File-INC/INC.pm

=head1 NAME

File::INC - find files via @INC

=head1 SYNOPSIS

   use File::INC;

=head1 DESCRIPTION

Perl has two almost identical facilities to load "library"
files: C<require> and C<do> (C<use> is basically a compile-time
C<require>).

These search C<@INC> for the file and compile it.

Unfortunately, sometimes you want to locate data (or even source) files
using the same mechanism. The problem is that Perl I<laways> evaluates the
files as Perl code, which is not something you want for data files.

This module implements the same (hopefully :) C<@INC> walk code as perl,
and gives you access to the resulting files, without evaluating them.

=head2 ALTERNATIVES

There are alternatives to this module, both of which I regularly employ,
but they come with their own drawbacks:

=over 4

=item Walking C<@INC> manually and treating it as an array of directories.

Basically, this:

   sub find_rcfile($) {
      my $path;

      for (@RC_PATH, "") {
         $path = "$RC_BASE/$_/$_[0]";
         return $path if -e $path;
      }

      die "FATAL: can't find required file \"$_[0]\" in \"$RC_BASE\"\n";
   }

   my $path = find_rcfile "My/Module/datafile.dat";

This is simple, but fails for any entries in C<@INC> that are not
directories. Not handling these makes it fail in many environments, such
as in L<App::Staticperl> or L<PAR::Packer>.

This module basically implements a full-featured version of this that
hopefully gets everything right.

=item Embed datafiles using C<do>.

You can embed datafiles by, say, uuencoding them and putting them into
a F<.pm> file (I think L<PAR::Packer>) does this. This is extremely
wasteful, but at least works around the C<@INC> problematic. A slightly
better way is to use C<do>. Take this file, put as F<My/Module/data.pl>
into the perl library:

   <<EOF
   text data...
   EOF

Then you can load the "text data..." part using a simple C<do> call:

   my $data = do "My/Module/data.pl";

You can handle arbirary binary data either by finding a suitable C<EOF>
marker that isn't part of it, or you could use utf8 encoding to the
rescue, by using a >255 character code as text delimiter:

   use utf8;
   # use U+2026 as delimiter
   q…arbitary binary data....…

While this takes care of C<@INC>, perl still has to compile and execute
it every time (which might not be a significant problem), and it requires
the data to be formatted specifically for this occasion, so is hard for
accessing the sources of third-party modules.

=back

=head1 FUNCTIONS

This module only provides one function, not exported, that creates
C<File::INC> objects.

=over 4

=cut

package File::INC;

use common::sense;

use Carp ();

our $VERSION = 0.2;

=item $inc = File::INC::find $name

The name is a file name of the same syntax as expected by C<do EXPR> or
C<require EXPR>, e.g. F<File/INC.pm> or F<My/Module/data.bin>. Unlike
C<require> et al., absolute paths are not supported.

If the file is found, it returns a C<File::INC> object. Otherwise, it
returns C<undef>.

To work around potential bugs in C<@INC> hooks, it is recommended to only
keep one C<File::INC> around at any single time.

=cut

sub find($) {
   my $file = shift;

   for my $inc (@INC) {
      if (ref $inc) {
         my $func;

         if (CODE:: eq ref $inc) {
            $func = $inc;
         } elsif (ARRAY:: eq ref $inc) {
            $func = $inc->[0];
         } else {
            $func = $inc->can ("INC");
         }

         if ($func) {
            my @r = $func->($inc, $file);;
            my ($cache, $fh, $sub, $state);

            # undocumented and unsupported
            if (!eval { fileno $r[0] } and CODE:: ne ref $r[0]) {
               $cache = shift @r;
            }

            if (defined eval { fileno $r[0] }) {
               $fh = shift @r;
            }
            
            if (CODE:: eq ref $r[0]) {
               $sub = shift @r;
            }

            $state = shift @r;

            if (defined $fh or defined $cache or defined $sub) {
               defined $cache
                  and Carp::croak "File::INC: undocumented filter caches are not supported\n";

               return bless [undef, $fh, $sub, $state, $cache];
            }
         }

      } elsif (-e "$inc/$file") {
         # what a relief, the simple case
         return bless ["$inc/$file"];
      }
   }

   undef
}

=back

=head1 THE C<File::INC> CLASS

Library files are represented by C<File::INC> objects. You can query it to
find more information about the file (such as whether it even is a file
:).

=over 4

=item $path = $inc->path

If the file is actually a file on disk (the most common, but not
guaranteed, case), then this method returns the path to it. In other
cases, it returns C<undef>.

