PROGRAMMING ASSIGNMENTS 3 & 4 TAO

Transcription

1 PROGRAMMING ASSIGNMENTS 3 & 4 TAO

2 INTRODUCTION Create network programs using Socket APIs Language is not limited C, Python, Java, Your program will interact with the CSE3300 server Server is hosted at tao.ite.uconn.edu, TCP/UDP, 3300/3301. There will also be a (simple) web interface, showing you the console output of server. Some parts require reversed connection (server will connect to you). It means: Your computer must have public IP address (mostly not true at your home, or inside a virtual machine) Easiest way to ensure is to use UConn network (wifi, ethernet, VPN: vpn.uconn.edu) DO NOT hard code your local address. Your program will be tested in a lab computer

3 Your computer tao.ite.uconn.edu Your program(s) CSE3300 Server program Only for debugging Server output Your browser Web service

4 OUTLINE Brief description Example Common mistakes

5 PROGRAMMING ASSIGNMENT 3 Exercise 0 (4-way handshake) Exercise 1 (Listening for a new connection)

6 EXERCISE 0 (4-WAY HANDSHAKE) Create a TCP outgoing connection Send and receive strings Construct strings Parse strings TCP Client CSE3300 Server

7 EXERCISE 0 (DETAILED) 1 - Send: (request type)(ws)(connection specifier)(ws)(usernum)(ws)(username)(newline) ex0 (server endpoint specifier)(ws)(client endpoint specifier) (dotted quad)-(port number) A random number you provide Your name (without space) \n ex I.M.Student\n

8 EXERCISE 0 (DETAILED) 2 - Recv: CSE 3300 Server Tue Feb 10 16:29:00 CDT 2005\n OK 4322 I.M.Student \n (usernum+1) (username) (servernum)

9 EXERCISE 0 (DETAILED) 3 - Send: (request type)(ws)(usernum+2)(ws)(servernum+1)(newline) ex \n

10 EXERCISE 0 (DETAILED) 4 Recv: CSE 3300 Server Tue Feb 10 16:29:02 CDT 2005 OK \n (servernum+2)

11 EXERCISE 0 (DETAILED) Where to get end-point specifier in 1 Send? (server endpoint specifier): after connect(), you can use getpeername() to get remote endpoint information, including IP address and Port number But is also fine if you hard code it in, since it doesn t change. (client endpoint specifier): after connect(), you can use getsockname() to get local endpoint information

12 EXAMPLE PSEUDO-CODE Socket() Connect() Getpeername(), getsockname() Sprintf() Send() Recv() Sscanf() Sprinf() Send() Recv(), maybe check the received string, if you want Close() String concatenates (+) String.split( \n ), split( ) or regex match String concatenates (+)

13 COMMON MISTAKES Wrong IP address (stuck at connect()) IP address of tao.ite.uconn.edu changed last year. (not as in the document) Either resolve name in your program or hardcode updated IP address (you can find out by ping) Endian Socket APIs use network endian big-endian, while most our systems uses little-endian Is common when specifying port number. Extra whitespaces, bad parsing Time syntax contains unknown whitespaces, make sure you only parse the second line

14 EXERCISE 1 (LISTENING FOR A NEW CONNECTION) Create an outgoing TCP connection Create an incoming TCP connection (Create a TCP server and accept) Send and receive strings on both TCP Server TCP Client CSE3300 Server Your (single) program

15 EXERCISE 1 (DETAILED) 1 - Send: (request type)(ws)(connection specifier)(ws)(usernum)(ws)(username)(newline) ex1 (server endpoint specifier)(ws)(your TCP server endpoint specifier) A random number you provide Your name (without space) \n ex I.M.Student\n

16 EXERCISE 1 (DETAILED) 2 - Recv: CSE 3300 Server Tue Feb 10 16:29:00 CDT 2005\n OK 4322 I.M.Student \n (usernum+1) (username) (servernum)

17 EXERCISE 1 (DETAILED) 3 Accept on server socket (it creates a incoming connection, new socket) 4 Recv on the new socket: CSE 3300 server calling (WS) (newservernum)(newline)

