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1=head1 NAME
2
3perlreapi - perl regular expression plugin interface
4
5=head1 DESCRIPTION
6
7As of Perl 5.9.5 there is a new interface for using other regexp engines than
8the default one. Each engine is supposed to provide access to a constant
9structure of the following format:
10
11 typedef struct regexp_engine {
3ab4a224 12 REGEXP* (*comp) (pTHX_ const SV * const pattern, const U32 flags);
49d7dfbc 13 I32 (*exec) (pTHX_ REGEXP * const rx, char* stringarg, char* strend,
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14 char* strbeg, I32 minend, SV* screamer,
15 void* data, U32 flags);
49d7dfbc 16 char* (*intuit) (pTHX_ REGEXP * const rx, SV *sv, char *strpos,
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17 char *strend, U32 flags,
18 struct re_scream_pos_data_s *data);
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19 SV* (*checkstr) (pTHX_ REGEXP * const rx);
20 void (*free) (pTHX_ REGEXP * const rx);
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21 void (*numbered_buff_FETCH) (pTHX_ REGEXP * const rx, const I32 paren,
22 SV * const sv);
23 void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren,
24 SV const * const value);
25 I32 (*numbered_buff_LENGTH) (pTHX_ REGEXP * const rx, const SV * const sv,
26 const I32 paren);
27 SV* (*named_buff_FETCH) (pTHX_ REGEXP * const rx, SV * const sv,
28 const U32 flags);
49d7dfbc 29 SV* (*qr_package)(pTHX_ REGEXP * const rx);
108003db 30 #ifdef USE_ITHREADS
49d7dfbc 31 void* (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
108003db 32 #endif
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33
34When a regexp is compiled, its C<engine> field is then set to point at
35the appropriate structure so that when it needs to be used Perl can find
36the right routines to do so.
37
38In order to install a new regexp handler, C<$^H{regcomp}> is set
39to an integer which (when casted appropriately) resolves to one of these
40structures. When compiling, the C<comp> method is executed, and the
41resulting regexp structure's engine field is expected to point back at
42the same structure.
43
44The pTHX_ symbol in the definition is a macro used by perl under threading
45to provide an extra argument to the routine holding a pointer back to
46the interpreter that is executing the regexp. So under threading all
47routines get an extra argument.
48
49The routines are as follows:
50
51=head2 comp
52
3ab4a224 53 REGEXP* comp(pTHX_ const SV * const pattern, const U32 flags);
108003db 54
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55Compile the pattern stored in C<pattern> using the given C<flags> and
56return a pointer to a prepared C<REGEXP> structure that can perform
57the match. See L</The REGEXP structure> below for an explanation of
58the individual fields in the REGEXP struct.
59
60The C<pattern> parameter is the scalar that was used as the
61pattern. previous versions of perl would pass two C<char*> indicating
62the start and end of the stringifed pattern, the following snippet can
63be used to get the old parameters:
64
65 STRLEN plen;
66 char* exp = SvPV(pattern, plen);
67 char* xend = exp + plen;
68
69Since any scalar can be passed as a pattern it's possible to implement
70an engine that does something with an array (C<< "ook" =~ [ qw/ eek
71hlagh / ] >>) or with the non-stringified form of a compiled regular
72expression (C<< "ook" =~ qr/eek/ >>). perl's own engine will always
73stringify everything using the snippet above but that doesn't mean
74other engines have to.
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75
76The C<flags> paramater is a bitfield which indicates which of the
77C<msixk> flags the regex was compiled with. In addition it contains
78info about whether C<use locale> is in effect and optimization info
79for C<split>. A regex engine might want to use the same split
80optimizations with a different syntax, for instance a Perl6 engine
81would treat C<split /^^/> equivalently to perl's C<split /^/>, see
82L<split documentation|perlfunc> and the relevant code in C<pp_split>
83in F<pp.c> to find out whether your engine should be setting these.