=cut

sub path {
   $_[0][0]
}

=item $path = $inc->force_path

#todo

=cut

sub force_path {
   die;
}

=item $fh = $inc->fh

=cut

sub fh {
   if (defined $_[0][0]) { # path?
      open my $fh, "<", $_[0][0];
      return $fh;
   } elsif (defined $_[0][1] && !defined $_[0][2]) { # fh. and no filter?
      return $_[0][1];
   } else {
      return undef;
   }
}

=item $fh = $inc->force_fh

#todo

=cut

sub force_fh {
   die;
}

=item $data = $inc->data

=cut

sub data {
   if ($_[0][0]) { # path
      open my $fh, "<", $_[0][0]
        or die "$_[0][0]: $!";

   } elsif (defined $_[0][1]) { # fh
      if (defined $_[0][2]) { # filter sub
         my @data;
         my $status;

         local $_;
         while () {
            $_ = <$_[0][1]>;
            $status = $_[0][2]->($_[0][3]);
            push @data, $_;
            last if $status <= 0;
         }

         return join "", @data;
      }

      # plain file, slurp
      local $/;
      return scalar <$_[0][1]>;

   } elsif (defined $_[0][2]) {
      # "filter" sub

      my @data;
      my $status;

      local $_;
      while () {
         $_ = "";
         $status = $_[0][2]->($_[0][3]);
         push @data, $_;
         last if $status <= 0;
      }

      return join "", @data;

   } else {
      die "internal error";
   }
}

=back

=head1 LIMITATIONS

As with many of the newer additions to perl, C<@INC> hooks have been
poorly designed (the interface is pretty chaotic and does not follow Perl
language rules, and the subroutine magically has to know whether the line
passed to it is the last line of the file) and documented (for example,
the filter cache is completely undocumented), and as a result, it's not
(to the best of my knowledge) possible implement this module in pure
Perl. I hope this implementation is good enough for real world C<@INC>
hooks.

Known deficiencies are that file handles are detected differently,
only a copy of the state argument is passed to the subroutine, and the
undocumented filter cache return value is ignored.

