summaryrefslogtreecommitdiff
path: root/lib/open.pm
blob: 1bfe0d68330af87ea7c52be475496231418c841c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
package open;
use warnings;

our $VERSION = '1.08';

require 5.008001; # for PerlIO::get_layers()

my $locale_encoding;

sub _get_encname {
    return ($1, Encode::resolve_alias($1)) if $_[0] =~ /^:?encoding\((.+)\)$/;
    return;
}

sub croak {
    require Carp; goto &Carp::croak;
}

sub _drop_oldenc {
    # If by the time we arrive here there already is at the top of the
    # perlio layer stack an encoding identical to what we would like
    # to push via this open pragma, we will pop away the old encoding
    # (+utf8) so that we can push ourselves in place (this is easier
    # than ignoring pushing ourselves because of the way how ${^OPEN}
    # works).  So we are looking for something like
    #
    #   stdio encoding(xxx) utf8
    #
    # in the existing layer stack, and in the new stack chunk for
    #
    #   :encoding(xxx)
    #
    # If we find a match, we pop the old stack (once, since
    # the utf8 is just a flag on the encoding layer)
    my ($h, @new) = @_;
    return unless @new >= 1 && $new[-1] =~ /^:encoding\(.+\)$/;
    my @old = PerlIO::get_layers($h);
    return unless @old >= 3 &&
	          $old[-1] eq 'utf8' &&
                  $old[-2] =~ /^encoding\(.+\)$/;
    require Encode;
    my ($loname, $lcname) = _get_encname($old[-2]);
    unless (defined $lcname) { # Should we trust get_layers()?
	croak("open: Unknown encoding '$loname'");
    }
    my ($voname, $vcname) = _get_encname($new[-1]);
    unless (defined $vcname) {
	croak("open: Unknown encoding '$voname'");
    }
    if ($lcname eq $vcname) {
	binmode($h, ":pop"); # utf8 is part of the encoding layer
    }
}

sub import {
    my ($class,@args) = @_;
    croak("open: needs explicit list of PerlIO layers") unless @args;
    my $std;
    my ($in,$out) = split(/\0/,(${^OPEN} || "\0"), -1);
    while (@args) {
	my $type = shift(@args);
	my $dscp;
	if ($type =~ /^:?(utf8|locale|encoding\(.+\))$/) {
	    $type = 'IO';
	    $dscp = ":$1";
	} elsif ($type eq ':std') {
	    $std = 1;
	    next;
	} else {
	    $dscp = shift(@args) || '';
	}
	my @val;
	foreach my $layer (split(/\s+/,$dscp)) {
            $layer =~ s/^://;
	    if ($layer eq 'locale') {
		require Encode;
		require encoding;
		$locale_encoding = encoding::_get_locale_encoding()
		    unless defined $locale_encoding;
		(warnings::warnif("layer", "Cannot figure out an encoding to use"), last)
		    unless defined $locale_encoding;
                $layer = "encoding($locale_encoding)";
		$std = 1;
	    } else {
		my $target = $layer;		# the layer name itself
		$target =~ s/^(\w+)\(.+\)$/$1/;	# strip parameters

		unless(PerlIO::Layer::->find($target,1)) {
		    warnings::warnif("layer", "Unknown PerlIO layer '$target'");
		}
	    }
	    push(@val,":$layer");
	    if ($layer =~ /^(crlf|raw)$/) {
		$^H{"open_$type"} = $layer;
	    }
	}
	if ($type eq 'IN') {
	    _drop_oldenc(*STDIN, @val);
	    $in  = join(' ', @val);
	}
	elsif ($type eq 'OUT') {
	    _drop_oldenc(*STDOUT, @val);
	    $out = join(' ', @val);
	}
	elsif ($type eq 'IO') {
	    _drop_oldenc(*STDIN,  @val);
	    _drop_oldenc(*STDOUT, @val);
	    $in = $out = join(' ', @val);
	}
	else {
	    croak "Unknown PerlIO layer class '$type' (need IN, OUT or IO)";
	}
    }
    ${^OPEN} = join("\0", $in, $out);
    if ($std) {
	if ($in) {
	    if ($in =~ /:utf8\b/) {
		    binmode(STDIN,  ":utf8");
		} elsif ($in =~ /(\w+\(.+\))/) {
		    binmode(STDIN,  ":$1");
		}
	}
	if ($out) {
	    if ($out =~ /:utf8\b/) {
		binmode(STDOUT,  ":utf8");
		binmode(STDERR,  ":utf8");
	    } elsif ($out =~ /(\w+\(.+\))/) {
		binmode(STDOUT,  ":$1");
		binmode(STDERR,  ":$1");
	    }
	}
    }
}