84
85The C<eogc> flags are stripped out before being passed to the comp
86routine. The regex engine does not need to know whether any of these
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87are set as those flags should only affect what perl does with the
88pattern and its match variables, not how it gets compiled & executed.
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89
90=over 4
91
92=item RXf_SKIPWHITE
93
94C<split ' '> or C<split> with no arguments (which really means
95C<split(' ', $_> see L<split|perlfunc>).
96
97=item RXf_START_ONLY
98
99Set if the pattern is C</^/> (C<<r->prelen == 1 && r->precomp[0] ==
100'^'>>). Will be used by the C<split> operator to split the given
101string on C<\n> (even under C</^/s>, see L<split|perlfunc>).
102
103=item RXf_WHITE
104
105Set if the pattern is exactly C</\s+/> and used by C<split>, the
106definition of whitespace varies depending on whether RXf_UTF8 or
107RXf_PMf_LOCALE is set.
108
109=item RXf_PMf_LOCALE
110
111Makes C<split> use the locale dependant definition of whitespace under C<use
112locale> when RXf_SKIPWHITE or RXf_WHITE is in effect. Under ASCII whitespace is
113defined as per L<isSPACE|perlapi/ISSPACE>, and by the internal macros
114C<is_utf8_space> under UTF-8 and C<isSPACE_LC> under C<use locale>.
115
116=item RXf_PMf_MULTILINE
117
118The C</m> flag, this ends up being passed to C<Perl_fbm_instr> by
119C<pp_split> regardless of the engine.
120
121=item RXf_PMf_SINGLELINE
122
123The C</s> flag. Guaranteed not to be used outside the regex engine.
124
125=item RXf_PMf_FOLD
126
127The C</i> flag. Guaranteed not to be used outside the regex engine.
128
129=item RXf_PMf_EXTENDED
130
131The C</x> flag. Guaranteed not to be used outside the regex
132engine. However if present on a regex C<#> comments will be stripped
133by the tokenizer regardless of the engine currently in use.
134
135=item RXf_PMf_KEEPCOPY
136
49d7dfbc 137The C</p> flag.
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138
139=item RXf_UTF8
140
141Set if the pattern is L<SvUTF8()|perlapi/SvUTF8>, set by Perl_pmruntime.
142
143=back
144
145In general these flags should be preserved in regex->extflags after
146compilation, although it is possible the regex includes constructs
147that changes them. The perl engine for instance may upgrade non-utf8
148strings to utf8 if the pattern includes constructs such as C<\x{...}>
149that can only match unicode values. RXf_SKIPWHITE should always be
150preserved verbatim in regex->extflags.
151
152=head2 exec
153
49d7dfbc 154 I32 exec(pTHX_ REGEXP * const rx,
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155 char *stringarg, char* strend, char* strbeg,
156 I32 minend, SV* screamer,
157 void* data, U32 flags);
158
159Execute a regexp.
160
161=head2 intuit
162
49d7dfbc 163 char* intuit(pTHX_ REGEXP * const rx,
108003db 164 SV *sv, char *strpos, char *strend,
49d7dfbc 165 const U32 flags, struct re_scream_pos_data_s *data);
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166
167Find the start position where a regex match should be attempted,
168or possibly whether the regex engine should not be run because the
169pattern can't match. This is called as appropriate by the core
170depending on the values of the extflags member of the regexp
171structure.
172
173=head2 checkstr
174
49d7dfbc 175 SV* checkstr(pTHX_ REGEXP * const rx);
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176
177Return a SV containing a string that must appear in the pattern. Used
178by C<split> for optimising matches.
179
180=head2 free
181
49d7dfbc 182 void free(pTHX_ REGEXP * const rx);
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183
184Called by perl when it is freeing a regexp pattern so that the engine
185can release any resources pointed to by the C<pprivate> member of the
186regexp structure. This is only responsible for freeing private data;
187perl will handle releasing anything else contained in the regexp structure.
