1/*-------------------------------------------------------------------------
2 *
3 * regexport.c
4 * Functions for exporting info about a regex's NFA
5 *
6 * In this implementation, the NFA defines a necessary but not sufficient
7 * condition for a string to match the regex: that is, there can be strings
8 * that match the NFA but don't match the full regex, but not vice versa.
9 * Thus, for example, it is okay for the functions below to treat lookaround
10 * constraints as no-ops, since they merely constrain the string some more.
11 *
12 * Notice that these functions return info into caller-provided arrays
13 * rather than doing their own malloc's. This simplifies the APIs by
14 * eliminating a class of error conditions, and in the case of colors
15 * allows the caller to decide how big is too big to bother with.
16 *
17 *
18 * Portions Copyright (c) 2013-2019, PostgreSQL Global Development Group
19 * Portions Copyright (c) 1998, 1999 Henry Spencer
20 *
21 * IDENTIFICATION
22 * src/backend/regex/regexport.c
23 *
24 *-------------------------------------------------------------------------
25 */
26
27#include "regex/regguts.h"
28
29#include "regex/regexport.h"
30
31
32/*
33 * Get total number of NFA states.
34 */
35int
36pg_reg_getnumstates(const regex_t *regex)
37{
38 struct cnfa *cnfa;
39
40 assert(regex != NULL && regex->re_magic == REMAGIC);
41 cnfa = &((struct guts *) regex->re_guts)->search;
42
43 return cnfa->nstates;
44}
45
46/*
47 * Get initial state of NFA.
48 */
49int
50pg_reg_getinitialstate(const regex_t *regex)
51{
52 struct cnfa *cnfa;
53
54 assert(regex != NULL && regex->re_magic == REMAGIC);
55 cnfa = &((struct guts *) regex->re_guts)->search;
56
57 return cnfa->pre;
58}
59
60/*
61 * Get final state of NFA.
62 */
63int
64pg_reg_getfinalstate(const regex_t *regex)
65{
66 struct cnfa *cnfa;
67
68 assert(regex != NULL && regex->re_magic == REMAGIC);
69 cnfa = &((struct guts *) regex->re_guts)->search;
70
71 return cnfa->post;
72}
73
74/*
75 * pg_reg_getnumoutarcs() and pg_reg_getoutarcs() mask the existence of LACON
76 * arcs from the caller, treating any LACON as being automatically satisfied.
77 * Since the output representation does not support arcs that consume no
78 * character when traversed, we have to recursively traverse LACON arcs here,
79 * and report whatever normal arcs are reachable by traversing LACON arcs.
80 * Note that this wouldn't work if it were possible to reach the final state
81 * via LACON traversal, but the regex library never builds NFAs that have
82 * LACON arcs leading directly to the final state. (This is because the
83 * regex executor is designed to consume one character beyond the nominal
84 * match end --- possibly an EOS indicator --- so there is always a set of
85 * ordinary arcs leading to the final state.)
86 *
87 * traverse_lacons is a recursive subroutine used by both exported functions
88 * to count and then emit the reachable regular arcs. *arcs_count is
89 * incremented by the number of reachable arcs, and as many as will fit in
90 * arcs_len (possibly 0) are emitted into arcs[].
91 */
92static void
93traverse_lacons(struct cnfa *cnfa, int st,
94 int *arcs_count,
95 regex_arc_t *arcs, int arcs_len)
96{
97 struct carc *ca;
98
99 /*
100 * Since this function recurses, it could theoretically be driven to stack
101 * overflow. In practice, this is mostly useful to backstop against a
102 * failure of the regex compiler to remove a loop of LACON arcs.
103 */
104 check_stack_depth();
105
106 for (ca = cnfa->states[st]; ca->co != COLORLESS; ca++)
107 {
108 if (ca->co < cnfa->ncolors)
109 {
110 /* Ordinary arc, so count and possibly emit it */
111 int ndx = (*arcs_count)++;
112
113 if (ndx < arcs_len)
114 {
115 arcs[ndx].co = ca->co;
116 arcs[ndx].to = ca->to;
117 }
118 }
119 else
120 {
121 /* LACON arc --- assume it's satisfied and recurse... */
122 /* ... but first, assert it doesn't lead directly to post state */
123 Assert(ca->to != cnfa->post);
124
125 traverse_lacons(cnfa, ca->to, arcs_count, arcs, arcs_len);
126 }
127 }
128}
129
130/*
131 * Get number of outgoing NFA arcs of state number "st".
