michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: const { Cu } = require("chrome");
michael@0: const { DebuggerServer } = require("devtools/server/main");
michael@0: const { DevToolsUtils } = Cu.import("resource://gre/modules/devtools/DevToolsUtils.jsm", {});
michael@0: 
michael@0: Cu.import("resource://gre/modules/jsdebugger.jsm");
michael@0: addDebuggerToGlobal(this);
michael@0: 
michael@0: // TODO bug 943125: remove this polyfill and use Debugger.Frame.prototype.depth
michael@0: // once it is implemented.
michael@0: if (!Object.getOwnPropertyDescriptor(Debugger.Frame.prototype, "depth")) {
michael@0:   Debugger.Frame.prototype._depth = null;
michael@0:   Object.defineProperty(Debugger.Frame.prototype, "depth", {
michael@0:     get: function () {
michael@0:       if (this._depth === null) {
michael@0:         if (!this.older) {
michael@0:           this._depth = 0;
michael@0:         } else {
michael@0:           // Hide depth from self-hosted frames.
michael@0:           const increment = this.script && this.script.url == "self-hosted"
michael@0:             ? 0
michael@0:             : 1;
michael@0:           this._depth = increment + this.older.depth;
michael@0:         }
michael@0:       }
michael@0: 
michael@0:       return this._depth;
michael@0:     }
michael@0:   });
michael@0: }
michael@0: 
michael@0: const { setTimeout } = require("sdk/timers");
michael@0: 
michael@0: /**
michael@0:  * The number of milliseconds we should buffer frame enter/exit packets before
michael@0:  * sending.
michael@0:  */
michael@0: const BUFFER_SEND_DELAY = 50;
michael@0: 
michael@0: /**
michael@0:  * The maximum number of arguments we will send for any single function call.
michael@0:  */
michael@0: const MAX_ARGUMENTS = 3;
michael@0: 
michael@0: /**
michael@0:  * The maximum number of an object's properties we will serialize.
michael@0:  */
michael@0: const MAX_PROPERTIES = 3;
michael@0: 
michael@0: /**
michael@0:  * The complete set of trace types supported.
michael@0:  */
michael@0: const TRACE_TYPES = new Set([
michael@0:   "time",
michael@0:   "return",
michael@0:   "throw",
michael@0:   "yield",
michael@0:   "name",
michael@0:   "location",
michael@0:   "callsite",
michael@0:   "parameterNames",
michael@0:   "arguments",
michael@0:   "depth"
michael@0: ]);
michael@0: 
michael@0: /**
michael@0:  * Creates a TraceActor. TraceActor provides a stream of function
michael@0:  * call/return packets to a remote client gathering a full trace.
michael@0:  */
michael@0: function TraceActor(aConn, aParentActor)
michael@0: {
michael@0:   this._attached = false;
michael@0:   this._activeTraces = new MapStack();
michael@0:   this._totalTraces = 0;
michael@0:   this._startTime = 0;
michael@0: 
michael@0:   // Keep track of how many different trace requests have requested what kind of
michael@0:   // tracing info. This way we can minimize the amount of data we are collecting
michael@0:   // at any given time.
michael@0:   this._requestsForTraceType = Object.create(null);
michael@0:   for (let type of TRACE_TYPES) {
michael@0:     this._requestsForTraceType[type] = 0;
michael@0:   }
michael@0: 
michael@0:   this._sequence = 0;
michael@0:   this._bufferSendTimer = null;
michael@0:   this._buffer = [];
michael@0:   this.onExitFrame = this.onExitFrame.bind(this);
michael@0: 
michael@0:   // aParentActor.window might be an Xray for a window, but it might also be a
michael@0:   // double-wrapper for a Sandbox.  We want to unwrap the latter but not the
michael@0:   // former.
michael@0:   this.global = aParentActor.window;
michael@0:   if (!Cu.isXrayWrapper(this.global)) {
michael@0:       this.global = this.global.wrappedJSObject;
michael@0:   }
michael@0: }
michael@0: 
michael@0: TraceActor.prototype = {
michael@0:   actorPrefix: "trace",
michael@0: 
michael@0:   get attached() { return this._attached; },
michael@0:   get idle()     { return this._attached && this._activeTraces.size === 0; },
michael@0:   get tracing()  { return this._attached && this._activeTraces.size > 0; },
michael@0: 
michael@0:   /**
michael@0:    * Buffer traces and only send them every BUFFER_SEND_DELAY milliseconds.
