like_match.c

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/*-------------------------------------------------------------------------
 *
 * like_match.c
 *    LIKE pattern matching internal code.
 *
 * This file is included by like.c four times, to provide matching code for
 * (1) single-byte encodings, (2) UTF8, (3) other multi-byte encodings,
 * and (4) case insensitive matches in single-byte encodings.
 * (UTF8 is a special case because we can use a much more efficient version
 * of NextChar than can be used for general multi-byte encodings.)
 *
 * Before the inclusion, we need to define the following macros:
 *
 * NextChar
 * MatchText - to name of function wanted
 * do_like_escape - name of function if wanted - needs CHAREQ and CopyAdvChar
 * MATCH_LOWER - define for case (4) to specify case folding for 1-byte chars
 *
 * Copyright (c) 1996-2013, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *  src/backend/utils/adt/like_match.c
 *
 *-------------------------------------------------------------------------
 */

/*
 *  Originally written by Rich $alz, mirror!rs, Wed Nov 26 19:03:17 EST 1986.
 *  Rich $alz is now <[email protected]>.
 *  Special thanks to Lars Mathiesen <[email protected]> for the LABORT code.
 *
 *  This code was shamelessly stolen from the "pql" code by myself and
 *  slightly modified :)
 *
 *  All references to the word "star" were replaced by "percent"
 *  All references to the word "wild" were replaced by "like"
 *
 *  All the nice shell RE matching stuff was replaced by just "_" and "%"
 *
 *  As I don't have a copy of the SQL standard handy I wasn't sure whether
 *  to leave in the '\' escape character handling.
 *
 *  Keith Parks. <[email protected]>
 *
 *  SQL lets you specify the escape character by saying
 *  LIKE <pattern> ESCAPE <escape character>. We are a small operation
 *  so we force you to use '\'. - ay 7/95
 *
 *  Now we have the like_escape() function that converts patterns with
 *  any specified escape character (or none at all) to the internal
 *  default escape character, which is still '\'. - tgl 9/2000
 *
 * The code is rewritten to avoid requiring null-terminated strings,
 * which in turn allows us to leave out some memcpy() operations.
 * This code should be faster and take less memory, but no promises...
 * - thomas 2000-08-06
 */


/*--------------------
 *  Match text and pattern, return LIKE_TRUE, LIKE_FALSE, or LIKE_ABORT.
 *
 *  LIKE_TRUE: they match
 *  LIKE_FALSE: they don't match
 *  LIKE_ABORT: not only don't they match, but the text is too short.
 *
 * If LIKE_ABORT is returned, then no suffix of the text can match the
 * pattern either, so an upper-level % scan can stop scanning now.
 *--------------------
 */

#ifdef MATCH_LOWER
#define GETCHAR(t) MATCH_LOWER(t)
#else
#define GETCHAR(t) (t)
#endif

static int
MatchText(char *t, int tlen, char *p, int plen,
          pg_locale_t locale, bool locale_is_c)
{
    /* Fast path for match-everything pattern */
    if (plen == 1 && *p == '%')
        return LIKE_TRUE;

    /*
     * In this loop, we advance by char when matching wildcards (and thus on
     * recursive entry to this function we are properly char-synced). On other
     * occasions it is safe to advance by byte, as the text and pattern will
     * be in lockstep. This allows us to perform all comparisons between the
     * text and pattern on a byte by byte basis, even for multi-byte
     * encodings.
     */
    while (tlen > 0 && plen > 0)
    {
        if (*p == '\\')
        {
            /* Next pattern byte must match literally, whatever it is */
            NextByte(p, plen);
            /* ... and there had better be one, per SQL standard */
            if (plen <= 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
                 errmsg("LIKE pattern must not end with escape character")));
            if (GETCHAR(*p) != GETCHAR(*t))
                return LIKE_FALSE;
        }
        else if (*p == '%')
        {
            char        firstpat;

            /*
             * % processing is essentially a search for a text position at
             * which the remainder of the text matches the remainder of the
             * pattern, using a recursive call to check each potential match.
             *
             * If there are wildcards immediately following the %, we can skip
             * over them first, using the idea that any sequence of N _'s and
             * one or more %'s is equivalent to N _'s and one % (ie, it will
             * match any sequence of at least N text characters).  In this way
             * we will always run the recursive search loop using a pattern
             * fragment that begins with a literal character-to-match, thereby
             * not recursing more than we have to.
             */
            NextByte(p, plen);

            while (plen > 0)
            {
                if (*p == '%')
                    NextByte(p, plen);
                else if (*p == '_')
                {
                    /* If not enough text left to match the pattern, ABORT */
                    if (tlen <= 0)
                        return LIKE_ABORT;
                    NextChar(t, tlen);
                    NextByte(p, plen);
                }
                else
                    break;      /* Reached a non-wildcard pattern char */
            }

            /*
             * If we're at end of pattern, match: we have a trailing % which
             * matches any remaining text string.
             */
            if (plen <= 0)
                return LIKE_TRUE;

