[whatwg] Issues with Web Sockets API

Kelly Norton knorton at google.com
Fri Jun 26 13:14:39 PDT 2009

One thing about postMessage that I'm curious about. Since it has to report
failure synchronously by throwing an INVALID_STATE_ERR, that seems to imply
that all data must be written to a socket before returning and cannot be
asynchronously delivered to an I/O thread without adding some risk of
silently dropping
messages. Seems like the right choice would be to allow outbound
messages to drop, which would mean that developers would be forced to
do their own handshaking.
I'm also not sure there is good coverage of error conditions in the spec.
The only methods of error notification are exceptions in postMessage and
onclose. I had assumed that a WebSocket that fails to connect would invoke
onclose asynchronously, but I didn't see that in the spec. Without that you
don't even have the ability to know if a socket failed to establish a
connection (short of readyState polling). The spec also doesn't indicate
that the readyState should transition to CLOSED on connection failure.
(Description of the disconnect() method is careful to mention that it closes
a connection or a connection attempt, but description of when onclose is
fired just mentions a connection closing). I definitely think there should
be a way to receive an event if a connection fails to establish; I would
hate to have to poll another readyState.


On Fri, Jun 26, 2009 at 1:34 PM, Drew Wilson <atwilson at google.com> wrote:

> Yes, but the "closed" state of a given WebSocket doesn't have to exactly
> match the state of the underlying TCP connection, in the same way that
> document.cookies doesn't exactly match the current set of cookies that the
> network stack may be tracking (they can differ when HTTP responses are
> received in the background while JS is executing).
> So if the remote server closes the TCP connection, it generates a "close"
> event which marks the WebSocket as closed. It means that you could have a
> situation where you post messages to a WebSocket which aren't received by
> the server because  the connection is closed, but that's true regardless due
> to the asynchronous nature of the networking protocol.
> -atw
> On Fri, Jun 26, 2009 at 9:52 AM, Darin Fisher <darin at chromium.org> wrote:
>> On Fri, Jun 26, 2009 at 9:46 AM, Drew Wilson <atwilson at google.com> wrote:
>>> On Fri, Jun 26, 2009 at 9:18 AM, James Robinson <jamesr at google.com>wrote:
>>>> However, users can't usefully check the readyState to see if the
>>>> WebSocket is still open because there are not and cannot be any
>>>> synchronization guarantees about when the WebSocket may close.
>>> Is this true? Based on our prior discussion surrounding cookies, it seems
>>> like as a general rule we try to keep state from changing dynamically while
>>> JS code is executing for exactly these reasons.
>> I think this is a very different beast.  The state of a network connection
>> may change asynchronously whether we like it or not.  Unlike "who" may
>> access cookies or local storage, the state of the network connection is not
>> something we solely control.
>> -Darin

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