1;
__END__

=head1 NAME

open - perl pragma to set default PerlIO layers for input and output

=head1 SYNOPSIS

    use open IN  => ":crlf", OUT => ":bytes";
    use open OUT => ':utf8';
    use open IO  => ":encoding(iso-8859-7)";

    use open IO  => ':locale';

    use open ':encoding(utf8)';
    use open ':locale';
    use open ':encoding(iso-8859-7)';

    use open ':std';

=head1 DESCRIPTION

Full-fledged support for I/O layers is now implemented provided
Perl is configured to use PerlIO as its IO system (which is now the
default).

The C<open> pragma serves as one of the interfaces to declare default
"layers" (also known as "disciplines") for all I/O. Any two-argument
open(), readpipe() (aka qx//) and similar operators found within the
lexical scope of this pragma will use the declared defaults.
Even three-argument opens may be affected by this pragma
when they don't specify IO layers in MODE.

With the C<IN> subpragma you can declare the default layers
of input streams, and with the C<OUT> subpragma you can declare
the default layers of output streams.  With the C<IO>  subpragma
you can control both input and output streams simultaneously.

If you have a legacy encoding, you can use the C<:encoding(...)> tag.

If you want to set your encoding layers based on your
locale environment variables, you can use the C<:locale> tag.
For example:

    $ENV{LANG} = 'ru_RU.KOI8-R';
    # the :locale will probe the locale environment variables like LANG
    use open OUT => ':locale';
    open(O, ">koi8");
    print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
    close O;
    open(I, "<koi8");
    printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
    close I;

These are equivalent

    use open ':encoding(utf8)';
    use open IO => ':encoding(utf8)';

as are these

    use open ':locale';
    use open IO => ':locale';

and these

    use open ':encoding(iso-8859-7)';
    use open IO => ':encoding(iso-8859-7)';

The matching of encoding names is loose: case does not matter, and
many encodings have several aliases.  See L<Encode::Supported> for
details and the list of supported locales.

When open() is given an explicit list of layers (with the three-arg
syntax), they override the list declared using this pragma.

The C<:std> subpragma on its own has no effect, but if combined with
the C<:utf8> or C<:encoding> subpragmas, it converts the standard
filehandles (STDIN, STDOUT, STDERR) to comply with encoding selected
for input/output handles.  For example, if both input and out are
chosen to be C<:encoding(utf8)>, a C<:std> will mean that STDIN, STDOUT,
and STDERR are also in C<:encoding(utf8)>.  On the other hand, if only
output is chosen to be in C<< :encoding(koi8r) >>, a C<:std> will cause
only the STDOUT and STDERR to be in C<koi8r>.  The C<:locale> subpragma
implicitly turns on C<:std>.

The logic of C<:locale> is described in full in L<encoding>,
but in short it is first trying nl_langinfo(CODESET) and then
guessing from the LC_ALL and LANG locale environment variables.

Directory handles may also support PerlIO layers in the future.

=head1 NONPERLIO FUNCTIONALITY

If Perl is not built to use PerlIO as its IO system then only the two
pseudo-layers C<:bytes> and C<:crlf> are available.

The C<:bytes> layer corresponds to "binary mode" and the C<:crlf>
layer corresponds to "text mode" on platforms that distinguish
between the two modes when opening files (which is many DOS-like
platforms, including Windows).  These two layers are no-ops on
platforms where binmode() is a no-op, but perform their functions
everywhere if PerlIO is enabled.

=head1 IMPLEMENTATION DETAILS

There is a class method in C<PerlIO::Layer> C<find> which is
implemented as XS code.  It is called by C<import> to validate the
layers:

   PerlIO::Layer::->find("perlio")

The return value (if defined) is a Perl object, of class
C<PerlIO::Layer> which is created by the C code in F<perlio.c>.  As
yet there is nothing useful you can do with the object at the perl
level.

=head1 SEE ALSO

L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>,
L<encoding>

=cut