michael@0:    */
michael@0:   _send: function(aPacket) {
michael@0:     this._buffer.push(aPacket);
michael@0:     if (this._bufferSendTimer === null) {
michael@0:       this._bufferSendTimer = setTimeout(() => {
michael@0:         this.conn.send({
michael@0:           from: this.actorID,
michael@0:           type: "traces",
michael@0:           traces: this._buffer.splice(0, this._buffer.length)
michael@0:         });
michael@0:         this._bufferSendTimer = null;
michael@0:       }, BUFFER_SEND_DELAY);
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Initializes a Debugger instance and adds listeners to it.
michael@0:    */
michael@0:   _initDebugger: function() {
michael@0:     this.dbg = new Debugger();
michael@0:     this.dbg.onEnterFrame = this.onEnterFrame.bind(this);
michael@0:     this.dbg.onNewGlobalObject = this.globalManager.onNewGlobal.bind(this);
michael@0:     this.dbg.enabled = false;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Add a debuggee global to the Debugger object.
michael@0:    */
michael@0:   _addDebuggee: function(aGlobal) {
michael@0:     try {
michael@0:       this.dbg.addDebuggee(aGlobal);
michael@0:     } catch (e) {
michael@0:       // Ignore attempts to add the debugger's compartment as a debuggee.
michael@0:       DevToolsUtils.reportException("TraceActor",
michael@0:                       new Error("Ignoring request to add the debugger's "
michael@0:                                 + "compartment as a debuggee"));
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Add the provided window and all windows in its frame tree as debuggees.
michael@0:    */
michael@0:   _addDebuggees: function(aWindow) {
michael@0:     this._addDebuggee(aWindow);
michael@0:     let frames = aWindow.frames;
michael@0:     if (frames) {
michael@0:       for (let i = 0; i < frames.length; i++) {
michael@0:         this._addDebuggees(frames[i]);
michael@0:       }
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * An object used by TraceActors to tailor their behavior depending
michael@0:    * on the debugging context required (chrome or content).
michael@0:    */
michael@0:   globalManager: {
michael@0:     /**
michael@0:      * Adds all globals in the global object as debuggees.
michael@0:      */
michael@0:     findGlobals: function() {
michael@0:       this._addDebuggees(this.global);
michael@0:     },
michael@0: 
michael@0:     /**
michael@0:      * A function that the engine calls when a new global object has been
michael@0:      * created. Adds the global object as a debuggee if it is in the content
michael@0:      * window.
michael@0:      *
michael@0:      * @param aGlobal Debugger.Object
michael@0:      *        The new global object that was created.
michael@0:      */
michael@0:     onNewGlobal: function(aGlobal) {
michael@0:       // Content debugging only cares about new globals in the content
michael@0:       // window, like iframe children.
michael@0:       if (aGlobal.hostAnnotations &&
michael@0:           aGlobal.hostAnnotations.type == "document" &&
michael@0:           aGlobal.hostAnnotations.element === this.global) {
michael@0:         this._addDebuggee(aGlobal);
michael@0:       }
michael@0:     },
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Handle a protocol request to attach to the trace actor.
michael@0:    *
michael@0:    * @param aRequest object
michael@0:    *        The protocol request object.
michael@0:    */
michael@0:   onAttach: function(aRequest) {
michael@0:     if (this.attached) {
michael@0:       return {
michael@0:         error: "wrongState",
michael@0:         message: "Already attached to a client"
michael@0:       };
michael@0:     }
michael@0: 
michael@0:     if (!this.dbg) {
michael@0:       this._initDebugger();
michael@0:       this.globalManager.findGlobals.call(this);
michael@0:     }
michael@0: 
michael@0:     this._attached = true;
michael@0: 
michael@0:     return {
michael@0:       type: "attached",
michael@0:       traceTypes: Object.keys(this._requestsForTraceType)
michael@0:         .filter(k => !!this._requestsForTraceType[k])
michael@0:     };
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Handle a protocol request to detach from the trace actor.
michael@0:    *
michael@0:    * @param aRequest object
michael@0:    *        The protocol request object.
