Add snap support (#60)

* Initial app daemon implementation

* Pass script path to child bridge processes

* Change WebSocket server port

* Fix error sending message whilst WebSocket connection is closing

* Initial ext daemon connection implementation

app/src/daemon/index.ts

@@ -0,0 +1,61 @@
+"use strict";
+
+import { spawn } from "child_process";
+import { Readable } from "stream";
+
+import path from "path";
+import WebSocket from "ws";
+
+import { DecodeTransform
+       , EncodeTransform } from "../transforms";
+
+
+const wss = new WebSocket.Server({ port: 9556 });
+
+wss.on("connection", socket => {
+
+    /**
+     * Daemon and bridge are the same binary, so spawn a new
+     * version of self in bridge mode.
+     */
+    const bridge = spawn(process.execPath, [ process.argv[1] ]);
+
+    // Stream for incoming WebSocket messages
+    const messageStream = new Readable({
+        objectMode: true
+    });
+
+    // tslint:disable-next-line:no-empty
+    messageStream._read = () => {};
+
+    /**
+     * Incoming JSON messages from the extension over the
+     * WebSocket connection are parsed and re-encoded to be sent
+     * to bridge stdin.
+     */
+    socket.on("message", (message: string) => {
+        messageStream.push(JSON.parse(message));
+    });
+
+    messageStream
+        .pipe(new EncodeTransform())
+        .pipe(bridge.stdin);
+
+    /**
+     * Incoming messages from the bridge are decoded and
+     * stringified and sent to the extension over the WebSocket
+     * connection.
+     */
+    bridge.stdout
+        .pipe(new DecodeTransform())
+        .on("data", data => {
+            // Socket can be CLOSING here
+            if (socket.readyState === WebSocket.OPEN) {
+                socket.send(JSON.stringify(data));
+            }
+        });
+
+    // Handle termination
+    socket.on("close", () => bridge.kill());
+    bridge.on("exit", () => socket.close());
+});