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) 1996-2018, 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
MatchText(char * t,int tlen,char * p,int plen,pg_locale_t locale,bool locale_is_c)79 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 if (plen == 1 && *p == '%')
84 return LIKE_TRUE;
85
86 /* Since this function recurses, it could be driven to stack overflow */
87 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 while (tlen > 0 && plen > 0)
98 {
99 if (*p == '\\')
100 {
101 /* Next pattern byte must match literally, whatever it is */
102 NextByte(p, plen);
103 /* ... and there had better be one, per SQL standard */
104 if (plen <= 0)
105 ereport(ERROR,
106 (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
107 errmsg("LIKE pattern must not end with escape character")));
108 if (GETCHAR(*p) != GETCHAR(*t))
109 return LIKE_FALSE;
110 }
111 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 NextByte(p, plen);
129
130 while (plen > 0)
131 {
132 if (*p == '%')
133 NextByte(p, plen);
134 else if (*p == '_')
135 {
136 /* If not enough text left to match the pattern, ABORT */
137 if (tlen <= 0)
138 return LIKE_ABORT;
139 NextChar(t, tlen);
140 NextByte(p, plen);
141 }
142 else
143 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 if (plen <= 0)
151 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 if (*p == '\\')
163 {
164 if (plen < 2)
165 ereport(ERROR,
166 (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
167 errmsg("LIKE pattern must not end with escape character")));
168 firstpat = GETCHAR(p[1]);
169 }
170 else
171 firstpat = GETCHAR(*p);
172
173 while (tlen > 0)
174 {
175 if (GETCHAR(*t) == firstpat)
176 {
177 int matched = MatchText(t, tlen, p, plen,
178 locale, locale_is_c);
179
180 if (matched != LIKE_FALSE)
181 return matched; /* TRUE or ABORT */
182 }
183
184 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 return LIKE_ABORT;
192 }
193 else if (*p == '_')
194 {
195 /* _ matches any single character, and we know there is one */
196 NextChar(t, tlen);
197 NextByte(p, plen);
198 continue;
199 }
200 else if (GETCHAR(*p) != GETCHAR(*t))
201 {
202 /* non-wildcard pattern char fails to match text char */
203 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 NextByte(t, tlen);
219 NextByte(p, plen);
220 }
221
222 if (tlen > 0)
223 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 while (plen > 0 && *p == '%')
230 NextByte(p, plen);
231 if (plen <= 0)
232 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 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 *
do_like_escape(text * pat,text * esc)248 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 p = VARDATA_ANY(pat);
259 plen = VARSIZE_ANY_EXHDR(pat);
260 e = VARDATA_ANY(esc);
261 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 result = (text *) palloc(plen * 2 + VARHDRSZ);
268 r = VARDATA(result);
269
270 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 while (plen > 0)
277 {
278 if (*p == '\\')
279 *r++ = '\\';
280 CopyAdvChar(r, p, plen);
281 }
282 }
283 else
284 {
285 /*
286 * The specified escape must be only a single character.
287 */
288 NextChar(e, elen);
289 if (elen != 0)
290 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 e = VARDATA_ANY(esc);
296
297 /*
298 * If specified escape is '\', just copy the pattern as-is.
299 */
300 if (*e == '\\')
301 {
302 memcpy(result, pat, VARSIZE_ANY(pat));
303 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 afterescape = false;
312 while (plen > 0)
313 {
314 if (CHAREQ(p, e) && !afterescape)
315 {
316 *r++ = '\\';
317 NextChar(p, plen);
318 afterescape = true;
319 }
320 else if (*p == '\\')
321 {
322 *r++ = '\\';
323 if (!afterescape)
324 *r++ = '\\';
325 NextChar(p, plen);
326 afterescape = false;
327 }
328 else
329 {
330 CopyAdvChar(r, p, plen);
331 afterescape = false;
332 }
333 }
334 }
335
336 SET_VARSIZE(result, r - ((char *) result));
337
338 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
360