michael@0:    */
michael@0:   onDetach: function() {
michael@0:     while (this.tracing) {
michael@0:       this.onStopTrace();
michael@0:     }
michael@0: 
michael@0:     this.dbg = null;
michael@0: 
michael@0:     this._attached = false;
michael@0:     return { type: "detached" };
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Handle a protocol request to start a new trace.
michael@0:    *
michael@0:    * @param aRequest object
michael@0:    *        The protocol request object.
michael@0:    */
michael@0:   onStartTrace: function(aRequest) {
michael@0:     for (let traceType of aRequest.trace) {
michael@0:       if (!TRACE_TYPES.has(traceType)) {
michael@0:         return {
michael@0:           error: "badParameterType",
michael@0:           message: "No such trace type: " + traceType
michael@0:         };
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     if (this.idle) {
michael@0:       this.dbg.enabled = true;
michael@0:       this._sequence = 0;
michael@0:       this._startTime = Date.now();
michael@0:     }
michael@0: 
michael@0:     // Start recording all requested trace types.
michael@0:     for (let traceType of aRequest.trace) {
michael@0:       this._requestsForTraceType[traceType]++;
michael@0:     }
michael@0: 
michael@0:     this._totalTraces++;
michael@0:     let name = aRequest.name || "Trace " + this._totalTraces;
michael@0:     this._activeTraces.push(name, aRequest.trace);
michael@0: 
michael@0:     return { type: "startedTrace", why: "requested", name: name };
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Handle a protocol request to end a trace.
michael@0:    *
michael@0:    * @param aRequest object
michael@0:    *        The protocol request object.
michael@0:    */
michael@0:   onStopTrace: function(aRequest) {
michael@0:     if (!this.tracing) {
michael@0:       return {
michael@0:         error: "wrongState",
michael@0:         message: "No active traces"
michael@0:       };
michael@0:     }
michael@0: 
michael@0:     let stoppedTraceTypes, name;
michael@0:     if (aRequest && aRequest.name) {
michael@0:       name = aRequest.name;
michael@0:       if (!this._activeTraces.has(name)) {
michael@0:         return {
michael@0:           error: "noSuchTrace",
michael@0:           message: "No active trace with name: " + name
michael@0:         };
michael@0:       }
michael@0:       stoppedTraceTypes = this._activeTraces.delete(name);
michael@0:     } else {
michael@0:       name = this._activeTraces.peekKey();
michael@0:       stoppedTraceTypes = this._activeTraces.pop();
michael@0:     }
michael@0: 
michael@0:     for (let traceType of stoppedTraceTypes) {
michael@0:       this._requestsForTraceType[traceType]--;
michael@0:     }
michael@0: 
michael@0:     if (this.idle) {
michael@0:       this.dbg.enabled = false;
michael@0:     }
michael@0: 
michael@0:     return { type: "stoppedTrace", why: "requested", name: name };
michael@0:   },
michael@0: 
michael@0:   // JS Debugger API hooks.
michael@0: 
michael@0:   /**
michael@0:    * Called by the engine when a frame is entered. Sends an unsolicited packet
michael@0:    * to the client carrying requested trace information.
michael@0:    *
michael@0:    * @param aFrame Debugger.frame
michael@0:    *        The stack frame that was entered.
michael@0:    */
michael@0:   onEnterFrame: function(aFrame) {
michael@0:     if (aFrame.script && aFrame.script.url == "self-hosted") {
michael@0:       return;
michael@0:     }
michael@0: 
michael@0:     let packet = {
michael@0:       type: "enteredFrame",
michael@0:       sequence: this._sequence++
michael@0:     };
michael@0: 
michael@0:     if (this._requestsForTraceType.name) {
michael@0:       packet.name = aFrame.callee
michael@0:         ? aFrame.callee.displayName || "(anonymous function)"
michael@0:         : "(" + aFrame.type + ")";
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.location && aFrame.script) {
michael@0:       // We should return the location of the start of the script, but
michael@0:       // Debugger.Script does not provide complete start locations (bug
michael@0:       // 901138). Instead, return the current offset (the location of the first
michael@0:       // statement in the function).
