TLA Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * like_match.c
4 : * LIKE pattern matching internal code.
5 : *
6 : * This file is included by like.c four times, to provide matching code for
7 : * (1) single-byte encodings, (2) UTF8, (3) other multi-byte encodings,
8 : * and (4) case insensitive matches in single-byte encodings.
9 : * (UTF8 is a special case because we can use a much more efficient version
10 : * of NextChar than can be used for general multi-byte encodings.)
11 : *
12 : * Before the inclusion, we need to define the following macros:
13 : *
14 : * NextChar
15 : * MatchText - to name of function wanted
16 : * do_like_escape - name of function if wanted - needs CHAREQ and CopyAdvChar
17 : * MATCH_LOWER - define for case (4) to specify case folding for 1-byte chars
18 : *
19 : * Copyright (c) 1996-2023, PostgreSQL Global Development Group
20 : *
21 : * IDENTIFICATION
22 : * src/backend/utils/adt/like_match.c
23 : *
24 : *-------------------------------------------------------------------------
25 : */
26 :
27 : /*
28 : * Originally written by Rich $alz, mirror!rs, Wed Nov 26 19:03:17 EST 1986.
29 : * Rich $alz is now <rsalz@bbn.com>.
30 : * Special thanks to Lars Mathiesen <thorinn@diku.dk> for the
31 : * LIKE_ABORT code.
32 : *
33 : * This code was shamelessly stolen from the "pql" code by myself and
34 : * slightly modified :)
35 : *
36 : * All references to the word "star" were replaced by "percent"
37 : * All references to the word "wild" were replaced by "like"
38 : *
39 : * All the nice shell RE matching stuff was replaced by just "_" and "%"
40 : *
41 : * As I don't have a copy of the SQL standard handy I wasn't sure whether
42 : * to leave in the '\' escape character handling.
43 : *
44 : * Keith Parks. <keith@mtcc.demon.co.uk>
45 : *
46 : * SQL lets you specify the escape character by saying
47 : * LIKE <pattern> ESCAPE <escape character>. We are a small operation
48 : * so we force you to use '\'. - ay 7/95
49 : *
50 : * Now we have the like_escape() function that converts patterns with
51 : * any specified escape character (or none at all) to the internal
52 : * default escape character, which is still '\'. - tgl 9/2000
53 : *
54 : * The code is rewritten to avoid requiring null-terminated strings,
55 : * which in turn allows us to leave out some memcpy() operations.
56 : * This code should be faster and take less memory, but no promises...
57 : * - thomas 2000-08-06
58 : */
59 :
60 :
61 : /*--------------------
62 : * Match text and pattern, return LIKE_TRUE, LIKE_FALSE, or LIKE_ABORT.
63 : *
64 : * LIKE_TRUE: they match
65 : * LIKE_FALSE: they don't match
66 : * LIKE_ABORT: not only don't they match, but the text is too short.
67 : *
68 : * If LIKE_ABORT is returned, then no suffix of the text can match the
69 : * pattern either, so an upper-level % scan can stop scanning now.
70 : *--------------------
71 : */
72 :
73 : #ifdef MATCH_LOWER
74 : #define GETCHAR(t) MATCH_LOWER(t)
75 : #else
76 : #define GETCHAR(t) (t)
77 : #endif
78 :
79 : static int
80 CBC 1510654 : MatchText(const char *t, int tlen, const char *p, int plen,
81 : pg_locale_t locale, bool locale_is_c)
82 : {
83 : /* Fast path for match-everything pattern */
84 1510654 : if (plen == 1 && *p == '%')
85 401 : return LIKE_TRUE;
86 :
87 : /* Since this function recurses, it could be driven to stack overflow */
88 1510253 : check_stack_depth();
89 :
90 : /*
91 : * In this loop, we advance by char when matching wildcards (and thus on
92 : * recursive entry to this function we are properly char-synced). On other
93 : * occasions it is safe to advance by byte, as the text and pattern will
94 : * be in lockstep. This allows us to perform all comparisons between the
95 : * text and pattern on a byte by byte basis, even for multi-byte
96 : * encodings.
