HTTP: The Definitive Guide

Name

Proxy-Connection

Synopsis

The Proxy-Connection header was meant to have similar semantics to the HTTP/1.0 Connection header. It was to be used between clients and proxies to specify options about the connections (chiefly keep-alive connections).^[8] It is not a standard header and is viewed as an ad hoc header by the standards committee. However, it is widely used by browsers and proxies.

Browser implementors created the Proxy-Connection header to solve the problem of a client sending an HTTP/1.0 Connection header that gets blindly forwarded by a dumb proxy. A server receiving the blindly forwarded Connection header could confuse the capabilities of the client connection with those of the proxy connection.

The Proxy-Connection header is sent instead of the Connection header when the client knows that it is going through a proxy. Because servers don’t recognize the Proxy-Connection header, they ignore it, allowing dumb proxies that blindly forward the header to do so without causing harm.

The problem with this solution occurs if there is more than one proxy in the path of the client to the server. If the first one blindly forwards the header to the second, which understands it, the second proxy can suffer from the same confusion the server did with the Connection header.

This is the problem that the HTTP working group had with this solution—they saw it as a hack that solved the case of a single proxy, but not the bigger problem. Nonetheless, it does handle some of the more common ...