// GetSSHEndpoint tries to determine how to connect to a particular host
// via SSH. GetSSHEndpoint first attempts to discover the endpoint via
// DNS SRV records of the form "_ssh._tcp.<hostname>". If found,
// GetSSHEndpoint will return the target host and port to connect to
// instead of the "bare" DNS hostname. If no SRV record is found, it
// will simply return the hostname and default SSH port (22).
func GetSSHEndpoint(hostname string) (target string, port uint16, err error) {
cname, srvAddrs, err := net.LookupSRV(serviceName, "tcp", hostname)
if err != nil {
if _, ok := err.(*net.DNSError); ok {
// DNS-related error. This is okay for now;
// we'll just fall back to trying the hostname
// as-is instead.
log.Verbosef("error: %v", err)
err = nil
} else {
// Non-DNS error. Probably want to stop now.
log.Fatal(err)
}
}
if len(srvAddrs) > 0 {
log.Verbosef("Found %d SRV record(s) for %v", len(srvAddrs), cname)
for i, r := range srvAddrs {
log.Verbosef("Record %d:\t%d %d %d %s", i, r.Priority, r.Weight, r.Port, r.Target)
}
// "The returned records are sorted by priority and randomized
// by weight within a priority", so return details for the first
// one in the list.
// The target DNS names are fully-specified with the root ("."),
// so trim that off.
target = strings.TrimRight(srvAddrs[0].Target, ".")
port = srvAddrs[0].Port
} else {
log.Verbosef("No SRV record found for %v", hostname)
target = hostname
port = defaultPort
}
// TODO: Extend this to return the entire list in priority-order
return
}
func main() {
if len(os.Args) < 2 {
usage()
os.Exit(1)
}
sshPath, err := exec.LookPath("ssh")
if err != nil {
log.Fatal("Could not find ssh!")
}
sshArgs, host, sshCommand := parseArgs(os.Args[1:])
targetHost, targetPort, err := GetSSHEndpoint(host)
if err != nil {
log.Fatal(err)
}
log.Verbosef("Target for %v is %v:%v", host, targetHost, targetPort)
args := []string{}
args = append(args, fmt.Sprintf("-p %d", targetPort))
args = append(args, sshArgs...)
args = append(args, targetHost)
args = append(args, sshCommand...)
log.Verbosef("command: %v %v", sshPath, strings.Join(args, " "))
cmd := exec.Command(sshPath, args...)
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
log.Verbosef("Connecting to %v:%v", targetHost, targetPort)
if err = cmd.Run(); err != nil {
if err, ok := err.(*exec.ExitError); !ok {
log.Fatal(err)
}
}
}