1 package encoding::warnings;
2 $encoding::warnings::VERSION = '0.10';
9 encoding::warnings - Warn on implicit encoding conversions
13 This document describes version 0.10 of encoding::warnings, released
18 use encoding::warnings; # or 'FATAL' to raise fatal exceptions
20 utf8::encode($a = chr(20000)); # a byte-string (raw bytes)
21 $b = chr(20000); # a unicode-string (wide characters)
23 # "Bytes implicitly upgraded into wide characters as iso-8859-1"
28 =head2 Overview of the problem
30 By default, there is a fundamental asymmetry in Perl's unicode model:
31 implicit upgrading from byte-strings to unicode-strings assumes that
32 they were encoded in I<ISO 8859-1 (Latin-1)>, but unicode-strings are
33 downgraded with UTF-8 encoding. This happens because the first 256
34 codepoints in Unicode happens to agree with Latin-1.
36 However, this silent upgrading can easily cause problems, if you happen
37 to mix unicode strings with non-Latin1 data -- i.e. byte-strings encoded
38 in UTF-8 or other encodings. The error will not manifest until the
39 combined string is written to output, at which time it would be impossible
40 to see where did the silent upgrading occur.
42 =head2 Detecting the problem
44 This module simplifies the process of diagnosing such problems. Just put
45 this line on top of your main program:
47 use encoding::warnings;
49 Afterwards, implicit upgrading of high-bit bytes will raise a warning.
50 Ex.: C<Bytes implicitly upgraded into wide characters as iso-8859-1 at
53 However, strings composed purely of ASCII code points (C<0x00>..C<0x7F>)
54 will I<not> trigger this warning.
56 You can also make the warnings fatal by importing this module as:
58 use encoding::warnings 'FATAL';
60 =head2 Solving the problem
62 Most of the time, this warning occurs when a byte-string is concatenated
63 with a unicode-string. There are a number of ways to solve it:
67 =item * Upgrade both sides to unicode-strings
69 If your program does not need compatibility for Perl 5.6 and earlier,
70 the recommended approach is to apply appropriate IO disciplines, so all
71 data in your program become unicode-strings. See L<encoding>, L<open> and
72 L<perlfunc/binmode> for how.
74 =item * Downgrade both sides to byte-strings
76 The other way works too, especially if you are sure that all your data
77 are under the same encoding, or if compatibility with older versions
80 You may downgrade strings with C<Encode::encode> and C<utf8::encode>.
81 See L<Encode> and L<utf8> for details.
83 =item * Specify the encoding for implicit byte-string upgrading
85 If you are confident that all byte-strings will be in a specific
86 encoding like UTF-8, I<and> need not support older versions of Perl,
87 use the C<encoding> pragma:
91 Similarly, this will silence warnings from this module, and preserve the
94 use encoding 'iso-8859-1';
96 However, note that C<use encoding> actually had three distinct effects:
100 =item * PerlIO layers for B<STDIN> and B<STDOUT>
102 This is similar to what L<open> pragma does.
104 =item * Literal conversions
106 This turns I<all> literal string in your program into unicode-strings
107 (equivalent to a C<use utf8>), by decoding them using the specified
110 =item * Implicit upgrading for byte-strings
112 This will silence warnings from this module, as shown above.
116 Because literal conversions also work on empty strings, it may surprise
121 my $byte_string = pack("C*", 0xA4, 0x40);
122 print length $a; # 2 here.
123 $a .= ""; # concatenating with a unicode string...
124 print length $a; # 1 here!
126 In other words, do not C<use encoding> unless you are certain that the
127 program will not deal with any raw, 8-bit binary data at all.
129 However, the C<Filter =E<gt> 1> flavor of C<use encoding> will I<not>
130 affect implicit upgrading for byte-strings, and is thus incapable of
131 silencing warnings from this module. See L<encoding> for more details.
137 For Perl 5.9.4 or later, this module's effect is lexical.
139 For Perl versions prior to 5.9.4, this module affects the whole script,
140 instead of inside its lexical block.
149 # Install a ${^ENCODING} handler if no other one are already in place.
152 my $fatal = shift || '';
155 return if ${^ENCODING} and ref(${^ENCODING}) ne $class;
156 return unless eval { require Encode; 1 };
158 my $ascii = Encode::find_encoding('us-ascii') or return;
159 my $latin1 = Encode::find_encoding('iso-8859-1') or return;
161 # Have to undef explicitly here
164 # Install a warning handler for decode()
169 (($fatal eq 'FATAL') ? 'Carp::croak' : 'Carp::carp'),
173 ${^ENCODING} = $decoder;
182 # Don't worry about source code literals.
185 return $self->[LATIN1]->cat_decode(@_);
188 # Warn if the data is not purely US-ASCII.
193 if ($] >= 5.009004) {
194 my $hints = (caller(0))[10];
195 $hints->{ref($self)} or last DO_WARN;
199 my $rv = eval { $self->[ASCII]->decode($_[0], Encode::FB_CROAK()) };
200 return $rv unless $@;
205 "Bytes implicitly upgraded into wide characters as iso-8859-1"
210 return $self->[LATIN1]->decode(@_);
213 sub name { 'iso-8859-1' }
221 L<perlunicode>, L<perluniintro>
223 L<open>, L<utf8>, L<encoding>, L<Encode>
231 Copyright 2004, 2005, 2006 by Audrey Tang E<lt>cpan@audreyt.orgE<gt>.
233 This program is free software; you can redistribute it and/or modify it
234 under the same terms as Perl itself.
236 See L<http://www.perl.com/perl/misc/Artistic.html>