 [semidet]tcp_getopt(+Socket, 
?Option)Get information about Socket. Defined properties are below. 
Requesting an unknown option results in a
[semidet]tcp_getopt(+Socket, 
?Option)Get information about Socket. Defined properties are below. 
Requesting an unknown option results in a domain_error 
exception.
- file_no(-File)
- Get the OS file handle as an integer. This may be used for debugging and 
integration.