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CS 317: Internet computing

Tutorial – Summer 2007. CS 317: Internet computing. The Tutorial Session . Total 6 weeks during the whole term. Two separate sessions 1 hour duration each Each session twice a week. T1A - Tue, Thu – 12:30 t0 13:30 T1B – Tue, Thu – 13:30 to 14:30 T1C – (has been blocked). Your TAs.

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CS 317: Internet computing

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  1. Tutorial – Summer 2007 CS 317: Internet computing 317 Summer 2007 - Tutorial

  2. The Tutorial Session • Total 6 weeks during the whole term. • Two separate sessions • 1 hour duration each • Each session twice a week. • T1A - Tue, Thu – 12:30 t0 13:30 • T1B – Tue, Thu – 13:30 to 14:30 • T1C – (has been blocked) 317 Summer 2007 - Tutorial

  3. Your TAs • AnirbanSinha (you can call me Ani) • GitikaAggarwal • Kan Cai • We are all affiliated to the Distributed Systems Research group under the supervision of separate profs. 317 Summer 2007 - Tutorial

  4. Tutorial Organization • In strict correspondence with the assignments. • Three assignments, each of 2 weeks duration. • Similarly, each of us will lead 2 weeks of the tutorial . • First two weeks, I will concentrate on the first assignment. • Next two weeks, Gitika will discuss the second assignment. • Last two weeks, Kan will help you out with the last and final assignment. 317 Summer 2007 - Tutorial

  5. What else to discuss? • Questions related to the weekly quiz. • Midterm questions and their solutions . • Grading (only general ones) • be careful to ask individual grading questions offline. • Debugging/testing/good practices. 317 Summer 2007 - Tutorial

  6. What else to discuss? • General queries/doubts/comments. • We will try our best to answer the questions. • If unable, we will answer it in the WebCT. • Please try to attend the tutorial sessions. • It will help you a lot in solving the assignments and the quizzes. • 1% bonus for being there in the tutorial !  317 Summer 2007 - Tutorial

  7. What not to discuss • Direct solutions to assignments • We have not solved the problems ourselves. • Violation of UBC policies. • What are the likely questions for midterm/final/quizzes • We are not mind readers – we do not know what Dr. Vuong would like to give in the exams. • Anything that is not related to 317- Canucks game?! • I would like to discuss that offline though  317 Summer 2007 - Tutorial

  8. What if I get stuck?! • Use WEBCT discussion group! • It is more likely that one of your peers has faced the same problem and solved it! • Group discussion helps to come up with a solution together – much better than getting off-the-shelf answer from the TAs. • If totally stuck with no one knowing what to do, Kan and possibly me will be there to help. • Do *not* email problems to TAs individually *unless* you really think its necessary. 317 Summer 2007 - Tutorial

  9. Useful suggestions, tips … • Read carefully the text and the lecture slides. • Understand the basic concepts. Ask questions if in doubt. • Write small simple code to test out your concepts – an excellent way to learn new things. • Know what is exactly being asked for. • Don’t procastinate. • Distribute the work over a longer period – helps your mind to think and come up with ideas. 317 Summer 2007 - Tutorial

  10. Useful suggestions, tips … • If stuck, go back to the text and the lecture slides – do not cry out for help at the first sign of trouble. • Talk to peers, help is not far away! • Be patient and take a deep breath when things go wrong. 317 Summer 2007 - Tutorial

  11. End of Introduction • Any questions, concerns, worries? 317 Summer 2007 - Tutorial

  12. What you need for the assignments? • Single most important resource: • Beej's Guide to Network Programming, Using Internet Sockets.http://beej.us/guide/bgnet/ • All you will ever need is there in this book. • Study the examples and the network APIs carefully. 317 Summer 2007 - Tutorial

