GAE: Only one channel to a page? How is this enforced?

Question

This may be a naive question but I was planning to create a new channel just before the existing channel timed out to make sure that my client was never without a channel. I thought I was being pretty clever until I read this caveat in the google channel api docs:

One Client Per Channel Per Page

A client can only connect to one channel per page. If an application needs to send multiple types of data to a client, aggregate it on the server side and send it to appropriate handlers in the client’s socket.onmessage callback.

I'm new to this, but it's not obvious to me how the channel unique identifies the page to which it is connected. Is there something in the javascript for channel.open() call that identifies the page it is being called in?

Thanks.

Answer 1

The channel javascript creates a hidden iframe with a given id (on production). The communications takes place within the iframe. The javascript code will always access that iframe (and hence channel).

When you close the socket and channel, the hidden iframe will be destroyed. Afterwards you can create a new channe for the page.