Skip to content

Request Headers

HTTP defines four general categories of header: * General headers * Request headers * Response headers * Entity headers * In HTTP the term entity refers to any content sent by the server or client. HTTP headers follow a format used by earlier protocols such as SMTP and NNTP. 

Header-name: [header value]
* The header name occurs at the beginning of a line. * Any following lines that begin with whitespace (space or tab) are part of the preceding header's value. * Header names are case-insensitive and do not contain spaces. * A header is not required to have a value.

Headers allow HTTP clients and servers to: * Exchange "meta-information" about documents. * Negotiate conditional requests (If-Modified-Since: date). * Negotiate preferred and acceptable content types. * Perform HTTP basic or digest access authentication. * Control caching and proxy server behavior.

Example HTTP GET Transaction

(Client connects to web server via socket connection on port 80) 

GET /index.html HTTP/1.0                                                             Request line
Connection: Keep-Alive                                                             General header
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0)                           Request header
Accept: image/gif, image/x-xbitmap, image/jpeg, */*                                Request header
                                                Carriage-return terminates client request headers
HTTP/1.1 200 OK                                                                     Response line
Connection: Close                                                                  General header
Date: Mon, 04 Aug 2014 20:28:06 GMT                                                General header
Server: Apache/2.2.29 (CentOS)                                                    Response header
Content-Type: text/html                                                             Entity header
Content-Length: 249                                                                 Entity header
                                               Carriage-return terminates server response headers
<HTML>                                                                    Entity body from server
<HEAD><TITLE>Welcome to my Web Site</TITLE></HEAD>                        Entity body from server
<BODY>This is a sample page...                                            Entity body from server
(Server closes socket connection after the entity-body is sent)

Example HTTP POST Transaction

(Client connects to web server via socket connection on port 80) 

POST /cgi-bin/guestbook HTTP/1.0                                                     Request line
Connection: Keep-Alive                                                             General header
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0)                           Request header
Accept: image/gif, image/x-xbitmap, image/jpeg, */*                                Request header
Content-Type: text/plain                                                            Entity header
Content-Length: 37                                                                  Entity header
                                                Carriage-return terminates client request headers
Hello, I’m Bob Dobbs! Nice web site!                                      Entity body from client
                                                                          Entity body from client
HTTP/1.1 200 OK                                                                     Response line
Connection: Close                                                                  General header
Date: Mon, 04 Aug 2014 20:28:06 GMT                                                General header
Server: Apache/2.2.29 (CentOS)                                                    Response header
Content-Type: text/html                                                             Entity header
Content-Length: 100                                                                 Entity header
                                               Carriage-return terminates server response headers
<HTML>                                                                    Entity body from server
<HEAD><TITLE>Thanks!</TITLE></HEAD>                                       Entity body from server
<BODY>You’ve been added to my guest book.</BODY>                          Entity body from server
</HTML>                                                                   Entity body from server
(Server closes socket connection after the entity-body is sent)

Prev -- Up -- Next