C client socket program timesout - c

Question

I have a very simple socket client program that I want to use to ping my mail server (as an example) to make sure it's alive and responding. I am using the following code to connect:
portno=25;
sockfd=socket(AF_INET,SOCK_STREAM,0);
if (sockfd<0) error("Cannot open socket");
server=gethostbyname(argv[2]);
if (server==NULL) {
printf("Error: No such host exists\n");
exit(3);
}
bzero((char*)&srvr,sizeof(srvr));
srvr.sin_family=AF_INET;
bcopy((char*)&server->h_addr,(char*)&srvr.sin_addr.s_addr,server->h_length);
srvr.sin_port=htons(portno);
if (connect(sockfd,(struct sockaddr*)&srvr,sizeof(srvr)) <0) error("Error connecting");
I pass the server name (as localhost) on the command line as the second parameter. It always hangs in the connect call. I have tried to also connect to one of google's mail servers with the same result.
I am able to telnet into port 25 on both my local server and the google server and issue the HELO command and get a response. I am running the program as root.
I am unsure how to proceed further in order to determine the problem. Any help would be appreciated.

Answer 1

The code is apparently not complete. You might want to make a couple of debug messaging including a check for the correct input to gethostbyname().
You should normally use IPPROTO_TCP as protocol, instead of 0.
sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)
You might want to use a tool like strace to see more details about how the system calls went on.
It's usually better to use getaddrinfo().
const char *node = "www.fedoraproject.org";
const char *service = "http";
struct addrinfo hints = {
.ai_family = AF_UNSPEC,
.ai_socktype = SOCK_STREAM,
.ai_protocol = IPPROTO_TCP,
.ai_flags = AI_ADDRCONFIG,
.ai_canonname = NULL,
.ai_addr = NULL,
.ai_next = NULL
};
struct addrinfo *result;
int error;
error = getaddrinfo(node, service, &hints, &result);
struct addrinfo *item;
int sock;
for (item = result; item; item = item->ai_next) {
sock = socket(item->ai_family, item->ai_socktype, item->ai_protocol);
if (sock == -1)
continue;
if (connect(sock, item->ai_addr, item->ai_addrlen) != -1) {
fprintf(stderr, "Connected successfully.");
break;
}
close(sock);
}
freeaddrinfo(result);
See: https://fedoraproject.org/wiki/Networking/NameResolution#Connecting_to_services_using_getaddrinfo.28.29