From 77b702649b75f3a8aced8c2c7f86ddbd43acd1e2 Mon Sep 17 00:00:00 2001
From: Charles Moog <moogcharlie@gmail.com>
Date: Thu, 4 Jun 2020 12:35:04 -0500
Subject: [PATCH] Browser client (#8)

Add browser reference implementation
---
 browser/client.ts | 99 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 browser/client.ts

diff --git a/browser/client.ts b/browser/client.ts
new file mode 100644
index 0000000..009912e
--- /dev/null
+++ b/browser/client.ts
@@ -0,0 +1,99 @@
+// "wsep" browser client reference implementation
+
+const DELIMITER = '\n'.charCodeAt(0);
+
+// Command describes initialization parameters for a remote command
+export interface Command {
+  command: string;
+  args?: string[];
+  tty?: boolean;
+  uid?: number;
+  gid?: number;
+  env?: string[];
+  working_dir?: string;
+}
+
+export type ClientHeader =
+  | { type: 'start'; command: Command }
+  | { type: 'stdin' }
+  | { type: 'close_stdin' }
+  | { type: 'resize'; cols: number; rows: number };
+
+export type ServerHeader =
+  | { type: 'stdout' }
+  | { type: 'stderr' }
+  | { type: 'pid'; pid: number }
+  | { type: 'exit_code'; exit_code: number };
+
+export type Header = ClientHeader | ServerHeader;
+
+export const setBinaryType = (ws: WebSocket) => {
+  ws.binaryType = 'arraybuffer';
+};
+
+export const sendStdin = (ws: WebSocket, data: Uint8Array) => {
+  if (data.byteLength < 1) return;
+  const msg = joinMessage({ type: 'stdin' }, data);
+  ws.send(msg.buffer);
+};
+
+export const closeStdin = (ws: WebSocket) => {
+  const msg = joinMessage({ type: 'close_stdin' });
+  ws.send(msg.buffer);
+};
+
+export const startCommand = (ws: WebSocket, command: Command) => {
+  const msg = joinMessage({ type: 'start', command: command });
+  ws.send(msg.buffer);
+};
+
+export const parseServerMessage = (
+  ev: MessageEvent
+): [ServerHeader, Uint8Array] => {
+  const [header, body] = splitMessage(ev.data);
+  return [header as ServerHeader, body];
+};
+
+export const resizeTerminal = (
+  ws: WebSocket,
+  rows: number,
+  cols: number
+): void => {
+  const msg = joinMessage({ type: 'resize', cols, rows });
+  ws.send(msg.buffer);
+};
+
+const joinMessage = (header: ClientHeader, body?: Uint8Array): Uint8Array => {
+  const encodedHeader = new TextEncoder().encode(JSON.stringify(header));
+  if (body && body.length > 0) {
+    const tmp = new Uint8Array(encodedHeader.byteLength + 1 + body.byteLength);
+    tmp.set(encodedHeader, 0);
+    tmp.set([DELIMITER], encodedHeader.byteLength);
+    tmp.set(body, encodedHeader.byteLength + 1);
+    return tmp;
+  }
+  return encodedHeader;
+};
+
+const splitMessage = (message: ArrayBuffer): [Header, Uint8Array] => {
+  let array: Uint8Array;
+  if (typeof message === 'string') {
+    array = new TextEncoder().encode(message);
+  } else {
+    array = new Uint8Array(message);
+  }
+
+  for (let i = 0; i < array.length; i++) {
+    if (array[i] === DELIMITER) {
+      const headerText = new TextDecoder().decode(array.slice(0, i));
+      const header: ServerHeader = JSON.parse(headerText);
+      const body =
+        array.length > i + 1
+          ? array.slice(i + 1, array.length)
+          : new Uint8Array(0);
+      return [header, body];
+    }
+  }
+
+  return [JSON.parse(new TextDecoder().decode(array)), new Uint8Array(0)];
+};