feat: chat stream messages

frontend/src/backend.js

@@ -1,5 +1,6 @@
 
 import * as ui from './ui';
+import Stream from './stream';
 
 export class ChatInfo {
   constructor({ id, name }) {
@@ -42,6 +43,16 @@ function createDeferred() {
   return {promise, resolve, reject};
 }
 
+function createDeferredStream(callback) {
+  let resolve, reject;
+  const promise = new Promise((res, rej) => {
+    resolve = res;
+    reject = rej;
+  });
+  let deferred = {promise, resolve, reject};
+  return {promise, resolve (value) { callback(value, deferred) }, reject}
+}
+
 function initState () {
   backendUrl = window.location.origin;
   const tk = localStorage.getItem('loginToken');
@@ -126,12 +137,12 @@ export async function newToken () {
 
 // --- Communication ---
 
-export function sendAction(action, body = {}) {
+export function sendAction(action, body = {}, callback = null) {
   if (socket?.readyState !== WebSocket.OPEN) {
     return Promise.reject(new Error("WebSocket is not open. Cannot send action."));
   }
   const nonce = nextNonce++;
-  const deferred = createDeferred();
+  const deferred = callback ? createDeferredStream(callback) : createDeferred();
 
   pendingActions[nonce] = deferred;
   deferred.promise.finally(() => {
@@ -320,6 +331,19 @@ export async function getAgent(agentId) {
   return allAgents.find(it => it.id == agentId);
 }
 
+export function readStream(streamId) {
+  let stream = new Stream(streamId);
+  sendAction("read-stream", {streamId}, (packet, deferred) => {
+    if (packet.eof) {
+      stream.close();
+      deferred.resolve();
+    } else if (packet.data != null) {
+      stream.feed(packet.data);
+    }
+  });
+  return stream;
+}
+
 export function invalidateCache({ chats=false, agents=false } = {}) {
   if (chats) cache.chats = null;
   if (agents) cache.agents = null;