97 : */
98 1854987 : while (tlen > 0 && plen > 0)
99 : {
100 1849751 : if (*p == '\\')
101 : {
102 : /* Next pattern byte must match literally, whatever it is */
103 6100 : NextByte(p, plen);
104 : /* ... and there had better be one, per SQL standard */
105 6100 : if (plen <= 0)
106 UBC 0 : ereport(ERROR,
107 : (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
108 : errmsg("LIKE pattern must not end with escape character")));
109 CBC 6100 : if (GETCHAR(*p) != GETCHAR(*t))
110 1654 : return LIKE_FALSE;
111 : }
112 1843651 : else if (*p == '%')
113 : {
114 : char firstpat;
115 :
116 : /*
117 : * % processing is essentially a search for a text position at
118 : * which the remainder of the text matches the remainder of the
119 : * pattern, using a recursive call to check each potential match.
120 : *
121 : * If there are wildcards immediately following the %, we can skip
122 : * over them first, using the idea that any sequence of N _'s and
123 : * one or more %'s is equivalent to N _'s and one % (ie, it will
124 : * match any sequence of at least N text characters). In this way
125 : * we will always run the recursive search loop using a pattern
126 : * fragment that begins with a literal character-to-match, thereby
127 : * not recursing more than we have to.
128 : */
129 84381 : NextByte(p, plen);
130 :
131 84663 : while (plen > 0)
132 : {
133 65911 : if (*p == '%')
134 3 : NextByte(p, plen);
135 65908 : else if (*p == '_')
136 : {
137 : /* If not enough text left to match the pattern, ABORT */
138 282 : if (tlen <= 0)
139 3 : return LIKE_ABORT;
140 279 : NextChar(t, tlen);
141 279 : NextByte(p, plen);
142 : }
143 : else
144 65626 : break; /* Reached a non-wildcard pattern char */
145 : }
146 :
147 : /*
148 : * If we're at end of pattern, match: we have a trailing % which
149 : * matches any remaining text string.
150 : */
151 84378 : if (plen <= 0)
152 18752 : return LIKE_TRUE;
153 :
154 : /*
155 : * Otherwise, scan for a text position at which we can match the
156 : * rest of the pattern. The first remaining pattern char is known
157 : * to be a regular or escaped literal character, so we can compare
158 : * the first pattern byte to each text byte to avoid recursing
159 : * more than we have to. This fact also guarantees that we don't
160 : * have to consider a match to the zero-length substring at the
161 : * end of the text.
162 : */
163 65626 : if (*p == '\\')
164 : {
165 2 : if (plen < 2)
166 UBC 0 : ereport(ERROR,
167 : (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
168 : errmsg("LIKE pattern must not end with escape character")));
169 CBC 2 : firstpat = GETCHAR(p[1]);
170 : }
171 : else
172 65624 : firstpat = GETCHAR(*p);
173 :
174 1911480 : while (tlen > 0)
175 : {
176 1860312 : if (GETCHAR(*t) == firstpat)
177 : {
178 53540 : int matched = MatchText(t, tlen, p, plen,
179 : locale, locale_is_c);
180 :
181 53540 : if (matched != LIKE_FALSE)
182 14458 : return matched; /* TRUE or ABORT */
183 : }
184 :
185 1845878 : NextChar(t, tlen);
186 : }
187 :
188 : /*
189 : * End of text with no match, so no point in trying later places
190 : * to start matching this pattern.
191 : */
192 51168 : return LIKE_ABORT;
193 : }
194 1759270 : else if (*p == '_')
195 : {
196 : /* _ matches any single character, and we know there is one */
197 4931 : NextChar(t, tlen);
198 4931 : NextByte(p, plen);
199 4931 : continue;
200 : }
201 1754339 : else if (GETCHAR(*p) != GETCHAR(*t))
202 : {
203 : /* non-wildcard pattern char fails to match text char */
204 1418982 : return LIKE_FALSE;
205 : }
206 :
207 : /*
208 : * Pattern and text match, so advance.
209 : *
210 : * It is safe to use NextByte instead of NextChar here, even for
211 : * multi-byte character sets, because we are not following immediately
212 : * after a wildcard character. If we are in the middle of a multibyte
213 : * character, we must already have matched at least one byte of the
214 : * character from both text and pattern; so we cannot get out-of-sync
215 : * on character boundaries. And we know that no backend-legal
216 : * encoding allows ASCII characters such as '%' to appear as non-first
217 : * bytes of characters, so we won't mistakenly detect a new wildcard.
