regexp.c

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/*-------------------------------------------------------------------------
 *
 * regexp.c
 *    Postgres' interface to the regular expression package.
 *
 * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/regexp.c
 *
 *      Alistair Crooks added the code for the regex caching
 *      agc - cached the regular expressions used - there's a good chance
 *      that we'll get a hit, so this saves a compile step for every
 *      attempted match. I haven't actually measured the speed improvement,
 *      but it `looks' a lot quicker visually when watching regression
 *      test output.
 *
 *      agc - incorporated Keith Bostic's Berkeley regex code into
 *      the tree for all ports. To distinguish this regex code from any that
 *      is existent on a platform, I've prepended the string "pg_" to
 *      the functions regcomp, regerror, regexec and regfree.
 *      Fixed a bug that was originally a typo by me, where `i' was used
 *      instead of `oldest' when compiling regular expressions - benign
 *      results mostly, although occasionally it bit you...
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_type.h"
#include "funcapi.h"
#include "regex/regex.h"
#include "utils/array.h"
#include "utils/builtins.h"

#define PG_GETARG_TEXT_PP_IF_EXISTS(_n) \
    (PG_NARGS() > (_n) ? PG_GETARG_TEXT_PP(_n) : NULL)


/* all the options of interest for regex functions */
typedef struct pg_re_flags
{
    int         cflags;         /* compile flags for Spencer's regex code */
    bool        glob;           /* do it globally (for each occurrence) */
} pg_re_flags;

/* cross-call state for regexp_matches(), also regexp_split() */
typedef struct regexp_matches_ctx
{
    text       *orig_str;       /* data string in original TEXT form */
    int         nmatches;       /* number of places where pattern matched */
    int         npatterns;      /* number of capturing subpatterns */
    /* We store start char index and end+1 char index for each match */
    /* so the number of entries in match_locs is nmatches * npatterns * 2 */
    int        *match_locs;     /* 0-based character indexes */
    int         next_match;     /* 0-based index of next match to process */
    /* workspace for build_regexp_matches_result() */
    Datum      *elems;          /* has npatterns elements */
    bool       *nulls;          /* has npatterns elements */
} regexp_matches_ctx;

/*
 * We cache precompiled regular expressions using a "self organizing list"
 * structure, in which recently-used items tend to be near the front.
 * Whenever we use an entry, it's moved up to the front of the list.
 * Over time, an item's average position corresponds to its frequency of use.
 *
 * When we first create an entry, it's inserted at the front of
 * the array, dropping the entry at the end of the array if necessary to
 * make room.  (This might seem to be weighting the new entry too heavily,
 * but if we insert new entries further back, we'll be unable to adjust to
 * a sudden shift in the query mix where we are presented with MAX_CACHED_RES
 * never-before-seen items used circularly.  We ought to be able to handle
 * that case, so we have to insert at the front.)
 *
 * Knuth mentions a variant strategy in which a used item is moved up just
 * one place in the list.  Although he says this uses fewer comparisons on
 * average, it seems not to adapt very well to the situation where you have
 * both some reusable patterns and a steady stream of non-reusable patterns.
 * A reusable pattern that isn't used at least as often as non-reusable
 * patterns are seen will "fail to keep up" and will drop off the end of the
 * cache.  With move-to-front, a reusable pattern is guaranteed to stay in
 * the cache as long as it's used at least once in every MAX_CACHED_RES uses.
 */

/* this is the maximum number of cached regular expressions */
#ifndef MAX_CACHED_RES
#define MAX_CACHED_RES  32
#endif

/* this structure describes one cached regular expression */
typedef struct cached_re_str
{
    char       *cre_pat;        /* original RE (not null terminated!) */
    int         cre_pat_len;    /* length of original RE, in bytes */
    int         cre_flags;      /* compile flags: extended,icase etc */
    Oid         cre_collation;  /* collation to use */
    regex_t     cre_re;         /* the compiled regular expression */
} cached_re_str;

static int  num_res = 0;        /* # of cached re's */
static cached_re_str re_array[MAX_CACHED_RES];  /* cached re's */


