feat(sse): support bidirectional messaging

docs/2.adapters/sse.md

@@ -1,59 +1,108 @@
 ---
-icon: oui:token-event
+icon: clarity:two-way-arrows-line
 ---
 
 # SSE
 
-> Integrate crossws with [server-sent events](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events).
+> Integrate crossws with server-sent events and fetch-api.
 
-If your deployment server is incapable of of handling WebSocket upgrades but support standard web API ([`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) and [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response)) you can integrate crossws to act as a one way (server to client) handler using [server-sent events](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events).
+If your deployment target does not supports handling WebSocket upgrades, crossws SSE adapter allows to add integration based on web platform standards ([`fetch`](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) and [`EventSource`](https://developer.mozilla.org/en-US/docs/Web/API/EventSource))
 
 > [!IMPORTANT]
-> This is an experimental adapter and works only with a limited subset of crossws functionalities.
+> This is an experimental adapter, requires server support and a different way of connection from clients.
 
-> [!IMPORTANT]
-> Instead of [`WebSocket`](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket) client you need to use [`EventSource`](https://developer.mozilla.org/en-US/docs/Web/API/EventSource) as client to connect such server.
+> [!NOTE]
+> HTTP/2 server support is recommended in order to increase browser limitations about number of SSE connections (from 6 to 100) and also to allow bidirectional messaging with streaming.
+
+## Usage
+
+### Server side
+
+Define adapter:
 
 ```ts
 import sseAdapter from "crossws/adapters/sse";
 
-const sse = sseAdapter({
+const ws = sseAdapter({
+  bidir: true, // Enable bidirectional messaging support
   hooks: {
     upgrade(request) {
-      // Handle upgrade logic
-      // You can return a custom response to abort
-      // You can return { headers } to override default headers
+      // In case of bidirectional mode, extra auth is recommended based on request
+      // You can return a new Response() instead to abort
+      return {
+        headers: {},
+      };
     },
     open(peer) {
       // Use this hook to send messages to peer
-      peer.send("hello!");
+      peer.send(`Welcome ${peer}`);
+    },
+    message(peer, message) {
+      // Accepting messages from peer (bidirectional mode)
+      console.log(`Message from ${peer}: ${message}`); // Message from <id>: ping
     },
   },
 });
 ```
 
-Inside your Web compatible server handler:
+Inside your web server handler:
 
 ```js
 async fetch(request) {
   const url = new URL(request.url)
 
   // Handle SSE
-  if (url.pathname === "/sse" && request.headers.get("accept") === "text/event-stream") {
-    return sse.fetch(request);
+  if (url.pathname === "/sse") {
+    return ws.fetch(request);
   }
 
-  return new Response("server is up!")
+  return new Response("default page")
 }
 ```
 
-In order to connect to the server, you need to use [`EventSource`](https://developer.mozilla.org/en-US/docs/Web/API/EventSource) as client:
+### Client side
+
+In order to receive messages from server, you need to use an [`EventSource`](https://developer.mozilla.org/en-US/docs/Web/API/EventSource) client.
+
+In order to send messages to the server make sure `bdir: true` option is enabled on the server, then you need to first wait for `crosswd-id` to get the peer id associated with connection and then use fetch calls to send messages to the server. You can optionally use a stream to send multiple messages to the server via single connection similar to WebSockets.
+
+> [!NOTE]
+> In theory, it is possible to bidirectional communication on a single HTTP/2 connection, however, due to a [current limitation in fetch standard](https://github.com/whatwg/fetch/issues/1254) we need 2 connections, one for receiving messages and one for sending.
 
 ```js
 const ev = new EventSource("http://<server>/sse");
 
 ev.addEventListener("message", (event) => {
-  console.log(event.data); // hello!
+  // Listen for messages from server
+  console.log("Message:", event.data); // Welcome <id>!
+});
+
+ev.addEventListener("crossws-id", (event) => {
+  // Using peer id we can send messages to the server
+  const peerId = event.id;
+
+  // Method 1: Send each message with a separated fetch call
+  fetch(url, {
+    method: "POST",
+    headers: { "x-crossws-id": peerId },
+    body: "ping", // message
+  });
+
+  // Method 2: Using body stream to send multiple messages (requires HTTP/2 + TLS)
+  fetch(url, {
+    method: "POST",
+    duplex: "half",
+    headers: {
+      "content-type": "application/octet-stream",
+      "x-crossws-id": peerId,
+    },
+    body: new ReadableStream({
+      start(controller) {
+        // You can send multiple messages to the server with single connection
+        controller.enqueue("ping");
+      },
+    }).pipeThrough(new TextEncoderStream()),
+  });
 });
 ```
 

