Have you ever wanted to test a connection to only one port, and found nmap overkill, and you like to do it in C?
\nNormally I’d recommend something like
\necho “~.” | telnet -r $H $X 2>&1| grep -i connected | wc -l | sed ‘s\/ \/\/g’`
\nBut, if the host doesn’t answer the default tcp\/ip timeout for a socket is 3 minutes!!!! You have to wait long
\ntime…
\nYou don’t want to wait too long for that, so you can use a program to test a socket connection, like socktest.c,
\nit tries to connect and if it can’t within 5 seconds it will bail out.
\nyou should compile with gcc, if using solaris “gcc -o socktest -lsocket -lnsl socktest.c” will suffice.
\nSo, for instance you want to test port 80 and port 44 in google.com:
\nbash-3.00$ .\/socktest google.com 80 ; echo $?
\nConnection to port successful
\nbash-3.00$ .\/socktest google.com 44 ; echo $?
\nERROR: Timeout or error() 4 – Interrupted system call
\n1
\nYou can get the exit code 0 as successful, 1 as not successful.
\nSource here:
\n#include <stdio.h>
\n#include <sys\/types.h>
\n#include <sys\/socket.h>
\n#include <netinet\/in.h>
\n#include <netdb.h>
\n#include <errno.h>
\n#include <sys\/fcntl.h>
\n\/\/—————————————–
\n\/\/ Roberto Dircio Palacios-Macedo
\n\/\/ socktest – program to test a connection
\n\/\/ to a host in a specific port
\n\/\/ usage – .\/socktest <host> <port>
\n\/\/—————————————–
\nvoid error(char *msg)
\n{
\nperror(msg);
\nexit(0);
\n}
\nint main(int argc, char *argv[])
\n80\/433
\n{
\nint res,valopt;
\nstruct timeval tv;
\nfd_set myset;
\nsocklen_t lon;
\nint soc, portno, n;
\nstruct sockaddr_in serv_addr;
\nstruct hostent *server;
\nchar buffer[256];
\nif (argc < 3) {
\nfprintf(stderr,”usage %s hostname portn”, argv[0]);
\nexit(1);
\n}
\nportno = atoi(argv[2]);
\nserver = gethostbyname(argv[1]);
\nsoc = socket(AF_INET, SOCK_STREAM, 0);
\nif (soc < 0) {
\nerror(“ERROR: opening socket”);
\nexit(1);
\n}
\nif (server == NULL) {
\nfprintf(stderr,”ERROR: no such hostn”);
\nexit(1);
\n}
\nbzero((char *) &serv_addr, sizeof(serv_addr));
\nserv_addr.sin_family = AF_INET;
\nbcopy((char *)server->h_addr,
\n(char *)&serv_addr.sin_addr.s_addr,
\nserver->h_length);
\nserv_addr.sin_port = htons(portno);
\nlong arg = fcntl(soc, F_GETFL, NULL);
\narg |= O_NONBLOCK;
\nfcntl(soc, F_SETFL, arg);
\nres=connect(soc, &serv_addr,sizeof(serv_addr));
\nif (res < 0) {
\nif (errno == EINPROGRESS) {
\ntv.tv_sec = 5;
\ntv.tv_usec = 0;
\nFD_ZERO(&myset);
\nFD_SET(soc, &myset);
\nif (select(soc+1, NULL, &myset, NULL, &tv) > 0) {
\nlon = sizeof(int);
\ngetsockopt(soc, SOL_SOCKET, SO_ERROR, (void*)(&valopt) , &lon);
\nif (valopt) {
\nfprintf(stderr, “ERROR: Error in connection() %d – %sn”, valopt, strerror(valopt) );
\nexit(1);
\n}
\n}
\nelse {
\nfprintf(stderr, “ERROR: Timeout or error() %d – %sn”, valopt, strerror(valopt) );
\nexit(1);
\n}
\n}
\n81\/433
\nelse {
\nfprintf(stderr, “ERROR: Error connecting %d – %sn”, errno, strerror(errno)) ;
\nexit(1);
\n}
\n}
\narg = fcntl(soc, F_GETFL, NULL);
\narg &= (~O_NONBLOCK) ;
\nfcntl(soc, F_SETFL, arg);
\nfprintf(stdout, “Connection to port successfuln”);
\nexit(0);
\n}
\nEnjoy!
\n82\/433<\/p>\n","protected":false},"excerpt":{"rendered":"
Have you ever wanted to test a connection to only one port, and found nmap overkill, and you like to do it in C? Normally I’d recommend something like echo “~.” | telnet -r $H $X 2>&1| grep -i connected | wc -l | sed ‘s\/ \/\/g’` But, if the host doesn’t answer the default […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-565","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"\/blog\/index.php\/wp-json\/wp\/v2\/posts\/565","targetHints":{"allow":["GET"]}}],"collection":[{"href":"\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=565"}],"version-history":[{"count":0,"href":"\/blog\/index.php\/wp-json\/wp\/v2\/posts\/565\/revisions"}],"wp:attachment":[{"href":"\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=565"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=565"},{"taxonomy":"post_tag","embeddable":true,"href":"\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=565"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}