NativeMessaging.jsm

/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
/* vim: set sts=2 sw=2 et tw=80: */
/* 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";

this.EXPORTED_SYMBOLS = ["NativeApp"];

ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");

const {EventEmitter} = ChromeUtils.import("resource://gre/modules/EventEmitter.jsm", {});

XPCOMUtils.defineLazyModuleGetters(this, {
  AppConstants: "resource://gre/modules/AppConstants.jsm",
  AsyncShutdown: "resource://gre/modules/AsyncShutdown.jsm",
  ExtensionChild: "resource://gre/modules/ExtensionChild.jsm",
  NativeManifests: "resource://gre/modules/NativeManifests.jsm",
  OS: "resource://gre/modules/osfile.jsm",
  Services: "resource://gre/modules/Services.jsm",
  Subprocess: "resource://gre/modules/Subprocess.jsm",
  clearTimeout: "resource://gre/modules/Timer.jsm",
  setTimeout: "resource://gre/modules/Timer.jsm",
});

// For a graceful shutdown (i.e., when the extension is unloaded or when it
// explicitly calls disconnect() on a native port), how long we give the native
// application to exit before we start trying to kill it.  (in milliseconds)
const GRACEFUL_SHUTDOWN_TIME = 3000;

// Hard limits on maximum message size that can be read/written
// These are defined in the native messaging documentation, note that
// the write limit is imposed by the "wire protocol" in which message
// boundaries are defined by preceding each message with its length as
// 4-byte unsigned integer so this is the largest value that can be
// represented.  Good luck generating a serialized message that large,
// the practical write limit is likely to be dictated by available memory.
const MAX_READ = 1024 * 1024;
const MAX_WRITE = 0xffffffff;

// Preferences that can lower the message size limits above,
// used for testing the limits.
const PREF_MAX_READ = "webextensions.native-messaging.max-input-message-bytes";
const PREF_MAX_WRITE = "webextensions.native-messaging.max-output-message-bytes";

const global = this;

var NativeApp = class extends EventEmitter {
  /**
   * @param {BaseContext} context The context that initiated the native app.
   * @param {string} application The identifier of the native app.
   */
  constructor(context, application) {
    super();

    this.context = context;
    this.name = application;

    // We want a close() notification when the window is destroyed.
    this.context.callOnClose(this);

    this.proc = null;
    this.readPromise = null;
    this.sendQueue = [];
    this.writePromise = null;
    this.sentDisconnect = false;

    this.startupPromise = NativeManifests.lookupManifest("stdio", application, context)
      .then(hostInfo => {
        // Report a generic error to not leak information about whether a native
        // application is installed to addons that do not have the right permission.
        if (!hostInfo) {
          throw new context.cloneScope.Error(`No such native application ${application}`);
        }

        let command = hostInfo.manifest.path;
        if (AppConstants.platform == "win") {
          // OS.Path.join() ignores anything before the last absolute path
          // it sees, so if command is already absolute, it remains unchanged
          // here.  If it is relative, we get the proper absolute path here.
          command = OS.Path.join(OS.Path.dirname(hostInfo.path), command);
        }

        let subprocessOpts = {
          command: command,
          arguments: [hostInfo.path, context.extension.id],
          workdir: OS.Path.dirname(command),
          stderr: "pipe",
        };
        return Subprocess.call(subprocessOpts);
      }).then(proc => {
        this.startupPromise = null;
        this.proc = proc;
        this._startRead();
        this._startWrite();
        this._startStderrRead();
      }).catch(err => {
        this.startupPromise = null;
        Cu.reportError(err instanceof Error ? err : err.message);
        this._cleanup(err);
      });
  }

  /**
   * Open a connection to a native messaging host.
   *
   * @param {BaseContext} context The context associated with the port.
   * @param {nsIMessageSender} messageManager The message manager used to send
   *     and receive messages from the port's creator.
   * @param {number} portId A unique internal ID that identifies the port.
   * @param {object} sender The object describing the creator of the connection
   *     request.
   * @param {string} application The name of the native messaging host.
   */
  static onConnectNative(context, messageManager, portId, sender, application) {
    let app = new NativeApp(context, application);
    let port = new ExtensionChild.Port(context, messageManager, [Services.mm], "", portId, sender, sender);
    app.once("disconnect", (what, err) => port.disconnect(err));

    /* eslint-disable mozilla/balanced-listeners */
    app.on("message", (what, msg) => port.postMessage(msg));
    /* eslint-enable mozilla/balanced-listeners */

    port.registerOnMessage(holder => app.send(holder));
    port.registerOnDisconnect(msg => app.close());
  }

  /**
   * @param {BaseContext} context The scope from where `message` originates.
   * @param {*} message A message from the extension, meant for a native app.
   * @returns {ArrayBuffer|SharedArrayBuffer} An ArrayBuffer that can be sent to the native app.
   */
  static encodeMessage(context, message) {
    message = context.jsonStringify(message);
    let buffer = new TextEncoder().encode(message).buffer;
    if (buffer.byteLength > NativeApp.maxWrite) {
      throw new context.cloneScope.Error("Write too big");
    }
    return buffer;
  }

