Linux/Unix server and client socket programming entry instance (including source code download)

Preface

This section describes how to use basic Linux/Unix functions to compile a complete server and client example that can be run on Linux (UBUNTU) and Unix (FreeBSD, the functions of the client and server are as follows:

The client reads a row from the standard input and sends it to the server.

The server reads a row from the network and then outputs the row to the client.

The client receives a response from the server and outputs this line to the standard output.

Server

CodeAs follows:

# Include <unistd. h>
# Include <sys/types. h> /*  Basic System Data Types  */ 
# Include <sys/socket. h> /*  Basic socket Definitions  */ 
# Include <netinet/ In . H> /*  Sockaddr_in {} and other Internet defns  */ 
# Include <ARPA/inet. h> /*  INet (3) Functions  */ 

# Include <stdlib. h>
# Include <errno. h>
# Include <stdio. h>
# Include < String . H>

 # Define Maxline 1024
 //  Typedef struct sockaddr SA;  
  Void Handle ( Int Connfd );

 Int Main ( Int Argc, Char ** Argv)
{
 Int Listenfd, connfd;
 Int SERVERPORT = 6888 ;
Int Listenq = 1024 ;
Pid_t childpid;
 Char Buf [maxline];
Socklen_t socklen;

 Struct Sockaddr_in cliaddr, servaddr;
Socklen = Sizeof (Cliaddr );

Bzero (& servaddr, Sizeof (Servaddr ));
Servaddr. sin_family = af_inet;
Servaddr. sin_addr.s_addr = htonl (inaddr_any );
Servaddr. sin_port = htons (SERVERPORT );

Listenfd = socket (af_inet, sock_stream, 0 );
 If (Listenfd < 0 ){
Perror ( "  Socket Error  " );
 Return - 1 ;
}
 If (BIND (listenfd ,( Struct Sockaddr *) & servaddr, socklen) < 0 ){
Perror ( "  BIND error  " );
 Return - 1 ;
}
 If (Listen (listenfd, listenq) < 0 ){
Perror ( "  Listen Error  " );
Return - 1 ;
}
Printf ( "  Echo server startup, listen on port: % d \ n  " , SERVERPORT );
 For (;;){
Connfd = accept (listenfd ,( Struct Sockaddr *) & cliaddr, & socklen );
 If (Connfd < 0 ){
Perror ( " Accept Error  " );
 Continue ;
}

Sprintf (BUF, "  Accept form % s: % d \ n  " , Inet_ntoa (cliaddr. sin_addr), cliaddr. sin_port );
Printf (BUF, "" );
Childpid = fork ();
 If (Childpid = 0 ){ /* Child Process  */ 
Close (listenfd ); /*  Close listening socket  */ 
Handle (connfd ); /*  Process the request  */ 
Exit ( 0 );
} Else   If (Childpid> 0 ){
Close (connfd ); /*  Parent closes connected socket  */ 
} Else {
Perror ( "  Fork Error  " );
}
}
}


 Void Handle ( Int Connfd)
{
Size_t N;
 Char Buf [maxline];

 For (;;){
N = read (connfd, Buf, maxline );
 If (N < 0 ){
 If (Errno! = Eintr ){
Perror ( "  Read Error  " );
 Break ;
}
}
If (N = 0 ){
 //  Connfd is closed by Client  
 Close (connfd );
Printf ( "  Client exit \ n  " );
 Break ;
}
 //  Client exit  
         If (Strncmp ( "  Exit  " , Buf, 4 ) = 0 ){
Close (connfd );
Printf ( "  Client exit \ n  " );
 Break ;
}
Write (connfd, Buf, N ); // Write maybe fail, here don't process failed Error  
 }
}

 

Client

The Code is as follows:

# Include <unistd. h>
# Include <sys/types. h> /*  Basic System Data Types  */ 
# Include <sys/socket. h> /*  Basic socket Definitions  */ 
# Include <netinet/ In . H> /*  Sockaddr_in {} and other Internet defns  */ 
# Include <ARPA/inet. h> /*  INet (3) Functions  */ 
# Include <netdb. h> /*  Gethostbyname Function  */ 

# Include <stdlib. h>
# Include <errno. h>
# Include <stdio. h>
# Include <String . H>

 # Define Maxline 1024

 Void Handle ( Int Connfd );

 Int Main ( Int Argc, Char ** Argv)
{
 Char * Servinetaddr = "  127.0.0.1  " ;
Int Servport = 6888 ;
 Char Buf [maxline];
 Int Connfd;
 Struct Sockaddr_in servaddr;

 If (Argc = 2 ){
Servinetaddr = argv [ 1 ];
}
 If (Argc = 3 ){
Servinetaddr = argv [ 1 ];
Servport = atoi (argv [ 2 ]);
}
 If (Argc> 3 ){
Printf ( "  Usage: echoclient <IPaddress> <port> \ n  " );
 Return - 1 ;
}

Connfd = socket (af_inet, sock_stream, 0 );

Bzero (& servaddr, Sizeof (Servaddr ));
Servaddr. sin_family = af_inet;
Servaddr. sin_port = htons (servport );
Inet_ton (af_inet, servinetaddr, & servaddr. sin_addr );

 If (Connect (connfd ,( Struct Sockaddr *) & servaddr, Sizeof (Servaddr) < 0 ){
Perror ("  Connect Error  " );
 Return - 1 ;
}
Printf ( "  Welcome to echoclient \ n  " );
Handle (connfd ); /*  Do it all  */ 
Close (connfd );
Printf ( " Exit \ n  " );
Exit ( 0 );
}

 Void Handle ( Int Sockfd)
{
 Char Sendline [maxline], recvline [maxline];
 Int N;
 For (;;){
 If (Fgets (sendline, maxline, stdin) = NULL ){
Break ; //  Read EOF  
 }
 /*  
// You can also directly use system functions without caching without using the buffer stream of the standard library
If (read (stdin_fileno, sendline, maxline) = 0 ){
Break; // read EOF
}
  */ 

N = write (sockfd, sendline, strlen (sendline ));
N = read (sockfd, recvline, maxline );
 If (N = 0 ){
Printf ("  Echoclient: Server terminated prematurely \ n  " );
 Break ;
}
Write (stdout_fileno, recvline, N );
 //  If the standard library's cache stream output is used, problems may occur sometimes.
  //  Fputs (recvline, stdout );  
 }
}

 

Download and compile

Compile and start the server:

GCC echoserver. C-o echoserver
./Echoserver
 

Compile and start the client

 
GCC echoclient. C-o echoclient
./Echoclient