URLs and HTTP. ICW Lecture 10 Tom Chothia

Size: px

Start display at page:

Download "URLs and HTTP. ICW Lecture 10 Tom Chothia"

Eleanore Scott
8 years ago
Views:

1 URLs and HTTP ICW Lecture 10 Tom Chothia

2 This Lecture The two basic building blocks of the web: URLs: Uniform Resource Locators HTTP: HyperText Transfer Protocol

3 Uniform Resource Locators Many Internet systems use URLs, e.g. Protocol Computer FilePath This URL refers to the file index.html on the computer which should be accessed using http.

html Protocol Computer FilePath This URL refers to the

4 URLs aren't just for HTTP ftp://ftp.funet.fi/pub/standards/rfc/ rfc959.txt rmi:// /process svn+ssh://svn.cwi.nl/projects

5 More complex URLs Port number Username Anchor

6 URL syntax The most general URL has the syntax: protocol:// /filepathname?query_string#anchor All parts are options!

7 URLs in Java The java.net.url class does URLs in Java e.g.: URL myurl = new URL ( myurl.gethost(); myurl.getport();

8 URLs in Java The URL knows the protocol therefore it can connect for you: InputStream = myurl.openstream(); More info at: docs/api/java/ net/url.html

9 HTTP HyperText Transfer Protocol Used to request and deliver webpages. Includes: Set of basic commands Header fields Status codes

10 GET and POST Key HTTP commands: GET: requests a resource, e.g. a webpage in HTTP POST: submits data to the server. e.g. from a form on a webpage.

11 OTHER COMMANDS HEAD like GET but only gets header PUT uploads resource to server DELETE deletes resource from server TRACE echoes back message OPTION returns supported HTTP CONNECT used for tunnelling TCP PATCH partially modify resource

server TRACE echoes back message OPTION returns supported

12 Example laptop:~ laptop$ telnet 80! Trying ! Connected to Escape character is '^]'.! GET /index.php! <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" " xhtml1-strict.dtd">! <html xmlns=" lang="en">! <head>!

DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.

13 Example laptop:~ laptop$ telnet 80! Trying ! Connected to Escape character is '^]'.! GET /! HTTP/ Found! Location: <HTML><HEAD><meta http-equiv="content-type" content="text/ html;charset=utf-8">! <TITLE>302 Moved</TITLE></HEAD><BODY>! <H1>302 Moved</H1>! The document has moved!

14 Example laptop:~ laptop$ telnet 80! Trying ! Connected to Escape character is '^]'.! GET /! HTTP/ Found! Location: <HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">! <TITLE>302 Moved</TITLE></HEAD><BODY>! <H1>302 Moved</H1>! The document has moved!

15 Headers and Bodies HTTP responses are made up of a header and a body: The header includes a reply code to tell the client what has happened. The body is the resource, e.g. the webpage

16 Status Codes 2--: Success 200 OK: the request worked 201 Created: request worked and server has created a new resource 204 No Context: request worked but there is nothing to return.

17 Status Codes 3--: Redirection 301 Moved Permanently: Website has moved 4--: Client Error 400 Bad Request: syntax error 401 Unauthorized: needs a cookie? 403 Forbidden: No access allowed

18 Status Codes 5--: Server Error 500 Internal Server Error: general error message 501 Not Implemented: command not supported Full list of status codes at: List_of_HTTP_status_codes!

command not supported Full list of status codes at:

19 Headers fields These provide extra information, e.g. Host: <host name> is compulsory for HTTP 1.1, GET /index.php HTTP/1.1! Host:

20 Other Headers Fields Cookie: gives the cookie! Accept: data types client can handle, e.g. Accept: text/plain! Content-Length: length of message in bytes. Full list at: List_of_HTTP_headers

21 Example laptop:~ laptop$ telnet 80! Trying ! Connected to Escape character is '^]'.! GET / HTTP/1.1! Host: HTTP/ OK! Date: Wed, 03 Nov :07:18 GMT! Expires: -1! Cache-Control: private, max-age=0! Content-Type: text/html; charset=iso ! Set-Cookie: PREF=ID=e5e59d5c56d4f722:FF=0:TM= :LM= :S =qb0mgmegvmqc7eu0; expires=fri, 02-Nov :07:18 GMT; path=/; domain=.google.co.uk!

22 The burp Proxy The burp Proxy lets you monitor and pause an Internet connection. Use it to look at your clients HTTP messages: 1. Run proxy (it opens port 8080), 2. Tell web client to use the proxy 3. See the messages

23 Conclusion Uniform Resource Locators (URLs): unqically name everything on the Internet. Name includes a lot of information about the resource: the protocol, the host, HyperText Transfer Protocol (HTTP): The protocol for getting webpages Use GET and POST Uses header fields status codes

24 Next Time: XML and Java XML tools. XML is the default file format of Internet systems. The next lecture will tell you what XML is and how to manipulate XML in Java.

HTTP Protocol. Bartosz Walter <Bartek.Walter@man.poznan.pl>

HTTP Protocol. Bartosz Walter <Bartek.Walter@man.poznan.pl> HTTP Protocol Bartosz Walter Agenda Basics Methods Headers Response Codes Cookies Authentication Advanced Features of HTTP 1.1 Internationalization HTTP Basics defined in