HTTP persistent connection vs TCP socket connectio

问题:

From this article on Wikipedia:

Keepalive messages were not officially supported in HTTP 1.0. In HTTP 1.1 all connections are considered persistent, unless declared otherwise.

• Does this mean that using this mechanism I can actually simulate a TCP socket connection?
• Using this can I make a Server "push" data to a client?
• Are all HTTP connections, even the one I am using to connect to Stack Overflow "HTTP persistent"?
• Does the COMET technology of server push use this mechanism of HTTP persistent connection to push data to clients?

回答1:

• Does this mean that using this mechanism I can actually simulate a TCP socket connection?

Not really, sockets have MANY more features and flexibility.

• Using this can I make a Server "push" data to a client?

Not directly, it's still a request/response protocol; the persistent connection just means the client can use the same underlying socket to send multiple requests and receive the respective responses.

• Are all HTTP connections, even the one I am using to connect to Stack Overflow "HTTP persistent"?

Unless your browser (or a peculiar server) says otherwise, yes.

• Does the COMET technology of server push use this mechanism of HTTP persistent connection to push data to clients?

Kinda (for streaming, at least), but with a lot of whipped cream on top. There are other Comet implementation approaches, such as hidden iframes and AJAX long polling, that may not require persistent connections (which give some firewalls &c the fits anyway;-).

回答2:

Actually, the HTTP server can "push" data to a connected http client without the client requesting it. See "HTTP server push" at http://en.wikipedia.org/wiki/Push_technology. However it does seem to be commonly implemented.