After receiving and interpreting a request message, a server responds with an HTTP response message:
HTTP status codes are extensible and HTTP applications are not
required to understand the meaning of all registered status codes. A
list of all the status codes has been given in a separate chapter for
your reference.
The response-header fields allow the server to pass additional information about the response which cannot be placed in the Status- Line. These header fields give information about the server and about further access to the resource identified by the Request-URI.
- A Status-line
- Zero or more header (General|Response|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 Status-Line
A Status-Line consists of the protocol version followed by a numeric status code and its associated textual phrase. The elements are separated by space SP characters.Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
HTTP Version
A server supporting HTTP version 1.1 will return the following version information:HTTP-Version = HTTP/1.1
Status Code
The Status-Code element is a 3-digit integer where first digit of the Status-Code defines the class of response and the last two digits do not have any categorization role. There are 5 values for the first digit:| S.N. | Code and Description |
|---|---|
| 1 | 1xx: Informational It means the request was received and the process is continuing. |
| 2 | 2xx: Success It means the action was successfully received, understood, and accepted. |
| 3 | 3xx: Redirection It means further action must be taken in order to complete the request. |
| 4 | 4xx: Client Error It means the request contains incorrect syntax or cannot be fulfilled. |
| 5 | 5xx: Server Error It means the server failed to fulfill an apparently valid request. |
Response 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 Response header fields are.The response-header fields allow the server to pass additional information about the response which cannot be placed in the Status- Line. These header fields give information about the server and about further access to the resource identified by the Request-URI.
- Accept-Ranges
- Age
- ETag
- Location
- Proxy-Authenticate
- Retry-After
- Server
- Vary
- WWW-Authenticate
Examples of Response Message
Now let's put it all together to form an HTTP response for a request to fetch the hello.htm page from the web server running on tutorialspoint.comHTTP/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
<html> <body> <h1>Hello, World!</h1> </body> </html>The following example shows an HTTP response message displaying error condition when the web server could not 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
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html> <head> <title>404 Not Found</title> </head> <body> <h1>Not Found</h1> <p>The requested URL /t.html was not found on this server.</p> </body> </html>Following is an example of HTTP response message showing error condition when the web server encountered a wrong HTTP version in the given HTTP request:
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
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html> <head> <title>400 Bad Request</title> </head> <body> <h1>Bad Request</h1> <p>Your browser sent a request that this server could not understand.</p> <p>The request line contained invalid characters following the protocol string.</p> </body> </html>
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