            /*
             * Otherwise, scan for a text position at which we can match the
             * rest of the pattern.  The first remaining pattern char is known
             * to be a regular or escaped literal character, so we can compare
             * the first pattern byte to each text byte to avoid recursing
             * more than we have to.  This fact also guarantees that we don't
             * have to consider a match to the zero-length substring at the
             * end of the text.
             */
            if (*p == '\\')
            {
                if (plen < 2)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
                             errmsg("LIKE pattern must not end with escape character")));
                firstpat = GETCHAR(p[1]);
            }
            else
                firstpat = GETCHAR(*p);

            while (tlen > 0)
            {
                if (GETCHAR(*t) == firstpat)
                {
                    int         matched = MatchText(t, tlen, p, plen,
                                                    locale, locale_is_c);

                    if (matched != LIKE_FALSE)
                        return matched; /* TRUE or ABORT */
                }

                NextChar(t, tlen);
            }

            /*
             * End of text with no match, so no point in trying later places
             * to start matching this pattern.
             */
            return LIKE_ABORT;
        }
        else if (*p == '_')
        {
            /* _ matches any single character, and we know there is one */
            NextChar(t, tlen);
            NextByte(p, plen);
            continue;
        }
        else if (GETCHAR(*p) != GETCHAR(*t))
        {
            /* non-wildcard pattern char fails to match text char */
            return LIKE_FALSE;
        }

        /*
         * Pattern and text match, so advance.
         *
         * It is safe to use NextByte instead of NextChar here, even for
         * multi-byte character sets, because we are not following immediately
         * after a wildcard character. If we are in the middle of a multibyte
         * character, we must already have matched at least one byte of the
         * character from both text and pattern; so we cannot get out-of-sync
         * on character boundaries.  And we know that no backend-legal
         * encoding allows ASCII characters such as '%' to appear as non-first
         * bytes of characters, so we won't mistakenly detect a new wildcard.
         */
        NextByte(t, tlen);
        NextByte(p, plen);
    }

    if (tlen > 0)
        return LIKE_FALSE;      /* end of pattern, but not of text */

    /*
     * End of text, but perhaps not of pattern.  Match iff the remaining
     * pattern can match a zero-length string, ie, it's zero or more %'s.
     */
    while (plen > 0 && *p == '%')
        NextByte(p, plen);
    if (plen <= 0)
        return LIKE_TRUE;

    /*
     * End of text with no match, so no point in trying later places to start
     * matching this pattern.
     */
    return LIKE_ABORT;
}   /* MatchText() */

/*
 * like_escape() --- given a pattern and an ESCAPE string,
 * convert the pattern to use Postgres' standard backslash escape convention.
 */
#ifdef do_like_escape

static text *
do_like_escape(text *pat, text *esc)
{
    text       *result;
    char       *p,
               *e,
               *r;
    int         plen,
                elen;
    bool        afterescape;

    p = VARDATA_ANY(pat);
    plen = VARSIZE_ANY_EXHDR(pat);
    e = VARDATA_ANY(esc);
    elen = VARSIZE_ANY_EXHDR(esc);

    /*
     * Worst-case pattern growth is 2x --- unlikely, but it's hardly worth
     * trying to calculate the size more accurately than that.
     */
    result = (text *) palloc(plen * 2 + VARHDRSZ);
    r = VARDATA(result);

    if (elen == 0)
    {
        /*
         * No escape character is wanted.  Double any backslashes in the
         * pattern to make them act like ordinary characters.
         */
        while (plen > 0)
        {
            if (*p == '\\')
                *r++ = '\\';
            CopyAdvChar(r, p, plen);
        }
    }
    else
    {
        /*
         * The specified escape must be only a single character.
         */
        NextChar(e, elen);
        if (elen != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
                     errmsg("invalid escape string"),
                  errhint("Escape string must be empty or one character.")));

        e = VARDATA_ANY(esc);

        /*
         * If specified escape is '\', just copy the pattern as-is.
         */
        if (*e == '\\')
        {
            memcpy(result, pat, VARSIZE_ANY(pat));
            return result;
        }

        /*
         * Otherwise, convert occurrences of the specified escape character to
         * '\', and double occurrences of '\' --- unless they immediately
         * follow an escape character!
         */
        afterescape = false;
        while (plen > 0)
        {
            if (CHAREQ(p, e) && !afterescape)
            {
                *r++ = '\\';
                NextChar(p, plen);
                afterescape = true;
            }
            else if (*p == '\\')
            {
                *r++ = '\\';
                if (!afterescape)
                    *r++ = '\\';
                NextChar(p, plen);
                afterescape = false;
            }
            else
            {
                CopyAdvChar(r, p, plen);
                afterescape = false;
            }
        }
    }

    SET_VARSIZE(result, r - ((char *) result));

    return result;
}
#endif   /* do_like_escape */

#ifdef CHAREQ
#undef CHAREQ
#endif

#undef NextChar
#undef CopyAdvChar
#undef MatchText

#ifdef do_like_escape
#undef do_like_escape
#endif

#undef GETCHAR

#ifdef MATCH_LOWER
#undef MATCH_LOWER

#endif