mkaddr c code

There is another version of mkaddr.c subroutine which is using inet_addr. The problem with inet_addr(3) is that it returns the value INADDR_NONE when an address is invalid. When the IP address 255.255.255.255 is converted to a 32-bit value, its return value is identical to the constant INADDR_NONE. Consequently, it becomes impossible to distinguish between a bad input IP address, and the general broadcast address. Use of the inet_aton(3) function avoids this ambiguity. /* mkaddr.c * The mkaddr() Subroutine using inet_aton * Make a socket address: */ #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <errno.h> #include <ctype.h> #include <string.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> /* * Create an AF_INET Address: * * ARGUMENTS: * 1. addr Ptr to area * where address is * to be placed. * 2. addrlen Ptr to int that * will hold the final * address length. * 3. str_addr The input string * format hostname, and * port. * 4. protocol The input string * indicating the * protocol being used. * NULL implies tcp . * RETURNS: * 0 Success. * -1 Bad host part. * -2 Bad port part. * * NOTES: * * for the host portion of the * address implies INADDR_ANY. * * * for the port portion will * imply zero for the port (assign * a port number). * * EXAMPLES: * www.lwn.net:80 * localhost:telnet * *:21 * *:* * ftp.redhat.com:ftp * sunsite.unc.edu * sunsite.unc.edu:* */ int mkaddr(void *addr, int *addrlen, char *str_addr, char *protocol) { char *inp_addr = strdup(str_addr); char *host_part = strtok(inp_addr, ":" ); char *port_part = strtok(NULL, "\n" ); struct sockaddr_in *ap = (struct sockaddr_in *) addr; struct hostent *hp = NULL; struct servent *sp = NULL; char *cp; long lv; /* * Set input defaults: */ if ( !host_part ) { host_part = "*" ; } if ( !port_part ) { port_part = "*" ; } if ( !protocol ) { protocol = "tcp" ; } /* * Initialize the address structure: */ memset(ap,0,*addrlen); ap->sin_family = AF_INET; ap->sin_port = 0; ap->sin_addr.s_addr = INADDR_ANY; /* * Fill in the host address: */ if ( strcmp(host_part, "*" ) == 0 ) { ; /* Leave as INADDR_ANY */ } else if ( isdigit(*host_part) ) { /* * Numeric IP address: */ ap->sin_addr.s_addr = inet_addr(host_part); // if ( ap->sin_addr.s_addr == INADDR_NONE ) { if ( !inet_aton(host_part,&ap->sin_addr) ) { return -1; } } else { /* * Assume a hostname: */ hp = gethostbyname(host_part); if ( !hp ) { return -1; } if ( hp->h_addrtype != AF_INET ) { return -1; } ap->sin_addr = * (struct in_addr *) hp->h_addr_list[0]; } /* * Process an optional port #: */ if ( !strcmp(port_part, "*" ) ) { /* Leave as wild (zero) */ } else if ( isdigit(*port_part) ) { /* * Process numeric port #: */ lv = strtol(port_part,&cp,10); if ( cp != NULL && *cp ) { return -2; } if ( lv < 0L || lv >= 32768 ) { return -2; } ap->sin_port = htons( (short)lv); } else { /* * Lookup the service: */ sp = getservbyname( port_part, protocol); if ( !sp ) { return -2; } ap->sin_port = (short) sp->s_port; } /* * Return address length */ *addrlen = sizeof *ap; free(inp_addr); return 0; }

Here is the complete udp broadcast client-server application