  13. Assignment 1: Proxy server • Work in groups of three • Smaller groups preferred but no bigger. • 15 hours total working time per team. (excluding review time). • If you have not read the assignment, here it is in nutshell: • Design a *caching* proxy server. • Design a mechanism for cleaning expired items from cache. 317 Summer 2007 - Tutorial

  14. Assignment 1: Proxy server • A proxy server works in between clients and the web server. • Helps several clients to share a single Internet connection – cost effective. • Also caches the requested pages so that pages that are revisited can be delivered immediately. • Firewalls and IP filters are generally set up along with the proxy servers. 317 Summer 2007 - Tutorial

  15. Basic Socket Programming • Client Side Programming: • Call socket(): get a new client socket • socket(PF_INET, SOCK_STREAM, 0): creates a new TCP/IP socket. • Fill in a structure with the server address & port: • structsockaddr_intheir_addr • Often we use gethostbyname() to obtain the remote server IP from its host name. 317 Summer 2007 - Tutorial

  16. Basic Socket Programming • Client Side Programming: • Connect() to the server. • connect(sockfd, (structsockaddr *)&their_addr, sizeof(structsockaddr)) : Connect to the remote client using the client side socket, sockfd obtained through call to socket() earlier. • Start Receiving data: • Call Recv(): recv(sockfd, buf, MAXDATASIZE-1, 0), where buf is the buffer where the data is received! 317 Summer 2007 - Tutorial

  17. Basic Socket Programming • Server Side Programming: • Generally servers “bind” to a specific well-known port. For example, all web-servers “bind” & then “listen” on port 80. • All clients (browsers) connect to this port by default. • Thus, server side programming involves a little more work. 317 Summer 2007 - Tutorial

  18. Basic Socket Programming • Server Side Programming: • Call Socket() to get a server side socket. Call is identical as before. • Fill in a structure as before. • structsockaddr_inmy_addrmy_addr.sin_family = AF_INET; my_addr.sin_port = htons(MYPORT); my_addr.sin_addr.s_addr = INADDR_ANY; memset(my_addr.sin_zero, '\0', sizeofmy_addr.sin_zero); • Fill in the structure with local port (MYPORT) and local server address (INADDR_ANY). 317 Summer 2007 - Tutorial

  19. Basic Socket Programming • Server Side Programming: • Call bind() : It will bind the server socket to the specific port. • This is done only on the server side, in order to listen on a specific port. • bind(sockfd, (structsockaddr*)&my_addr, sizeof(structsockaddr))Here, sockfd is the socket file descriptor obtained from call to socket() and my_addr is the same as discussed before. 317 Summer 2007 - Tutorial

  20. Basic Socket Programming • Server Side Programming: • Now “listen” for connections from clients: • listen(sockfd, BACKLOG), where backlog is the number of outstanding connection requests to queue. Generally, its something around 10 to 20 depending on the server load expected. • Now “accept” new connections from clients. • Accept() blocks (in general, unless you set the socket into non-blocking mode) until a client connect()s to a server. • It returns a new socked file descriptor for the corresponding connection. • Also fills astructsockaddr_inwith information about the remote client address. 317 Summer 2007 - Tutorial

  21. Basic Socket Programming • Server Side Programming: • There are two ways to deal with multiple incoming client requests: • Set the server side socket into non-blocking mode, poll the socket at certain intervals for any outstanding requests from clients and dispatch an event handler to service the request – event driven programming. • Fork a new thread to service the request and the main thread keeps accepting new connections in a tight loop: Multithreaded programming. 317 Summer 2007 - Tutorial

  22. Basic Socket Programming • Server Side programming: • Unless you really know event driven style, I would suggest you to use multithreaded style • Simpler to understand and code • You are familiar with threaded programming already from 213. • The thread processing client requests can now send() or recv() data from clients. • If you really want to serve only one client, no need of threads. Just one main thread can do all the work. 317 Summer 2007 - Tutorial

