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Manual Reference Pages  -  NET::UDP (3)

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Net::UDP - UDP sockets interface module



    use Net::Gen;               # optional
    use Net::Inet;              # optional
    use Net::UDP;


The Net::UDP module provides services for UDP communications over sockets. It is layered atop the Net::Inet and Net::Gen modules, which are part of the same distribution.

    Public Methods

The following methods are provided by the Net::UDP module itself, rather than just being inherited from Net::Inet or Net::Gen.
new Usage:

    $obj = new Net::UDP;
    $obj = new Net::UDP $desthost, $destservice;
    $obj = new Net::UDP \%parameters;
    $obj = new Net::UDP $desthost, $destservice, \%parameters;
    $obj = Net::UDP->new();
    $obj = Net::UDP->new($desthost);
    $obj = Net::UDP->new($desthost, $destservice);
    $obj = Net::UDP->new(\%parameters);
    $obj = Net::UDP->new($desthost, $destservice, \%parameters);

Returns a newly-initialised object of the given class. If called for a derived class, no validation of the supplied parameters will be performed. (This is so that the derived class can add the parameter validation it needs to the object before allowing the validation.) Otherwise, it will cause the parameters to be validated by calling its init method, which Net::UDP inherits from Net::Inet. In particular, this means that if both a host and a service are given, that an object will only be returned if a connect() call was successful.

The examples above show the indirect object syntax which many prefer, as well as the guaranteed-to-be-safe static method call. There are occasional problems with the indirect object syntax, which tend to be rather obscure when encountered. See for details.

PRINT Usage:

    $ok = $obj->PRINT(@args);
    $ok = print $tied_fh @args;

This method, intended to be used with tied filehandles, behaves like one of two inherited methods from the Net::Gen class, depending on the setting of the object parameter unbuffered_output. If that parameter is false (the default), then the normal print() builtin is used. If the unbuffered_output parameter is true, then each print() operation will actually result in a call to the send method, requiring that the object be connected or that its message is in response to its last normal recv() (with a flags parameter of 0). The value of the $\ variable is ignored in that case, but the $, variable is still used if the @args array has multiple elements.


    $line_or_datagram = $obj->READLINE;
    $line_or_datagram = <TIED_FH>;
    $line_or_datagram = readline(TIED_FH);
    @lines_or_datagrams = $obj->READLINE;
    @lines_or_datagrams = <TIED_FH>;
    @lines_or_datagrams = readline(TIED_FH);

This method, intended to be used with tied filehandles, behaves like one of two inherited methods from the Net::Gen class, depending on the setting of the object parameter unbuffered_input. If that parameter is false (the default), then this method does line-buffering of its input as defined by the current setting of the $/ variable. If the <unbuffered_input> parameter is true, then the input records will be exact recv() datagrams, disregarding the setting of the $/ variable. Note that invoking the READLINE method in list context is likely to hang, since UDP sockets typically don’t return EOF.

    Protected Methods


    Known Socket Options

There are no object parameters registered by the Net::UDP module itself.

    Known Object Parameters

The following object parameters are registered by the Net::UDP module (as distinct from being inherited from Net::Gen or Net::Inet):
unbuffered_input If true, the READLINE operation on tied filehandles will return each recv() buffer as though it were a single separate line, independently of the setting of the $/ variable. The default is false, which causes the READLINE interface to return lines split at boundaries as appropriate for $/. (The READLINE method for tied filehandles is the <FH> operation.) Note that calling the READLINE method in list context is likely to hang for UDP sockets.
unbuffered_output If true, the PRINT operation on tied filehandles will result in calls to the send() builtin rather than the print() builtin, as described in PRINT above. The default is false, which causes the PRINT method to use the print() builtin.
unbuffered_IO This object parameter’s value is unreliable on getparam or getparams method calls. It is provided as a handy way to set both the unbuffered_output and unbuffered_input object parameters to the same value at the same time during new calls.

    TIESCALAR support

Tieing of scalars to a UDP handle is supported by inheritance from the TIESCALAR method of Net::Gen. That method only succeeds if a call to a new method results in an object for which the isconnected method returns true, which is why it is mentioned in regard to this module.


    tie $x,Net::UDP,0,daytime or die "tie to Net::UDP: $!";
    $x = "\n"; $x = "\n";
    print $y if defined($y = $x);
    untie $x;

This is an expensive re-implementation of date on many machines.

Each assignment to the tied scalar is really a call to the put method (via the STORE method), and each read from the tied scalar is really a call to the READLINE method (via the FETCH method).

    TIEHANDLE support

As inherited from Net::Inet and Net::Gen, with the addition of unbuffered I/O options for the READLINE and PRINT methods.


    tie *FH,Net::UDP,{unbuffered_IO => 1, thisport => $n, thishost => 0}
        or die;
    while (<FH>) {
        last if is_shutdown_msg($_);
        print FH response($_);
    untie *FH;

This shows how to make a UDP-based filehandle return (and send) datagrams even when used in the usual perlish paradigm. For some applications, this can be helpful to avoid cluttering the message processing code with the details of handling datagrams. In particular, this example relies on the underlying support for replying to the last address in a recvfrom() for datagram sockets, thus hiding the details of tracking and using that information.




This module has been tested with threaded perls, and should be as thread-safe as perl itself. (As of 5.005_03 and 5.005_57, that’s not all that safe just yet.) It also works with interpreter-based threads (’ithreads’) in more recent perl releases.


Net::Inet(3), Net::Gen(3)


Spider Boardman <>
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perl v5.20.3 NET::UDP (3) 2016-03-17

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