Websocket subscription for fallback server health status

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;