1 files changed, 124 insertions, 0 deletions
diff --git a/devtools/shared/transport/child-transport.js b/devtools/shared/transport/child-transport.js
new file mode 100644
index 0000000000..735d5e1d08
--- /dev/null
+++ b/devtools/shared/transport/child-transport.js
@@ -0,0 +1,124 @@
+/* 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";
+
+const flags = require("resource://devtools/shared/flags.js");
+
+/**
+ * A transport for the debugging protocol that uses nsIMessageManagers to
+ * exchange packets with servers running in child processes.
+ *
+ * In the parent process, |mm| should be the nsIMessageSender for the
+ * child process. In a child process, |mm| should be the child process
+ * message manager, which sends packets to the parent.
+ *
+ * |prefix| is a string included in the message names, to distinguish
+ * multiple servers running in the same child process.
+ *
+ * This transport exchanges messages named 'debug:<prefix>:packet', where
+ * <prefix> is |prefix|, whose data is the protocol packet.
+ */
+function ChildDebuggerTransport(mm, prefix) {
+  this._mm = mm;
+  this._messageName = "debug:" + prefix + ":packet";
+}
+
+/*
+ * To avoid confusion, we use 'message' to mean something that
+ * nsIMessageSender conveys, and 'packet' to mean a remote debugging
+ * protocol packet.
+ */
+ChildDebuggerTransport.prototype = {
+  constructor: ChildDebuggerTransport,
+
+  hooks: null,
+
+  _addListener() {
+    this._mm.addMessageListener(this._messageName, this);
+  },
+
+  _removeListener() {
+    try {
+      this._mm.removeMessageListener(this._messageName, this);
+    } catch (e) {
+      if (e.result != Cr.NS_ERROR_NULL_POINTER) {
+        throw e;
+      }
+      // In some cases, especially when using messageManagers in non-e10s mode, we reach
+      // this point with a dead messageManager which only throws errors but does not
+      // seem to indicate in any other way that it is dead.
+    }
+  },
+
+  ready() {
+    this._addListener();
+  },
+
+  close(options) {
+    this._removeListener();
+    if (this.hooks.onTransportClosed) {
+      this.hooks.onTransportClosed(null, options);
+    }
+  },
+
+  receiveMessage({ data }) {
+    this.hooks.onPacket(data);
+  },
+
+  /**
+   * Helper method to ensure a given `object` can be sent across message manager
+   * without being serialized to JSON.
+   * See https://searchfox.org/mozilla-central/rev/6bfadf95b4a6aaa8bb3b2a166d6c3545983e179a/dom/base/nsFrameMessageManager.cpp#458-469
+   */
+  _canBeSerialized(object) {
+    try {
+      const holder = new StructuredCloneHolder(object);
+      holder.deserialize(this);
+    } catch (e) {
+      return false;
+    }
+    return true;
+  },
+
+  pathToUnserializable(object) {
+    for (const key in object) {
+      const value = object[key];
+      if (!this._canBeSerialized(value)) {
+        if (typeof value == "object") {
+          return [key].concat(this.pathToUnserializable(value));
+        }
+        return [key];
+      }
+    }
+    return [];
+  },
+
+  send(packet) {
+    if (flags.testing && !this._canBeSerialized(packet)) {
+      const attributes = this.pathToUnserializable(packet);
+      let msg =
+        "Following packet can't be serialized: " + JSON.stringify(packet);
+      msg += "\nBecause of attributes: " + attributes.join(", ") + "\n";
+      msg += "Did you pass a function or an XPCOM object in it?";
+      throw new Error(msg);
+    }
+    try {
+      this._mm.sendAsyncMessage(this._messageName, packet);
+    } catch (e) {
+      if (e.result != Cr.NS_ERROR_NULL_POINTER) {
+        throw e;
+      }
+      // In some cases, especially when using messageManagers in non-e10s mode, we reach
+      // this point with a dead messageManager which only throws errors but does not
+      // seem to indicate in any other way that it is dead.
+    }
+  },
+
+  startBulkSend() {
+    throw new Error("Can't send bulk data to child processes.");
+  },
+};
+
+exports.ChildDebuggerTransport = ChildDebuggerTransport;