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) 1996-2020, 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
MatchText(const char * t,int tlen,const char * p,int plen,pg_locale_t locale,bool locale_is_c)80 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 if (plen == 1 && *p == '%')
85 return LIKE_TRUE;
86
87 /* Since this function recurses, it could be driven to stack overflow */
88 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 while (tlen > 0 && plen > 0)
99 {
100 if (*p == '\\')
101 {
102 /* Next pattern byte must match literally, whatever it is */
103 NextByte(p, plen);
104 /* ... and there had better be one, per SQL standard */
105 if (plen <= 0)
106 ereport(ERROR,
107 (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
108 errmsg("LIKE pattern must not end with escape character")));
109 if (GETCHAR(*p) != GETCHAR(*t))
110 return LIKE_FALSE;
111 }
112 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 NextByte(p, plen);
130
131 while (plen > 0)
132 {
133 if (*p == '%')
134 NextByte(p, plen);
135 else if (*p == '_')
136 {
137 /* If not enough text left to match the pattern, ABORT */
138 if (tlen <= 0)
139 return LIKE_ABORT;
140 NextChar(t, tlen);
141 NextByte(p, plen);
142 }
143 else
144 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 if (plen <= 0)
152 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 if (*p == '\\')
164 {
165 if (plen < 2)
166 ereport(ERROR,
167 (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
168 errmsg("LIKE pattern must not end with escape character")));
169 firstpat = GETCHAR(p[1]);
170 }
171 else
172 firstpat = GETCHAR(*p);
173
174 while (tlen > 0)
175 {
176 if (GETCHAR(*t) == firstpat)
177 {
178 int matched = MatchText(t, tlen, p, plen,
179 locale, locale_is_c);
180
181 if (matched != LIKE_FALSE)
182 return matched; /* TRUE or ABORT */
183 }
184
185 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 return LIKE_ABORT;
193 }
194 else if (*p == '_')
195 {
196 /* _ matches any single character, and we know there is one */
197 NextChar(t, tlen);
198 NextByte(p, plen);
199 continue;
200 }
201 else if (GETCHAR(*p) != GETCHAR(*t))
202 {
203 /* non-wildcard pattern char fails to match text char */
204 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 NextByte(t, tlen);
220 NextByte(p, plen);
221 }
222
223 if (tlen > 0)
224 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 while (plen > 0 && *p == '%')
231 NextByte(p, plen);
232 if (plen <= 0)
233 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 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 *
do_like_escape(text * pat,text * esc)249 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 p = VARDATA_ANY(pat);
260 plen = VARSIZE_ANY_EXHDR(pat);
261 e = VARDATA_ANY(esc);
262 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 result = (text *) palloc(plen * 2 + VARHDRSZ);
269 r = VARDATA(result);
270
271 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 while (plen > 0)
278 {
279 if (*p == '\\')
280 *r++ = '\\';
281 CopyAdvChar(r, p, plen);
282 }
283 }
284 else
285 {
286 /*
287 * The specified escape must be only a single character.
288 */
289 NextChar(e, elen);
290 if (elen != 0)
291 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 e = VARDATA_ANY(esc);
297
298 /*
299 * If specified escape is '\', just copy the pattern as-is.
300 */
301 if (*e == '\\')
302 {
303 memcpy(result, pat, VARSIZE_ANY(pat));
304 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 afterescape = false;
313 while (plen > 0)
314 {
315 if (CHAREQ(p, e) && !afterescape)
316 {
317 *r++ = '\\';
318 NextChar(p, plen);
319 afterescape = true;
320 }
321 else if (*p == '\\')
322 {
323 *r++ = '\\';
324 if (!afterescape)
325 *r++ = '\\';
326 NextChar(p, plen);
327 afterescape = false;
328 }
329 else
330 {
331 CopyAdvChar(r, p, plen);
332 afterescape = false;
333 }
334 }
335 }
336
337 SET_VARSIZE(result, r - ((char *) result));
338
339 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
361