Net::Spooler - A Perl extension for writing spooling daemons


  # Create a subclass of Net::Spooler
  use Net::Spooler;
  package MySpooler;
  @MySpooler::ISA = qw(Net::Spooler);

  # Inherit everything, except a single method:
  sub ProcessFile {
    my $self = shift; my $file = shift;

    # Try to process the file here

    # Raise an exception, if something went wrong:
    die "Failed: $!" unless Something();

    # Return to indicate sucess.

  # Create and run the spooler
  package main;
  my $spooler = Net::Spooler->new(
      'spool-dir' => '/var/myspooler'


This package contains a spooling daemon, in other words a process, that accepts files from an outside source (currently a Unix or TCP/IP socket), stores them in a spooling directory and processes them.

The package is implemented as an abstract base class: It is not usefull in itself, but you can get your spooling daemon easily by deriving a concrete subclass from Net::Spooler. In the best case you can inherit everything and overwrite just a single method, the ProcessFile method, which attempts to process a single file from the spooling directory.

Net::Spooler is in turn derived from the Net::Daemon package, thus it borrows class design, in particular methods and attributes, from Net::Daemon. See Net::Daemon for details on this superclass.

However, there are a few additions to Net::Daemon:


Like in Net::Daemon, attributes can be set via the command line, in the config file or as constructor arguments (order descending from most important). And remember, that you can use the Net::Daemon attributes too! See Net::Daemon.

admin (--admin=<email>)

The administrators email address. From time to time it may happen, that the admin receives an email in case of problems.

expiretime (--expiretime=<time>)

If processing a file fails repeatedly, the file may finally expire. This means that the file will be removed from the spool directory and a message is sent to the administrator.

The default value are 432000 seconds (5 days). A value of 0 means that expiration never happens.

Example: Expire after 3 days.

maxsixe (--maxsize=<maxsize>)

By default the maximum size of a file is restricted to 100000 bytes and larger files will be rejected. This option is changing the size, a value of 0 means disabling the limitation.

Example: Disable max size

processtimeout (--processtimeout=<timeout>)

If processing a single file may result in an endless loop, or simply run too long, then you may specify a timeout. The daemon will raise a signal after the given amount of seconds and stop processing the file, as if the method ProcessFile raised an exception.

The default value is 0 seconds which means that no timeout is used.

Example: Use a timeout of 30 seconds.

loop-timeout (--loop-timeout=<time>)

If processing a file failed, the spooler will reprocess the file later by forking a child process after the given amount of seconds, by default 300 seconds (5 minutes). This child process will run through all scheduled file

spool-dir (--spool-dir=<dir>)

If the daemon accepts files, they are stored in the spool directory. There's no default, you must set this attribute.

Example: Use /var/myspooler as a spool directory.


This attribute is for internal use only. It contains an hash ref, the keys being temporary file names to be removed later.


As already said, the Net::Spooler package inherits from Net::Daemon. All methods of the superclass are still valid in Net::Spooler, in particular access control and the like. See Net::Daemon for details.

Processing a file

(Instance method) Called for processing a single file. This is typically the only method you have to overwrite.

The method raises an exception in case of errors. If an exception is raised, the scheduler will later retry to process the file until it expires. See the queuetime and expiretime attributes above.

If processing a file exceeds the processtimeout (see above), then the scheduler will cancel processing the method and continue as if it raised an exception. (This timeout can be disabled by setting it to 0, the default value.)

If the method returns without raising an exception, then the scheduler assumes that the file was processed successfully and remove it from the spool directory.

Choosing file names
  my $sfile = $self->SequenceFile();
  my $seq = $self->Sequence($sfile);
  my $dfile = $self->DataFile($seq);
  my $cfile = $self->ControlFile($seq);

(Instance methods) If the daemon receives a new file, it has to choose a name for it. These names are constructed as follows:

First of all, a so-called sequence number is generated by calling the method Sequence. By default these are the numbers 1, 2, 3, ... in 8 hex digits (00000001, 00000002, 00000003, ...). The last generated sequence number is always stored in the sequence file (by default $spool-dir/.sequence, set by calling the SequenceFile method).

Two files are generated for processing the file: The data file is the unmodified file, as received by the client. The control file contains information used internally by Net::Spooler, for example the time and date of spooling this file. By default the names $spool-dir/$seq.dat and $spool-dir/$seq.ctl are used, generated by calling the methods DataFile and ControlFile. Temporary file names are derived by adding the suffix .tmp.

Typically you rarely need to overwrite these methods.

Accepting a file from the client
  $self->ReadFile($socket, $fh, $file, $control);

(Instance method) This method is actually reading the file $file from the socket $socket. The file is already opened and the method must use the file handle $fh for writing into $file. (The file name is passed for creating error messages only.)

The method may store arbitrary data in the hash ref $control: This hash ref is stored in the control file later.

The default implementation is accepting a raw file on the socket. You should overwrite the method, if you are accepting structured data, for example 4 bytes of file size and then the raw file. However, if you do overwrite this method, you should consider the maxsize attribute. (See above.)

A Perl exception is raised in case of problems.

Creating the control file
  $self->ControlFile($fh, $file, $control);

(Instance method) Creates the control file $file by writing the hash ref $control into the open file handle $fh. (The file name $file is passed for use in error messages only.)

The default implementation is using the Data::Dumper module for serialization of $control and then writing the dumped hash ref into $fh.

A Perl exception is raised in case of problems; nothing is returned otherwise.

Reading the control file
  my $ctrl = $self->ReadControlFile($file);

(Instance method) This method reads a control file, as created by the ControlFile method and creates an instance of Net::Spooler::Control.

The default implementation does a simple require (in a Safe compartment for security reasons, see the Safe package for details) for loading the hash ref from the file. The hash ref is then blessed into the package corresponding to $self: The package name of $self is taken by appending the string ::Control.

The method returns nothing, a Perl exception is thrown in case of trouble.


This package is

  Copyright (C) 1999            Jochen Wiedmann
                                Am Eisteich 9
                                72555 Metzingen


  All rights reserved.

You may distribute under the terms of either the GNU General Public License or the Artistic License, as specified in the Perl README file.



3 POD Errors

The following errors were encountered while parsing the POD:

Around line 130:

Unterminated B<...> sequence

Around line 358:

'=item' outside of any '=over'

Around line 684:

You forgot a '=back' before '=head1'