@ class ElectrsApi implements AbstractBitcoinApi {
   public startHealthChecks(): void {
     this.failoverRouter.startHealthChecks();
   }
+
+  public getHealthStatus(): HealthCheckHost[] {
+    return this.failoverRouter.sortHosts().map(host => ({
+      host: host.host,
+      active: host === this.failoverRouter.activeHost,
+      rtt: host.rtt,
+      latestHeight: host.latestHeight || 0,
+      socket: !!host.socket,
+      outOfSync: !!host.outOfSync,
+      unreachable: !!host.unreachable,
+      checked: !!host.checked,
+    }));
+  }
 }
 
 export default ElectrsApi;

backend/src/api/websocket-handler.ts

@@ -26,6 +26,7 @@ import mempool from './mempool';
 import statistics from './statistics/statistics';
 import accelerationCosts from './acceleration';
 import accelerationRepository from '../repositories/AccelerationRepository';
+import bitcoinApi from './bitcoin/bitcoin-api-factory';
 
 interface AddressTransactions {
   mempool: MempoolTransactionExtended[],
@@ -39,6 +40,7 @@ const wantable = [
   'mempool-blocks',
   'live-2h-chart',
   'stats',
+  'tomahawk',
 ];
 
 class WebsocketHandler {
@@ -123,7 +125,7 @@ class WebsocketHandler {
             for (const sub of wantable) {
               const key = `want-${sub}`;
               const wants = parsedMessage.data.includes(sub);
-              if (wants && client['wants'] && !client[key]) {
+              if (wants && !client[key]) {
                 wantNow[key] = true;
               }
               client[key] = wants;
@@ -147,6 +149,10 @@ class WebsocketHandler {
             response['da'] = this.socketData['da'];
           }
 
+          if (wantNow['want-tomahawk'] && config.MEMPOOL.BACKEND === 'esplora' && config.ESPLORA.FALLBACK?.length) {
+            response['tomahawk'] = JSON.stringify(bitcoinApi.getHealthStatus());
+          }
+
           if (parsedMessage && parsedMessage['track-tx']) {
             if (/^[a-fA-F0-9]{64}$/.test(parsedMessage['track-tx'])) {
               client['track-tx'] = parsedMessage['track-tx'];
@@ -546,6 +552,10 @@ class WebsocketHandler {
         response['mempool-blocks'] = getCachedResponse('mempool-blocks', mBlocks);
       }
 
+      if (client['want-tomahawk'] && config.MEMPOOL.BACKEND === 'esplora' && config.ESPLORA.FALLBACK?.length) {
+        response['tomahawk'] = getCachedResponse('tomahawk', bitcoinApi.getHealthStatus());
+      }
+
       if (client['track-mempool-tx']) {
         const tx = newTransactions.find((t) => t.txid === client['track-mempool-tx']);
         if (tx) {
@@ -909,6 +919,10 @@ class WebsocketHandler {
         response['mempool-blocks'] = getCachedResponse('mempool-blocks', mBlocks);
       }
 
+      if (client['want-tomahawk'] && config.MEMPOOL.BACKEND === 'esplora' && config.ESPLORA.FALLBACK?.length) {
+        response['tomahawk'] = getCachedResponse('tomahawk', bitcoinApi.getHealthStatus());
+      }
+
       if (client['track-tx']) {
         const trackTxid = client['track-tx'];
         if (trackTxid && confirmedTxids[trackTxid]) {