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It is a means for the browser to tell the server and any intermediate caches that it wants a fresh version of the resource. The Pragma: no-cache header field, defined in the HTTP/1.0 spec, has the same purpose. It, however, is only defined for the request header. Its meaning in a response header is not specified. [77]
Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a server check the request's headers, a client must send Expect: 100-continue as a header in its initial request and receive a 100 Continue status code in response before sending the body. If the client receives an ...
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).
Freshness allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for.
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.
Hypertext Caching Protocol (abbreviated to HTCP) is used for discovering HTTP caches and cached data, managing sets of HTTP caches and monitoring cache activity. It permits full request and response headers to be used in cache management and expands the domain of cache management to include monitoring a remote cache's additions and deletions, requesting immediate deletions and sending hints ...
Because ETags are cached by the browser and returned with subsequent requests for the same resource, a tracking server can simply repeat any ETag received from the browser to ensure an assigned ETag persists indefinitely (in a similar way to persistent cookies). Additional caching headers can also enhance the preservation of ETag data. [8]
Browser support for HTTP/3 Browser Version implemented (disabled by default) Version shipped (enabled by default) Comment Chrome: Stable build (79) December 2019 87 [7] April 2020 [25] Earlier versions implemented other drafts of QUIC Edge: Stable build (79) December 2019 87 April 2020 Edge 79 was the first version based on Chromium Firefox