Introduce experimental real time channels

src-docs/SUMMARY.md

@@ -10,8 +10,9 @@
       - [sendToChat](./spec/sendToChat.md)
       - [importFiles](./spec/importFiles.md)
       - [selfAddr & selfName](./spec/selfAddr_and_selfName.md)
+      - [setRealtimeListener](./spec/setRealtimeListener.md)
+      - [sendRealtimeData](./spec/sendRealtimeData.md)
   - [Messenger implementations](./spec/messenger.md)
-
 - [Shared Web Application state](./shared_state/README.md)
   - [Detecting conflicts](./shared_state/conflicts.md)
   - [Theory of Conflict-free Replicated Data Types (CRDTs)](./shared_state/crdts.md)

src-docs/spec/sendRealtimeData.md

@@ -0,0 +1,48 @@
+# sendRealtimeData()
+
+```js
+window.webxdc.sendRealtimeData(data);
+```
+
+**Note that this API is experimental and not fully settled (April 2024)**
+
+Send `Uint8Array` data to other realtime peers for this app. 
+This will implicitely trigger the setup of realtime connections
+if they are not established yet. 
+Note that any data sent before a first peer is connected might not arrive. 
+See [`setRealtimeListener`](./setRealtimeListener.md) for how data can be received. 
+It is up to the app to implement a "synchronization" protocol
+so that peers can detect each other's presence. 
+
+Any sent data is 
+
+- **private to the chat**: Only chat members can receive realtime data. 
+
+- **scoped to the app**: different apps in a
+  chat can not discover or receive realtime data of other apps in the chat. 
+
+- **ephemeral**: any sent data will only be received by the currently
+  connected chat peers but not by peers joining later.
+  There is no guarantee anyone is receiving the sent data
+  because there might be no currently listening peers,
+  or network connections broke. 
+
+## Example
+
+```js
+
+window.webxdc.setRealtimeListener((data) => {
+    console.log("Received realtime data: ", data);
+    const msg = new TextDecoder().decode(data);
+    console.log("decoded message: ", msg);
+})
+
+let pings = 0
+setInterval(() => {
+    const myId = window.webxdc.selfAddr;
+    const data = new TextEncoder().encode(`[${pings}] hello from ${myId}`);
+    pings += 1
+    console.log("Sending message", data);
+    window.webxdc.sendRealtimeData(data);
+}, 1000)
+```

src-docs/spec/setRealtimeListener.md

@@ -0,0 +1,38 @@
+# setRealtimeListener
+
+```js
+window.webxdc.setRealtimeListener((data) => {});
+```
+
+**Note that this API is experimental and not fully settled (April 2024)**
+
+Register a listener callback for realtime data arriving from other peers. 
+This will implicitely trigger the setup of realtime connections
+if they were not established yet. 
+The `setRealtimeListener` callback receives `Uint8Array` data items 
+that were sent from connected peers. 
+See [`sendRealtimeData(data)`](./sendRealtimeData.md) for more info. 
+
+Calling `setRealtimeListener` with a `null` value 
+will disconnect from receiving and sending realtime data. 
+You may afterwards call `setRealtimeListener` again with a callback
+to re-establish participation in realtime sending and receiving. 
+
+## Example 
+
+```js
+window.webxdc.setRealtimeListener((data) => {
+    console.log("Received realtime data: ", data);
+    const msg = new TextDecoder().decode(data);
+    console.log("decoded message: ", msg);
+})
+
+let pings = 0
+setInterval(() => {
+    const myId = window.webxdc.selfAddr;
+    const data = new TextEncoder().encode(`[${pings}] hello from ${myId}`);
+    pings += 1
+    console.log("Sending message", data);
+    window.webxdc.sendRealtimeData(data);
+}, 1000)
+```