michael@0:       packet.location = {
michael@0:         url: aFrame.script.url,
michael@0:         line: aFrame.script.getOffsetLine(aFrame.offset),
michael@0:         column: getOffsetColumn(aFrame.offset, aFrame.script)
michael@0:       };
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.callsite
michael@0:         && aFrame.older
michael@0:         && aFrame.older.script) {
michael@0:       let older = aFrame.older;
michael@0:       packet.callsite = {
michael@0:         url: older.script.url,
michael@0:         line: older.script.getOffsetLine(older.offset),
michael@0:         column: getOffsetColumn(older.offset, older.script)
michael@0:       };
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.time) {
michael@0:       packet.time = Date.now() - this._startTime;
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.parameterNames && aFrame.callee) {
michael@0:       packet.parameterNames = aFrame.callee.parameterNames;
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.arguments && aFrame.arguments) {
michael@0:       packet.arguments = [];
michael@0:       let i = 0;
michael@0:       for (let arg of aFrame.arguments) {
michael@0:         if (i++ > MAX_ARGUMENTS) {
michael@0:           break;
michael@0:         }
michael@0:         packet.arguments.push(createValueSnapshot(arg, true));
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.depth) {
michael@0:       packet.depth = aFrame.depth;
michael@0:     }
michael@0: 
michael@0:     const onExitFrame = this.onExitFrame;
michael@0:     aFrame.onPop = function (aCompletion) {
michael@0:       onExitFrame(this, aCompletion);
michael@0:     };
michael@0: 
michael@0:     this._send(packet);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Called by the engine when a frame is exited. Sends an unsolicited packet to
michael@0:    * the client carrying requested trace information.
michael@0:    *
michael@0:    * @param Debugger.Frame aFrame
michael@0:    *        The Debugger.Frame that was just exited.
michael@0:    * @param aCompletion object
michael@0:    *        The debugger completion value for the frame.
michael@0:    */
michael@0:   onExitFrame: function(aFrame, aCompletion) {
michael@0:     let packet = {
michael@0:       type: "exitedFrame",
michael@0:       sequence: this._sequence++,
michael@0:     };
michael@0: 
michael@0:     if (!aCompletion) {
michael@0:       packet.why = "terminated";
michael@0:     } else if (aCompletion.hasOwnProperty("return")) {
michael@0:       packet.why = "return";
michael@0:     } else if (aCompletion.hasOwnProperty("yield")) {
michael@0:       packet.why = "yield";
michael@0:     } else {
michael@0:       packet.why = "throw";
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.time) {
michael@0:       packet.time = Date.now() - this._startTime;
michael@0:     }
michael@0: 
michael@0:     if (this._requestsForTraceType.depth) {
michael@0:       packet.depth = aFrame.depth;
michael@0:     }
michael@0: 
michael@0:     if (aCompletion) {
michael@0:       if (this._requestsForTraceType.return && "return" in aCompletion) {
michael@0:         packet.return = createValueSnapshot(aCompletion.return, true);
michael@0:       }
michael@0: 
michael@0:       else if (this._requestsForTraceType.throw && "throw" in aCompletion) {
michael@0:         packet.throw = createValueSnapshot(aCompletion.throw, true);
michael@0:       }
michael@0: 
michael@0:       else if (this._requestsForTraceType.yield && "yield" in aCompletion) {
michael@0:         packet.yield = createValueSnapshot(aCompletion.yield, true);
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     this._send(packet);
michael@0:   }
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * The request types this actor can handle.
michael@0:  */
michael@0: TraceActor.prototype.requestTypes = {
michael@0:   "attach": TraceActor.prototype.onAttach,
michael@0:   "detach": TraceActor.prototype.onDetach,
michael@0:   "startTrace": TraceActor.prototype.onStartTrace,
michael@0:   "stopTrace": TraceActor.prototype.onStopTrace
michael@0: };
michael@0: 
michael@0: exports.register = function(handle) {
michael@0:   handle.addTabActor(TraceActor, "traceActor");
michael@0: };
michael@0: 
michael@0: exports.unregister = function(handle) {
michael@0:   handle.removeTabActor(TraceActor, "traceActor");
michael@0: };
michael@0: 
michael@0: 
michael@0: /**
michael@0:  * MapStack is a collection of key/value pairs with stack ordering,
michael@0:  * where keys are strings and values are any JS value. In addition to
michael@0:  * the push and pop stack operations, supports a "delete" operation,
michael@0:  * which removes the value associated with a given key from any
michael@0:  * location in the stack.