218 : */
219 339803 : NextByte(t, tlen);
220 339803 : NextByte(p, plen);
221 : }
222 :
223 5236 : if (tlen > 0)
224 152 : return LIKE_FALSE; /* end of pattern, but not of text */
225 :
226 : /*
227 : * End of text, but perhaps not of pattern. Match iff the remaining
228 : * pattern can match a zero-length string, ie, it's zero or more %'s.
229 : */
230 5381 : while (plen > 0 && *p == '%')
231 297 : NextByte(p, plen);
232 5084 : if (plen <= 0)
233 2342 : return LIKE_TRUE;
234 :
235 : /*
236 : * End of text with no match, so no point in trying later places to start
237 : * matching this pattern.
238 : */
239 2742 : return LIKE_ABORT;
240 : } /* MatchText() */
241 :
242 : /*
243 : * like_escape() --- given a pattern and an ESCAPE string,
244 : * convert the pattern to use Postgres' standard backslash escape convention.
245 : */
246 : #ifdef do_like_escape
247 :
248 : static text *
249 112 : do_like_escape(text *pat, text *esc)
250 : {
251 : text *result;
252 : char *p,
253 : *e,
254 : *r;
255 : int plen,
256 : elen;
257 : bool afterescape;
258 :
259 112 : p = VARDATA_ANY(pat);
260 112 : plen = VARSIZE_ANY_EXHDR(pat);
261 112 : e = VARDATA_ANY(esc);
262 112 : elen = VARSIZE_ANY_EXHDR(esc);
263 :
264 : /*
265 : * Worst-case pattern growth is 2x --- unlikely, but it's hardly worth
266 : * trying to calculate the size more accurately than that.
267 : */
268 112 : result = (text *) palloc(plen * 2 + VARHDRSZ);
269 112 : r = VARDATA(result);
270 :
271 112 : if (elen == 0)
272 : {
273 : /*
274 : * No escape character is wanted. Double any backslashes in the
275 : * pattern to make them act like ordinary characters.
276 : */
277 64 : while (plen > 0)
278 : {
279 48 : if (*p == '\\')
280 UBC 0 : *r++ = '\\';
281 CBC 96 : CopyAdvChar(r, p, plen);
282 : }
283 : }
284 : else
285 : {
286 : /*
287 : * The specified escape must be only a single character.
288 : */
289 96 : NextChar(e, elen);
290 96 : if (elen != 0)
291 UBC 0 : ereport(ERROR,
292 : (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
293 : errmsg("invalid escape string"),
294 : errhint("Escape string must be empty or one character.")));
295 :
296 CBC 96 : e = VARDATA_ANY(esc);
297 :
298 : /*
299 : * If specified escape is '\', just copy the pattern as-is.
300 : */
301 96 : if (*e == '\\')
302 : {
303 UBC 0 : memcpy(result, pat, VARSIZE_ANY(pat));
304 0 : return result;
305 : }
306 :
307 : /*
308 : * Otherwise, convert occurrences of the specified escape character to
309 : * '\', and double occurrences of '\' --- unless they immediately
310 : * follow an escape character!
311 : */
312 CBC 96 : afterescape = false;
313 582 : while (plen > 0)
314 : {
315 486 : if (CHAREQ(p, e) && !afterescape)
316 : {
317 96 : *r++ = '\\';
318 96 : NextChar(p, plen);
319 96 : afterescape = true;
320 : }
321 390 : else if (*p == '\\')
322 : {
323 UBC 0 : *r++ = '\\';
324 0 : if (!afterescape)
325 0 : *r++ = '\\';
326 0 : NextChar(p, plen);
327 0 : afterescape = false;
328 : }
329 : else
330 : {
331 CBC 762 : CopyAdvChar(r, p, plen);
332 390 : afterescape = false;
333 : }
334 : }
335 : }
336 :
337 112 : SET_VARSIZE(result, r - ((char *) result));
338 :
339 112 : return result;
340 : }
341 : #endif /* do_like_escape */
342 :
343 : #ifdef CHAREQ
344 : #undef CHAREQ
345 : #endif
346 :
347 : #undef NextChar
348 : #undef CopyAdvChar
349 : #undef MatchText
350 :
351 : #ifdef do_like_escape
352 : #undef do_like_escape
353 : #endif
354 :
355 : #undef GETCHAR
356 :
357 : #ifdef MATCH_LOWER
358 : #undef MATCH_LOWER
359 :
360 : #endif
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