An HTTP client sends an HTTP request to a server in the form of a request message which includes following format:
- A Request-line
- Zero or more header (General|Request|Entity) fields followed by CRLF
- An empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header fields
- Optionally a message-body
The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The elements are separated by space SP characters.
The request method indicates the method to be performed on the resource identified by the given Request-URI. The method is case-sensitive and should always be mentioned in uppercase. The following table lists all the supported methods in HTTP/1.1.
|S.N.||Method and Description|
|1||GETThe GET method is used to retrieve information from the given server using a given URI. Requests using GET should only retrieve data and should have no other effect on the data.|
|2||HEADSame as GET, but it transfers the status line and the header section only.|
|3||POSTA POST request is used to send data to the server, for example, customer information, file upload, etc. using HTML forms.|
|4||PUTReplaces all the current representations of the target resource with the uploaded content.|
|5||DELETERemoves all the current representations of the target resource given by URI.|
|6||CONNECTEstablishes a tunnel to the server identified by a given URI.|
|7||OPTIONSDescribe the communication options for the target resource.|
|8||TRACEPerforms a message loop back test along with the path to the target resource.|
The Request-URI is a Uniform Resource Identifier and identifies the resource upon which to apply the request. Following are the most commonly used forms to specify an URI:
Request-URI = "*" | absoluteURI | abs_path | authority
|S.N.||Method and Description|
|1||The asterisk * is used when an HTTP request does not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily apply to a resource. For example:OPTIONS * HTTP/1.1|
|2||The absoluteURI is used when an HTTP request is being made to a proxy. The proxy is requested to forward the request or service from a valid cache, and return the response. For example:GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1|
|3||The most common form of Request-URI is that used to identify a resource on an origin server or gateway. For example, a client wishing to retrieve a resource directly from the origin server would create a TCP connection to port 80 of the host “www.w3.org” and send the following lines:GET /pub/WWW/TheProject.html HTTP/1.1
Note that the absolute path cannot be empty; if none is present in the original URI, it MUST be given as “/” (the server root).
Request Header Fields
We will study General-header and Entity-header in a separate chapter when we will learn HTTP header fields. For now, let’s check what Request header fields are.
The request-header fields allow the client to pass additional information about the request, and about the client itself, to the server. These fields act as request modifiers.Here is a list of some important Request-header fields that can be used based on the requirement:
You can introduce your custom fields in case you are going to write your own custom Client and Web Server.