michael@0:  */
michael@0: function MapStack()
michael@0: {
michael@0:   // Essentially a MapStack is just sugar-coating around a standard JS
michael@0:   // object, plus the _stack array to track ordering.
michael@0:   this._stack = [];
michael@0:   this._map = Object.create(null);
michael@0: }
michael@0: 
michael@0: MapStack.prototype = {
michael@0:   get size() { return this._stack.length; },
michael@0: 
michael@0:   /**
michael@0:    * Return the key for the value on the top of the stack, or
michael@0:    * undefined if the stack is empty.
michael@0:    */
michael@0:   peekKey: function() {
michael@0:     return this._stack[this.size - 1];
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Return true iff a value has been associated with the given key.
michael@0:    *
michael@0:    * @param aKey string
michael@0:    *        The key whose presence is to be tested.
michael@0:    */
michael@0:   has: function(aKey) {
michael@0:     return Object.prototype.hasOwnProperty.call(this._map, aKey);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Return the value associated with the given key, or undefined if
michael@0:    * no value is associated with the key.
michael@0:    *
michael@0:    * @param aKey string
michael@0:    *        The key whose associated value is to be returned.
michael@0:    */
michael@0:   get: function(aKey) {
michael@0:     return this._map[aKey];
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Push a new value onto the stack. If another value with the same
michael@0:    * key is already on the stack, it will be removed before the new
michael@0:    * value is pushed onto the top of the stack.
michael@0:    *
michael@0:    * @param aKey string
michael@0:    *        The key of the object to push onto the stack.
michael@0:    *
michael@0:    * @param aValue
michael@0:    *        The value to push onto the stack.
michael@0:    */
michael@0:   push: function(aKey, aValue) {
michael@0:     this.delete(aKey);
michael@0:     this._stack.push(aKey);
michael@0:     this._map[aKey] = aValue;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Remove the value from the top of the stack and return it.
michael@0:    * Returns undefined if the stack is empty.
michael@0:    */
michael@0:   pop: function() {
michael@0:     let key = this.peekKey();
michael@0:     let value = this.get(key);
michael@0:     this._stack.pop();
michael@0:     delete this._map[key];
michael@0:     return value;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Remove the value associated with the given key from the stack and
michael@0:    * return it. Returns undefined if no value is associated with the
michael@0:    * given key.
michael@0:    *
michael@0:    * @param aKey string
michael@0:    *        The key for the value to remove from the stack.
michael@0:    */
michael@0:   delete: function(aKey) {
michael@0:     let value = this.get(aKey);
michael@0:     if (this.has(aKey)) {
michael@0:       let keyIndex = this._stack.lastIndexOf(aKey);
michael@0:       this._stack.splice(keyIndex, 1);
michael@0:       delete this._map[aKey];
michael@0:     }
michael@0:     return value;
michael@0:   }
michael@0: };
michael@0: 
michael@0: // TODO bug 863089: use Debugger.Script.prototype.getOffsetColumn when
michael@0: // it is implemented.
michael@0: function getOffsetColumn(aOffset, aScript) {
michael@0:   return 0;
michael@0: }
michael@0: 
michael@0: // Serialization helper functions. Largely copied from script.js and modified
michael@0: // for use in serialization rather than object actor requests.
michael@0: 
michael@0: /**
michael@0:  * Create a grip for the given debuggee value.
michael@0:  *
michael@0:  * @param aValue Debugger.Object|primitive
michael@0:  *        The value to describe with the created grip.
michael@0:  *
michael@0:  * @param aDetailed boolean
michael@0:  *        If true, capture slightly more detailed information, like some
michael@0:  *        properties on an object.
michael@0:  *
michael@0:  * @return Object
michael@0:  *         A primitive value or a snapshot of an object.
