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HyperText Transfer Protocol
HTTP (Hypertext Transfer Protocol) is a stateless, request-response protocol for transferring hypermedia documents across the internet. It runs on top of TCP and uses port 80 by default. HTTP specifies the messages that clients and servers can send and the responses received. Common HTTP methods include GET, HEAD, POST, PUT, DELETE, and OPTIONS. Status codes inform the client if the request was successful or not. HTTP headers provide additional metadata in requests and responses.
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HyperText Transfer Protocol
- 1. HT –H TP ypertext Transfer Protocol PONDU MTECH CSE 1
- 2. Introduction • Transfer protocolused throughout the WWW • is a request-response protocol • it is stateless • latest version is HTTP/1.1 • runs on top of TCP on the standardized port 80 2
- 3. conti… • Specifies whatmessages client may send to servers and what response they get back • Each interaction consists of one ASCII request followed by one RFC 822 MIME like response • All client and servers must obey this protocol 3
- 4. connections • In http1.0, after the connection established, a single request sent over and a single response sent back • It is efficient for normal web page containing html text • When web page contain large no of icons, images etc, establishing a TCP connection to transport a single icon become very expensive 4
- 5. Conti…. • HTTP 1.1support persistent connections • establish a TCP connection send a request and get a response • Then send additional requests and get additional responses • The relative overload due to TCP is much less per request • It is possible to pipeline the requests 5
- 6. Methods • Although HTTPwas designed for use in the Web, it has been intentionally made to future object-oriented applications. • so operations, called methods, other than just requesting a Web page are supported • Each request consists of one or more lines of ASCII text, with first word on first line being the name of the method requested. 6
- 7. Conti… • The names are case sensitive • The methods are: • GET method requests the server to send the page. page is suitably encoded in MIME. vast majority of requests to Web servers are GETs. The usual form of GET is GET filename HTTP/1.1 7
- 8. conti… • HEAD method: asks for the message header, without the actual page used to get a page's time of last modification, to collect information for indexing purposes to test a URL for validity. 8
- 9. Conti…. • PUT method: reverse of GET instead of reading the page, it writes the page makes it possible to build a collection of Web pages on a remote server request contains the page It may be encoded using MIME 9
- 10. Conti…. • POST method: PUT is similar to POST method. bears a URL, but instead of replacing the existing data, the new data is ''appended'' to it neither PUT nor POST is used very much. 10
- 11. Conti…. • DELETE method: it removes the page. authentication and permission play a major role There is no guarantee that DELETE succeeds Because even if the remote HTTP server is willing to delete the page, the underlying file may have a mode that forbids the HTTP server from modifying 11
- 12. Conti…. • TRACE method: for debugging instructs the server to send back the request useful when requests are not being processed correctly and the client wants to know what request the server actually got. 12
- 13. Conti…. • CONNECT method: reserved for future use. • OPTIONS method: provides a way for the client to query the server about its properties or those of a specific file 13
- 14. The built-in HTTPrequest methods Method Description GET Request to read a Web page HEAD Request to read a Web page’s header PUT Request to store a Web page POST Append to a named recourse DELETE Remove the Web page TRACE Echo the incoming request CONNECT Reserved for future use OPTIONS Query certain options 14
- 15. Status lines • Everyrequest gets a response consisting of a status line, and possibly additional information • It contains a three-digit status code telling whether the request was satisfied, and if not, why not • first digit is used to divide the responses into five major groups 15
- 16. The status coderesponse groups Code Meaning Example 1xx Information 100=server agrees to handle clients request 2xx Success 200=request succeeded;204=no content present 3xx Redirection 301=page moved;304=cached page still valid 4xx Client error 403=forbidden page;404=page not found 5xx Server error 500=internal server error;503=try again later 16
- 17. Message Headers • requestline may be followed by additional lines with more information called request headers • Responses may also have response headers • Some headers can be used in either direction 17
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- 19. Conti…. • User-Agent headerallows the client to inform the server about its browser, os, and other properties • It is used by the client to provide the server with the information • four Accept headers tell the server what the client is willing to accept in the event 19
- 20. Conti…. • Acceptheader specifies the MIME types that are welcome • Accept-Charset header gives the character set • Accept-encode header deals with compression methods • Accept-Language header indicates a natural language 20
- 21. Conti…. • If theserver has a choice of pages, it can use this information to supply the one the client is looking for • If it is unable to satisfy the request, an error code is returned and the request fails • Host header names the server • It is taken from the URL • This header is mandatory 21
- 22. Conti…. • It isused because some IP addresses may serve multiple DNS names and the server needs some way to tell which host to hand the request to. • Authorization header is needed for pages that are protected • client may have to prove it has a right to see the page requested. 22
- 23. Conti…. • Although cookiesare dealt with in RFC 2109 rather than RFC 2616, they also have two headers • Cookie header is used by clients to return to server a cookie that was previously sent by some machine in server's domain • Date header can be used in both directions and contains the time and date the message was sent 23
- 24. Conti…. • Upgrade headeris used to make it easier to make the transition to a future version of the HTTP protocol. • It allows the client to announce what it can support and the server to assert what it is using. • Server, allows the server to tell who it is and some of its properties if it wishes. 24
- 25. Conti…. • next fourheaders, all starting with Content-, allow the server to describe properties of page it is sending. • Last-Modified header tells when the page was last modified. • This header plays an important role in page caching. 25
- 26. Conti…. • Location headercan be used if the page has moved or to allow multiple URLs to refer to the same page • If a page is very large, a small client may not want it all at once • Some servers will accept requests for byte ranges, so page can be fetched in multiple small units. 26
- 27. Conti…. • Accept-Ranges headerannounces server's willingness to handle this type of partial page request. • Set-Cookie, is how servers send cookies to clients. • client is expected to save the cookie and return it on subsequent requests to the server. 27
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