![]() These guidelines are intended to improve HTTP response times and avoid congestion. be conservative when opening multiple connections". The previous version of the HTTP/1.1 specification stated specific maximum values but in the words of RFC 7230 "this was found to be impractical for many applications. Errors can be reported without the penalty of closing the TCP connection.Īccording to RFC 7230, section 6.4, "a client ought to limit the number of simultaneous open connections that it maintains to a given server".Reduced network congestion (fewer TCP connections).Enables HTTP pipelining of requests and responses.Reduced CPU usage and round-trips because of fewer new connections and TLS handshakes.Reduced latency in subsequent requests (no handshaking and no slow start).The last-chunk bit is set at the end of each response so that the client knows where the next response begins. To solve this problem, HTTP 1.1 introduced a chunked transfer coding that defines a last-chunk bit. This is a serious problem when Content-Length cannot be used due to streaming. Keepalive makes it difficult for the client to determine where one response ends and the next response begins, particularly during pipelined HTTP operation. Keepalive with chunked transfer encoding The advantage of a short timeout is the ability to deliver multiple components of a web page quickly while not consuming resources to run multiple server processes or threads for too long. However, the default connection timeout of Apache httpd 1.3 and 2.0 is as little as 15 seconds and just 5 seconds for Apache httpd 2.2 and above. ![]() The HTTP persistent connections do not use separate keepalive messages, they just allow multiple requests to use a single connection. In HTTP 1.1, all connections are considered persistent unless declared otherwise. Since 1997, the various versions of HTTP/1.1 specifications acknowledged the usage of this unofficial extension and included a few caveats regarding the interoperability between HTTP/1.0 (keep-alive) and HTTP/1.1 clients / servers. This will continue until either the client or the server decides that the conversation is over and in this case they omit the "Connection:" header from the last message sent or, better, they add the keyword "close" to it:Īfter that the connection is closed following specified rules. When the client sends another request, it uses the same connection. Following this, the connection is not dropped, but is instead kept open. When the server receives this request and generates a response, if it supports keep-alive then it also adds the same above header to the response. If the client supports keep-alive, it adds an additional header to the request: ![]() Since late 1996, developers of popular products (browsers, web servers, etc.) using HTTP/1.0, started to add an unofficial extension (to the protocol) named "keep-alive" in order to allow the reuse of a connection for multiple requests/responses. Under HTTP 1.0, connections should always be closed by the server after sending the response. 1.2.1 Keepalive with chunked transfer encoding.
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