michael@0:  */
michael@0: function createValueSnapshot(aValue, aDetailed=false) {
michael@0:   switch (typeof aValue) {
michael@0:     case "boolean":
michael@0:       return aValue;
michael@0:     case "string":
michael@0:       if (aValue.length >= DebuggerServer.LONG_STRING_LENGTH) {
michael@0:         return {
michael@0:           type: "longString",
michael@0:           initial: aValue.substring(0, DebuggerServer.LONG_STRING_INITIAL_LENGTH),
michael@0:           length: aValue.length
michael@0:         };
michael@0:       }
michael@0:       return aValue;
michael@0:     case "number":
michael@0:       if (aValue === Infinity) {
michael@0:         return { type: "Infinity" };
michael@0:       } else if (aValue === -Infinity) {
michael@0:         return { type: "-Infinity" };
michael@0:       } else if (Number.isNaN(aValue)) {
michael@0:         return { type: "NaN" };
michael@0:       } else if (!aValue && 1 / aValue === -Infinity) {
michael@0:         return { type: "-0" };
michael@0:       }
michael@0:       return aValue;
michael@0:     case "undefined":
michael@0:       return { type: "undefined" };
michael@0:     case "object":
michael@0:       if (aValue === null) {
michael@0:         return { type: "null" };
michael@0:       }
michael@0:       return aDetailed
michael@0:         ? detailedObjectSnapshot(aValue)
michael@0:         : objectSnapshot(aValue);
michael@0:     default:
michael@0:       DevToolsUtils.reportException("TraceActor",
michael@0:                       new Error("Failed to provide a grip for: " + aValue));
michael@0:       return null;
michael@0:   }
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Create a very minimal snapshot of the given debuggee object.
michael@0:  *
michael@0:  * @param aObject Debugger.Object
michael@0:  *        The object to describe with the created grip.
michael@0:  */
michael@0: function objectSnapshot(aObject) {
michael@0:   return {
michael@0:     "type": "object",
michael@0:     "class": aObject.class,
michael@0:   };
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Create a (slightly more) detailed snapshot of the given debuggee object.
michael@0:  *
michael@0:  * @param aObject Debugger.Object
michael@0:  *        The object to describe with the created descriptor.
michael@0:  */
michael@0: function detailedObjectSnapshot(aObject) {
michael@0:   let desc = objectSnapshot(aObject);
michael@0:   let ownProperties = desc.ownProperties = Object.create(null);
michael@0: 
michael@0:   if (aObject.class == "DeadObject") {
michael@0:     return desc;
michael@0:   }
michael@0: 
michael@0:   let i = 0;
michael@0:   for (let name of aObject.getOwnPropertyNames()) {
michael@0:     if (i++ > MAX_PROPERTIES) {
michael@0:       break;
michael@0:     }
michael@0:     let desc = propertySnapshot(name, aObject);
michael@0:     if (desc) {
michael@0:       ownProperties[name] = desc;
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   return desc;
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * A helper method that creates a snapshot of the object's |aName| property.
michael@0:  *
michael@0:  * @param aName string
michael@0:  *        The property of which the snapshot is taken.
michael@0:  *
michael@0:  * @param aObject Debugger.Object
michael@0:  *        The object whose property the snapshot is taken of.
michael@0:  *
michael@0:  * @return Object
michael@0:  *         The snapshot of the property.
michael@0:  */
michael@0: function propertySnapshot(aName, aObject) {
michael@0:   let desc;
michael@0:   try {
michael@0:     desc = aObject.getOwnPropertyDescriptor(aName);
michael@0:   } catch (e) {
michael@0:     // Calling getOwnPropertyDescriptor on wrapped native prototypes is not
michael@0:     // allowed (bug 560072). Inform the user with a bogus, but hopefully
michael@0:     // explanatory, descriptor.
michael@0:     return {
michael@0:       configurable: false,
michael@0:       writable: false,
michael@0:       enumerable: false,
michael@0:       value: e.name
michael@0:     };
michael@0:   }
michael@0: 
michael@0:   // Only create descriptors for simple values. We skip objects and properties
michael@0:   // that have getters and setters; ain't nobody got time for that!
michael@0:   if (!desc
michael@0:       || typeof desc.value == "object" && desc.value !== null
michael@0:       || !("value" in desc)) {
michael@0:     return undefined;
michael@0:   }
michael@0: 
michael@0:   return {
michael@0:     configurable: desc.configurable,
michael@0:     enumerable: desc.enumerable,
michael@0:     writable: desc.writable,
michael@0:     value: createValueSnapshot(desc.value)
michael@0:   };
michael@0: }