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AFS::Command::Base -- Base OO Class for AFS::Command::* API

AFS::Command::Base -- Base OO Class for AFS::Command::* API


NAME

AFS::Command::Base -- Base OO Class for AFS::Command::* API


SYNOPSIS

This module is NOT used directly by applications, but indirectly by the various command wrapper classes:


    use AFS::Command::VOS;

    use AFS::Command::BOS;

    use AFS::Command::PTS;

    use AFS::Command::FS;

All of these classes inherit from this base class, and the inherited methods are documented here.


DESCRIPTION

The AFS::Command suite provides an programmatic API to several of the key AFS command line utilities, namely: vos, bos, pts and fs. This module is <NOT> a replacement for the AFS::* modules, which are an XS interface to the lower level AFS C programming APIs.

This module attempts to fill a huge void in the APIs available for developing AFS systems management applications in perl. Norbert Gruener's AFS module implements wrapper classes for the various C programming APIs available for AFS, however most of the systems management for AFS is implemented in the command line utilities themselves, not in any of the C libraries. Far too much of the logic in vos, by far the most important utility, is in the application itself, not the underlying libraries. This makes it very difficult for an XS-only approach to support the vos functionality.

These classes take an entirely different approach, since they are simply wrappers around the command line executables themselves, and implemented entirely in pure perl (no XS code at all). This has some advantages and disadvantages, of course. The primary advantage is that we are not forced to re-implement the complex logic in the vos command using the low level primitive C API calls. The primary disadvantage is that we are tightly coupled with the format of the text output of each of these commands, but this is a problem space that perl excels in.

This document covers general programming with the API, and the details of the specific wrapper classes are documented separately (eg. AFS::Command::VOS).


CLASS METHODS

new

All of the AFS::Command subclasses use this inherited method as an object constructor. In its simplest usage, it can be called with no arguments, but there are several which control global behavior of the commands, simplifying subsequent coding a bit.

command
This key has the pathname to the command to be used for execution. By default, this is the simple command name ``vos'', ``bos'', etc, and the command will simply be found in your $PATH by exec().

If you want to run a specific version of vos not found in the $PATH, then for example:


   my $vos = AFS::Command::VOS->new

     (

      command           => "/ms/dist/openafs/PROJ/core/1.2.9/bin/vos",

     );

If the path given is invalid, then expect the API to implode on itself when it can't be found, or it isn't an AFS vos command.

localauth, noauth, encrypt
All of these arguments correspond to command line arguments common across the entire command line suite. Typically, if an application uses this flag once, it will be using it for all subsequent calls as well. Therefore, the state of these flags can be set globally by setting them when creating the command object.

    my $vos = AFS::Command::VOS->new

      (

       localauth        => 1,

       encrypt          => 1,

      );

NOTE: The encrypt option is only available in more recent versions of AFS, and may be unsupported by the underlying commands.

XXX: What should the default behavior be? Croak or carp? we can figure out dynamically if the command supports it, and have the constructor fail, or we can be lazy and let the first command fail.

quiet
The default behavior for the common -verbose flag is inverted. By default, all commands are run with the -verbose flag, in order to capture maximum diagnostics when an error occurs. Normally, the chatty output is all trapped by the API anyway, so there is no application visible noise, just more verbose errors.

There should be no need to disable verbosity, but for completeness, specifying 'quiet' will turn off the default verbose output.

setCarp

This class method configures the carp and/or croak subroutines used throughout the API. By default, the obviously sensible thing is done: the carp an croak subroutines exported by the Carp module are used. These normally print output to stderr, and this method provides a mechanism for trapping these errors and redirecting them elsewhere.

For example, stderr in a system daemon may be entirely ignored, and syslog may be a more appropriate destination. In this case, the setCarp method may be used to configure this, globally, for the entire API.


    AFS::Command->setCarp

      (

       carp => sub {

           my ($lines) = @_;

           foreach my $line ( split(/\n+/,$lines) ) {

               syslog('warning',$line);

           }

       },

       croak => sub {

           my ($lines) = @_;

           foreach my $line ( split(/\n+/,$lines) ) {

               syslog('error',$line);

           }

           die $lines; # If we're dying, whine at stderr, too.

       },

      );

This method takes a list of key/value pairs, with only two supported keys (anything else will be quietly ignored): carp an croak. The values are CODE references (anonymous subroutines, or references to existing subroutines). The carp CODE should not be fatal, however the croak CODE should. The API calls the croak method in very few places, but when it does, it assumes that call will be fatal, so if you provide a croak subroutine that doesn't die, the results will be unpredictable, and unsupportable.

This method returns true of false, depending on whether or not the carp and/or croak subroutines were properly configured. If the values are not CODE references, then this method will itself croak.


INSTANCE METHODS

errors

This method takes no arguments, and it returns a string, containing the unparsed errors from the last command method invoked. This string is reset with each subsequent command method invocation. The string is normally the output written to stderr by the process, but in the case of unparsed boolean commands, it contains both the stdout as well as the stderr output.


    my $result = $vos->examine

      (

       id               => $volname,

       cell             => $cell,

      );

    unless ( $result ) {

        die "Unable to examine volname '$volname' in cell '$cell':" .

          $vos->errors();

    }

supportsOperation

This class method allows the developer to test whether or not any given operation is supported by the underlying command line utility. For example, the ``vos changeloc'' operation is not supported in older release of vos.


    unless ( $vos->supportsOperation('changeloc') {

        die "Unable to continue -- 'vos changeloc' is unsupported.\n";

    }

The return value is simply true or false.

supportsArgument

Similar to supportsOperation, supportsArgument will test whether or not a given argument is a support command line argument for the specified operation. For example, the -encrypt argument is only supported in more recent versions of vos, so that support can be tested for easily.


    unless ( $vos->supportsArgument('listvldb','encrypt') ) {

        warn "Encryption is not support by your version of vos.\n";

    }

The return value is simply true or false.


SEE ALSO

AFS::Command::VOS(1), AFS::Command::BOS(1), AFS::Command::PTS(1), AFS::Command::FS(1), AFS::Command::Base(1), AFS::Command(1)

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