  // A port is definitely "alive" if this.proc is non-null.  But we have
  // to provide a live port object immediately when connecting so we also
  // need to consider a port alive if proc is null but the startupPromise
  // is still pending.
  get _isDisconnected() {
    return (!this.proc && !this.startupPromise);
  }

  _startRead() {
    if (this.readPromise) {
      throw new Error("Entered _startRead() while readPromise is non-null");
    }
    this.readPromise = this.proc.stdout.readUint32()
      .then(len => {
        if (len > NativeApp.maxRead) {
          throw new this.context.cloneScope.Error(`Native application tried to send a message of ${len} bytes, which exceeds the limit of ${NativeApp.maxRead} bytes.`);
        }
        return this.proc.stdout.readJSON(len);
      }).then(msg => {
        this.emit("message", msg);
        this.readPromise = null;
        this._startRead();
      }).catch(err => {
        if (err.errorCode != Subprocess.ERROR_END_OF_FILE) {
          Cu.reportError(err instanceof Error ? err : err.message);
        }
        this._cleanup(err);
      });
  }

  _startWrite() {
    if (this.sendQueue.length == 0) {
      return;
    }

    if (this.writePromise) {
      throw new Error("Entered _startWrite() while writePromise is non-null");
    }

    let buffer = this.sendQueue.shift();
    let uintArray = Uint32Array.of(buffer.byteLength);

    this.writePromise = Promise.all([
      this.proc.stdin.write(uintArray.buffer),
      this.proc.stdin.write(buffer),
    ]).then(() => {
      this.writePromise = null;
      this._startWrite();
    }).catch(err => {
      Cu.reportError(err.message);
      this._cleanup(err);
    });
  }

  _startStderrRead() {
    let proc = this.proc;
    let app = this.name;
    (async function() {
      let partial = "";
      while (true) {
        let data = await proc.stderr.readString();
        if (data.length == 0) {
          // We have hit EOF, just stop reading
          if (partial) {
            Services.console.logStringMessage(`stderr output from native app ${app}: ${partial}`);
          }
          break;
        }

        let lines = data.split(/\r?\n/);
        lines[0] = partial + lines[0];
        partial = lines.pop();

        for (let line of lines) {
          Services.console.logStringMessage(`stderr output from native app ${app}: ${line}`);
        }
      }
    })();
  }

  send(holder) {
    if (this._isDisconnected) {
      throw new this.context.cloneScope.Error("Attempt to postMessage on disconnected port");
    }
    let msg = holder.deserialize(global);
    if (Cu.getClassName(msg, true) != "ArrayBuffer") {
      // This error cannot be triggered by extensions; it indicates an error in
      // our implementation.
      throw new Error("The message to the native messaging host is not an ArrayBuffer");
    }

    let buffer = msg;

    if (buffer.byteLength > NativeApp.maxWrite) {
      throw new this.context.cloneScope.Error("Write too big");
    }

    this.sendQueue.push(buffer);
    if (!this.startupPromise && !this.writePromise) {
      this._startWrite();
    }
  }

  // Shut down the native application and also signal to the extension
  // that the connect has been disconnected.
  _cleanup(err) {
    this.context.forgetOnClose(this);

    let doCleanup = () => {
      // Set a timer to kill the process gracefully after one timeout
      // interval and kill it forcefully after two intervals.
      let timer = setTimeout(() => {
        this.proc.kill(GRACEFUL_SHUTDOWN_TIME);
      }, GRACEFUL_SHUTDOWN_TIME);

      let promise = Promise.all([
        this.proc.stdin.close()
          .catch(err => {
            if (err.errorCode != Subprocess.ERROR_END_OF_FILE) {
              throw err;
            }
          }),
        this.proc.wait(),
      ]).then(() => {
        this.proc = null;
        clearTimeout(timer);
      });

      AsyncShutdown.profileBeforeChange.addBlocker(
        `Native Messaging: Wait for application ${this.name} to exit`,
        promise);

      promise.then(() => {
        AsyncShutdown.profileBeforeChange.removeBlocker(promise);
      });

      return promise;
    };

    if (this.proc) {
      doCleanup();
    } else if (this.startupPromise) {
      this.startupPromise.then(doCleanup);
    }

    if (!this.sentDisconnect) {
      this.sentDisconnect = true;
      if (err && err.errorCode == Subprocess.ERROR_END_OF_FILE) {
        err = null;
      }
      this.emit("disconnect", err);
    }
  }

  // Called from Context when the extension is shut down.
  close() {
    this._cleanup();
  }

  sendMessage(holder) {
    let responsePromise = new Promise((resolve, reject) => {
      this.once("message", (what, msg) => { resolve(msg); });
      this.once("disconnect", (what, err) => { reject(err); });
    });

    let result = this.startupPromise.then(() => {
      this.send(holder);
      return responsePromise;
    });

    result.then(() => {
      this._cleanup();
    }, () => {
      // Prevent the response promise from being reported as an
      // unchecked rejection if the startup promise fails.
      responsePromise.catch(() => {});

      this._cleanup();
    });

    return result;
  }
};

XPCOMUtils.defineLazyPreferenceGetter(NativeApp, "maxRead", PREF_MAX_READ, MAX_READ);
XPCOMUtils.defineLazyPreferenceGetter(NativeApp, "maxWrite", PREF_MAX_WRITE, MAX_WRITE);