  23. Basic Socket Programming • General APIs • Close() and shutdown() : Used to de-allocate the socket resources and shut down the connection. • Gethostname() : get the local host name of the machine. • fcntl(sockfd, F_SETFL, O_NONBLOCK): - set a socket in non-blocking mode. More details on blocking issues in the guide. • setsockopt(listener,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) : to get rid of “address already in use message” 317 Summer 2007 - Tutorial

  24. Basic Socket Programming – Tips and Suggestions • Read the APIs carefully. • Use man pages when help is needed with APIs. • Always check for return values and take appropriate actions on errors. • Work in steps – do not try to do everything all at once. • Use tools like telnet, ftp etc to test run your program before proceeding to next steps. 317 Summer 2007 - Tutorial

  25. Assignment 1: Proxy serverBasic Idea • Create a server socket and listen for incoming client request. • When a new client connect()s, fork a new thread to process the client request. • Parse for remote server address from the client request. • Create a client socket and connect to the remote server. • Forward your client’s request to the remote server. Send back response (separate threads?). Keep doing it in a loop or terminate after one iteration (?) 317 Summer 2007 - Tutorial

  26. Assignment 1: Proxy serverCaching • Cache requested pages. No need for elaborate caching scheme. • If requested page is already in cache, do not go to the server. • Terminate when either remote server or your client disconnects. 317 Summer 2007 - Tutorial

  27. Assignment 1: Proxy serverCache Invalidation & Cleanup • Objects in cache expire with time. • Use a suitable mechanism to find expired items. • Fork a new thread that cleans up expired items from cache. • The expired time limit is a command line parameter that is provided by the user. 317 Summer 2007 - Tutorial

  28. Discussion … (5/10/07) • Concurrency Issues • how many threads are needed? • Caching Issues • How to detect expired items? • Persistent HTTP connection issues. • How to detect a change in requested server address etc … • How robust should be your code?! 317 Summer 2007 - Tutorial

  29. Discussion … (5/15/07) • Tutorials T1A and T1B will probably be combined into a single one … • Any problems with anyone here? • Any other administrative issues? 317 Summer 2007 - Tutorial

  30. Discussion … (05/15/07) • How’s things are with WebCT? • Questions related to text (eg. prop & trans delay) • They are in the text itself! • Besides TAs, you can ask Son the next day in class. • Assignment 1 is due this Thursday • Issues, problems, questions? ... • Browser configuration (demo) 317 Summer 2007 - Tutorial

  31. Discussion … (05/17/07) • Tutorials T1A and T1B has been merged! • Any conflicts? • Do not forget to check the attendance sheet in my homepage later and report any inconsistencies immediately. • Final set of updated slides will be posted today. • Gitika takes over from next week • Will discuss assignment 2. 317 Summer 2007 - Tutorial

  32. Discussion … (05/17/07) • Assignment 1 is due next Tuesday, 22nd of May. • No more discussion on Assignment 1 after today! • I will try to grade Assignment 1 as soon as I can, according to the guidelines provided by Son. • Make sure you put the names of *all* group members in the source code itself. • Use electronic handin – no written material. • All members of a group will be treated uniformly. • Be patient for the grades and comments. • I will try to be lenient.  yay!!!! 317 Summer 2007 - Tutorial

  33. Discussion … (05/17/07) • Grading (Assignment 1) … • If you have questions on grading, you can send me email directly (anirbans@cs.ubc.ca) BUT: • Send all your questions in a single mail all at once. • Only one mail per group will be answered. • Write names, stud ID and CWL of all group members in email. • No later than 5 days after the grades/comments has been sent out. • Check instructor’s policy in the course webpage. • Any response will follow the policy guidelines in the course webpage. 317 Summer 2007 - Tutorial

  34. Discussion … (05/17/07) • Quiz 1 will be graded by all TAs together. • Have patience. • Any question on Quiz1 – ask any TA during the tutorials. • Grades will be posted in the WebCT as soon as possible. • That’s all from me! • Any questions, comments?? 317 Summer 2007 - Tutorial

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