Assignment 4: Client Server Chatroom

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Assignment 4 Client Server Chatroom
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SOCKET

• socket creates an endpoint for communication.
• Two useful headers for socket programming
• include ltsignal.hgt
• include ltsys/socket.hgt

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• Server Side Implementation

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Data Stuctures

• Client structure
• members clientName
• clientId // 0 initially
• sockaddr_in self AF_INET,htons(SERVER_PORT)
• In the Internet address family, the SOCKADDR_IN
  structure is used by Windows Sockets to specify a
  local or remote endpoint address to which to
  connect a socket.
• struct sigaction instance used to set interrupt
  action
• Thread for clients

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Create New Socket

• socket() - creates an unbound socket in a
  communications domain, and return a file
  descriptor that can be used in later function
  calls that operate on sockets.
• socket(int domain, int type, int protocol)
• domain - communications domain in which a socket
  is to be created.
• type - type of socket to be created.
• protocol - particular protocol to be used with
  the socket.
• Protocol 0 gt use an unspecified default
  protocol appropriate for the requested socket
  type.
• Example
• soc socket(AF_INET, SOCK_STREAM, 0)

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bind socket

• bind() - bind a name to a socket
• int bind(int socket, const struct sockaddr
  address,       socklen_t address_len)
• socket -file descriptor of the socket to be
  bound. address -points to a sockaddr structure
  containing the address to be bound to the socket.
  
• address_len - length of the sockaddr structure
  pointed to by the address argument.
• Example
• Bind(soc, (sockaddr)self, sizeof(self))

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listen for new connections

• listen() - listen for socket connections and
  limit the queue of incoming connections.
• int listen(int socket, int backlog)
• Backlog provides a hint to the implementation
  which the implementation shall use to limit the
  number of outstanding connections in the socket's
  listen queue.
• Example
• listen(soc, 1)

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Accept a new connection

• accept() - accepts a new connection on a socket
• int accept(int socket, struct sockaddr restrict
  address, socklen_t restrict address_len)
• Address - Either a null pointer, or a pointer to
  a sockaddr structure where the address of the
  connecting socket shall be returned
• address_len - Points to a socklen_t structure
  which on input specifies the length of the
  supplied sockaddr structure, and on output
  specifies the length of the stored address.
• var accept(soc, (sockaddr)peer,
  (socklen_t)peerlen)

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create new threads for each connection

• Each client is handled using a seperate thread.
• pthread_create(myThread, NULL, ClientHandler,
  var)

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Error Control

• bind
• accept
• listen
• thread create
• read and write operations
• etc..

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set interrupt action

• If the SA_SIGINFO flag is cleared in the
  sa_flags field of the sigaction structure, the
  sa_handler field identifies the action to be
  associated with the specified signal.
• sa_sigaction Pointer to a signal-catching
  function.
• int sigaction(int signum, const struct sigaction
  act, struct sigaction oldact)
• The sigaction system call is used to change the
  action taken by a process on receipt of a
  specific signal.
• signum specifies the signal and can be any valid
  signal except SIGKILL and SIGSTOP.
• If act is non-null, the new action for signal
  signum is installed from act.
• If oldact is non-null, the previous action is
  saved in oldact.

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Example

• Struct sigaction act
• act.sa_flags SA_SIGINFO
• act.sa_sigaction SigHandler
• sigaction(SIGINT, act, NULL)

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Ctrl-C signal handler

• SigHandler(int sig, siginfo_t si, void b)
• Print message in server that it is shutting down
• strcat to write buffer the message that server
  is shutting down and call the function to write
  all clients using this buffer
• sleep for 10 sec
• exit

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Writing to all clients

• allClientwrite()
• Mutex lock the thread for client
• For all clients except thisClient and clientId0
• Write the message stored in write buffer
• Unlock mutex
• End

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ClientHandler

• Declare arrays as read buffer, write buffer,
  thisName
• Mutex lock on client thread
• Set client IDs from 1 to n
• Unlock mutex
• Write to the client using write buffer a welcome
  message
• Eg strncpy(writeBuf, "Welcome ", 8)

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• Print to all clients that thisClient has entered
  the room
• The data that clients send is stored in read
  buffer
• Print read buffer data to all clients except
  thisClient
• If readbuffer data is special messages like
  /exit etc
• then print goodbye message to all clients
• make clientId0
• Exit
• However, make sure you implement all the special
  exit messages mentioned in the assignment
  (/exit,/part,/quit)

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Client Side Implementation
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Data Stuctures functions

• struct sockaddr_in peer AF_INET,
  htons(SERVER_PORT)
• Buffer an array used for writing data
• void EchoHandler(void soc) thread handler
  function
• struct sigaction act - used to set interrupt
  action
• void siginthandler(int signum) if ctrl-c is
  pressed for client, it wont let it exit, rather
  print message asking to type /exit or /part
  etc..

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Connect the client to the server

• Prompt to enter the hostname to which user wants
  to connect.
• Use gethostbyname to save the hostname
• gethostbyname() is used to get its IP address
  and store it in a struct in_addr
• Takes a string (like www.yahoo.com or
  rc01xcs213.managed.mst.edu) as parameter.
• Print an error message if return value is NULL
  (unable to connect)
• Input the clients name

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Call signal()

• The signal() function chooses one of three ways
  in which receipt of the signal number sig is to
  be subsequently handled.
• void (signal(int sig, void (func)(int)))(int)
  
• If the value of func is SIG_DFL, default
  handling for that signal will occur. If the value
  of func is SIG_IGN, the signal will be ignored.
  Otherwise, func must point to a function to be
  called when that signal occurs. Such a function
  is called a signal handler.
• signal(SIGINT, siginthandler)
• siginthandler deals with ctrl-c. On pressing
  ctrl-c on a client, it should prompt a message
  instead of exiting.

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Copy the host address into peer socket

• The bcopy() function shall copy n bytes from the
  area pointed to by s1 to the area pointed to by
  s2.
• bcopy(hp-gth_addr_list0, (char)peer.sin_addr,
  hp-gth_length)
• Where host is saved by gethostname in hp.

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create a socket and connect to server

• socket() function to create a client socket
• Connect() to connect to the server
• int connect(int socket, const struct sockaddr
  address,       socklen_t address_len)
• socket Specifies the file descriptor associated
  with the socket. address Points to a sockaddr
  structure containing the peer address. The length
  and format of the address depend on the address
  family of the socket. address_len Specifies the
  length of the sockaddr structure pointed to by
  the address argument.
• Error control

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Thread for Client

• Create threads to handle read and write the
  client
• The thread handler function will take care of
  different errors and special messages to be
  printed.
• Example
• pthread_create(myThread, NULL, EchoHandler,
  socket)

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Operations of a Client

• write
• write(soc, buffer, strlen(buffer))
• read -
• read(soc, buffer, strlen(buffer))
• In case it is writing /exit etc, sleep for
  sometime and exit
• Ctrl-C handler
• Print an error message, but dont exit client on
  Ctrl-C

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Other Functions

• Read buffer and check for different quitting
  conditions
• If the server shutting down message is read from
  buffer, print server is shutting and exit
• If the client wants to quit, print goodbye
  message and exit

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THANKS ?