Have a look at the post_accept() routine in Server.pm in the module Net::Server. You might even find Net::Server is exactly what you are looking for (as it has all the code for creating a daemon, and then switching the socket to STDIN/STDOUT before handing it to your callback function).

Something along the lines of:

      if( defined $fileno ){
          open STDIN,  "<&$fileno" 
              or die "Couldn't open STDIN to the client socket: $!";
          open STDOUT, ">&$fileno"
              or die "Couldn't open STDOUT to the client socket: $!";
      } else {
          *STDIN= \*{ $sock };
          *STDOUT= \*{ $sock };
      }
      STDIN->autoflush(1);
      STDOUT->autoflush(1);
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(untested).