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 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 * 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