src/adapters/sse.ts

@@ -1,7 +1,8 @@
 import type { AdapterOptions, AdapterInstance } from "../adapter.ts";
-import { toBufferLike } from "../utils.ts";
+import { toString } from "../utils.ts";
 import { defineWebSocketAdapter, adapterUtils } from "../adapter.ts";
 import { AdapterHookable } from "../hooks.ts";
+import { Message } from "../message.ts";
 import { Peer } from "../peer.ts";
 
 // --- types ---
@@ -10,43 +11,86 @@ export interface SSEAdapter extends AdapterInstance {
   fetch(req: Request): Promise<Response>;
 }
 
-export interface SSEOptions extends AdapterOptions {}
+export interface SSEOptions extends AdapterOptions {
+  bidir?: boolean;
+}
 
 // --- adapter ---
 
 // https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events
-export default defineWebSocketAdapter<SSEAdapter, SSEOptions>(
-  (options = {}) => {
-    const hooks = new AdapterHookable(options);
-    const peers = new Set<SSEPeer>();
-
-    return {
-      ...adapterUtils(peers),
-      fetch: async (request: Request) => {
-        const _res = await hooks.callHook("upgrade", request);
-        if (_res instanceof Response) {
-          return _res;
-        }
+export default defineWebSocketAdapter<SSEAdapter, SSEOptions>((opts = {}) => {
+  const hooks = new AdapterHookable(opts);
+  const peers = new Set<SSEPeer>();
+  const peersMap = opts.bidir ? new Map<string, SSEPeer>() : undefined;
+
+  return {
+    ...adapterUtils(peers),
+    fetch: async (request: Request) => {
+      const _res = await hooks.callHook("upgrade", request);
+      if (_res instanceof Response) {
+        return _res;
+      }
 
-        const peer = new SSEPeer({ peers, sse: { request, hooks } });
-
-        let headers: HeadersInit = {
-          "Content-Type": "text/event-stream",
-          "Cache-Control": "no-cache",
-          Connection: "keep-alive",
-        };
-        if (_res?.headers) {
-          headers = new Headers(headers);
-          for (const [key, value] of new Headers(_res.headers)) {
-            headers.set(key, value);
+      let peer: SSEPeer;
+
+      if (opts.bidir && request.body && request.headers.has("x-crossws-id")) {
+        // Accept bidirectional streaming request
+        const id = request.headers.get("x-crossws-id")!;
+        peer = peersMap?.get(id) as SSEPeer;
+        if (!peer) {
+          return new Response("invalid peer id", { status: 400 });
+        }
+        const stream = request.body.pipeThrough(new TextDecoderStream());
+        try {
+          for await (const chunk of stream) {
+            hooks.callHook("message", peer, new Message(chunk));
           }
+        } catch {
+          await stream.cancel().catch(() => {});
         }
+        // eslint-disable-next-line unicorn/no-null
+        return new Response(null, {});
+      } else {
+        // Add a new peer
+        peer = new SSEPeer({
+          peers,
+          sse: {
+            request,
+            hooks,
+            onClose: () => {
+              peers.delete(peer);
+              if (opts.bidir) {
+                peersMap!.delete(peer.id);
+              }
+            },
+          },
+        });
+        peers.add(peer);
+        if (opts.bidir) {
+          peersMap!.set(peer.id, peer);
+          peer._sendEvent("crossws-id", peer.id);
+        }
+      }
 
-        return new Response(peer._sseStream, { ..._res, headers });
-      },
-    };
-  },
-);
+      let headers: HeadersInit = {
+        "Content-Type": "text/event-stream",
+        "Cache-Control": "no-cache",
+        Connection: "keep-alive",
+      };
+      if (opts.bidir) {
+        headers["x-crossws-id"] = peer.id;
+      }
+      if (_res?.headers) {
+        headers = new Headers(headers);
+        for (const [key, value] of new Headers(_res.headers)) {
+          headers.set(key, value);
+        }
+      }
+
+      return new Response(peer._sseStream, { ..._res, headers });
+    },
+  };
+});
 