=head1 AUTHOR AND CONTACT INFORMATION

 Marc Lehmann <schmorp@schmorp.de>
 http://software.schmorp.de/pkg/File-INC

=cut

1

Revision:	1.2
Committed:	Wed May 1 03:08:29 2013 UTC (13 years, 4 months ago) by root
Branch:	MAIN
Changes since 1.1:	+9 -8 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			File::INC - find files via @INC
4
5			=head1 SYNOPSIS
6
7			use File::INC;
8
9			=head1 DESCRIPTION
10
11			Perl has two almost identical facilities to load "library"
12			files: C<require> and C<do> (C<use> is basically a compile-time
13			C<require>).
14
15			These search C<@INC> for the file and compile it.
16
17			Unfortunately, sometimes you want to locate data (or even source) files
18			using the same mechanism. The problem is that Perl I<laways> evaluates the
19			files as Perl code, which is not something you want for data files.
20
21			This module implements the same (hopefully :) C<@INC> walk code as perl,
22			and gives you access to the resulting files, without evaluating them.
23
24			=head2 ALTERNATIVES
25
26			There are alternatives to this module, both of which I regularly employ,
27			but they come with their own drawbacks:
28
29			=over 4
30
31			=item Walking C<@INC> manually and treating it as an array of directories.
32
33			Basically, this:
34
35			sub find_rcfile($) {
36			my $path;
37
38			for (@RC_PATH, "") {
39			$path = "$RC_BASE/$_/$_[0]";
40			return $path if -e $path;
41			}
42
43			die "FATAL: can't find required file \"$_[0]\" in \"$RC_BASE\"\n";
44			}
45
46			my $path = find_rcfile "My/Module/datafile.dat";
47
48			This is simple, but fails for any entries in C<@INC> that are not
49			directories. Not handling these makes it fail in many environments, such
50			as in L<App::Staticperl> or L<PAR::Packer>.
51
52			This module basically implements a full-featured version of this that
53			hopefully gets everything right.
54
55			=item Embed datafiles using C<do>.
56
57			You can embed datafiles by, say, uuencoding them and putting them into
58			a F<.pm> file (I think L<PAR::Packer>) does this. This is extremely
59			wasteful, but at least works around the C<@INC> problematic. A slightly
60			better way is to use C<do>. Take this file, put as F<My/Module/data.pl>
61			into the perl library:
62
63			<<EOF
64			text data...
65			EOF
66
67			Then you can load the "text data..." part using a simple C<do> call:
68
69			my $data = do "My/Module/data.pl";
70
71			You can handle arbirary binary data either by finding a suitable C<EOF>
72			marker that isn't part of it, or you could use utf8 encoding to the
73			rescue, by using a >255 character code as text delimiter:
74
75			use utf8;
76			# use U+2026 as delimiter
77			q…arbitary binary data....…
78
79			While this takes care of C<@INC>, perl still has to compile and execute
80			it every time (which might not be a significant problem), and it requires
81			the data to be formatted specifically for this occasion, so is hard for
82			accessing the sources of third-party modules.
83
84			=back
85
86			=head1 FUNCTIONS
87
88			This module only provides one function, not exported, that creates
89			C<File::INC> objects.
90
91			=over 4
92
93			=cut
94
95			package File::INC;
96
97			use common::sense;
98
99			use Carp ();
100
101			our $VERSION = 0.2;
102
103			=item $inc = File::INC::find $name
104
105			The name is a file name of the same syntax as expected by C<do EXPR> or
106			C<require EXPR>, e.g. F<File/INC.pm> or F<My/Module/data.bin>. Unlike
107			C<require> et al., absolute paths are not supported.
108
109			If the file is found, it returns a C<File::INC> object. Otherwise, it
110			returns C<undef>.
111
112			To work around potential bugs in C<@INC> hooks, it is recommended to only
113			keep one C<File::INC> around at any single time.
114
115			=cut
116
117			sub find($) {
118			my $file = shift;
119
120			for my $inc (@INC) {
121			if (ref $inc) {
122			my $func;
123
124			if (CODE:: eq ref $inc) {
125			$func = $inc;
126			} elsif (ARRAY:: eq ref $inc) {
127			$func = $inc->[0];
128			} else {
129			$func = $inc->can ("INC");
130			}
131
132			if ($func) {
133			my @r = $func->($inc, $file);;
134			my ($cache, $fh, $sub, $state);
135
136			# undocumented and unsupported
137			if (!eval { fileno $r[0] } and CODE:: ne ref $r[0]) {
138			$cache = shift @r;
139			}
140
141			if (defined eval { fileno $r[0] }) {
142			$fh = shift @r;
143			}
144
145			if (CODE:: eq ref $r[0]) {
146			$sub = shift @r;
147			}
148
149			$state = shift @r;
150
151			if (defined $fh or defined $cache or defined $sub) {
152			defined $cache
153			and Carp::croak "File::INC: undocumented filter caches are not supported\n";
154
155			return bless [undef, $fh, $sub, $state, $cache];
156			}
157			}
158
159			} elsif (-e "$inc/$file") {
160			# what a relief, the simple case
161			return bless ["$inc/$file"];
162			}
163			}
164
165			undef
166			}
167
168			=back
169
170			=head1 THE C<File::INC> CLASS
171
172			Library files are represented by C<File::INC> objects. You can query it to
173			find more information about the file (such as whether it even is a file
174			:).
175
176			=over 4
177
178			=item $path = $inc->path
179
180			If the file is actually a file on disk (the most common, but not
181			guaranteed, case), then this method returns the path to it. In other
182			cases, it returns C<undef>.
183
184			=cut
185
186			sub path {
187			$_[0][0]
188			}
189
190			=item $path = $inc->force_path
191
192			#todo
193
194			=cut
195
196			sub force_path {
197			die;
198			}
199
200			=item $fh = $inc->fh
201
202			=cut
203
204			sub fh {
205			if (defined $_[0][0]) { # path?
206			open my $fh, "<", $_[0][0];
207			return $fh;
208			} elsif (defined $_[0][1] && !defined $_[0][2]) { # fh. and no filter?
209			return $_[0][1];
210			} else {
211			return undef;
212			}
213			}
214
215			=item $fh = $inc->force_fh
216
217			#todo
218
219			=cut
220
221			sub force_fh {
222			die;
223			}
224
225			=item $data = $inc->data
226
227			=cut
228
229			sub data {
230			if ($_[0][0]) { # path
231			open my $fh, "<", $_[0][0]
232			or die "$_[0][0]: $!";
233
234			} elsif (defined $_[0][1]) { # fh
235			if (defined $_[0][2]) { # filter sub
236			my @data;
237			my $status;
238
239			local $_;
240	root	1.2	while () {
241			$_ = <$_[0][1]>;
242	root	1.1	$status = $_[0][2]->($_[0][3]);
243			push @data, $_;
244			last if $status <= 0;
245			}
246
247			return join "", @data;
248			}
249
250			# plain file, slurp
251			local $/;
252			return scalar <$_[0][1]>;
253
254			} elsif (defined $_[0][2]) {
255			# "filter" sub
256
257			my @data;
258			my $status;
259
260			local $_;
261			while () {
262			$_ = "";
263			$status = $_[0][2]->($_[0][3]);
264			push @data, $_;
265			last if $status <= 0;
266			}
267
268			return join "", @data;
269
270			} else {
271			die "internal error";
272			}
273			}
274
275			=back
276
277			=head1 LIMITATIONS
278
279			As with many of the newer additions to perl, C<@INC> hooks have been
280	root	1.2	poorly designed (the interface is pretty chaotic and does not follow Perl
281			language rules, and the subroutine magically has to know whether the line
282			passed to it is the last line of the file) and documented (for example,
283			the filter cache is completely undocumented), and as a result, it's not
284			(to the best of my knowledge) possible implement this module in pure
285			Perl. I hope this implementation is good enough for real world C<@INC>
286			hooks.
287	root	1.1
288			Known deficiencies are that file handles are detected differently,
289			only a copy of the state argument is passed to the subroutine, and the
290			undocumented filter cache return value is ignored.
291
292			=head1 AUTHOR AND CONTACT INFORMATION
293
294			Marc Lehmann <schmorp@schmorp.de>
295			http://software.schmorp.de/pkg/File-INC
296
297			=cut
298
299			1
300