Editing HTTP (section)

=== Server response ===
<syntaxhighlight lang="http">
HTTP/1.1 200 OK
Date: Mon, 23 May 2005 22:38:34 GMT
Content-Type: text/html; charset=UTF-8
Content-Length: 155
Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux)
ETag: "3f80f-1b6-3e1cb03b"
Accept-Ranges: bytes
Connection: close

<html>
  <head>
    <title>An Example Page</title>
  </head>
  <body>
    <p>Hello World, this is a very simple HTML document.</p>
  </body>
</html>
</syntaxhighlight>

The [[HTTP ETag|ETag]] (entity tag) header field is used to determine if a cached version of the requested resource is identical to the current version of the resource on the server. <code>"Content-Type"</code> specifies the [[Internet media type]] of the data conveyed by the HTTP message, while <code>"Content-Length"</code> indicates its length in bytes. The HTTP/1.1 [[webserver]] publishes its ability to respond to requests for certain byte ranges of the document by setting the field <code>"Accept-Ranges: bytes"</code>. This is useful, if the client needs to have only certain portions<ref>{{cite IETF |draft=draft-ietf-http-range-retrieval-00 |title=Byte Range Retrieval Extension to HTTP |first1=Ari |last1=Luotonen |first2=John |last2=Franks |publisher=IETF |date=February 22, 1996}}</ref> of a resource sent by the server, which is called [[byte serving]]. When <code>"Connection: close"</code> is sent, it means that the [[web server]] will close the [[Transmission Control Protocol|TCP]] connection immediately after the end of the transfer of this response.<ref name="rfc9112-9.1" />

Most of the header lines are optional but some are mandatory. When header <code>"Content-Length: number"</code> is missing in a response with an entity body then this should be considered an error in HTTP/1.0 but it may not be an error in HTTP/1.1 if header <code>"Transfer-Encoding: chunked"</code> is present. Chunked transfer encoding uses a chunk size of 0 to mark the end of the content. Some old implementations of HTTP/1.0 omitted the header <code>"Content-Length"</code> when the length of the body entity was not known at the beginning of the response and so the transfer of data to client continued until server closed the socket.

A <code>"Content-Encoding: [[gzip]]"</code> can be used to inform the client that the body entity part of the transmitted data is compressed by gzip algorithm.