 // --- peer ---
 
@@ -55,10 +99,12 @@ class SSEPeer extends Peer<{
   sse: {
     request: Request;
     hooks: AdapterHookable;
+    onClose: (peer: SSEPeer) => void;
   };
 }> {
   _sseStream: ReadableStream;
   _sseStreamController?: ReadableStreamDefaultController;
+
   constructor(internal: SSEPeer["_internal"]) {
     super(internal);
     this._sseStream = new ReadableStream({
@@ -67,9 +113,10 @@ class SSEPeer extends Peer<{
         this._internal.sse.hooks.callHook("open", this);
       },
       cancel: () => {
+        this._internal.sse.onClose(this);
         this._internal.sse.hooks.callHook("close", this);
       },
-    });
+    }).pipeThrough(new TextEncoderStream());
   }
 
   get url() {
@@ -80,21 +127,23 @@ class SSEPeer extends Peer<{
     return this._internal.sse.request.headers;
   }
 
+  _sendEvent(event: string, data: string) {
+    const lines = data.split("\n");
+    this._sseStreamController?.enqueue(
+      `event: ${event}\n${lines.map((l) => `data: ${l}`)}\n\n`,
+    );
+  }
+
   send(message: any) {
-    let data = toBufferLike(message);
-    if (typeof data !== "string") {
-      // eslint-disable-next-line unicorn/prefer-code-point
-      data = btoa(String.fromCharCode(...new Uint8Array(data)));
-    }
-    this._sseStreamController?.enqueue(`event: message\ndata: ${data}\n\n`);
+    this._sendEvent("message", toString(message));
     return 0;
   }
 
   publish(topic: string, message: any) {
-    const data = toBufferLike(message);
+    const data = toString(message);
     for (const peer of this._internal.peers) {
       if (peer !== this && peer._topics.has(topic)) {
-        peer._sseStreamController?.enqueue(data);
+        peer._sendEvent("message", data);
       }
     }
   }

src/utils.ts

@@ -30,6 +30,19 @@ export function toBufferLike(val: any): BufferLike {
   return val;
 }
 
+export function toString(val: any): string {
+  if (typeof val === "string") {
+    return val;
+  }
+  const data = toBufferLike(val);
+  if (typeof data === "string") {
+    return data;
+  }
+  // eslint-disable-next-line unicorn/prefer-code-point
+  const base64 = btoa(String.fromCharCode(...new Uint8Array(data)));
+  return `data:application/octet-stream;base64,${base64}`;
+}
+
 // Forked from sindresorhus/is-plain-obj (MIT)
 // Copyright (c) Sindre Sorhus <sindresorhus@gmail.com> (https://sindresorhus.com)
 // From https://github.com/unjs/defu/blob/main/src/_utils.ts

test/adapters/sse.test.ts

@@ -3,18 +3,22 @@ import { wsTestsExec } from "../_utils";
 import EventSource from "eventsource";
 
 describe("sse", () => {
-  wsTestsExec("bun run ./sse.ts", { adapter: "sse" }, (getURL, opts) => {
-    test("connects to the server", async () => {
-      const url = getURL().replace("ws", "http");
-      const ev = new EventSource(url);
-      const messages: string[] = [];
-      ev.addEventListener("message", (event) => {
-        messages.push(event.data);
+  wsTestsExec(
+    "deno run --unstable-byonm -A ./sse.ts",
+    { adapter: "sse" },
+    (getURL) => {
+      test("connects to the server", async () => {
+        const url = getURL().replace("ws", "http") + "_sse";
+        const ev = new EventSource(url);
+        const messages: string[] = [];
+        ev.addEventListener("message", (event) => {
+          messages.push(event.data);
+        });
+        await new Promise((resolve) => ev.addEventListener("open", resolve));
+        ev.close();
+        expect(messages[0]).toMatch(/Welcome to the server \w+/);
+        expect(messages.length).toBe(1);
       });
-      await new Promise((resolve) => ev.addEventListener("open", resolve));
-      ev.close();
-      expect(messages[0]).toMatch(/Welcome to the server \w+/);
-      expect(messages.length).toBe(1);
-    });
-  });
+    },
+  );
 });