udp broadcast server c

/* udp-broadcast-server.c: * udp broadcast server example * Example Stock Index Broadcast: */ #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> #ifndef TRUE #define TRUE 1 #define FALSE 0 #endif extern int mkaddr( void *addr, int *addrlen, char *str_addr, char *protocol); #define MAXQ 4 static struct { char *index; int start; int volit; int current; } quotes[] = { { "DJIA", 1030330, 375 }, { "NASDAQ", 276175, 125 }, { "S&P 500", 128331, 50 }, { "TSE 300", 689572, 75 }, }; /* * Initialize: */ static void initialize(void) { short x; time_t td; /* * Seed the random number generator: */ time(&td); srand((int)td); for ( x=0; x < MAXQ; ++x ) quotes[x].current = quotes[x].start; } /* * Randomly change one index quotation: */ static void gen_quote(void) { short x; /* Index */ short v; /* Volatility of index */ short h; /* Half of v */ short r; /* Random change */ x = rand() % MAXQ; v = quotes[x].volit; h = (v / 2) - 2; r = rand() % v; if ( r < h ) r = -r; quotes[x].current += r; } /* * 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) { short x; /* index of Stock Indexes */ double I0; /* Initial index value */ double I; /* Index value */ char bcbuf[512], *bp;/* Buffer and ptr */ int z; /* Status return code */ int s; /* Socket */ struct sockaddr_in adr_srvr;/* AF_INET */ int len_srvr; /* length */ struct sockaddr_in adr_bc; /* AF_INET */ int len_bc; /* length */ static int so_broadcast = TRUE; static char *sv_addr = "127.0.0.:*", *bc_addr = "127.255.255.2 9097"; /* * Form a server address: */ if ( argc > 2 ) /* Server address: */ sv_addr = argv[2]; if ( argc > 1 ) /* Broadcast address: */ bc_addr = argv[1]; /* * Form the server address: */ len_srvr = sizeof adr_srvr; z = mkaddr( &adr_srvr, /* Returned address */ &len_srvr, /* Returned length */ sv_addr, /* Input string addr */ "udp"); /* UDP protocol */ if ( z == -1 ) displayError("Bad server address"); /* * Form the broadcast address: */ len_bc = sizeof adr_bc; z = mkaddr( &adr_bc, /* Returned address */ &len_bc, /* Returned length */ bc_addr, /* Input string addr */ "udp"); /* UDP protocol */ if ( z == -1 ) displayError("Bad broadcast address"); /* * Create a UDP socket to use: */ s = socket(AF_INET,SOCK_DGRAM,0); if ( s == -1 ) displayError("socket()"); /* * Allow broadcasts: */ z = setsockopt(s, SOL_SOCKET, SO_BROADCAST, &so_broadcast, sizeof so_broadcast); if ( z == -1 ) displayError("setsockopt(SO_BROADCAST)"); /* * Bind an address to our socket, so that * client programs can listen to this * server: */ z = bind(s, (struct sockaddr *)&adr_srvr, len_srvr); if ( z == -1 ) displayError("bind()"); /* * Now start serving quotes: */ initialize(); for (;;) { /* * Update one quote in the list: */ gen_quote(); /* * Form a packet to send out: */ bp = bcbuf; for ( x=0; x<MAXQ; ++x ) { I0 = quotes[x].start / 100.0; I = quotes[x].current / 100.0; sprintf(bp, "%-7.7s %8.2f %+.2f\n", quotes[x].index, I, I - I0); bp += strlen(bp); } /* * Broadcast the updated info: */ z = sendto(s, bcbuf, strlen(bcbuf), 0, (struct sockaddr *)&adr_bc, len_bc); if ( z == -1 ) displayError("sendto()"); sleep(4); } return 0; }  

Here is the step by step code flow of the abover udp server: The server shown in Listing above is functionally divided into the following sections: 

1. The table of stock market indexes is declared in lines 27 to 39. Four indexes are defined with starting values and a crude form of volatility value, which is used for the simulation.  
2. The function initialize() in lines 44 to 58 is called once to initialize for the simulation.  
3. The function gen_quote() is called to randomly change the simulated value of a randomly selected stock market index (lines 63 to 77).  
4. The main() program, which forms the basis of the server, is contained within lines 92 to 222. 

The basic operation of this stock market server is as follows:

1. Default addresses are declared in lines 106 and 107. These are used when no command-line arguments are supplied. 
2. If two command-line arguments are supplied, then the server address takes the address from the second argument (line 114).
3. If one or more command-line arguments are supplied, then the broadcast argument is taken from argument one (line 118).
4. The server address is formed (lines 123 to 132).
5. The broadcast address is formed (lines 137 to 146).
6. A socket is created (lines 151 to 153). 
7. The SO_BROADCAST option is enabled on the socket (lines 158 to 165).
8. The server address is bound (lines 172 to 177). 
9. The stock market indices are initialized (line 182).
10. The server loop begins in line 184. 

Compiling the above server:

Take this version of mkaddr.c

[root@rhel54x64 socket]# gcc -c -D_GNU_SOURCE -Wall -Wreturn-type -g udp-broadcast-server.c

[root@rhel54x64 socket]# gcc -c -D_GNU_SOURCE -Wall -Wreturn-type -g mkaddr.c 

[root@rhel54x64 socket]# gcc -g udp-broadcast-server.o mkaddr.o -o udp-broadcast-server

Here is the complete udp broadcast client-server application