Long held AJAX connections being blocked by Anti-Virus

This is a tough one. The kind of anti-virus feature that causes this tries to prevent malicious code running in the browser from uploading your personal data to a remote server. To do that, the anti-virus tries to buffer all outgoing traffic before it hits the network, and scan it for pre-defined strings.

This works when the application sends a complete HTTP request on the socket, because the anti-virus sees the end of the the HTTP request and knows that it can stop scanning and send the data.

In your case, there's probably just a header without a length field, so until you send enough data to fill the anti-virus's buffer, nothing will be written to the network.

If that's not a good reason to turn that particular feature off, I don't know what is. I ran into this with AVast and McAfee - at this point, the rest of the anti-virus industry is probably doing something like that. Specifically, I ran into this with McAfee's Personal Information Protection feature, which as far as I can tell, is simply too buggy to use.

If you can, just keep sending data on the socket, or send the data in HTTP messages that have a length field. I tried reporting this to a couple of anti-virus vendors - one of them fixed it, the other one didn't, to the best of my knowledge.

Of course, this sort of feature is completely useless. All a malicious application would need to do to get around it is to ROT13 the data before sending it.

Try using https instead of http. There are scanners that intercept https, too, but they're less common and the feature defaulted to off last time I checked. It also broke Firefox SSL connectivity when activated, so I think very few people will activate it and the vendor will hopefully kill the feature.

The problem is that some files can't be scanned in order - later parts are required to determine if the earlier parts are malicious.

So scanners have a problem with channels that are streaming data. I doubt your stream of data is able to be recognised as a clean file type, so the scanner is attempting to scan the data as best it can, and I guess holding up your stream in the process.

The only think I can suggest is to do the data transfer in small transactions, and use the COMET connection for notification only (closing each channel after a single notification).