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

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

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

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

Persistent Connections HTTP 1.0 -- Connections close by Default No need for Content-length, end signaled by EOF (in-band signal) HTTP 1.1 -- Persistent by Default Must use Content-length

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

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 http://www.foo.com host:www.foo.com

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

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

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

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

Why Proxy Servers? Content Router

Why Proxy Servers? Content Router

Why Content Routers? Content Router

Why Proxy Servers? Content Router

Why Proxy Servers? Anonymizer

Why Proxy Servers? Translation

Why Proxy Servers? Translation http://translate.google.com/translate?hl=en&sl=es&u=http://espanol.yahoo.com/&prev=/search%3Fq%3Dspanish%26hl%3Den%26lr%3D%26ie%3DUTF-8

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://www.yahoo.com/ HTTP/1.0

Five Minute Break

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

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());

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

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

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

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