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hostalive.c
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hostalive.c
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#include <stdlib.h>
#include <stdio.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <netdb.h>
#include <sys/socket.h>
#include <unistd.h>
int main (int argc, const char *argv[]) {
int socketid;
struct sockaddr_in server_address;
struct hostent* hostinfo;
const char *hostname;
int port_number;
int tries=10; // number of tries to connect
int timeout=5; // connecting timeout in seconds
int sleep_seconds=30; // sleep before retry
fd_set fdset; // file descritor set for monitoring the socket
struct timeval tv; // time out struct
//TODO: validate arguments
//TODO: get executable name for usage information
//TODO: configurable timeout
//TODO: configurable tries
//TODO: configurable sleep
if (argc != 3){
fprintf(stderr,"Usage: <hostname> <port>\n");
return 1;
}else {
hostname = argv[1];
port_number = strtol(argv[2],(char **)NULL,10);
}
server_address.sin_family = AF_INET;
printf("Resolving %s ...\n",hostname);
hostinfo = gethostbyname (hostname);
if (hostinfo == NULL){
fprintf(stderr,"Could not resolve IP address for %s\n",hostname);
return 1;
}else {
server_address.sin_addr = *((struct in_addr *) hostinfo->h_addr);
}
server_address.sin_port = htons(port_number);
while(tries--){
socketid = socket(PF_INET,SOCK_STREAM,0);
// setting socket to non-blocking so I can control the timeout
fcntl(socketid, F_SETFL, O_NONBLOCK);
if (socketid != -1){
printf("Trying to connect...\n");
connect(socketid,(struct sockaddr *)&server_address,sizeof(struct sockaddr_in));
FD_ZERO(&fdset); // clear set
FD_SET(socketid, &fdset); // assign set to socket
tv.tv_sec = timeout; // prepare timeout struct for select
tv.tv_usec = 0;
// monitoring socket state with select usint the file descriptor set and timeout
if (select(socketid + 1, NULL, &fdset, NULL, &tv) == 1)
{
// something happend to socket
int socket_error;
socklen_t len = sizeof socket_error;
// getting socket state
getsockopt(socketid, SOL_SOCKET, SO_ERROR, &socket_error, &len);
if (socket_error == 0) {
printf("Connected.\n");
close(socketid);
//TODO: run something
return 0;
}else {
perror("Connect");
}
}
else {
printf("Timeout... Sleeping %d seconds... \n",sleep_seconds);
sleep(sleep_seconds);
}
}else {
fprintf(stderr,"Could not create socket...\n");
return -1;
}
}
return 0;
}