HTTP - Requests

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

Message Request-Line
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.
Request-Line   = Method SP Request-URI SP HTTP-Version CRLF

Request Method
The request Method indicates the method to be performed on the resource identified by the given Request-URI.
GET
The 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.
HEAD
Same as GET, but only transfer the status line and header section.
POST
A POST request is used to send data to the server, for example customer information, file upload etc using HTML forms.
PUT
Replace all current representations of the target resource with the uploaded content.
DELETE
Remove all current representations of the target resource given by URI.
CONNECT
Establish a tunnel to the server identified by a given URI.
OPTIONS
Describe the communication options for the target resource.
TRACE
Perform a message loop-back test along the path to the target resource.

Request-URI

Request Header Fields
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 and there are following important Request-header fields available which can be used based on requirement.

Request Message Examples

Now let's put it all together to form an HTTP request to fetch hello.htm page from the web server running on tutorialspoint.com

GET /hello.htm HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT)
Host: www.tutorialspoint.com
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
Here we are not sending any request data to the server because we are fetching a plan HTML page from the server. Connection is a general-header used here and rest of the headers are request headers. Following is one more example where we send form data to the server using request message body:

POST /cgi-bin/process.cgi HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT)
Host: www.tutorialspoint.com
Content-Type: application/x-www-form-urlencoded
Content-Length: length
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Connection: Keep-Alive

licenseID=string&content=string&/paramsXML=string
Here given URL /cgi-bin/process.cgi will be used to process the passed data and accordingly a response will be retuned. Here content-type tells the server that passed data is simple web form data and length will be actual length of the data put in the message body. Following example shows how you can pass plan XML to your web server:

POST /cgi-bin/process.cgi HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT)
Host: www.tutorialspoint.com
Content-Type: text/xml; charset=utf-8
Content-Length: length
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Connection: Keep-Alive

<?xml version="1.0" encoding="utf-8"?>

<string xmlns="http://clearforest.com/">string</string>