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Building a Simple Web Proxy

Building a Simple Web Proxy. COS 461 Assignment 1. A Brief History of HTTP. Mar 1989 - "Information Management: A Proposal " Oct 1990 - "WorldWideWeb" coined Oct 1994 - W3C founded May 1996 - RFC 1945 (HTTP 1.0) June 1999 - RFC 2616 (HTTP 1.1). Anatomy of HTTP 1.0. Web Client.

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Building a Simple Web Proxy

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  1. Building a Simple Web Proxy • COS 461 Assignment 1

  2. A Brief History of HTTP • Mar 1989 - "Information Management: A Proposal" • Oct 1990 - "WorldWideWeb" coined • Oct 1994 - W3C founded • May 1996 - RFC 1945 (HTTP 1.0) • June 1999 - RFC 2616 (HTTP 1.1)

  3. Anatomy of HTTP 1.0 Web Client Connect: Request Web Server GET / HTTP/1.0 Host: www.yahoo.com CRLF Response: Close HTTP/1.0 200 OK Date: Tue, 16 Feb 2010 19:21:24 GMT Content-Type: text/html; CRLF <html><head><title>Yahoo!</title>

  4. Anatomy of HTTP 1.0 Web Client Connect: Request Web Server Request Line Request Header Request Delimiter GET/HTTP/1.0 Host: www.yahoo.com CRLF Response: Close Response Status Response Header Response Delimiter Response Body HTTP/1.0200OK Date: Tue, 16 Feb 2010 19:21:24 GMT Content-Type: text/html; CRLF <html><head><title>Yahoo!</title>

  5. HTTP 1.1 vs 1.0 • Additional Methods (PUT, DELETE, TRACE, CONNECT + GET, HEAD, POST) • Additional Headers • Transfer Coding (chunk encoding) • Persistent Connections (content-length matters) • Request Pipelining

  6. Why Use a Proxy? Caching Content Filtering Privacy

  7. Building a Simple Web Proxy • Forward client requests to the remote server and return response to the client • Handle HTTP 1.0 (GET) • Multi-process, non-caching web proxy • ./proxy <port>

  8. Handling Requests • What you need from a client request: host, port, and URI pathGET http://www.princeton.edu:80/ HTTP/1.0 • What you send to a remote server:GET / HTTP/1.0Host: www.princeton.edu:80 Connection: close Check request line and header format

  9. Handling Responses Web Client Web Server Parse Request: Host, Port, Path Simple Proxy Forward Response to Client Including Errors

  10. Handling Errors • Method != GET: Not Implemented (501) • Unparseable request: Bad Request (400) • Parse using the Parsing library • Postel’s law: Be liberal in what you accept, and conservative in what you sendconvert HTTP 1.1 request to HTTP 1.0convert \r to \r\netc...

  11. Testing Your Proxy • Telnet to your proxy and issue a request> ./proxy 5000> telnet localhost 5000Trying 127.0.0.1...Connected to localhost.localdomain (127.0.0.1).Escape character is '^]'.GET http://www.google.com/ HTTP/1.0(HTTP response...) • Direct your browser to use your proxy • Use the supplied proxy_tester.py and proxy_tester_conc.py

  12. Proxy Guidance • Assignment page • Assignment FAQ • RFC 1945 (HTTP 1.0) • Google, wikipedia, man pages • Must build on Friend 010 machines

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