Add transparent support for EventSource streaming. (#12887)

This activates if the streaming base URL does not start with "ws".
All currently-live streaming base URLs start with "wss://".

app/javascript/mastodon/stream.js

@@ -2,6 +2,14 @@ import WebSocketClient from '@gamestdio/websocket';
 
 const randomIntUpTo = max => Math.floor(Math.random() * Math.floor(max));
 
+const knownEventTypes = [
+  'update',
+  'delete',
+  'notification',
+  'conversation',
+  'filters_changed',
+];
+
 export function connectStream(path, pollingRefresh = null, callbacks = () => ({ onConnect() {}, onDisconnect() {}, onReceive() {} })) {
   return (dispatch, getState) => {
     const streamingAPIBaseURL = getState().getIn(['meta', 'streaming_api_base_url']);
@@ -69,14 +77,42 @@ export function connectStream(path, pollingRefresh = null, callbacks = () => ({
 
 
 export default function getStream(streamingAPIBaseURL, accessToken, stream, { connected, received, disconnected, reconnected }) {
-  const params = [ `stream=${stream}` ];
-
-  const ws = new WebSocketClient(`${streamingAPIBaseURL}/api/v1/streaming/?${params.join('&')}`, accessToken);
-
-  ws.onopen      = connected;
-  ws.onmessage   = e => received(JSON.parse(e.data));
-  ws.onclose     = disconnected;
-  ws.onreconnect = reconnected;
+  const params = stream.split('&');
+  stream = params.shift();
+
+  if (streamingAPIBaseURL.startsWith('ws')) {
+    params.unshift(`stream=${stream}`);
+    const ws = new WebSocketClient(`${streamingAPIBaseURL}/api/v1/streaming/?${params.join('&')}`, accessToken);
+
+    ws.onopen      = connected;
+    ws.onmessage   = e => received(JSON.parse(e.data));
+    ws.onclose     = disconnected;
+    ws.onreconnect = reconnected;
+
+    return ws;
+  }
+
+  params.push(`access_token=${accessToken}`);
+  const es = new EventSource(`${streamingAPIBaseURL}/api/v1/streaming/${stream}?${params.join('&')}`);
+
+  let firstConnect = true;
+  es.onopen = () => {
+    if (firstConnect) {
+      firstConnect = false;
+      connected();
+    } else {
+      reconnected();
+    }
+  };
+  for (let type of knownEventTypes) {
+    es.addEventListener(type, (e) => {
+      received({
+        event: e.type,
+        payload: e.data,
+      });
+    });
+  }
+  es.onerror = disconnected;
 
-  return ws;
+  return es;
 };