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