HTTP persistent connection

一、需要注意，HTTP是application layer protocol，它的传输层使用的TCP，HTTP persistent connection指的是它的TCP connection是长连接还是短连接

这在 jianshu http的长连接和短连接（史上最通俗！） 中，进行了非常好的解释

wanweibaike HTTP persistent connection

HTTP persistent connection, also called HTTP keep-alive, or HTTP connection reuse, is the idea of using a single TCP connection to send and receive multiple HTTP requests/responses, as opposed to opening a new connection for every single request/response pair. The newer HTTP/2 protocol uses the same idea and takes it further to allow multiple concurrent requests/responses to be multiplexed over a single connection.

Operation

Keepalive with chunked transfer encoding

NOTE:

message boundary、粘包

Keepalive makes it difficult for the client to determine where one response ends and the next response begins, particularly during pipelined HTTP operation.[8] This is a serious problem when Content-Length cannot be used due to streaming.[9] To solve this problem, HTTP 1.1 introduced a chunked transfer coding that defines a last-chunk bit.[10] The last-chunk bit is set at the end of each response so that the client knows where the next response begins.

Use in web browsers

All modern web browsers including Google Chrome, Firefox, Internet Explorer (since 4.01), Opera (since 4.0)[14] and Safari use persistent connections.

TODO

jianshu http的长连接和短连接（史上最通俗！）

csdn HTTP协议浅谈（一）之TCP长连接