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A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly one HTTP2-Settings header field. The HTTP2-Settings header field is a connection-specific header field that includes parameters that govern the HTTP/2 connection, provided in anticipation of the server accepting the request to upgrade. [19] [20] HTTP2-Settings: token64: Obsolete
The request/response message consists of the following: Request line, such as GET /logo.gif HTTP/1.1 or Status line, such as HTTP/1.1 200 OK, Headers; An empty line; Optional HTTP message body data; The request/status line and headers must all end with <CR><LF> (that is, a carriage return followed by a line feed).
The same is usually true even for programmers writing CGI scripts, though some servers allow scripts to add custom headers (e.g. by enabling "non-parsed-headers"). Many web servers will generate a 3xx status code if a script outputs a "Location:" header line. For example, in PHP, one can use the "header" function:
The response provided by a cache is stale (the content's age exceeds a maximum age set by a Cache-Control header or heuristically chosen lifetime). 111 Revalidation Failed The cache was unable to validate the response, due to an inability to reach the origin server. 112 Disconnected Operation
Each response header field has a defined meaning which can be further refined by the semantics of the request method or response status code. HTTP/1.1 example of request / response transaction Below is a sample HTTP transaction between an HTTP/1.1 client and an HTTP/1.1 server running on www.example.com , port 80.
In computing, the User-Agent header is an HTTP header intended to identify the user agent responsible for making a given HTTP request. Whereas the character sequence User-Agent comprises the name of the header itself, the header value that a given user agent uses to identify itself is colloquially known as its user agent string .
A server implements an HSTS policy by supplying a header over an HTTPS connection (HSTS headers over HTTP are ignored). [1] For example, a server could send a header such that future requests to the domain for the next year (max-age is specified in seconds; 31,536,000 is equal to one non-leap year) use only HTTPS: Strict-Transport-Security: max-age=31536000.
Generation of Expires and Cache-Control HTTP headers according to user-specified criteria. [57] mod_ext_filter: Version 1.3 and newer: Stable Extension: Apache Software Foundation: Apache License, Version 2.0: Pass the response body through an external program before delivery to the client. [58] mod_file_cache: Version 2.0 and newer: Stable ...