recvfrom example c code

/* dgramsrvr.c: * * a simple datagram server using the recvfrom function sample c code */ #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <errno.h> #include <string.h> #include <time.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> /* * This function reports the error and * exits back to the shell: */ static void displayError(const char *on_what) { fputs(strerror(errno),stderr); fputs(": ",stderr); fputs(on_what,stderr); fputc('\n',stderr); exit(1); } int main(int argc,char **argv) { int z; char *srvr_addr = NULL; struct sockaddr_in adr_inet; // AF_INET struct sockaddr_in adr_clnt; // AF_INET int len_inet; // length int s; // Socket char dgram[512]; // Recv buffer char dtfmt[512]; // Date/Time Result time_t td; // Current Time and Date struct tm tm; // Date time values /* * Use a server address from the command * line, if one has been provided. * Otherwise, this program will default * to using the arbitrary address * 127.0.0. */ if ( argc >= 2 ) { // Addr on cmdline: srvr_addr = argv[1]; } else { // Use default address: srvr_addr = "127.0.0.23"; } /* * Create a UDP socket to use: */ s = socket(AF_INET,SOCK_DGRAM,0); if ( s == -1 ) { displayError("socket()"); } /* * Create a socket address, for use * with bind(2): */ memset(&adr_inet,0,sizeof adr_inet); adr_inet.sin_family = AF_INET; adr_inet.sin_port = htons(9090); adr_inet.sin_addr.s_addr = inet_addr(srvr_addr); if ( adr_inet.sin_addr.s_addr == INADDR_NONE ) { displayError("bad address."); } len_inet = sizeof adr_inet; /* * Bind a address to our socket, so that * client programs can contact this * server: */ z = bind(s, (struct sockaddr *)&adr_inet, len_inet); if ( z == -1 ) { displayError("bind()"); } /* * Now wait for requests: */ for (;;) { /* * see the usage of recvfrom below. * watch the arguments of the function * Block until the program receives a * datagram at our address and port: */ len_inet = sizeof adr_clnt; z = recvfrom(s, // Socket dgram, // Receiving buffer sizeof dgram, // Max recv buf size 0, // Flags: no options (struct sockaddr *)&adr_clnt, // Addr &len_inet); // Addr len, in & out if ( z < 0 ) { displayError("recvfrom(2)"); } /* * Process the request: */ dgram[z] = 0; // null terminate if ( !strcasecmp(dgram,"QUIT") ) { break; // Quit server } /* * Get the current date and time: */ time(&td); // Get current time & date tm = *localtime(&td); // Get components /* * Format a new date and time string, * based upon the input format string: */ strftime(dtfmt, // Formatted result sizeof dtfmt,// Max result size dgram, // Input date/time format &tm); // Input date/time values /* * Send the formatted result back to the * client program: */ z = sendto(s, // Socket to send result dtfmt, // The datagram result to snd strlen(dtfmt), // The datagram lngth 0, // Flags: no options (struct sockaddr *)&adr_clnt,// addr len_inet); // Client address length if ( z < 0 ) { displayError("sendto(2)"); } } /* * Close the socket and exit: */ close(s); return 0; } /* * When we run this program our server will come in listen * state and is waiting to accept the client connection * [sgupta@rhel55x86 chap6]$ gcc dgramserver.c -o dgramserver [sgupta@rhel55x86 chap6]$ ./dgramserver 192.168.22.55 */
See the UDP datagram client from here for complete appication