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) 1996-2017, 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 LABORT code.
31 : *
32 : * This code was shamelessly stolen from the "pql" code by myself and
33 : * slightly modified :)
34 : *
35 : * All references to the word "star" were replaced by "percent"
36 : * All references to the word "wild" were replaced by "like"
37 : *
38 : * All the nice shell RE matching stuff was replaced by just "_" and "%"
39 : *
40 : * As I don't have a copy of the SQL standard handy I wasn't sure whether
41 : * to leave in the '\' escape character handling.
42 : *
43 : * Keith Parks. <keith@mtcc.demon.co.uk>
44 : *
45 : * SQL lets you specify the escape character by saying
46 : * LIKE <pattern> ESCAPE <escape character>. We are a small operation
47 : * so we force you to use '\'. - ay 7/95
48 : *
49 : * Now we have the like_escape() function that converts patterns with
50 : * any specified escape character (or none at all) to the internal
51 : * default escape character, which is still '\'. - tgl 9/2000
52 : *
53 : * The code is rewritten to avoid requiring null-terminated strings,
54 : * which in turn allows us to leave out some memcpy() operations.
55 : * This code should be faster and take less memory, but no promises...
56 : * - thomas 2000-08-06
57 : */
58 :
59 :
60 : /*--------------------
61 : * Match text and pattern, return LIKE_TRUE, LIKE_FALSE, or LIKE_ABORT.
62 : *
63 : * LIKE_TRUE: they match
64 : * LIKE_FALSE: they don't match
65 : * LIKE_ABORT: not only don't they match, but the text is too short.
66 : *
67 : * If LIKE_ABORT is returned, then no suffix of the text can match the
68 : * pattern either, so an upper-level % scan can stop scanning now.
69 : *--------------------
70 : */
71 :
72 : #ifdef MATCH_LOWER
73 : #define GETCHAR(t) MATCH_LOWER(t)
74 : #else
75 : #define GETCHAR(t) (t)
76 : #endif
77 :
78 : static int
79 50879 : MatchText(char *t, int tlen, char *p, int plen,
80 : pg_locale_t locale, bool locale_is_c)
81 : {
82 : /* Fast path for match-everything pattern */
83 50879 : if (plen == 1 && *p == '%')
84 0 : return LIKE_TRUE;
85 :
86 : /* Since this function recurses, it could be driven to stack overflow */
87 50879 : check_stack_depth();
88 :
89 : /*
90 : * In this loop, we advance by char when matching wildcards (and thus on
91 : * recursive entry to this function we are properly char-synced). On other
92 : * occasions it is safe to advance by byte, as the text and pattern will
93 : * be in lockstep. This allows us to perform all comparisons between the
94 : * text and pattern on a byte by byte basis, even for multi-byte
95 : * encodings.
96 : */
97 128179 : while (tlen > 0 && plen > 0)
98 : {
99 76952 : if (*p == '\\')
100 : {
101 : /* Next pattern byte must match literally, whatever it is */
102 1160 : NextByte(p, plen);
103 : /* ... and there had better be one, per SQL standard */
104 1160 : if (plen <= 0)
105 0 : ereport(ERROR,
106 : (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
107 : errmsg("LIKE pattern must not end with escape character")));
108 1160 : if (GETCHAR(*p) != GETCHAR(*t))
109 511 : return LIKE_FALSE;
110 : }
111 75792 : else if (*p == '%')
112 : {
113 : char firstpat;
114 :
115 : /*
116 : * % processing is essentially a search for a text position at
117 : * which the remainder of the text matches the remainder of the
118 : * pattern, using a recursive call to check each potential match.
119 : *
120 : * If there are wildcards immediately following the %, we can skip
121 : * over them first, using the idea that any sequence of N _'s and
122 : * one or more %'s is equivalent to N _'s and one % (ie, it will
123 : * match any sequence of at least N text characters). In this way
124 : * we will always run the recursive search loop using a pattern
125 : * fragment that begins with a literal character-to-match, thereby
126 : * not recursing more than we have to.
127 : */
128 7320 : NextByte(p, plen);
129 :
130 14665 : while (plen > 0)
131 : {
132 5392 : if (*p == '%')
133 1 : NextByte(p, plen);
134 5391 : else if (*p == '_')
135 : {
136 : /* If not enough text left to match the pattern, ABORT */
137 25 : if (tlen <= 0)
138 1 : return LIKE_ABORT;
139 24 : NextChar(t, tlen);
140 24 : NextByte(p, plen);
141 : }
142 : else
143 5366 : break; /* Reached a non-wildcard pattern char */
144 : }
145 :
146 : /*
147 : * If we're at end of pattern, match: we have a trailing % which
148 : * matches any remaining text string.
149 : */
150 7319 : if (plen <= 0)
151 1953 : return LIKE_TRUE;
152 :
153 : /*
154 : * Otherwise, scan for a text position at which we can match the
155 : * rest of the pattern. The first remaining pattern char is known
156 : * to be a regular or escaped literal character, so we can compare
157 : * the first pattern byte to each text byte to avoid recursing
158 : * more than we have to. This fact also guarantees that we don't
159 : * have to consider a match to the zero-length substring at the
160 : * end of the text.
161 : */
162 5366 : if (*p == '\\')
163 : {
164 0 : if (plen < 2)
165 0 : ereport(ERROR,
166 : (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
167 : errmsg("LIKE pattern must not end with escape character")));
168 0 : firstpat = GETCHAR(p[1]);
169 : }
170 : else
171 5366 : firstpat = GETCHAR(*p);
172 :
173 143032 : while (tlen > 0)
174 : {
175 133833 : if (GETCHAR(*t) == firstpat)
176 : {
177 2666 : int matched = MatchText(t, tlen, p, plen,
178 : locale, locale_is_c);
179 :
180 2666 : if (matched != LIKE_FALSE)
181 1533 : return matched; /* TRUE or ABORT */
182 : }
183 :
184 132300 : NextChar(t, tlen);
185 : }
186 :
187 : /*
188 : * End of text with no match, so no point in trying later places
189 : * to start matching this pattern.