188
2fdbfb4d 189=head2 numbered_buff_FETCH
108003db 190
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191 void numbered_buff_FETCH(pTHX_ REGEXP * const rx, const I32 paren,
192 SV * const sv);
108003db 193
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194Called to get the value of C<$`>, C<$'>, C<$&> (and their named
195equivalents, see L<perlvar>) and the numbered capture buffers (C<$1>,
196C<$2>, ...).
197
198The C<paren> paramater will be C<-2> for C<$`>, C<-1> for C<$'>, C<0>
199for C<$&>, C<1> for C<$1> and so forth.
200
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201C<sv> should be set to the scalar to return, the scalar is passed as
202an argument rather than being returned from the function because when
203it's called perl already has a scalar to store the value, creating
204another one would be redundant. The scalar can be set with
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205C<sv_setsv>, C<sv_setpvn> and friends, see L<perlapi>.
206
207This callback is where perl untaints its own capture variables under
208taint mode (see L<perlsec>). See the C<Perl_reg_numbered_buff_get>
209function in F<regcomp.c> for how to untaint capture variables if
210that's something you'd like your engine to do as well.
108003db 211
2fdbfb4d 212=head2 numbered_buff_STORE
108003db 213
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214 void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren,
215 SV const * const value);
108003db 216
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217Called to set the value of a numbered capture variable. C<paren> is
218the paren number (see the L<mapping|/numbered_buff_FETCH> above) and
219C<value> is the scalar that is to be used as the new value. It's up to
220the engine to make sure this is used as the new value (or reject it).
221
222Example:
223
224 if ("ook" =~ /(o*)/) {
225 # `paren' will be `1' and `value' will be `ee'
226 $1 =~ tr/o/e/;
227 }
228
229Perl's own engine will croak on any attempt to modify the capture
230variables, to do this in another engine use the following callack
231(copied from C<Perl_reg_numbered_buff_store>):
232
233 void
234 Example_reg_numbered_buff_store(pTHX_ REGEXP * const rx, const I32 paren,
235 SV const * const value)
236 {
237 PERL_UNUSED_ARG(rx);
238 PERL_UNUSED_ARG(paren);
239 PERL_UNUSED_ARG(value);
240
241 if (!PL_localizing)
242 Perl_croak(aTHX_ PL_no_modify);
243 }
244
245Actually perl 5.10 will not I<always> croak in a statement that looks
246like it would modify a numbered capture variable. This is because the
247STORE callback will not be called if perl can determine that it
248doesn't have to modify the value. This is exactly how tied variables
249behave in the same situation:
250
251 package CaptureVar;
252 use base 'Tie::Scalar';
253
254 sub TIESCALAR { bless [] }
255 sub FETCH { undef }
256 sub STORE { die "This doesn't get called" }
257
258 package main;
259
260 tie my $sv => "CatptureVar";
261 $sv =~ y/a/b/;
262
263Because C<$sv> is C<undef> when the C<y///> operator is applied to it
264the transliteration won't actually execute and the program won't
265C<die>. This is different to how 5.8 behaved since the capture
266variables were READONLY variables then, now they'll just die on
267assignment in the default engine.
268
269=head2 numbered_buff_LENGTH
270
271 I32 numbered_buff_LENGTH (pTHX_ REGEXP * const rx, const SV * const sv,
272 const I32 paren);
273
274Get the C<length> of a capture variable. There's a special callback
275for this so that perl doesn't have to do a FETCH and run C<length> on
276the result, since the length is (in perl's case) known from a memory
277offset this is much more efficient:
278
279 I32 s1 = rx->offs[paren].start;
280 I32 s2 = rx->offs[paren].end;
281 I32 len = t1 - s1;
282
283This is a little bit more complex in the case of UTF-8, see what
284C<Perl_reg_numbered_buff_length> does with
285L<is_utf8_string_loclen|perlapi/is_utf8_string_loclen>.
