Lab 1 Fundamentals of Socket Programming

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Lab 1 Fundamentals of Socket Programming

• Dr. Tony K. C. Chan

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• Acknowledgements
• Thanks for Prof. Y. W. Leung providing valuable
  materials by which this teaching materials is
  prepared.

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• References
• 1 D. E. Comer and D. L. Stevens,
  Internetworking with TCP/IP Volume III
  Client-Server Programming and Applications,
  Prentice-Hall, Inc, 1997.
• 2 Beejs Guide to Network Programming Using
  Internet Sockets Online Available
  http//beej.us/guide/bgnet/
• 3 Winsock Functions Online Available
  http//msdn2.microsoft.com/en-us/library/ms741394.
  aspx.

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1. Review of C Programming

• 1.1 Some data types
• u_char unsigned 8-bit character
• u_short unsigned 16-bit integer
• u_long unsigned 32-bit integer

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1. Review of C Programming

• 1.1 Some data types, cont.
• structure a group of different types of data
• Example
• struct info
• char name20
• int id
• struct info student40
• student0.name Tony
• student0.id 1234

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1. Review of C Programming

• 1.2 Casting of Data Types
• Casting to change the data type of a variable or
  expression to the designated one.
• Example
• If x is an int, the data type of the following
  expression is
• double
• (double)(x1)

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1. Review of C Programming

• 1.3 Pointers
• Every memory location has an address? we can use
  this address to access the content in this memory
  location.
• A pointer is a variable that stores the memory
  address (not the value) of a data item.

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1. Review of C Programming

• 1.3 Pointers
• Declare a pointer data-type pointer-variable
• Dereference operator p gives the content
  stored in the memory location with address p.
• Address operator The address storing the first
  memory byte of the variable x in x.
• Example
• float x, y, p / declare p as a pointer of
  float
• p x / assign the address of x to p
• y p / assign the content of p to y

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1. Review of C Programming

• 1.4 Pointers and array
• The name of an array is actually a pointer to the
  first element in the array.
• If x is a one-dimensional array,
• ? The address of the 1st array element is x0
  or x
• ? The address of the 2nd array element is x1
  or (x1)
• ?

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1. Review of C Programming

• 1.5 Byte-manipulation functions
• We may not use string functions in network
  programming. Why?
• Three byte-manipulation functions
• void memset(void dest, int chr, int len)
• void memcpy(void dest, const void src, int
  len)
• int memcmp(const void first, const void secnd,
  int len)
• memset() specified number of bytes to a value.
• Example
• Stores zeros in a field called x
• memset(x, 0, sizeof(x))

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1. Review of C Programming

• 1.5 Byte-manipulation functions
• memcpy() copies the value of one field to another
• Example
• Copy the value of y field to the x field
• memcpy(x, y, sizeof(x))
• memcmp() compares two fields
• Example
• Compares the first 10 bytes of fields x and y
• if (memcpy(x, y,10) 0)
• printf(x and y are the same)

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2. Byte Order

• Different computers may have different internal
  representation of 16/32-bit integer (called host
  byte order)
• Big-endian byte order (e.g., used by Motorola
  6800)

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2. Byte Order

• Little-endian byte order (e.g., used by Intel
  80x86)

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2. Byte Order

• TCP/IP specifies a network byte order which is
  the big-endian byte order.
• Functions for converting between host byte order
  and network byte order
• u_short htons(u_short host_short)
• u_short ntohs(u_short network_short)
• u_long htonl(u_long host_long)
• u_long ntohl(u_long network_long)

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3. Endpoint Address

• structure holds socket address information for
  many types of sockets
• struct sockaddr
• u_short sa_family / type of address
  family /
• char sa_data14 / value of address /

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3. Endpoint Address

• For TCP/IP, an endpoint address is composed of
  the following items
• Address family is AF_INET (Address Family for
  InterNET).
• Endpoint address in that family is composed of an
  IP address and a port number.

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3. Endpoint Address

• Port number
• A port number identifies an application running
  on a computer.
• The port number is composed of 16 bits, and its
  possible values are used in the following manner
• 0-1023 for well-known server applications.
• 1024-49151 for user-defined server applications.
• 49152-65535 for client programs.

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3. Endpoint Address

• To deal with struct sockaddr, a compatible
  structure for TCP/IP endpoint address was created
  as follows.
• struct sockaddr_in
• u_short sin_family / address family /
• u_short sin_port / port number /
• struct in_addr sin_addr / IP address /
• char sin_zero8 / unused (set to zero) /

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3. Endpoint Address

• The structure of in_addr is as follows.
• struct in_addr
• u_long s_addr / that's a 32-bit long, or 4
  bytes /

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3. Endpoint Address

• sockaddr and sockaddr_in are compatible
• If you only use TCP/IP, you can use sockaddr_in
  without using sockaddr.

