fundamental of HTTP

HTTP (Hypertext Transfer Protocol)

FUNDAMENTAL OF HTTP:-

Hypertext Transfer protocol is a request response protocol. It is an application layer in TCP/IP protocol suite. It was originally developed to transfer files and data in distributed, collaborative, hypermedia information system. According to this protocol a process is run which create and store the resources like HTML image, files etc. On request this process provides these resources and is called web server. A web server waits for request and response when required.

- Its main purpose is to transfer web pages from one computer (web server) to another computer (client server).

- It is useful to transfer web pages containing links in an environment where there are rapid jumps among such hyperlink web pages.

- It allows us to transfer a wide variety of data such as text, image, audio, video or even the result of a query.

- It is used to access virtually all types of resources on web.

WORKING OF HTTP

·        HTTP server process is created on a port which waits for clients to make a TCP connection.

·        HTTP client initiates a TCP connection with HTTP server.

·        HTTP server accepts the connection.

·        Then HTTP client sends a request for a resource to the server.

·        After receiving the request the server process the request and perform the desired task and sends a response back to the client.

·        HTTP server closes the TCP connection.

·        The HTTP client receives the response containing the information.

HTTP Message- There are two types of HTTP message.

·        Request Message- Message sent by the client

·        Response Message- Message sent by the server

Request Message- It consists of following parts-          

Request Line

Header

Empty Line

Body (available for some message)

·        Request Line- It consists of three parts: Request type, URL and HTTP version. These three are separated by a space.

Ø Request type-It indicates the type of request the client want to send. It is also known as methods. Some of the methods are following-

      I.            Get- it is specified when a client wants retrieve a resource from server.

   II.            Head- it is used when the client wants to know header information about a resource but not the resource contain the response of the HEAD request contains only headers request and status line but not document content.

III.            Post-it is used when a client wants to sent some information to the server. The commonest form of the post method is to submit an HTML form to the server

IV.            Put-it is used to upload a new resource or replace an existing document.

   V.            Patch-this is similar to the put method except that it specifies a list of difference that must be applied on the existing file.

VI.        Copy- this method is used to copy a file to one location to another

VII.            Move-it is similar to copy method except that it deletes the source file.

VIII.            Delete- this method is used to remove the document from the server.

IX.            Link-this is used to create a link or links from one document to another.

  X.        Options- it is used to retrieve the set of method supported by the server. It usually checks whether a server is functioning properly before performing other task.

XI.        Connect-it is used to convert a request connection into the transparent TCP/IP tunnel.

XII.        Trace- it is used to instruct the web server to echo the request back to client.

XIII.        Unlink- it is used to remove a link or links created by the Link method.

·        URL-this is URL of the resource.

·        HTTP Version-this field specifies the version of the HTTP protocol being used. It can have the following values: HTTP/1.0 and HTTP/1.1.

RESPONSE MESSAGE- It consists of following parts:

   

Status Line

Header

Empty Line

Body (available for some message)

·        Status Line- Status Line consists of three parts: HTTP Version, Status code and Status phrase. These three are separated by the space.

Ø HTTP Version: this field specifies the version of the HTTP protocol being used. It can have the following values: HTTP/1.0 and HTTP/1.1.

Ø Status code: it is a three digit code that indicates the status of the response. These are classified with respect to their functionality into five groups as follow:

1.    1XX series (informational): it represents provisional responses. it is an informational resource. Some of its codes are-      

                                            

Status code	Status phase	description
100	Continue	The server receives the initial part and response back to client.
101	Switching	Server switches the protocol when receive the request from client.
102	Processing	Server receives the request which is currently under process.

2.   2XX series (Success): it represents the clients request received, understood and accepted successfully.

Status code	Status phase	Description
200	Ok	This represents the request was valid and response depends on methods used.
201	Created	The request was successful  and desired resource was created.
202	Accepted	The request was accepted for further processing.
203	Non-authoritative information	The server is not authoritative to information back.
204	No content	The body of response has no content.
205	Reset content	In this client needs to reset the document.
206	Partial content	Server sends partial content in response to the header.
207	Multi-status	Number of response codes depends on the number of request made.

3.  3XX (Redirectional): this represents the additional actions must be taken by the client to complete the request.

Status code	Status phase	Description
300	Multiple choices	Client can follow multiple options for resource.
301	Moved permanently	Resource request no longer exists.
302	Found	Request is not found currently
303	See other	Method is possibly wrong.
304	Not modified	Request resource is not modified since last request.

4.    4XX Series (client error): these codes are used to indicate the client request had an error and therefore it cannot be fulfilled

Status code	Status Phrase	Description
400	Bad request	Request contains syntax error and cannot be fulfilled.
401	Unauthorized	The request has failed to be authorized.
403	Forbidden	Request was valid but server is refusing to respond to it.
404	Not found	Request resource was not found on the server.
405	Method not allowed	Method specified the request message is not supported by the resource.
406	Not acceptable	Requested resource can generate the content in the format mentioned.
408	Request time out	The server timed out waiting for the request.
409	Conflict	The request could not be processes due to conflict.
410	Gone	Requested resource is no longer available.
411	Length required	The length of the content which is required was not specified in the request message.
412	Precondition failed	Server fails to follow the preconditions of the request message.
413	Request entity too large	The request is too large for the server to process.
414	Request URI to long	URI specify was too long for server to process
415	Unsupported media type	Server does not support the media type specified
416	Requested range is not satisfied	Server unable to send the portion of the file is requested
417	Expectation failed	Server fails to meet the values specified by the expect request header field
422	Unprocessable entity	The request contains semantic errors and cannot be fulfilled.
423	Locked	The request resource is locked
424	Failed dependency	The request fails due to the failure of previous request.

5.  5XX Series (server errors): this code represents that the server encountered some problem and hence request cannot be satisfied at the given time.

Status code	Status phrase	Description
500	Internal server error	A message indicating that a problem has occurred in the server.
501	Not implemented	The server fails to recognize the method specified.
502	Bad gateway	The server is gateway or proxy, has received and invalid response from the downstream server.
503	Service unavailable	The service is unavailable due to maintenance, shutting down overload.
504	Gateway time out	The server receive a timeout response from the downstream server
505	HTTP Version not supported	Server fails to support the HTTP Version specified.