Checking if a port is listening

[Lucien via Digitalmars-d-learn]

On Saturday, 19 March 2016 at 18:24:38 UTC, Marc Schütz wrote:
> On Saturday, 19 March 2016 at 09:55:13 UTC, Lucien wrote:
>>     const int MAX = 64;
>>     Socket[] sockets = new Socket[MAX];
>>     string ipb = "192.168.0.";
>>
>>     for (int i = 1; i < MAX; i++) {
>
> Here's the reason for your SEGV: You need to start at 0, 
> because otherwise `sockets[0]` is `null`. When you add that to 
> the SocketSet, it will trigger the segfault. I guess you want 
> to skip the 0 because it represents the subnet address; in that 
> case, you simply mustn't add `sockets[0]` to the set.
>
> But then there is another problems: You're using `select()` the 
> wrong way. The point of using select() is that you can check 
> things asynchronously. Your code should be structured like this 
> (pseudo code):
>
> auto ss = new SocketSet();
> for(i; 1 .. MAX) {
>     auto s = new Socket(...);
>     s.blocking = false;
>     s.connect(...);
>     ss.add(s);
> }
>
> while(ss.count > 0) {
>     auto write_ss = ss.dup;
>     auto status = Socket.select(null /* read */, write_ss /* 
> write */, null /* error */, 500.msecs);
>     // for a connect()ing socket, writeability means connected
>     if(status < 0)
>         writeln("interrupted, retrying");
>     else if(status == 0)
>         writeln("timeout, retrying");
>     else {
>         writeln(status, " socket(s) changed state");
>         for(fd; 0 .. write_ss.maxfd+1) {
>             // check whether this socket has changed
>             if(!write_ss.isSet(fd)) continue;
>             // if yes, remove it from the original SocketSet
>             ss.remove(fd);
>             writeln("successfully connected to 192.168.0.", 
> fd+1);
>         }
>     }
> }

thanks, but what's the type of fd ?

current code:
--------------------------------
const int MAX = 64;
// usefull ?
Socket[] sockets = new Socket[MAX];
string ipb = "192.168.0.";
SocketSet ss = new SocketSet();

for (int i = 0; i < MAX; i++) {
     string ip = ipb~to!string(i+1);

     Socket s = new Socket(AddressFamily.INET, 
std.socket.SocketType.STREAM, ProtocolType.TCP);
     s.blocking = false;
     InternetAddress ia = new InternetAddress(ip, 22);
     sockets[i] = s;
     s.connect(ia);
     ss.add(s);
}

while (ss.max > 0)
{
     SocketSet write_ss = ss;
     auto status = Socket.select(null, write_ss, null, 50.msecs);
     // for a connect()ing socket, writeability means connected
     if(status < 0)
         writeln("interrupted, retrying");
     else if(status == 0)
         writeln("timeout, retrying");
     else {
         writeln(status, " socket(s) changed state");
         for (int i = 0; i < write_ss.tupleof[1]; i++) {
             // tried to do something
             //Socket fd = write_ss.tupleof[0][i];
             string ip = ipb~to!string(i+1);
             if(!write_ss.isSet(fd))
                 continue;
             ss.remove(fd);
             writeln("successfully connected to ", ip);
         }
     }
}

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