After receiving and interpreting a request message, a Server sends a response signal with an HTTP response message.

1. A status line (Status-Line)
2. No more or more Header (General | Response | Entity) fields followed by CRLF.
3. A blank line (for example, a line that has nothing before CRLF) indicates the end of the Header fields.
4. An informative body part.

The following areas explain the usage of each object in an HTTP response message.

Status line

A status line includes the protocol version followed by a numeric encoding and its associated text.

 Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF 

HTTP version

A server supporting HTTP / 1.1 version will return version information as follows:

 HTTP-Version = HTTP / 1.1 

Encrypt status

The Status-Code element is a 3-character integer, in which the first character of the status encoding defines the response type and the last two characters do not have any sorting role. There are 5 values ​​of the first character:

It means that the request has been received and the process is continuing.

It means that the activity has been received, understood, and successfully accepted.

It means that the operation must be done to fulfill the request.

It means that the request contains an incorrect or not implemented syntax.

It means that Server failed with making a request that looks like it looks feasible.

HTTP status encoding is scalable and HTTP applications are not required to understand the meaning of all registered status codes. A list of all status codes has been provided in a separate chapter for your reference.

Feedback Header fields

We will learn General-Header and Entity-Header in a separate chapter when we will learn about Header fields. Now, let's find out what feedback Header fields are:

The Feedback Header fields allow the Server to transmit additional information about responses that cannot be placed in the Status-Line line. These header fields provide information about the server and remote access to the source identified by the Request-URI.

Accept-Ranges

Age

ETag

Location

Proxy-Authenticate

Retry-After

Server

Vary

WWW-Authenticate

You can create your own fields in case you are writing Client and Server for yourself.

Examples of Feedback Notifications

Now we put all of the above together to create an HTTP response for a request to instruct the hello.jsp page from the Server running on tutorialspoint.com.

HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT Content-Length: 88 Content-Type: text/html Connection: Closed 

 Hello, World! 

The following example shows an HTTP response message that displays the error status when the Server cannot find the requested page:

HTTP/1.1 404 Not Found Date: Sun, 18 Oct 2012 10:36:20 GMT Server: Apache/2.2.14 (Win32) Content-Length: 230 Connection: Closed Content-Type: text/html; charset=iso-8859-1

 404 Not Found 

 Not Found 

 The requested URL /t.html was not found on this server. 

Next is an example of an HTTP response message indicating the error state when the Server enters a wrong HTTP version in the HTTP request provided:

HTTP/1.1 400 Bad Request Date: Sun, 18 Oct 2012 10:36:20 GMT Server: Apache/2.2.14 (Win32) Content-Length: 230 Content-Type: text/html; charset=iso-8859-1 Connection: Closed 

 400 Bad Request 

 Bad Request 

 Your browser sent a request that this server could not understand. 

 The request line contained invalid characters following the protocol string. 

According to Tutorialspoint

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