286
287=head2 named_buff_FETCH
288
289 SV* named_buff_FETCH(pTHX_ REGEXP * const rx, SV * const key,
290 const U32 flags);
291
292Called to get the value of key in the C<%+> and C<%-> hashes, C<key>
293is the hash key being requested and if C<flags & 1> is true C<%-> is
294being requested (and C<%+> if it's not).
108003db 295
49d7dfbc 296=head2 qr_package
108003db 297
49d7dfbc 298 SV* qr_package(pTHX_ REGEXP * const rx);
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299
300The package the qr// magic object is blessed into (as seen by C<ref
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301qr//>). It is recommended that engines change this to their package
302name for identification regardless of whether they implement methods
303on the object.
304
305A callback implementation might be:
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306
307 SV*
49d7dfbc 308 Example_reg_qr_package(pTHX_ REGEXP * const rx)
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309 {
310 PERL_UNUSED_ARG(rx);
311 return newSVpvs("re::engine::Example");
312 }
313
314Any method calls on an object created with C<qr//> will be dispatched to the
315package as a normal object.
316
317 use re::engine::Example;
318 my $re = qr//;
319 $re->meth; # dispatched to re::engine::Example::meth()
320
321To retrieve the C<REGEXP> object from the scalar in an XS function use the
322following snippet:
323
324 void meth(SV * rv)
325 PPCODE:
326 MAGIC * mg;
327 REGEXP * re;
328
329 if (SvMAGICAL(sv))
330 mg_get(sv);
331 if (SvROK(sv) &&
332 (sv = (SV*)SvRV(sv)) && /* assignment deliberate */
333 SvTYPE(sv) == SVt_PVMG &&
334 (mg = mg_find(sv, PERL_MAGIC_qr))) /* assignment deliberate */
335 {
336 re = (REGEXP *)mg->mg_obj;
337 }
338
339Or use the (CURRENTLY UNDOCUMENETED!) C<Perl_get_re_arg> function:
340
341 void meth(SV * rv)
342 PPCODE:
343 const REGEXP * const re = (REGEXP *)Perl_get_re_arg( aTHX_ rv, 0, NULL );
344
345=head2 dupe
346
49d7dfbc 347 void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
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348
349On threaded builds a regexp may need to be duplicated so that the pattern
350can be used by mutiple threads. This routine is expected to handle the
351duplication of any private data pointed to by the C<pprivate> member of
352the regexp structure. It will be called with the preconstructed new
353regexp structure as an argument, the C<pprivate> member will point at
354the B<old> private structue, and it is this routine's responsibility to
355construct a copy and return a pointer to it (which perl will then use to
356overwrite the field as passed to this routine.)
357
358This allows the engine to dupe its private data but also if necessary
359modify the final structure if it really must.
360
361On unthreaded builds this field doesn't exist.
362
363=head1 The REGEXP structure
364
365The REGEXP struct is defined in F<regexp.h>. All regex engines must be able to
366correctly build such a structure in their L</comp> routine.
367
368The REGEXP structure contains all the data that perl needs to be aware of
369to properly work with the regular expression. It includes data about
370optimisations that perl can use to determine if the regex engine should
371really be used, and various other control info that is needed to properly
372execute patterns in various contexts such as is the pattern anchored in
373some way, or what flags were used during the compile, or whether the
374program contains special constructs that perl needs to be aware of.
375
376In addition it contains two fields that are intended for the private use
377of the regex engine that compiled the pattern. These are the C<intflags>
378and pprivate members. The C<pprivate> is a void pointer to an arbitrary
379structure whose use and management is the responsibility of the compiling
380engine. perl will never modify either of these values.
