gecko-dev/remote/server/WebSocket.jsm

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

"use strict";

var EXPORTED_SYMBOLS = ["WebSocketServer"];

// This file is an XPCOM service-ified copy of ../devtools/server/socket/websocket-server.js.

const CC = Components.Constructor;

const {Services} = ChromeUtils.import("resource://gre/modules/Services.jsm");
const {Stream} = ChromeUtils.import("chrome://remote/content/server/Stream.jsm");
const {XPCOMUtils} = ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");

XPCOMUtils.defineLazyGetter(this, "WebSocket", () => {
  return Services.appShell.hiddenDOMWindow.WebSocket;
});

const CryptoHash = CC("@mozilla.org/security/hash;1", "nsICryptoHash", "initWithString");
const threadManager = Cc["@mozilla.org/thread-manager;1"].getService();

// limit the header size to put an upper bound on allocated memory
const HEADER_MAX_LEN = 8000;

// TODO(ato): Merge this with httpd.js so that we can respond to both HTTP/1.1
// as well as WebSocket requests on the same server.

/**
 * Read a line from async input stream
 * and return promise that resolves to the line once it has been read.
 * If the line is longer than HEADER_MAX_LEN, will throw error.
 */
function readLine(input) {
  return new Promise((resolve, reject) => {
    let line = "";
    const wait = () => {
      input.asyncWait(stream => {
        try {
          const amountToRead = HEADER_MAX_LEN - line.length;
          line += Stream.delimitedRead(input, "\n", amountToRead);

          if (line.endsWith("\n")) {
            resolve(line.trimRight());
            return;
          }

          if (line.length >= HEADER_MAX_LEN) {
            throw new Error(
                `Failed to read HTTP header longer than ${HEADER_MAX_LEN} bytes`);
          }

          wait();
        } catch (ex) {
          reject(ex);
        }
      }, 0, 0, threadManager.currentThread);
    };

    wait();
  });
}

/**
 * Write a string of bytes to async output stream
 * and return promise that resolves once all data has been written.
 * Doesn't do any UTF-16/UTF-8 conversion.
 * The string is treated as an array of bytes.
 */
function writeString(output, data) {
  return new Promise((resolve, reject) => {
    const wait = () => {
      if (data.length === 0) {
        resolve();
        return;
      }

      output.asyncWait(stream => {
        try {
          const written = output.write(data, data.length);
          data = data.slice(written);
          wait();
        } catch (ex) {
          reject(ex);
        }
      }, 0, 0, threadManager.currentThread);
    };

    wait();
  });
}

/**
 * Read HTTP request from async input stream.
 *
 * @return Request line (string) and Map of header names and values.
 */
const readHttpRequest = async function(input) {
  let requestLine = "";
  const headers = new Map();

  while (true) {
    const line = await readLine(input);
    if (line.length == 0) {
      break;
    }

    if (!requestLine) {
      requestLine = line;
    } else {
      const colon = line.indexOf(":");
      if (colon == -1) {
        throw new Error(`Malformed HTTP header: ${line}`);
      }

      const name = line.slice(0, colon).toLowerCase();
      const value = line.slice(colon + 1).trim();
      headers.set(name, value);
    }
  }

  return {requestLine, headers};
};

/** Write HTTP response (array of strings) to async output stream. */
function writeHttpResponse(output, response) {
  const s = response.join("\r\n") + "\r\n\r\n";
  return writeString(output, s);
}

/**
 * Process the WebSocket handshake headers and return the key to be sent in
 * Sec-WebSocket-Accept response header.
 */
function processRequest({requestLine, headers}) {
  const method = requestLine.split(" ")[0];
  if (method !== "GET") {
    throw new Error("The handshake request must use GET method");
  }

  const upgrade = headers.get("upgrade");
  if (!upgrade || upgrade !== "websocket") {
    throw new Error("The handshake request has incorrect Upgrade header");
  }

  const connection = headers.get("connection");
  if (!connection || !connection.split(",").map(t => t.trim()).includes("Upgrade")) {
    throw new Error("The handshake request has incorrect Connection header");
  }

  const version = headers.get("sec-websocket-version");
  if (!version || version !== "13") {
    throw new Error("The handshake request must have Sec-WebSocket-Version: 13");
  }

  // Compute the accept key
  const key = headers.get("sec-websocket-key");
  if (!key) {
    throw new Error("The handshake request must have a Sec-WebSocket-Key header");
  }

  return { acceptKey: computeKey(key) };
}

function computeKey(key) {
  const str = `${key}258EAFA5-E914-47DA-95CA-C5AB0DC85B11`;
  const data = Array.from(str, ch => ch.charCodeAt(0));
  const hash = new CryptoHash("sha1");
  hash.update(data, data.length);
  return hash.finish(true);
}

/**
 * Perform the server part of a WebSocket opening handshake
 * on an incoming connection.
 */
async function serverHandshake(request, output) {
  try {
    // Check and extract info from the request
    const {acceptKey} = processRequest(request);

    // Send response headers
    await writeHttpResponse(output, [
      "HTTP/1.1 101 Switching Protocols",
      "Upgrade: websocket",
      "Connection: Upgrade",
      `Sec-WebSocket-Accept: ${acceptKey}`,
    ]);
  } catch (error) {
    // Send error response in case of error
    await writeHttpResponse(output, [ "HTTP/1.1 400 Bad Request" ]);
    throw error;
  }
}

async function createWebSocket(transport, input, output) {
  const transportProvider = {
    setListener(upgradeListener) {
      // onTransportAvailable callback shouldn't be called synchronously
      Services.tm.dispatchToMainThread(() => {
        upgradeListener.onTransportAvailable(transport, input, output);
      });
    },
  };

  return new Promise((resolve, reject) => {
    const socket = WebSocket.createServerWebSocket(null, [], transportProvider, "");
    socket.addEventListener("close", () => {
      input.close();
      output.close();
    });

    socket.onopen = () => resolve(socket);
    socket.onerror = err => reject(err);
  });
}

/**
 * Accept an incoming WebSocket server connection.
 * Takes an established nsISocketTransport in the parameters.
 * Performs the WebSocket handshake and waits for the WebSocket to open.
 * Returns Promise with a WebSocket ready to send and receive messages.
 */
async function accept(transport, input, output) {
  const request = await readHttpRequest(input);
  await serverHandshake(request, output);
  return createWebSocket(transport, input, output);
}

/** Upgrade an existing HTTP request from httpd.js to WebSocket. */
async function upgrade(request, response) {
  // handle response manually, allowing us to send arbitrary data
  response._powerSeized = true;

  const {transport, input, output} = response._connection;

  const headers = new Map();
  for (let [key, values] of Object.entries(request._headers._headers)) {
    headers.set(key, values.join("\n"));
  }
  const convertedRequest = {
    requestLine: `${request.method} ${request.path}`,
    headers,
  };
  await serverHandshake(convertedRequest, output);

  return createWebSocket(transport, input, output);
}

const WebSocketServer = {accept, upgrade};