devtools/shared/transport/child-transport.js

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 "use strict";
   6
   7 const flags = require("resource://devtools/shared/flags.js");
   8
   9 /**
  10  * A transport for the debugging protocol that uses nsIMessageManagers to
  11  * exchange packets with servers running in child processes.
  12  *
  13  * In the parent process, |mm| should be the nsIMessageSender for the
  14  * child process. In a child process, |mm| should be the child process
  15  * message manager, which sends packets to the parent.
  16  *
  17  * |prefix| is a string included in the message names, to distinguish
  18  * multiple servers running in the same child process.
  19  *
  20  * This transport exchanges messages named 'debug:<prefix>:packet', where
  21  * <prefix> is |prefix|, whose data is the protocol packet.
  22  */
  23 function ChildDebuggerTransport(mm, prefix) {
  24   this._mm = mm;
  25   this._messageName = "debug:" + prefix + ":packet";
  26 }
  27
  28 /*
  29  * To avoid confusion, we use 'message' to mean something that
  30  * nsIMessageSender conveys, and 'packet' to mean a remote debugging
  31  * protocol packet.
  32  */
  33 ChildDebuggerTransport.prototype = {
  34   constructor: ChildDebuggerTransport,
  35
  36   hooks: null,
  37
  38   _addListener() {
  39     this._mm.addMessageListener(this._messageName, this);
  40   },
  41
  42   _removeListener() {
  43     try {
  44       this._mm.removeMessageListener(this._messageName, this);
  45     } catch (e) {
  46       if (e.result != Cr.NS_ERROR_NULL_POINTER) {
  47         throw e;
  48       }
  49       // In some cases, especially when using messageManagers in non-e10s mode, we reach
  50       // this point with a dead messageManager which only throws errors but does not
  51       // seem to indicate in any other way that it is dead.
  52     }
  53   },
  54
  55   ready() {
  56     this._addListener();
  57   },
  58
  59   close(options) {
  60     this._removeListener();
  61     if (this.hooks.onTransportClosed) {
  62       this.hooks.onTransportClosed(null, options);
  63     }
  64   },
  65
  66   receiveMessage({ data }) {
  67     this.hooks.onPacket(data);
  68   },
  69
  70   /**
  71    * Helper method to ensure a given `object` can be sent across message manager
  72    * without being serialized to JSON.
  73    * See https://searchfox.org/mozilla-central/rev/6bfadf95b4a6aaa8bb3b2a166d6c3545983e179a/dom/base/nsFrameMessageManager.cpp#458-469
  74    */
  75   _canBeSerialized(object) {
  76     try {
  77       const holder = new StructuredCloneHolder(
  78         "ChildDebuggerTransport._canBeSerialized",
  79         null,
  80         object
  81       );
  82       holder.deserialize(this);
  83     } catch (e) {
  84       return false;
  85     }
  86     return true;
  87   },
  88
  89   pathToUnserializable(object) {
  90     for (const key in object) {
  91       const value = object[key];
  92       if (!this._canBeSerialized(value)) {
  93         if (typeof value == "object") {
  94           return [key].concat(this.pathToUnserializable(value));
  95         }
  96         return [key];
  97       }
  98     }
  99     return [];
 100   },
 101
 102   send(packet) {
 103     if (flags.testing && !this._canBeSerialized(packet)) {
 104       const attributes = this.pathToUnserializable(packet);
 105       let msg =
 106         "Following packet can't be serialized: " + JSON.stringify(packet);
 107       msg += "\nBecause of attributes: " + attributes.join(", ") + "\n";
 108       msg += "Did you pass a function or an XPCOM object in it?";
 109       throw new Error(msg);
 110     }
 111     try {
 112       this._mm.sendAsyncMessage(this._messageName, packet);
 113     } catch (e) {
 114       if (e.result != Cr.NS_ERROR_NULL_POINTER) {
 115         throw e;
 116       }
 117       // In some cases, especially when using messageManagers in non-e10s mode, we reach
 118       // this point with a dead messageManager which only throws errors but does not
 119       // seem to indicate in any other way that it is dead.
 120     }
 121   },
 122
 123   startBulkSend() {
 124     throw new Error("Can't send bulk data to child processes.");
 125   },
 126 };
 127
 128 exports.ChildDebuggerTransport = ChildDebuggerTransport;