190 : */
191 3833 : return LIKE_ABORT;
192 : }
193 68472 : else if (*p == '_')
194 : {
195 : /* _ matches any single character, and we know there is one */
196 712 : NextChar(t, tlen);
197 712 : NextByte(p, plen);
198 712 : continue;
199 : }
200 67760 : else if (GETCHAR(*p) != GETCHAR(*t))
201 : {
202 : /* non-wildcard pattern char fails to match text char */
203 42700 : return LIKE_FALSE;
204 : }
205 :
206 : /*
207 : * Pattern and text match, so advance.
208 : *
209 : * It is safe to use NextByte instead of NextChar here, even for
210 : * multi-byte character sets, because we are not following immediately
211 : * after a wildcard character. If we are in the middle of a multibyte
212 : * character, we must already have matched at least one byte of the
213 : * character from both text and pattern; so we cannot get out-of-sync
214 : * on character boundaries. And we know that no backend-legal
215 : * encoding allows ASCII characters such as '%' to appear as non-first
216 : * bytes of characters, so we won't mistakenly detect a new wildcard.
217 : */
218 25709 : NextByte(t, tlen);
219 25709 : NextByte(p, plen);
220 : }
221 :
222 348 : if (tlen > 0)
223 9 : return LIKE_FALSE; /* end of pattern, but not of text */
224 :
225 : /*
226 : * End of text, but perhaps not of pattern. Match iff the remaining
227 : * pattern can match a zero-length string, ie, it's zero or more %'s.
228 : */
229 704 : while (plen > 0 && *p == '%')
230 26 : NextByte(p, plen);
231 339 : if (plen <= 0)
232 288 : return LIKE_TRUE;
233 :
234 : /*
235 : * End of text with no match, so no point in trying later places to start
236 : * matching this pattern.
237 : */
238 51 : return LIKE_ABORT;
239 : } /* MatchText() */
240 :
241 : /*
242 : * like_escape() --- given a pattern and an ESCAPE string,
243 : * convert the pattern to use Postgres' standard backslash escape convention.
244 : */
245 : #ifdef do_like_escape
246 :
247 : static text *
248 30 : do_like_escape(text *pat, text *esc)
249 : {
250 : text *result;
251 : char *p,
252 : *e,
253 : *r;
254 : int plen,
255 : elen;
256 : bool afterescape;
257 :
258 30 : p = VARDATA_ANY(pat);
259 30 : plen = VARSIZE_ANY_EXHDR(pat);
260 30 : e = VARDATA_ANY(esc);
261 30 : elen = VARSIZE_ANY_EXHDR(esc);
262 :
263 : /*
264 : * Worst-case pattern growth is 2x --- unlikely, but it's hardly worth
265 : * trying to calculate the size more accurately than that.
266 : */
267 30 : result = (text *) palloc(plen * 2 + VARHDRSZ);
268 30 : r = VARDATA(result);
269 :
270 30 : if (elen == 0)
271 : {
272 : /*
273 : * No escape character is wanted. Double any backslashes in the
274 : * pattern to make them act like ordinary characters.
275 : */
276 0 : while (plen > 0)
277 : {
278 0 : if (*p == '\\')
279 0 : *r++ = '\\';
280 0 : CopyAdvChar(r, p, plen);
281 : }
282 : }
283 : else
284 : {
285 : /*
286 : * The specified escape must be only a single character.
287 : */
288 30 : NextChar(e, elen);
289 30 : if (elen != 0)
290 0 : ereport(ERROR,
291 : (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
292 : errmsg("invalid escape string"),
293 : errhint("Escape string must be empty or one character.")));
294 :
295 30 : e = VARDATA_ANY(esc);
296 :
297 : /*
298 : * If specified escape is '\', just copy the pattern as-is.
299 : */
300 30 : if (*e == '\\')
301 : {
302 0 : memcpy(result, pat, VARSIZE_ANY(pat));
303 0 : return result;
304 : }
305 :
306 : /*
307 : * Otherwise, convert occurrences of the specified escape character to
308 : * '\', and double occurrences of '\' --- unless they immediately
309 : * follow an escape character!
310 : */
311 30 : afterescape = false;
312 214 : while (plen > 0)
313 : {
314 154 : if (CHAREQ(p, e) && !afterescape)
315 : {
316 30 : *r++ = '\\';
317 30 : NextChar(p, plen);
318 30 : afterescape = true;
319 : }
320 124 : else if (*p == '\\')
321 : {
322 0 : *r++ = '\\';
323 0 : if (!afterescape)
324 0 : *r++ = '\\';
325 0 : NextChar(p, plen);
326 0 : afterescape = false;
327 : }
328 : else
329 : {
330 124 : CopyAdvChar(r, p, plen);
331 124 : afterescape = false;
332 : }
333 : }
334 : }
335 :
336 30 : SET_VARSIZE(result, r - ((char *) result));
337 :
338 30 : return result;
339 : }
340 : #endif /* do_like_escape */
341 :
342 : #ifdef CHAREQ
343 : #undef CHAREQ
344 : #endif
345 :
346 : #undef NextChar
347 : #undef CopyAdvChar
348 : #undef MatchText
349 :
350 : #ifdef do_like_escape
351 : #undef do_like_escape
352 : #endif
353 :
354 : #undef GETCHAR
355 :
356 : #ifdef MATCH_LOWER
357 : #undef MATCH_LOWER
358 :
359 : #endif
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