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3. Endpoint Address

• Example 1
• The IP address of a server is 192.168.20.56. Its
  decimal value is 3232240696. We can specify the
  endpoint address for this server as follows.
• struct sockaddr_in serverAddr
• serverAddr.sin_family AF_INET
• serverAddr.sin_port htons(2000)
• serverAddr.sin_addr.s_addr htonl(3232240696)

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3. Endpoint Address

• Example 1, cont.
• Uses inet_addr() converts a string in dotted
  decimal (e.g., 192.168.20.56) to an integer value
  suitable for use as an Internet address.
• struct sockaddr_in serverAddr
• char serverIP "192.168.20.56"
• serverAddr.sin_family AF_INET
• serverAddr.sin_port htons(2000)
• serverAddr.sin_addr.s_addr inet_addr(serverIP)

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3. Endpoint Address

• Example 2
• We specify the endpoint address for a server as
  follows
• struct sockaddr_in serverAddr
• serverAddr.sin_family AF_INET
• serverAddr.sin_port htons(2000)
• serverAddr.sin_addr.s_addr htonl(INADDR_ANY)
• Where the symbolic constant INADDR_ANY represents
  a wildcard address that matches any of the
  computer's IP address.

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Exercises

• pragma comment( linker, "/defaultlibws2_32.lib"
  ) / Specify the linker to link with ws2_32.lib
  /
• include ltstdio.hgt
• include ltwinsock2.hgt
• define WSVERS MAKEWORD(2, 0) / MAKEWORD(2,0)
  macro creates WORD value / / that specifies
  version 2.0
• int main(int argc, char argv)
• WSADATA wsaData / Declare variables /
• WSAStartup(WSVERS, wsaData) / Initialize
  socket software /
• / Use socket functions here /
• WSACleanup() / Deallocate all data structures
  and socket bindings /
• return 0

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Exercises

• 1. Write a program to print the IP address in
  32-bit integer value.
• 2. If you do not convert the byte order, what
  happen?

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4. Details of Each Function Call

• General Sequence of Function Calls

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4. Details of EachFunction Call

• Must call WSAStartup() before using socket
  functions.
• Example
• define WSVERS MAKEWORD(2, 0)
• WSADATA wsaData
• WSAStartup(WSVERS, wsaData)

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4. Details of EachFunction Call

• Creates a socket
• Example
• SOCKET s
• s socket(PF_INET, SOCK_STREAM, 0)

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4. Details of EachFunction Call

• Specifies the endpoint address for a socket.
• Example
• struct sockaddr_in serverAddr
• / Specify the server's endpoint address in
  serverAddr here /
• bind(s, (struct sockaddr )serverAddr,
  sizeof(serverAddr))

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4. Details of EachFunction Call

• Makes socket ready to accept incoming request.
• Example
• listen(s, 1)

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4. Details of EachFunction Call

• Establishes connection to a specified remote
  server
• Example
• struct sockaddr_in serverAddr
• / Specify the server's endpoint address in
  serverAddr here /
• connect(s, (struct sockaddr )serverAddr,
  sizeof(serverAddr))

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4. Details of EachFunction Call

• Accepts the next incoming connection, return a
  new socket for the connection
• Example
• struct sockaddr_in clientAddr
• Int len
• SOCKET ss
• ssaccept(s, (struct sockaddr )clientAddr,
  len)

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4. Details of EachFunction Call

• Sends message
• Example
• char message "Hello"
• send(s, message, strlen(message), 0)

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4. Details of EachFunction Call

• Receives message
• Example
• define BUFMAX 5
• char bufBUFMAX
• recv(s, buf, BUFMAX, 0)

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4. Details of EachFunction Call

• Terminates connection
• Example
• closesocket(s)

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4. Details of EachFunction Call

• When an application finishes using sockets, it
  call WSACleanup() to deallocate all data
  structures and socket bindings.
• Example
• WSACleanup()

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4. Details of Each Function Call

• General Sequence of Function Calls

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5. Three simple services of TCP/IP

• Three simple services of TCP/IP
• DAYTIME
• Triggered by TCP connection or UDP datagram
• Return the date and time in a format for human
• TIME
• Triggered by TCP connection or UDP datagram
• Return the time in a 32-bit integer
• ECHO
• Return all the data it receives from a client.

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Exercises

• 1. Write a TCP client for the DAYTIME service.
• 2. Write a UDP client for the TIME service.
• 3. Write a TCP server to provide DAYTIME service.
• 4. Write a UDP server to provide TIME service.
• 5. Write a TCP server to provide ECHO service.
• 6. Write a TCP client for the ECHO service.
• 7. Repeat 1 - 6 with different sockets.
• 8. Modify the TIME client so it computes E, the
  time that elapses between when it sends the
  request and when it receives a response. Add
  one-half of E to the time the server sends.

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THE END