[whatwg] Changing postMessage() to allow sending unentangled ports

Ian Hickson ian at hixie.ch
Fri Aug 28 12:11:49 PDT 2009

On Mon, 17 Aug 2009, Drew Wilson wrote:
> Following up on this issue:
> Currently, the checks specified for MessagePort.postMessage() are different
> from the checks done in window.postMessage() (as described in section 7.2.4
> "Posting messages with message ports").
> In particular, step 4 of section 7.2.4 says:
> If any of the entries in ports are null, *if any of the entries in 
> **ports** are not entangled **MessagePort** objects*, or if any 
> MessagePort object is listed in ports more than once, then throw an 
> INVALID_STATE_ERR exception.

It appears that this is fixed.

> Also, as written, the spec now incorrectly lets us send a cloned port 
> multiple times. So code like this would not generate an error:
> var channel = new MessageChannel();
> otherWindow.postMessage("message1", channel.port1);
> otherWindow.postMessage("message2", channel.port1);   // Sent the same port
> again

That's intentional. By the second call, channel.port1 is not entangled; 
the 'message2' event will have a lame duck port as its port.

> The current WebKit behavior is to throw an INVALID_STATE_ERR in this 
> case, while still allowing closed ports to be sent, which I believe is 
> the intended behavior based on previous discussions. If this is correct, 
> we should update the spec to prohibit resending cloned ports.

I don't see how this could be correct.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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