COMP445 Fall 2006

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COMP445Fall 2006

• Lab assignment 1

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CALLER
RECEIVER
STEP1 Get the name of the second party
STEP1 Plug the phone, and listen for incoming
calls on a certain line
STEP2 Get phone number from white pages
STEP2 Get a call and accept it. Caller ID will
give you the callers phone number.
STEP3 Copy the number for your records
Connection Established. Chat
STEP4 Call the other party
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Program architecture
Server port 7070
Client
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Socket Programming

• Berkeley added a new interface to the operating
  system to support network communication. This
  interface is generally known as the Berkeley
  Sockets Interface and is the basis for almost all
  existing TCP/IP network protocol interfaces,
  including Windows Sockets (commonly referred to
  as WinSock).
• A socket is very much like a telephone - it's the
  endpoint of a two-way communications channel. By
  connecting two sockets together you can pass data
  between processes running on different computers.

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Main steps client side

• Creating a socket
• SOCKET socket(int domain, int type, int
  protocol)
• s socket(AF_INET,SOCK_STREAM,0)
• The structure we fill in is defined below.
• struct sockaddr_in
• short sin_family // address family u_short
• sin_port// service port struct in_addr 16 bit
  TCP or UDP port number, network byte order
  sin_addr // internet address char 32 bits IPv4
  address, Network Bytes Order
• sin_zero8 // filler
• sa_in

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Main steps client side

• Client needs the address of the server.
• User inputs the servers hostname.
• rpgethostbyname(remotehost)
• Fill in the server address
• memset(sa_in,0,sizeof(sa_in))
  memcpy(sa_in.sin_addr,rp-h_addr,rp-h_length)
  sa_in.sin_family rp-h_addrtype
• sa_in.sin_port htons(port) //port 7070 host
  to network 16 bits
• Connecting
• if (connect(s,(LPSOCKADDR)sa_in,sizeof(sa_in))
  SOCKET_ERROR) throw "connect failed\n"
• Sending frames
• ibytessent send(s, (char)message_frame,
  sizeof(message_frame), 0)
• Receiving frames
• ibytesrecv recv(s, (char) data_frame,
  sizeof(data_frame),0)

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Main steps server side

• Creating a socket
• s socket(AF_INET,SOCK_STREAM,0)
• Fill in the server port and address info
• sa.sin_family AF_INET
• sa.sin_port htons(port)
• sa.sin_addr.s_addr htonl(INADDR_ANY)
• Bind the server port
• if (bind(s,(LPSOCKADDR)sa,sizeof(sa))
  SOCKET_ERROR)
• Listen for client requests
• if(listen(s,10) SOCKET_ERROR)

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Main steps server side

• Watching for new messages
• FD_SET(s,readfds) //always check the listener
  if(!(outfdsselect(infds,readfds,NULL,NULL,tp)))
  else if (outfds SOCKET_ERROR)
• throw "failure in Select"
• else if (FD_ISSET(s,readfds))
• cout
• Accept the request
• if((s1accept(s,ca.generic,calen))INVALID_SOC
  KET) throw "Couldn't accept connection\n"
• Read a message
• if((ibytesrecv recv(s1,szbuffer,128,0))
  SOCKET_ERROR)
• Send a message
• if((ibytessent send(s1,szbuffer,ibufferlen,0))
  SOCKET_ERROR)

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Socket Functions

• int socket(int family, int type, int protocol)
• returns nonnegative
  descriptor if OK, -1 on error
• int connect(int sockfd, const struct sockaddr
  servaddr, int addrlen)
• return0 if OK -1 on error
• int bind(int sockfd, const struct sockaddr
  myaddr, int addrlen)
• return 0 if OK, -1 on
  error
• int listen(int sockfd, int backlog)
• return 0 of OK, -1 on
  error
• int accept(int sockfd, struct sockaddr cliaddr,
  int addrlen)
• returns nonnegative
  descriptor if OK,-1 on error

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CLIENT
SERVER

• PURPOSE File Transfer
• Get a file
• Send a file

• Should inform the server if
• the required action is to get
• a file from the server
• to upload a file to the server.
• Should specify the name of the
• File.
• Respond to possible error messages.

• If a file is asked for, then it should
• send an error message if file doesnt exist.
• If file exists, send it.
• If file is being sent to you, save it.

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Transferring the data in and from the packet
structure

• Struct CONTROL_FRAME
• unsigned char direction //GET or PUT
• char fnameMAX //filename
• struct MESSAGE_FRAME
• unsigned char header //ERROR,DATA,LASTPACKET,
  etc.
• char dataMAX_SIZE //data or error message
• message_frame
• YOU ARE FREE TO DESIGN YOUR OWN STRUCTURES

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Reading from a file

• void main( void )
• FILE stream
• int numread, numwritten
• if( (stream fopen( "fread.out", "rb" )) !
  NULL )
• numread fread(message_frame.data,sizeof(char),
  MAX_SIZE, stream)
• else
• printf( "File could not be opened\n" )
• fclose( stream )
• Be careful if you use strcpy when reading from a
  binary file use memcpy.

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Writing in a file

• void main( void )
• FILE stream
• int numread, numwritten
• if( (stream fopen( "fread.out", "w" )) ! NULL
  )
• numwritten fwrite(szbuffer, sizeof(char),
  MAX_SIZE, stream )
• else
• printf( "Problem opening the file\n" )
• fclose( stream )

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Decrypting the header

• Use a switch to treat each of the cases
• switch (message_frame.header)   
• case 1        break   
• case 2        break   
• case 3        break
• default

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Hints

• Use a log file in each side in order to monitor
  all the actions
• receiving a packet
• sending a packet, etc.
• Open and close the log file after each read/write
  operation if your program freezes and you cannot
  read the log file.
• Do not use any string library function! You will
  be able to send only text files but not binary
  ones (jpeg or exe for example).
• Instead use memcpy for transferring data.
• Do not care about the order of the receiving
  packets in this assignment (TCP will do it for
  you).

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Assignment 1

• No GUI
• Use Visual C 6
• Groups of NOT more than 2
• wsock32.lib or you add the following command to
  your codepragma comment(lib,"wsock32.lib")
• Implement only whatever youre asked to do.

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Multi-thread in Windows

• uintptr_t _beginthread( void( __cdecl
  start_address )( void ), unsigned stack_size,
  void arglist )
• Parameters
• start_address
• Start address of routine that begins execution
  of new thread.
• stack_size
• Stack size for new thread or 0.
• arglist
• Argument list to be passed to new thread or
  NULL.

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The C Thread Class provided to you

• define STKSIZE 16536
• class Thread
• publicThread()
• virtual Thread()
• static void pthread_callback (void ptrThis)
• virtual void run () 0
• void start()
• void Threadpthread_callback (void ptrThis)
  
• if ( ptrThis NULL ) return NULL
• Thread ptr_this (Thread )(ptrThis)
• ptr_this-run()
• return NULL
• void Threadstart ()
• int result
• if(( result _beginthread((void ()(void
  ))Threadpthread_callback,STKSIZE,this ))

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How to make _beginthread work in VC6.00
Right click the project and go to the
Setting-C/C-Category. Change the Category to
Code Generation and change Use run-time library
to Multithreaded. NoteYou will encounter such
a error error C2065 '_beginthread' undeclared
identifier at the compile time if you dont do
the above setting.