Checking if a port is listening

[Lucien via Digitalmars-d-learn]

On Wednesday, 16 March 2016 at 22:22:15 UTC, Anonymouse wrote:
> On Wednesday, 16 March 2016 at 20:44:12 UTC, Lucien wrote:
>> Hello,
>>
>> I want to know if a port of an ip address is listening, 
>> actually, I've this :
>> http://pastebin.com/pZhm0ujy
>> (checking port 22/ssh)
>>
>> It works, but it took me ~10min to scan 30 addresses.
>>
>> How can reduce the expiration delay ?
>
> I don't know if they apply here, but you can lower the send and 
> receive timeouts for the socket. I'm not sure which (or if 
> either) of them you want to tweak.
>
> https://dlang.org/library/std/socket/socket_option.html
>
>
> import core.thread;  // for .seconds
> s.setOption(SocketOptionLevel.SOCKET, SNDTIMEO, 10.seconds);
> s.setOption(SocketOptionLevel.SOCKET, RCVTIMEO, 10.seconds);
>
>
> I guess you could also use a non-blocking socket and decide 
> yourself when enough time has passed to declare it a failed 
> attempt.

When it's non-blocking, all adresses have the open 22 open, but 
it isn't the case..

When I setOption like you said, it's too long.

Is there a good technique ?
nmap can do it in only ~2 seconds.

My current code :
--------------------------------------------------------

import std.process;
import std.socket;

import core.time;

// ...

// 32 for the moment
for (int i = 1; i < 32; i++) {
     string ip = "192.168.0."~to!string(i);
     Socket s = new Socket(AddressFamily.INET, 
std.socket.SocketType.STREAM, ProtocolType.TCP);
     s.blocking = false;
     //s.setOption(SocketOptionLevel.SOCKET, 
SocketOption.SNDTIMEO, 1.seconds);
     //s.setOption(SocketOptionLevel.SOCKET, 
SocketOption.RCVTIMEO, 1.seconds);
     InternetAddress ia = new InternetAddress(ip, 22);
     try {
         s.connect(ia);
         writeln("\nDONE: ", ip, ":22");
     } catch (Exception e) {
         writeln("\n\nFAIL: ", ip, ":22 is unreachable :\n", 
e.toString(), "\n");
     }
     s.close();
}

// ...

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