/* Local functions */
static regexp_matches_ctx *setup_regexp_matches(text *orig_str, text *pattern,
                     text *flags,
                     Oid collation,
                     bool force_glob,
                     bool use_subpatterns,
                     bool ignore_degenerate);
static void cleanup_regexp_matches(regexp_matches_ctx *matchctx);
static ArrayType *build_regexp_matches_result(regexp_matches_ctx *matchctx);
static Datum build_regexp_split_result(regexp_matches_ctx *splitctx);


/*
 * RE_compile_and_cache - compile a RE, caching if possible
 *
 * Returns regex_t *
 *
 *  text_re --- the pattern, expressed as a TEXT object
 *  cflags --- compile options for the pattern
 *  collation --- collation to use for LC_CTYPE-dependent behavior
 *
 * Pattern is given in the database encoding.  We internally convert to
 * an array of pg_wchar, which is what Spencer's regex package wants.
 */
static regex_t *
RE_compile_and_cache(text *text_re, int cflags, Oid collation)
{
    int         text_re_len = VARSIZE_ANY_EXHDR(text_re);
    char       *text_re_val = VARDATA_ANY(text_re);
    pg_wchar   *pattern;
    int         pattern_len;
    int         i;
    int         regcomp_result;
    cached_re_str re_temp;
    char        errMsg[100];

    /*
     * Look for a match among previously compiled REs.  Since the data
     * structure is self-organizing with most-used entries at the front, our
     * search strategy can just be to scan from the front.
     */
    for (i = 0; i < num_res; i++)
    {
        if (re_array[i].cre_pat_len == text_re_len &&
            re_array[i].cre_flags == cflags &&
            re_array[i].cre_collation == collation &&
            memcmp(re_array[i].cre_pat, text_re_val, text_re_len) == 0)
        {
            /*
             * Found a match; move it to front if not there already.
             */
            if (i > 0)
            {
                re_temp = re_array[i];
                memmove(&re_array[1], &re_array[0], i * sizeof(cached_re_str));
                re_array[0] = re_temp;
            }

            return &re_array[0].cre_re;
        }
    }

    /*
     * Couldn't find it, so try to compile the new RE.  To avoid leaking
     * resources on failure, we build into the re_temp local.
     */

    /* Convert pattern string to wide characters */
    pattern = (pg_wchar *) palloc((text_re_len + 1) * sizeof(pg_wchar));
    pattern_len = pg_mb2wchar_with_len(text_re_val,
                                       pattern,
                                       text_re_len);

    regcomp_result = pg_regcomp(&re_temp.cre_re,
                                pattern,
                                pattern_len,
                                cflags,
                                collation);

    pfree(pattern);

    if (regcomp_result != REG_OKAY)
    {
        /* re didn't compile (no need for pg_regfree, if so) */
        pg_regerror(regcomp_result, &re_temp.cre_re, errMsg, sizeof(errMsg));
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_REGULAR_EXPRESSION),
                 errmsg("invalid regular expression: %s", errMsg)));
    }

    /*
     * We use malloc/free for the cre_pat field because the storage has to
     * persist across transactions, and because we want to get control back on
     * out-of-memory.  The Max() is because some malloc implementations return
     * NULL for malloc(0).
     */
    re_temp.cre_pat = malloc(Max(text_re_len, 1));
    if (re_temp.cre_pat == NULL)
    {
        pg_regfree(&re_temp.cre_re);
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
    }
    memcpy(re_temp.cre_pat, text_re_val, text_re_len);
    re_temp.cre_pat_len = text_re_len;
    re_temp.cre_flags = cflags;
    re_temp.cre_collation = collation;

    /*
     * Okay, we have a valid new item in re_temp; insert it into the storage
     * array.  Discard last entry if needed.
     */
    if (num_res >= MAX_CACHED_RES)
    {
        --num_res;
        Assert(num_res < MAX_CACHED_RES);
        pg_regfree(&re_array[num_res].cre_re);
        free(re_array[num_res].cre_pat);
    }

    if (num_res > 0)
        memmove(&re_array[1], &re_array[0], num_res * sizeof(cached_re_str));

    re_array[0] = re_temp;
    num_res++;

    return &re_array[0].cre_re;
}

/*
 * RE_wchar_execute - execute a RE on pg_wchar data
 *
 * Returns TRUE on match, FALSE on no match
 *
 *  re --- the compiled pattern as returned by RE_compile_and_cache
 *  data --- the data to match against (need not be null-terminated)
 *  data_len --- the length of the data string
 *  start_search -- the offset in the data to start searching
 *  nmatch, pmatch  --- optional return area for match details
 *
 * Data is given as array of pg_wchar which is what Spencer's regex package
 * wants.
 */
static bool
RE_wchar_execute(regex_t *re, pg_wchar *data, int data_len,
                 int start_search, int nmatch, regmatch_t *pmatch)
{
    int         regexec_result;
    char        errMsg[100];

