1. PL-IV- Group A HTTP Request & Response Header
By Prof. B.A.Khivsara
Assistant Prof.
Department of Computer Engg.
SNJB’s KBJ COE, Chandwad

2. OUTLINE
HTTP Working
HTTP Messages
Program in Java
Introduction

3. Web and HTTP First some jargon Web page consists of objects
Object can be HTML file, JPEG image, Java applet, audio file,…
Web page consists of base HTML-file which includes several referenced objects
Each object is addressable by a URL
Example URL:
host name
path name

4. HTTP overview HTTP: hypertext transfer protocol
Web’s application layer protocol
client/server model
client: browser that requests, receives, “displays” Web objects
server: Web server sends objects in response to requests
HTTP uses port no 80
HTTP request
PC running
Explorer
HTTP response
HTTP request
Server
running
Apache Web
server
HTTP response
Mac running
Navigator

5. HTTP overview (continued)
Uses TCP:
client initiates TCP connection (creates socket) to server, port 80
server accepts TCP connection from client
HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server)
TCP connection closed
HTTP is “stateless”
server maintains no information about past client requests
2: Application Layer

6. OUTLINE
HTTP Working
HTTP Messages
Program in Java

7. HTTP Message Formats Two types of message HTTP Request message
HTTP Response Message

8. HTTP request message: general format

9. HTTP request message Example
ASCII (human-readable format)
request line
(GET, POST,
HEAD commands)
GET /somedir/page.html HTTP/1.1
Host:
User-agent: Mozilla/4.0
Connection: close
Accept-language:fr
(extra carriage return, line feed)
header
lines
Carriage return,
line feed
indicates end
of message

10. Uploading form input Post method: Web page often includes form input
Input is uploaded to server in entity body
GET method:
Uses GET method
Input is uploaded in URL field of request line:
Example - GET Method (

11. HTTP Methods
The GET method requests the server to send the page . The page is suitably encoded in MIME. The vast majority of the requests on the web are GETs.
GET filename HTTP/1.1
Where filename is the resource name to be fetched and 1.1 is the protocol version being used
The HEAD method just asks for the message header, without the actual page. This method can be used to get a page’s time of last modification, to collect information for indexing purposes, or just to test an URL for validity
The PUT method is the reverse of GET. Instead of reading a page, it writes a page. This method makes it possible to build a collection of web pages on a remote web server. The body of the request contains the page. It may be encoded using MIME, in which case, the lines following the PUT might include Content-Type and authentication headers to prove that the caller indeed has permission to perform the operation
POST is similar to PUT. It too, bears an URL, but instead of replacing the existing data, it appends it to any existing data. Posting a message to a newsgroup or adding a file to a bulletin board are example of the usage.
DELETE does what you expect: deletes a page from a remote web server; authentication and permissions play a major role here. There is no guarantee that a DELETE operation is successful since even if the remote web server is willing to delete a page, the file permissions may be set in such a way that the server process doesn’t have rights to do it.
TRACE method is used for debugging. It instructs the server to send back the request. This is useful when requests are not processed correctly and the client wants to know it sent the proper request.
CONNECT – is not used at the moment
OPTIONS – provides a way for the client to query the server about its properties or those of a specified file
DELETE does what you expect: deletes a page from a remote web server; authentication and permissions play a major role here. There is no guarantee that a DELETE operation is successful since even if the remote web server is willing to delete a page, the file permissions may be set in such a way that the server process doesn’t have rights to do it.
TRACE method is used for debugging. It instructs the server to send back the request. This is useful when requests are not processed correctly and the client wants to know it sent the proper request.
CONNECT – is not used at the moment
OPTIONS – provides a way for the client to query the server about its properties or those of a specified file
The PUT method is the reverse of GET. Instead of reading a page, it writes a page. This method makes it possible to build a collection of web pages on a remote web server. The body of the request contains the page. It may be encoded using MIME, in which case, the lines following the PUT might include Content-Type and authentication headers to prove that the caller indeed has permission to perform the operation
The GET method requests the server to send the page . The page is suitably encoded in MIME. The vast majority of the requests on the web are GETs.
GET filename HTTP/1.1
Where filename is the resource name to be fetched and 1.1 is the protocol version being used
The HEAD method just asks for the message header, without the actual page. This method can be used to get a page’s time of last modification, to collect information for indexing purposes, or just to test an URL for validity
POST is similar to PUT. It too, bears an URL, but instead of replacing the existing data, it appends it to any existing data. Posting a message to a newsgroup or adding a file to a bulletin board are example of the usage.

12. HTTP response message: general format

13. HTTP response message example
status line
(protocol
status code
status phrase)
HTTP/ OK
Connection close
Date: Thu, 06 Aug :00:15 GMT
Server: Apache/1.3.0 (Unix)
Last-Modified: Mon, 22 Jun 1998 …...
Content-Length: 6821
Content-Type: text/html
data data data data data ...
header
lines
data, e.g.,
requested
HTML file

14. Different Header fields in HTTP Response Message
Connection
Date
Expires
Cache-Control
Content-Encoding
Content-Language
Content-Length
Content-Location ………. And many more

15. HTTP response status codes
A few sample codes:
200 OK
request succeeded, requested object later in this message
301 Moved Permanently
requested object moved, new location specified later in this message (Location:)
400 Bad Request
request message not understood by server
404 Not Found
requested document not found on this server
505 HTTP Version Not Supported

16. HTTP Version differences
Have only 16 status codes
Provides only basic authentication
Uses Non persistent connection
RTT is more so bandwidth waste is vast
Stateless
Supports only GET POST and HEAD method
HTTP/1.1
Have introduced new 24 status code
Provides strong authentication
Uses Persistent connection
RTT is less so bandwidth utilization is good
Uses cookies as state management mechanism
Supports GET, POST, HEAD,PUT and DELETE

17. Web caches (proxy server)
Goal: satisfy client request without involving origin server
user sets browser: Web accesses via cache
browser sends all HTTP requests to cache
object in cache: cache returns object
else cache requests object from origin server, then returns object to client
origin
server
HTTP response
Proxy
server
HTTP request
client
HTTP request
HTTP response
client
origin
server
2: Application Layer

18. OUTLINE
HTTP Working
HTTP Messages
Program in Java
Introduction

19. Program in Java import java.net.*; import java.util.*;
public class HTTPResponseHeader {
public static void main(String[] args) {
try {

20. Program in Java URLConnection conn = obj.openConnection();
URL obj = new URL("
URLConnection conn = obj.openConnection();
Map<String, List<String>> map = conn.getHeaderFields();
System.out.println("Printing Response Header for URL:” + obj.toString() + "\n");

21. Program in Java }
System.out.println(entry.getKey() + " : " + entry.getValue()); {
for (Map.Entry<String, List<String>> entry : map.entrySet())
e.printStackTrace();}
catch (Exception e) {

22. Sample Output of Program