18 EXERCISE 1 (DETAILED) 5 Send, on new socket: (servernum+1)(ws)(newservernum+1)(newline)

19 EXERCISE 1 (DETAILED) 6 Recv: CSE 3300 Server Tue Feb 10 16:29:02 CDT 2005 OK \n

20 EXERCISE 1 (DETAILED) How to get your TCP server endpoint specifier? You must: Use getsockname() on the client socket, and get only the IP address The port number you get here is used by client socket, not server socket Use getsockname() on the server socket, and get only the port number The IP address is the bounded address, usually ( ) Combine 2 parts together to form your specifier

21 EXAMPLE PSEUDO-CODE (SINGLE THREAD) sock = socket(), psock= socket() psock.bind( :0 ), psock.listen() sock.connect() sock.getpeername(), sock.getsockname(), psock.getsockname() Construct string sock.send() newsock.recv() Parse strings Construct string newsock.send() sock.recv() sock.close, newsock.close(), psock.close() newsock = psock.accept() sock.recv()

22 COMMON MISTAKES Endian!! Incorrect (your) TCP server endpoint specifier (make sure it looks correct at least) Your TCP server is unreachable from CSE3300 server (firewall, NAT) Your TCP server is not listening when CSE3300 tries to connect

23 PROGRAMMING ASSIGNMENT 4 Exercise 0 (UDP client) Exercise 1 (UDP server) User input UDP Client SSN P.O. Box UDP Server

24 User input EXERCISE 0 (UDP CLIENT) UDP Client SSN P.O. Box CSE3300 Server Create a UDP connection (send/recv) Send and receive bytes / buffer / memory block (16 bytes) Not string anymore struct(c) / struct(python) / ByteBuffer (Java) Include manipulating bits Compute correct checksum Application checksum

25 PSEUDO-CODE (HIGH LEVEL PROCEDURE) User input Construct buffer without checksum (checksum field = 0) Compute checksum and fill in Send buffer Receive buffer Interpret received buffer and print the output

26 MINIMUM ACCESSIBLE SIZE Most languages don t provide bit access in those data structures Some fields must be combined: 16-bit, 8-bit, 8-bit 32-bit 32-bit 16-bit, 16-bit Bit access using bitwise operators AND(&), OR( ), NOT(~), XOR(^) Leftshift(<<, lsh), rightshift(>>, rsh)

27 COMMON MISTAKES Buffer Check by the actual sending size. It should be exactly 16 bytes Endian! Only 16-bit or 32-bit fields need conversion Checksum Overflow wraparound Checksum endian: don t overcorrect it! Bitwise operators

28 EXERCISE 1 (UDP SERVER) Create a server, functioning same as the CSE3300 Server (for UDP client) Dictionary lookup (Fully) interpret client request Identify possible errors Test your UDP server using your own UDP client Construct a type 1 request to ask CSE3300 server to test your User input UDP Client SSN P.O. Box (Your) UDP Server

29 PSEUDO-CODE (HIGH LEVEL PROCEDURE) Load database (from file) Create UDP socket Bind While True: Recvfrom Interpret message, Error checking locate SSN, P.O.Box, construct response Sendto

30 EXERCISE 1 (FINAL TEST) Function test CSE3300 Server SSN P.O. Box Test request (Your) UDP Server Type 1 requester Two programs can be separated

31 COMMON MISTAKES Error handling You can learn from what server tests you Checksum Network connectivity Make sure your UDP server is accessible from CSE3300 server, and you provided the correct address and port in type 1 requester

32 HOW TO ACCESS THESE SUBFIELDS Bitwise operators AND(&), OR( ), NOT(~), XOR(^) Leftshift(<<, lsh), rightshift(>>, rsh) 1 and 1 = 1, 0 and 1 = 0, 1 and 0 = 0, 0 and 0 = 0 1 << 3 = 8 (1000b) 8 >> 3 = 1

33 EXAMPLE: ENCODE (16 bits) 3300 = We want to set 1 at the 15 th bit = = Simplify: 1<<15 = 32768! (1 << 15) The decimal representation doesn t help now.

34 EXAMPLE: DECODE Bitmask 01 & 00 =? & 11 =? & 0011 = 0001 You get only lower 2 bits from 0101!

35 EXAMPLE: DECODE Get 3300 out of You know a number (3300) stores at lower 14 bits You create a bitmask, in decimal it is & =? & =? Simplify: =? = 1 << & ((1<<14)-1) =3300!

36 EXAMPLE: DECODE How to get highest bit out of Create a bitmask: (1<<15) & (1<<15) =? 1<<15 Doesn t matter. Zero or non-zero!