- Recipe (steps)
for coding a
TCP client application
("client-side" programming):
- Create a
TCP socket
- You do not
need to bind
the socket:
- The client can use an arbitrary TCP port# to communicate with the server
- You do not
need to bind
the socket:
- Setup
a network address
(using astruct sockaddr_in
variable)
containing:
- The (IP address, TCP port#) of the server
- Establish
the TCP connection to
the server using:
connect ( s, server-Netw-addr, sizeof(struct sockaddr_in) );connect( ) will:
- Allocate the
send/receive buffer space for
the descriptor s in
the OS kernel
- Send the
TCP connection request
- Complete the TCP connection protocol (3-way handshake !!!)
Result of connect( ):
- Allocate the
send/receive buffer space for
the descriptor s in
the OS kernel
- Create a
TCP socket
- Syntax of the
connect() system call:
int connect(int s, struct sockaddr *server, length)
Input: s = an unbounded socket !!! server = a "struct sockaddr_in" structure containing the IP-address and the port# of the server length = must be equal to "sizieof(struct sockaddr_in)" Return value: 0 = success -1 = failed
- Effect:
- The
connect() system call
will establish a
reliable connection
between the client and
the server application given at
the Internet address
in server
- The server structure must contains the listen port of the server program
- The connect( ) function
will reserve an
unused TCP port in
the Operating System and
bind this
TCP port to the
descriptor entry s
- The state information (such as send sequence number and receive sequence number used in the reliable transfer protocol) of the TCP connection is stored in the socket descriptor table entry (and accessed through the socket variable s)
- The
connect() system call
will establish a
reliable connection
between the client and
the server application given at
the Internet address
in server
- Result:
- After the connect() call
is completed,
the client application can use
the socket variable s
to:
- send messages (= requests) to the server's data TCP port
- receive messages (= replies) from the server's data TCP port
- After the connect() call
is completed,
the client application can use
the socket variable s
to:
- Structure of
a TCP client application:
int s; // Socket variable struct sockaddr_in server; // Network addr for server /* --------------------------- Create TCP socket --------------------------- */ s = socket( AF_INET, SOCK_STREAM, 0 ); / Create a TCP socket /* ------------------------------------ Setup the server's Network Address ------------------------------------ */ server.sin_family = AF_INET; server.sin_addr.s_addr = htonl(SrvIP-address); server.sin_port = htons(SrvPortNumber); /* --------------------------------------------------------- Make a connection request to the server (The server must be in an accept() call to be successful) --------------------------------------------------------- */ if ( connect(s, server, sizeof(struct sockaddr_in) ) == 0 ) { perror("connect: "); exit(1); } // After this, the client can use the TCP socket s to communicate // (to the data TCP port) with server // // Use: read(s, ....) to get server's replies write(s, ....) to send data to server close(s) to disconnect