3 re::engine::Plugin - API to write custom regex engines
11 As of perl 5.9.5 it's possible to lexically replace perl's built-in
12 regular expression engine with your own (see L<perlreapi> and
13 L<perlpragma>). This module provides a glue interface to the relevant
14 parts of the perl C API enabling you to write an engine in Perl
15 instead of the C/XS interface provided by the core.
17 =head2 The gory details
19 Each regex in perl is compiled into an internal C<REGEXP> structure
20 (see L<perlreapi|perlreapi/The REGEXP structure>), this can happen
21 either during compile time in the case of patterns in the format
22 C</pattern/> or runtime for C<qr//> patterns, or something inbetween
23 depending on variable interpolation etc.
25 When this module is loaded into a scope it inserts a hook into
26 C<$^H{regcomp}> (as described in L<perlreapi> and L<perlpragma>) to
27 have each regexp constructed in its lexical scope handled by this
28 engine, but it differs from other engines in that it also inserts
29 other hooks into C<%^H> in the same scope that point to user-defined
30 subroutines to use during compilation, execution etc, these are
31 described in L</CALLBACKS> below.
33 The callbacks (e.g. L</comp>) then get called with a
34 L<re::engine::Plugin> object as their first argument. This object
35 provies access to perl's internal REGEXP struct in addition to its own
36 state (e.g. a L<stash|/stash>). The L<methods|/METHODS> on this object
37 allow for altering the C<REGEXP> struct's internal state, adding new
42 Callbacks are specified in the C<re::engine::Plugin> import list as
43 key-value pairs of names and subroutine references:
45 use re::engine::Plugin (
50 To write a custom engine which imports your functions into the
51 caller's scope use use the following snippet:
53 package re::engine::Example;
54 use re::engine::Plugin ();
58 # Sets the caller's $^H{regcomp} his %^H with our callbacks
59 re::engine::Plugin->import(
65 *unimport = \&re::engine::Plugin::unimport;
67 # Implementation of the engine
78 # return value discarded
81 Called when a regex is compiled by perl, this is always the first
82 callback to be called and may be called multiple times or not at all
83 depending on what perl sees fit at the time.
85 The first argument will be a freshly constructed C<re::engine::Plugin>
86 object (think of it as C<$self>) which you can interact with using the
87 L<methods|/METHODS> below, this object will be passed around the other
88 L<callbacks|/CALLBACKS> and L<methods|/METHODS> for the lifetime of
91 Calling C<die> or anything that uses it (such as C<carp>) here will
92 not be trapped by an C<eval> block that the pattern is in, i.e.
95 use re::engine::Plugin(
98 croak "Your pattern is invalid"
99 unless $rx->pattern ~~ /pony/;
103 # Ignores the eval block
104 eval { /you die in C<eval>, you die for real/ };
106 This happens because the real subroutine call happens indirectly at
107 compile time and not in the scope of the C<eval> block. This is how
108 perl's own engine would behave in the same situation if given an
109 invalid pattern such as C</(/>.
116 # We always like ponies!
117 return 1 if $str ~~ /pony/;
123 Called when a regex is being executed, i.e. when it's being matched
124 against something. The scalar being matched against the pattern is
125 available as the second argument (C<$str>) and through the L<str|/str>
126 method. The routine should return a true value if the match was
127 successful, and a false one if it wasn't.
129 This callback can also be specified on an individual basis with the
130 L</callbacks> method.
137 # in comp/exec/methods:
140 The last scalar to be matched against the L<pattern|/pattern> or
141 C<undef> if there hasn't been a match yet.
143 perl's own engine always stringifies the scalar being matched against
144 a given pattern, however a custom engine need not have such
145 restrictions. One could write a engine that matched a file handle
146 against a pattern or any other complex data structure.
150 The pattern that the engine was asked to compile, this can be either a
151 classic Perl pattern with modifiers like C</pat/ix> or C<qr/pat/ix> or
152 an arbitary scalar. The latter allows for passing anything that
153 doesn't fit in a string and five L<modifier|/mod> characters, such as
154 hashrefs, objects, etc.
159 say "has /ix" if %mod ~~ 'i' and %mod ~~ 'x';
161 A key-value pair list of the modifiers the pattern was compiled with.
162 The keys will zero or more of C<imsxp> and the values will be true
163 values (so that you don't have to write C<exists>).
165 You don't get to know if the C<eogc> modifiers were attached to the
166 pattern since these are internal to perl and shouldn't matter to
171 comp => sub { shift->stash( [ 1 .. 5 ) },
172 exec => sub { shift->stash }, # Get [ 1 .. 5 ]
174 Returns or sets a user defined stash that's passed around as part of
175 the C<$rx> object, useful for passing around all sorts of data between
176 the callback routines and methods.
181 my $minlen = $rx->minlen // "not set";
183 The minimum C<length> a string must be to match the pattern, perl will
184 use this internally during matching to check whether the stringified
185 form of the string (or other object) being matched is at least this
186 long, if not the regexp engine in effect (that means you!) will not be
189 The length specified will be used as a a byte length (using
190 L<SvPV|perlapi/SvPV>), not a character length.
198 # A dumb regexp engine that just tests string equality
199 use re::engine::Plugin comp => sub {
202 my $pat = $re->pattern;
212 Takes a list of key-value pairs of names and subroutines, and replace the
213 callback currently attached to the regular expression for the type given as
214 the key by the code reference passed as the corresponding value.
