The request (most always a get) really has only three parts...

• The request line (the first line),
• the Header Fields,
• and the Payload (message)

Example:

GET /kennyl HTTP/1.1
Host: 24.10.2.100:6443
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:13.0) Gecko/20100101 Firefox/13.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: keep-alive
Cache-Control: max-age=0"

The First lin is the Request Line followed by the header fields. Since this request is a GET... It traditionally has no payload.

The request line has three parts, each seperated by a space or spaces: Example

• The method
• the Request URI,
• the protocol (HTTP/1.01)

The method is GET, the path to execute that method is /kennyl and the protocol is HTTP/1.1. The default entity located at /kennyl will be rendered by the server.

The Request Line is terminated by a carrage return and a line feed (CR/LF). No other CR or LF are allowed on this line.

The Method is the action the requestor wants to enact. Methods are directed to the resource located at the Request URI. RFC 2616 supports these methods:

• GET - Retrieve whatever information in the form of an entity served up by resource
• HEAD - Like GET but return only the header information the resource renders
• POST - requests an enclosed entity be processed by the resource
• PUT - request that something be added to the resource
• DELETE - requests that an entity be deleted from the resource
• TRACE - sends back a copy of the request message
• CONNECT - used for tunneling

To be a real server, the GET and HEAD methods must be supported. Otherwise the server can respond to the requestor in one of three ways... 1: give them what they want... 2: return a status code of 501 (method not implemented) or 3: return a status code 405 (method not allowed):

The Request URI indicates which resource the method applies to. The Request URI has four options:

• * - Action is intended for the server
• absoluteURI - required when the request is being made to a proxy, however, it is a must for a server to accept.
• abs_path - most common, identifies the path to the resource, if it were appended to the end of the HOST header field.
• authority - Used with the CONNECT method.

The protocol is which version of HTTP is being used. HTTP/1.1 or HTTP/1.0.

Header fields are transmitted in name/value pairs seperated by a semi-colon ":". Unlike the Request Line, spaces (32) are ignored in this section. Names are on the left and values are on the right. The names are easy - they are simple names.

• Common and uncommon header field names.
• Header Field Definitions

Values can be more difficult because there can be more than one value for each field.

Single Value:

Host: www.kenny-l.com

This field has only one value, the host the request is being sent to, "www.kenny-l.com" The Field name is "Host" and the value is "www.kenny-l.com"

Multiple Values:

Accept: text/html,application/xhtml-xml,application/xml;q=0.9,*/*;q=0.8

The ReadyState of the request (response) is a number from 1 to 4

• 1 - after the request object has been open sucessfully
• 2 - adter the send is invoked and the response is received
• 3 - response content is loading
• 4 - response content is loaded.

The listener must be invoked before any state has changed in order to capture the change.

var reqObject = new XMLHttpRequest(); reqObject.onreadystatechange =
function{
 if(reqObject.readyState == 1){
  alert("Request Object Open");
 }else if(reqObject.readyState == 2){
  alert("Request Object Sent");
 }else if(reqObject.readyState == 3){
  alert("Receiving ResponseObject");
 }else if(reqObject.readyState == 4){
  alert("Request Object Received");
 }
 reqObject.open;   <-- the ready state is 1
 reqObject.send(null);   <-- the readyState is 2