381
382 typedef struct regexp {
383 /* what engine created this regexp? */
384 const struct regexp_engine* engine;
385
386 /* what re is this a lightweight copy of? */
387 struct regexp* mother_re;
388
389 /* Information about the match that the perl core uses to manage things */
390 U32 extflags; /* Flags used both externally and internally */
391 I32 minlen; /* mininum possible length of string to match */
392 I32 minlenret; /* mininum possible length of $& */
393 U32 gofs; /* chars left of pos that we search from */
394
395 /* substring data about strings that must appear
396 in the final match, used for optimisations */
397 struct reg_substr_data *substrs;
398
399 U32 nparens; /* number of capture buffers */
400
401 /* private engine specific data */
402 U32 intflags; /* Engine Specific Internal flags */
403 void *pprivate; /* Data private to the regex engine which
404 created this object. */
405
406 /* Data about the last/current match. These are modified during matching*/
407 U32 lastparen; /* last open paren matched */
408 U32 lastcloseparen; /* last close paren matched */
409 regexp_paren_pair *swap; /* Swap copy of *offs */
410 regexp_paren_pair *offs; /* Array of offsets for (@-) and (@+) */
411
412 char *subbeg; /* saved or original string so \digit works forever. */
413 SV_SAVED_COPY /* If non-NULL, SV which is COW from original */
414 I32 sublen; /* Length of string pointed by subbeg */
415
416 /* Information about the match that isn't often used */
417 I32 prelen; /* length of precomp */
418 const char *precomp; /* pre-compilation regular expression */
419
420 /* wrapped can't be const char*, as it is returned by sv_2pv_flags */
421 char *wrapped; /* wrapped version of the pattern */
422 I32 wraplen; /* length of wrapped */
423
424 I32 seen_evals; /* number of eval groups in the pattern - for security checks */
425 HV *paren_names; /* Optional hash of paren names */
426
427 /* Refcount of this regexp */
428 I32 refcnt; /* Refcount of this regexp */
429 } regexp;
430
431The fields are discussed in more detail below:
432
433=over 4
434
435=item C<engine>
436
437This field points at a regexp_engine structure which contains pointers
438to the subroutines that are to be used for performing a match. It
439is the compiling routine's responsibility to populate this field before
440returning the regexp object.
441
442Internally this is set to C<NULL> unless a custom engine is specified in
443C<$^H{regcomp}>, perl's own set of callbacks can be accessed in the struct
444pointed to by C<RE_ENGINE_PTR>.
445
446=item C<mother_re>
447
448TODO, see L<http://www.mail-archive.com/perl5-changes@perl.org/msg17328.html>
449
450=item C<extflags>
451
452This will be used by perl to see what flags the regexp was compiled with, this
453will normally be set to the value of the flags parameter on L</comp>.
454
455=item C<minlen> C<minlenret>
456
457The minimum string length required for the pattern to match. This is used to
458prune the search space by not bothering to match any closer to the end of a
459string than would allow a match. For instance there is no point in even
460starting the regex engine if the minlen is 10 but the string is only 5
461characters long. There is no way that the pattern can match.
462
463C<minlenret> is the minimum length of the string that would be found
464in $& after a match.
465
466The difference between C<minlen> and C<minlenret> can be seen in the
467following pattern:
468
469 /ns(?=\d)/
470
471where the C<minlen> would be 3 but C<minlenret> would only be 2 as the \d is
472required to match but is not actually included in the matched content. This
473distinction is particularly important as the substitution logic uses the
474C<minlenret> to tell whether it can do in-place substition which can result in
475considerable speedup.
476
477=item C<gofs>
478
479Left offset from pos() to start match at.
480
481=item C<substrs>
482
483TODO: document
484
485=item C<nparens>, C<lasparen>, and C<lastcloseparen>
486
487These fields are used to keep track of how many paren groups could be matched
488in the pattern, which was the last open paren to be entered, and which was
489the last close paren to be entered.
490
491=item C<intflags>
492
493The engine's private copy of the flags the pattern was compiled with. Usually
494this is the same as C<extflags> unless the engine chose to modify one of them
495
496=item C<pprivate>
497
498A void* pointing to an engine-defined data structure. The perl engine uses the
499C<regexp_internal> structure (see L<perlreguts/Base Structures>) but a custom
500engine should use something else.
