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like_match.c
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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 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 */
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 *
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
#define LIKE_FALSE
Definition: like.c:30
int errhint(const char *fmt,...)
Definition: elog.c:987
#define VARDATA_ANY(PTR)
Definition: postgres.h:347
#define VARDATA(PTR)
Definition: postgres.h:303
#define GETCHAR(t)
Definition: like_match.c:75
#define VARHDRSZ
Definition: c.h:445
#define do_like_escape
Definition: like.c:130
#define LIKE_TRUE
Definition: like.c:29
int errcode(int sqlerrcode)
Definition: elog.c:575
return result
Definition: formatting.c:1618
static int MatchText(char *t, int tlen, char *p, int plen, pg_locale_t locale, bool locale_is_c)
Definition: like_match.c:79
#define NextChar(p, plen)
Definition: like.c:143
#define ERROR
Definition: elog.h:43
void check_stack_depth(void)
Definition: postgres.c:3102
#define ereport(elevel, rest)
Definition: elog.h:122
#define CopyAdvChar(dst, src, srclen)
Definition: like.c:127
#define CHAREQ(p1, p2)
Definition: like.c:125
#define NextByte(p, plen)
Definition: like.c:106
#define VARSIZE_ANY(PTR)
Definition: postgres.h:334
#define LIKE_ABORT
Definition: like.c:31
e
Definition: preproc-init.c:82
#define VARSIZE_ANY_EXHDR(PTR)
Definition: postgres.h:340
void * palloc(Size size)
Definition: mcxt.c:849
int errmsg(const char *fmt,...)
Definition: elog.c:797
static char * locale
Definition: initdb.c:123
Definition: c.h:439
#define SET_VARSIZE(PTR, len)
Definition: postgres.h:328