1. HTTP and Sockets Lecture 6
cs193i – Internet Technologies
Summer 2004
Stanford University

2. Administrative Stuff Lab #2 due today HW #2 due July 21
Midterm Monday, July 19, in class

3. Midterm In class, Monday, July 19 Previous quarter’s exam online
Closed-book
1 8x11 cheat sheet
Short-answer

4. Today’s Discussion HTTP Wrap-up Sockets in Java HTTP 1.1 additions
HTTP Proxies
Sockets in Java

5. Persistent Connections
HTTP Connections close by Default
No need for Content-length, end signaled by EOF (in-band signal)
HTTP Persistent by Default
Must use Content-length

6. Chunked-Transfer Encoding
Problem: Content-length costly for server
May not know if generated dynamically
Solution
Server omits Content-Length
Transfer-encoding: chunked
Send Data in Chunks, Prefixed by length in Hex
End is marked with Chunk Length 0

7. HTTP 1.1 Virtual Hosts Problem: Solution:
Want multiple web sites hosted on single server
Incoming requests must be directed to return appropriate web site’s page
Solution:
Request includes host name header
host:

8. Try This At Home telnet cva.stanford.edu 80 GET / HTTP/1.1
Host:cva.stanford.edu
Connection:Keep-Alive
GET /group_mtg.html HTTP/1.1
Connection:Close

9. HTTP Proxy Servers "Middlemen" between clients and servers
May "rewrite" HTTP requests and responses
Proxy
Server
Looks like a server
sending responses
Looks like a client
making requests

10. Why Proxy Servers? Content filtering
Packet filter
Prevent children from accessing sites
Used to contact server in special way
Firewall or circuit relay
Security
Rewrite content
Swedish chef
Redirect requests
Content router
To improve performance
Logging activity

11. Why Proxy Servers? Web cache is also a type of proxy!
RT latency reduced

12. Why Proxy Servers?
Content Router

13. Why Proxy Servers?
Content Router

14. Why Content Routers?
Content Router

15. Why Proxy Servers?
Content Router

16. Why Proxy Servers?
Anonymizer

17. Why Proxy Servers?
Translation

18. Why Proxy Servers? Translation

19. Requests via Proxy Client must realize talking to proxy
Request header:
GET path HTTP/1.0
Client must use absolute path!
GET / HTTP/1.0
GET HTTP/1.0

20. Five Minute Break

21. Sockets in Java (Client)
java.net.socket
Create Socket
Socket c = new Socket(“hostname”, port); OR
Socket c = new Socket(“IP addr”, port);

22. Reading/Writing to Sockets
Just like performing file I/O in Java
Create input/output streams to read/write to/from socket
Output example: PrintWriter class
new PrintWriter(c.getOutputStream(), true);
Input example: BufferedReader class
new BufferedReader(new InputSreamReader(c.getInputStream());

23. Sockets in Java (Server)
Create ServerSocket
Socket listen = new ServerSocket(port);
Create Socket
ServerSocket.accept()
Blocks until connection established
Socket s =new listenSocket.accept();
Create input/output streams
Close when finished

24. Exceptions Sockets throw exceptions when something goes wrong
UnknownHostExcpetion
Handle using try/catch pairs
try{
(statement;)*
}catch(ExceptionType e){
}finally{ }
Can have multiple catch clauses for handling different exceptions

25. URL Class Automatically decomposes string into parts: getHost()
getPort()
getProtocol()
getFile() // path

26. What do you do with this stuff?
StringTokenizer class
Allows you to grab tokenized strings one at a time
You can specify what delineates strings
Example: < or > could be delineators
Pattern and Matcher classes
Create pattern
Use Matcher class to compare strings to pattern