501
502=item C<swap>
503
504TODO: document
505
506=item C<offs>
507
508A C<regexp_paren_pair> structure which defines offsets into the string being
509matched which correspond to the C<$&> and C<$1>, C<$2> etc. captures, the
510C<regexp_paren_pair> struct is defined as follows:
511
512 typedef struct regexp_paren_pair {
513 I32 start;
514 I32 end;
515 } regexp_paren_pair;
516
517If C<< ->offs[num].start >> or C<< ->offs[num].end >> is C<-1> then that
518capture buffer did not match. C<< ->offs[0].start/end >> represents C<$&> (or
519C<${^MATCH> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where
520C<$paren >= 1>.
521
522=item C<precomp> C<prelen>
523
524Used for debugging purposes. C<precomp> holds a copy of the pattern
525that was compiled and C<prelen> its length.
526
527=item C<paren_names>
528
529This is a hash used internally to track named capture buffers and their
530offsets. The keys are the names of the buffers the values are dualvars,
531with the IV slot holding the number of buffers with the given name and the
532pv being an embedded array of I32. The values may also be contained
533independently in the data array in cases where named backreferences are
534used.
535
536=item C<reg_substr_data>
537
538Holds information on the longest string that must occur at a fixed
539offset from the start of the pattern, and the longest string that must
540occur at a floating offset from the start of the pattern. Used to do
541Fast-Boyer-Moore searches on the string to find out if its worth using
542the regex engine at all, and if so where in the string to search.
543
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544=item C<subbeg> C<sublen> C<saved_copy>
545
546 #define SAVEPVN(p,n) ((p) ? savepvn(p,n) : NULL)
547 if (RX_MATCH_COPIED(ret))
548 ret->subbeg = SAVEPVN(ret->subbeg, ret->sublen);
549 else
550 ret->subbeg = NULL;
551
552C<PL_sawampersand || rx->extflags & RXf_PMf_KEEPCOPY>
553
554These are used during execution phase for managing search and replace
555patterns.
556
557=item C<wrapped> C<wraplen>
558
559Stores the string C<qr//> stringifies to, for example C<(?-xism:eek)>
560in the case of C<qr/eek/>.
561
562When using a custom engine that doesn't support the C<(?:)> construct for
563inline modifiers it's best to have C<qr//> stringify to the supplied pattern,
564note that this will create invalid patterns in cases such as:
565
566 my $x = qr/a|b/; # "a|b"
567 my $y = qr/c/; # "c"
568 my $z = qr/$x$y/; # "a|bc"
569
570There's no solution for such problems other than making the custom engine
571understand some for of inline modifiers.
572
573The C<Perl_reg_stringify> in F<regcomp.c> does the stringification work.
574
575=item C<seen_evals>
576
577This stores the number of eval groups in the pattern. This is used for security
578purposes when embedding compiled regexes into larger patterns with C<qr//>.
579
580=item C<refcnt>
581
582The number of times the structure is referenced. When this falls to 0 the
583regexp is automatically freed by a call to pregfree. This should be set to 1 in
584each engine's L</comp> routine.
585
586=back
587
588=head2 De-allocation and Cloning
589
590Any patch that adds data items to the REGEXP struct will need to include
591changes to F<sv.c> (C<Perl_re_dup()>) and F<regcomp.c> (C<pregfree()>). This
592involves freeing or cloning items in the regexp's data array based on the data
593item's type.
594
595=head1 HISTORY
596
597Originally part of L<perlreguts>.
598
599=head1 AUTHORS
600
601Originally written by Yves Orton, expanded by E<AElig>var ArnfjE<ouml>rE<eth>
602Bjarmason.
603
604=head1 LICENSE
605
606Copyright 2006 Yves Orton and 2007 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason.
607
608This program is free software; you can redistribute it and/or modify it under
609the same terms as Perl itself.
610
611=cut