Naming a Socket

1
Naming a Socket

• Recall network sketch
• Open a socket.
• Name the socket
• Associate with another socket.
• Send messages between sockets.
• Close socket.
• Requires declaring and filling in socket address
  variable
• struct sockaddr_in

2

• struct sockaddr_in sa
• sa.sin_family AF_INET
• sa.sin_port htons (3000)
• sa.sin_addr.s_addr inet_addr (32.33.14.55 )

3
Completing the Naming with bind()

• Requires sockaddr_in and unbound socket.
• SOCKET sock
• sock socket(AF_INET, SOCK_STREAM, 0)
• int ret_val bind(sock, (struct sock_addr )
  sa, sizeof(sa))
• Now sock is bound to the IP Address, Port Number
  and protocol declared within the sockaddr_in
  structure.
• In client/server computing, the client does not
  have to bind its socket.

4
Step3 Associate with another socket.

• Client and sever set up the association in
  different ways.
• Client
• Fill in a struct sockaddr_in structure with IP
  Address and Port of the server.
• Call connect() function with open socket (bound
  or unbound) and address of server.
• Once return from connect() function, the TCP
  connection has been established.
• Can send/receive messages.

5
Step3 Associate with another socket.

• Server
• Name a socket and bind it to IP address and port
  number of service.
• Call the listen() function to listen for
  connection requests.
• Once detect request, call accept() function to
  complete the connection.

6
Client Actions

• SOCKET sock
• struct sockaddr_in sa // Fill in with local
  IP, port
• sock socket(AF_INET, SOCK_STREAM, 0)
• Success Returns socket descriptor.
• Fail Returns INVALID_SOCKET
• int ret_val bind(sock, (struct sock_addr )
  sa, sizeof(sa))
• Success Returns 0
• Fail Returns SOCKET_ERROR.

7
Prepare to Connect

• Fill in sockaddr_in structure with IP address and
  port number of server.
• sa.sin_family AF_INET
• sa.sin_port htons (Server_Port)
• sa.sin_addr.s_addr inet_addr(xxx.xxx.xx.XX)
• int ret_val connect(sock, (struct sock_addr )
  sa, sizeof(sa))
• Success Returns 0
• Fail Returns SOCKET_ERROR

8

• Connect will fail if the server is not in the
  listening state and accepts the connection.
• On success, the client has established a virtual
  TCP connection on which it can send and receive
  data reliably.

9
Server

• 1) Declare two sockets and one struct
  sockaddr_in
• SOCKET l_sock, a_sock
• struct sockaddr_in sa
• 2) Name one of the sockets (fill in sa with local
  information and call bind with one. Assume
  l_sock)
• 3) ret_val listen(l_sock, 1) // 1 is wait
  queue length
• Success Returns 0
• Fail Returns SOCKET_ERROR

10
Server

• a_sock accept( l_sock, (struct sock_addr )
  sa, sizeof (sa))
• Success Returns valid socket (a_sock in this
  case)
• Fail Returns INVALID_SOCKET
• sa filled in by OS with name of connected socket.
• Use a_sock to send and receive messages.
• l_sock still listening for more connection
  requests.

11
Sending/Receiving Messages

• Must use a connected socket.
• char buf1024
• ret_val send(a_sock, buf, 1024, 0)
• on success returns the actual number of bytes
  sent.
• if fails returns SOCKET_ERROR.
• Note May not send all data requested.

12
Receive

• Must use a connected socket.
• char buf1024
• int ret_val recv(a_sock, buf, 1024, 0)
• Success Returns number of bytes actually
  received
• Fail Returns SOCKET_ERROR
• NOTE May not return all requested data.

13

• int done 0
• int bytes_received 0
• while (!done)
• bytes_received recv(a_sock, buf
  bytes_received,
• 1024 - bytes_received, 0)
• if (bytes_received 1024)
• done 1

14
Synchronous Communication Calls

• recv() is a synchronous communications call.
• Application will block until there is some data
  available on the socket.