216 The only valid key is currently C<exec>. See L</exec> for more details about
223 my ($re, $paren) = @_;
228 my ($re, $paren, $rhs) = @_;
230 # return value discarded
233 my ($re, $paren) = @_;
239 Takes a list of key-value pairs of names and subroutines that
240 implement numbered capture variables. C<FETCH> will be called on value
241 retrieval (C<say $1>), C<STORE> on assignment (C<$1 = "ook">) and
242 C<LENGTH> on C<length $1>.
244 The second paramater of each routine is the paren number being
245 requested/stored, the following mapping applies for those numbers:
247 -2 => $` or ${^PREMATCH}
248 -1 => $' or ${^POSTMATCH}
253 Assignment to capture variables makes it possible to implement
254 something like Perl 6 C<:rw> semantics, and since it's possible to
255 make the capture variables return any scalar instead of just a string
256 it becomes possible to implement Perl 6 match object semantics (to
259 =head2 named_captures
263 perl internals still needs to be changed to support this but when it's
264 done it'll allow the binding of C<%+> and C<%-> and support the
265 L<Tie::Hash> methods FETCH, STORE, DELETE, CLEAR, EXISTS, FIRSTKEY,
270 =head2 C<REP_THREADSAFE>
272 True iff the module could have been built with thread-safety features
275 =head2 C<REP_FORKSAFE>
277 True iff this module could have been built with fork-safety features
278 enabled. This will always be true except on Windows where it's false
279 for perl 5.10.0 and below.
283 The only way to untaint an existing variable in Perl is to use it as a
284 hash key or referencing subpatterns from a regular expression match
285 (see L<perlsec|perlsec/Laundering and Detecting Tainted Data>), the
286 latter only works in perl's regex engine because it explicitly
287 untaints capture variables which a custom engine will also need to do
288 if it wants its capture variables to be untanted.
290 There are basically two ways to go about this, the first and obvious
291 one is to make use of Perl'l lexical scoping which enables the use of
292 its built-in regex engine in the scope of the overriding engine's
295 use re::engine::Plugin (
297 my ($re, $str) = @_; # $str is tainted
301 my ($re, $paren) = @_;
303 # This is perl's engine doing the match
306 # $1 has been untainted
313 The second is to use something like L<Taint::Util> which flips the
314 taint flag on the scalar without invoking the perl's regex engine:
317 use re::engine::Plugin (
319 my ($re, $str) = @_; # $str is tainted
323 my ($re, $paren) = @_;
325 # Copy $str and untaint the copy
326 untaint(my $ret = $str);
328 # Return the untainted value
335 In either case a regex engine using perl's L<regex api|perlapi> or
336 this module is responsible for how and if it untaints its variables.
340 L<perlreapi>, L<Taint::Util>
342 =head1 TODO & CAVEATS
350 Engines implemented with this module don't support C<s///> and C<split
351 //>, the appropriate parts of the C<REGEXP> struct need to be wrapped
356 Still not a complete wrapper for L<perlreapi> in other ways, needs
357 methods for some C<REGEXP> struct members, some callbacks aren't
362 Support overloading operations on the C<qr//> object, this allow
363 control over the of C<qr//> objects in a manner that isn't limited by
364 C<wrapped>/C<wraplen>.
368 '@{}' => sub { ... },
374 Support the dispatch of arbitary methods from the re::engine::Plugin
375 qr// object to user defined subroutines via AUTOLOAD;
377 package re::engine::Plugin;
381 my ($name) = $AUTOLOAD =~ /.*::(.*?)/;
382 my $cv = getmeth($name); # or something like that
386 package re::engine::SomeEngine;
392 $re->add_method( # or something like that
394 my ($re, @arg) = @_; # re::engine::Plugin, 1..5
400 use re::engine::SomeEngine;
404 $re->foshizzle(1..5);
408 Implement the dupe callback, test this on a threaded perl (and learn
409 how to use threads and how they break the current model).
413 Allow the user to specify ->offs either as an array or a packed
414 string. Can pack() even pack I32? Only IV? int?
418 Add tests that check for different behavior when curpm is and is not
423 Add tests that check the refcount of the stash and other things I'm
424 mucking with, run valgrind and make sure everything is destroyed when
429 Run the debugger on the testsuite and find cases when the intuit and
430 checkstr callbacks are called. Write wrappers around them and add
440 This module may happen to build with a C++ compiler as well, but don't rely on it, as no guarantee is made in this regard.
442 L<XSLoader> (standard since perl 5.006).
446 Please report any bugs that aren't already listed at
447 L<http://rt.cpan.org/Dist/Display.html?Queue=re-engine-Plugin> to
448 L<http://rt.cpan.org/Public/Bug/Report.html?Queue=re-engine-Plugin>
452 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason C<< <avar at cpan.org> >>
454 Vincent Pit C<< <perl at profvince.com> >>
458 Copyright 2007,2008 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason.
460 Copyright 2009,2010,2011 Vincent Pit.
462 This program is free software; you can redistribute it and/or modify it
463 under the same terms as Perl itself.