On Sep 28, 2010, at 10:48 PM, Kinuko Yasuda wrote:
Hi Webkit folks,
I'm writing a JSC binding code (custom binding code for now) for a method that can take JSON-format parameters, and I want to know what would be the right/recommended way. I mean, I want to write a binding code that can executes javascript code like:
directoryEntry.getFile("lockfile.txt", {create: true, exclusive: true});
Where the getFile() method is defined as:
interface DirectoryEntry : Entry { void getFile(in DOMString path, in Flags flags, /* ... */); }; interface Flags { attribute boolean create; attribute boolean exclusive; };
(They are from the File API: Directories and System's draft [1])
And what I have written for this is like following:
if (!exec->argument(1).isNull() && !exec->argument(1).isUndefined() && exec->argument(1).isObject() && !exec->argument(1).inherits(&JSFlags::s_info)) { JSObject* object = exec->argument(1).getObject(); flags = Flags::create(); JSValue jsCreate = object->get(exec, Identifier(exec, "create")); flags->setCreate(jsCreate.toBoolean(exec)); JSValue jsExclusive = object->get(exec, Identifier(exec, "exclusive")); flags->setExclusive(jsExclusive.toBoolean(exec)); }
Basically the code calls JSObject::get() to get values for the given property names. This looked straightforward, but I was told that the get(exec) re-enters Javascript and could do any arbitrary thing.
This much is true. In principle, any property can be a getter, so get() could re-enter into arbitrary JS code.
This means that during the get() even the parameter object or the calling object (imp) may get deallocated.
This part, I think not. As long as they are referenced by currently executing code (either by JS or by the machine stack via a local variable) they won't get deallocated. That being said, others may have suggestions for better ways to code this. Perhaps Geoff or Oliver have suggestions.
So here I have two questions:
1) How can I write a safe binding code that reads JSON-format parameters? Is there some recommended way or any good idea?
2) I saw several other code doing the same/similar thing as I do (calling JSObject::get()) to get arbitrary parameter values. Are they safe? Is there a guarantee that the code executed during get() doesn't deallocate some objects?
Nothing that has a live reference to it will get collected, and there's no such thing as explicit deallocation in JS.
Any help/suggestions/comments would be highly appreciated. Thanks! Kinuko
[1] http://dev.w3.org/2009/dap/file-system/file-dir-sys.html [2] http://trac.webkit.org/browser/trunk/WebCore/bindings/js/JSDirectoryEntryCus... _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev