return value of recv() function in perl

Question

I have non blocking UDP socket in perl created this way ``` my $my_sock = IO::Socket::INET->new(LocalPort => $MY_PORT, Proto => 'udp', Blocking => '0') or die "socket: $@"; ``` The recv call is ``` my $retValue = $sock->recv($my_message, 64); ``` I need to know a) when there is no data left to read b) if there is data, how much data was read c) any error conditions Surprisingly, I didn't see any return value for recv in perldoc. When I tried it myself, recv returns undef in (a), for b it is an unprintable character This seems to be an elementary issue. However, I still cannot find the info on googling or on stack overflow.Thanks for any inputs

Accepted Answer

According to the perldoc, recv "returns the address of the sender if SOCKET's protocol supports this; returns an empty string otherwise. If there's an error, returns the undefined value."

If you are getting an undef, this means recv is encountering an error.

The error in your code is in the following line:

```
$retValue = $sock->recv($my_message, 64);
```

The function prototype for recv is:

```
recv SOCKET,SCALAR,LENGTH,FLAGS 
```

According to perldoc, recv "Attempts to receive LENGTH characters of data into variable SCALAR from the specified SOCKET filehandle. SCALAR will be grown or shrunk to the length actually read."

Try:

```
$retvalue = recv($sock, $my_message, 64)
```

This is where I got all the information: http://perldoc.perl.org/functions/recv.html

return value of recv() function in perl

Solution

Problem