Extra Connection Support Proposal

Extra Connection Support

The XMLHttpRequest should define a property called "extraConnection". When 
extraConnection is set to true, it indicates that this XHR object's 
connection SHOULD NOT be counted against the user agent's connection limit. 
That is if the user agent adheres to the two-connection limit as recommended 
by RFC 2616 section 8.1.4, it SHOULD allow two connections not counting this 
XHR object's connection. If the user agent has other or additional connection 
limits, this connection should not be counted in the accounting for these 
connection limits.

Only one XHR object should be allowed to gain extra connection status per 
document per server. Each document in the browser may be permitted one extra 
connection per server. Within a document if an XHR object has an extra 
connection status for domain1.com, no other XHR objects may have extra 
connection status for that server until the first XHR object has terminated 
it's connection. However, another XHR object may have extra connection 
status to domain2.com. Each document in the browser should have it's own set 
of extra connections for XHR objects. This limitation is intended to prevent 
a vector of denial of service attacks.


To gain extra connection status, the extraConnection property on the XHR 
object can be set to true. When it is set to true, if the XHR object is 
allowed to gain extra connection status (no other XHR objects currently have 
extra connection status in this document for the specified target server), 
the XHR object will be given extra connection status and subsequent access 
to the property will return true. If the XHR object is not allowed to gain 
extra connection status, subsequent access to the property should return 
false. The following is an example of valid usage:

var xhr = new XMLHttpRequest();
xhr.open("GET","/resource",true);
xhr.extraConnection = true;
var succesful = xhr.extraConnection;

Setting the extraConnection property should throw an exception if it is 
called before a URL is provided to the XHR object (through the open method 
or the constructor). The extra connection status remains in effect until the 
connection is closed (by network error on normal termination), at which point 
the property should return false.

Since the extraConnection property usually indicates that the response will be a 
long-lived streaming response, user agents SHOULD NOT pipeline requests on this 
connection unless the author explicitly specifies such pipelines using pipelining 
control (see the Pipelining Control Proposal).