Cache electrum address history fetch a couple of seconds to prevent double requests on address page load.

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

@@ -11,6 +11,7 @@ import * as ElectrumClient from '@mempool/electrum-client';
 import * as sha256 from 'crypto-js/sha256';
 import * as hexEnc from 'crypto-js/enc-hex';
 import loadingIndicators from '../loading-indicators';
+import memoryCache from '../memory-cache';
 
 class BitcoindElectrsApi extends BitcoinApi implements AbstractBitcoinApi {
   private electrumClient: any;
@@ -158,7 +159,15 @@ class BitcoindElectrsApi extends BitcoinApi implements AbstractBitcoinApi {
   }
 
   private $getScriptHashHistory(scriptHash: string): Promise<IElectrumApi.ScriptHashHistory[]> {
-    return this.electrumClient.blockchainScripthash_getHistory(this.encodeScriptHash(scriptHash));
+    const fromCache = memoryCache.get<IElectrumApi.ScriptHashHistory[]>('Scripthash_getHistory', scriptHash);
+    if (fromCache) {
+      return Promise.resolve(fromCache);
+    }
+    return this.electrumClient.blockchainScripthash_getHistory(this.encodeScriptHash(scriptHash))
+      .then((history) => {
+        memoryCache.set('Scripthash_getHistory', scriptHash, history, 2);
+        return history;
+      });
   }
 
   private encodeScriptHash(scriptPubKey: string): string {

backend/src/api/memory-cache.ts

@@ -0,0 +1,38 @@
+interface ICache {
+  type: string;
+  id: string;
+  expires: Date;
+  data: any;
+}
+
+class MemoryCache {
+  private cache: ICache[] = [];
+  constructor() {
+    setInterval(this.cleanup.bind(this), 1000);
+  }
+
+  public set(type: string, id: string, data: any, secondsExpiry: number) {
+    const expiry = new Date();
+    expiry.setSeconds(expiry.getSeconds() + secondsExpiry);
+    this.cache.push({
+      type: type,
+      id: id,
+      data: data,
+      expires: expiry,
+    });
+  }
+
+  public get<T>(type: string, id: string): T | null {
+    const found = this.cache.find((cache) => cache.type === type && cache.id === id);
+    if (found) {
+      return found.data;
+    }
+    return null;
+  }
+
+  private cleanup() {
+    this.cache = this.cache.filter((cache) => cache.expires < (new Date()));
+  }
+}
+
+export default new MemoryCache();