1 files changed, 60 insertions, 0 deletions
diff --git a/frontend/src/api/websocket.ts b/frontend/src/api/websocket.ts
new file mode 100644
index 00000000..e9393836
--- /dev/null
+++ b/frontend/src/api/websocket.ts
@@ -0,0 +1,60 @@
+import SockJS from 'sockjs-client';
+import { Client, Frame, Message, Options, Subscription } from 'webstomp-client';
+import * as Stomp from 'webstomp-client';
+
+const DEFAULT_DEBUG_OPTIONS = {
+  debug: process.env.NODE_ENV !== 'production',
+};
+
+export type Callback<T> = (value: T) => void;
+export type UnsubscribeFn = () => void;
+export type SubscribeFn<T> = (callback: Callback<T>) => UnsubscribeFn;
+
+export class JsonStompClient {
+  client: Client;
+
+  constructor(client: Client) {
+    this.client = client;
+  }
+
+  connect(headers: Stomp.ConnectionHeaders = {}): Promise<Frame | void> {
+    return new Promise((resolve, reject) => {
+      this.client.connect(headers, resolve, reject);
+    });
+  }
+
+  subscribe<T>(path: string, callback: Callback<T>): UnsubscribeFn {
+    const socketSubscription: Subscription = this.client.subscribe(path, (message: Message) => {
+      // not all frames have a JSON body
+      const value: T | void = message && JsonStompClient.parseBody(message);
+      callback(value || {} as T);
+    });
+    return () => socketSubscription.unsubscribe();
+  }
+
+  static parseBody<T>(message: Message): T | void {
+    try {
+      return message.body ? JSON.parse(message.body) : undefined;
+    } catch (jsonParseError) {
+      throw new Error('Cannot parse websocket message as JSON: ' + jsonParseError.message);
+    }
+  }
+
+  subscriber<T>(path: string): SubscribeFn<T> {
+    return (callback: Callback<T>) => this.subscribe(path, callback);
+  }
+
+  send(url: string, body?: Object) {
+    const strBody = body ? JSON.stringify(body) : '';
+    this.client.send(url, strBody);
+  }
+}
+
+function createStompClient(url: string, options: Options = {}): Client {
+  const optionsWithDebug = Object.assign({}, DEFAULT_DEBUG_OPTIONS, options);
+  return Stomp.over(new SockJS(url), optionsWithDebug);
+}
+
+export function createJsonStompClient(url: string, options: Options = {}): JsonStompClient {
+  return new JsonStompClient(createStompClient(url, options));
+}