132 */
133int
134pg_reg_getnumoutarcs(const regex_t *regex, int st)
135{
136 struct cnfa *cnfa;
137 int arcs_count;
138
139 assert(regex != NULL && regex->re_magic == REMAGIC);
140 cnfa = &((struct guts *) regex->re_guts)->search;
141
142 if (st < 0 || st >= cnfa->nstates)
143 return 0;
144 arcs_count = 0;
145 traverse_lacons(cnfa, st, &arcs_count, NULL, 0);
146 return arcs_count;
147}
148
149/*
150 * Write array of outgoing NFA arcs of state number "st" into arcs[],
151 * whose length arcs_len must be at least as long as indicated by
152 * pg_reg_getnumoutarcs(), else not all arcs will be returned.
153 */
154void
155pg_reg_getoutarcs(const regex_t *regex, int st,
156 regex_arc_t *arcs, int arcs_len)
157{
158 struct cnfa *cnfa;
159 int arcs_count;
160
161 assert(regex != NULL && regex->re_magic == REMAGIC);
162 cnfa = &((struct guts *) regex->re_guts)->search;
163
164 if (st < 0 || st >= cnfa->nstates || arcs_len <= 0)
165 return;
166 arcs_count = 0;
167 traverse_lacons(cnfa, st, &arcs_count, arcs, arcs_len);
168}
169
170/*
171 * Get total number of colors.
172 */
173int
174pg_reg_getnumcolors(const regex_t *regex)
175{
176 struct colormap *cm;
177
178 assert(regex != NULL && regex->re_magic == REMAGIC);
179 cm = &((struct guts *) regex->re_guts)->cmap;
180
181 return cm->max + 1;
182}
183
184/*
185 * Check if color is beginning of line/string.
186 *
187 * (We might at some point need to offer more refined handling of pseudocolors,
188 * but this will do for now.)
189 */
190int
191pg_reg_colorisbegin(const regex_t *regex, int co)
192{
193 struct cnfa *cnfa;
194
195 assert(regex != NULL && regex->re_magic == REMAGIC);
196 cnfa = &((struct guts *) regex->re_guts)->search;
197
198 if (co == cnfa->bos[0] || co == cnfa->bos[1])
199 return true;
200 else
201 return false;
202}
203
204/*
205 * Check if color is end of line/string.
206 */
207int
208pg_reg_colorisend(const regex_t *regex, int co)
209{
210 struct cnfa *cnfa;
211
212 assert(regex != NULL && regex->re_magic == REMAGIC);
213 cnfa = &((struct guts *) regex->re_guts)->search;
214
215 if (co == cnfa->eos[0] || co == cnfa->eos[1])
216 return true;
217 else
218 return false;
219}
220
221/*
222 * Get number of member chrs of color number "co".
223 *
224 * Note: we return -1 if the color number is invalid, or if it is a special
225 * color (WHITE or a pseudocolor), or if the number of members is uncertain.
226 * Callers should not try to extract the members if -1 is returned.
227 */
228int
229pg_reg_getnumcharacters(const regex_t *regex, int co)
230{
231 struct colormap *cm;
232
233 assert(regex != NULL && regex->re_magic == REMAGIC);
234 cm = &((struct guts *) regex->re_guts)->cmap;
235
236 if (co <= 0 || co > cm->max) /* we reject 0 which is WHITE */
237 return -1;
238 if (cm->cd[co].flags & PSEUDO) /* also pseudocolors (BOS etc) */
239 return -1;
240
241 /*
242 * If the color appears anywhere in the high colormap, treat its number of
243 * members as uncertain. In principle we could determine all the specific
244 * chrs corresponding to each such entry, but it would be expensive
245 * (particularly if character class tests are required) and it doesn't
246 * seem worth it.
247 */
248 if (cm->cd[co].nuchrs != 0)
249 return -1;
250
251 /* OK, return the known number of member chrs */
252 return cm->cd[co].nschrs;
253}
254
255/*
256 * Write array of member chrs of color number "co" into chars[],
257 * whose length chars_len must be at least as long as indicated by
258 * pg_reg_getnumcharacters(), else not all chars will be returned.
259 *
260 * Fetching the members of WHITE or a pseudocolor is not supported.
261 *
262 * Caution: this is a relatively expensive operation.
263 */
264void
265pg_reg_getcharacters(const regex_t *regex, int co,
266 pg_wchar *chars, int chars_len)
267{
268 struct colormap *cm;
269 chr c;
270
271 assert(regex != NULL && regex->re_magic == REMAGIC);
272 cm = &((struct guts *) regex->re_guts)->cmap;
273
274 if (co <= 0 || co > cm->max || chars_len <= 0)
275 return;
276 if (cm->cd[co].flags & PSEUDO)
277 return;
278
279 /*
280 * We need only examine the low character map; there should not be any
281 * matching entries in the high map.
282 */
283 for (c = CHR_MIN; c <= MAX_SIMPLE_CHR; c++)
284 {
285 if (cm->locolormap[c - CHR_MIN] == co)
286 {
287 *chars++ = c;
288 if (--chars_len == 0)
289 break;
290 }
291 }
292}
293