    /* Perform RE match and return result */
    regexec_result = pg_regexec(re,
                                data,
                                data_len,
                                start_search,
                                NULL,   /* no details */
                                nmatch,
                                pmatch,
                                0);

    if (regexec_result != REG_OKAY && regexec_result != REG_NOMATCH)
    {
        /* re failed??? */
        pg_regerror(regexec_result, re, errMsg, sizeof(errMsg));
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_REGULAR_EXPRESSION),
                 errmsg("regular expression failed: %s", errMsg)));
    }

    return (regexec_result == REG_OKAY);
}

/*
 * RE_execute - execute a RE
 *
 * Returns TRUE on match, FALSE on no match
 *
 *  re --- the compiled pattern as returned by RE_compile_and_cache
 *  dat --- the data to match against (need not be null-terminated)
 *  dat_len --- the length of the data string
 *  nmatch, pmatch  --- optional return area for match details
 *
 * Data is given in the database encoding.  We internally
 * convert to array of pg_wchar which is what Spencer's regex package wants.
 */
static bool
RE_execute(regex_t *re, char *dat, int dat_len,
           int nmatch, regmatch_t *pmatch)
{
    pg_wchar   *data;
    int         data_len;
    bool        match;

    /* Convert data string to wide characters */
    data = (pg_wchar *) palloc((dat_len + 1) * sizeof(pg_wchar));
    data_len = pg_mb2wchar_with_len(dat, data, dat_len);

    /* Perform RE match and return result */
    match = RE_wchar_execute(re, data, data_len, 0, nmatch, pmatch);

    pfree(data);
    return match;
}

/*
 * RE_compile_and_execute - compile and execute a RE
 *
 * Returns TRUE on match, FALSE on no match
 *
 *  text_re --- the pattern, expressed as a TEXT object
 *  dat --- the data to match against (need not be null-terminated)
 *  dat_len --- the length of the data string
 *  cflags --- compile options for the pattern
 *  collation --- collation to use for LC_CTYPE-dependent behavior
 *  nmatch, pmatch  --- optional return area for match details
 *
 * Both pattern and data are given in the database encoding.  We internally
 * convert to array of pg_wchar which is what Spencer's regex package wants.
 */
static bool
RE_compile_and_execute(text *text_re, char *dat, int dat_len,
                       int cflags, Oid collation,
                       int nmatch, regmatch_t *pmatch)
{
    regex_t    *re;

    /* Compile RE */
    re = RE_compile_and_cache(text_re, cflags, collation);

    return RE_execute(re, dat, dat_len, nmatch, pmatch);
}


/*
 * parse_re_flags - parse the options argument of regexp_matches and friends
 *
 *  flags --- output argument, filled with desired options
 *  opts --- TEXT object, or NULL for defaults
 *
 * This accepts all the options allowed by any of the callers; callers that
 * don't want some have to reject them after the fact.
 */
static void
parse_re_flags(pg_re_flags *flags, text *opts)
{
    /* regex flavor is always folded into the compile flags */
    flags->cflags = REG_ADVANCED;
    flags->glob = false;

    if (opts)
    {
        char       *opt_p = VARDATA_ANY(opts);
        int         opt_len = VARSIZE_ANY_EXHDR(opts);
        int         i;

        for (i = 0; i < opt_len; i++)
        {
            switch (opt_p[i])
            {
                case 'g':
                    flags->glob = true;
                    break;
                case 'b':       /* BREs (but why???) */
                    flags->cflags &= ~(REG_ADVANCED | REG_EXTENDED | REG_QUOTE);
                    break;
                case 'c':       /* case sensitive */
                    flags->cflags &= ~REG_ICASE;
                    break;
                case 'e':       /* plain EREs */
                    flags->cflags |= REG_EXTENDED;
                    flags->cflags &= ~(REG_ADVANCED | REG_QUOTE);
                    break;
                case 'i':       /* case insensitive */
                    flags->cflags |= REG_ICASE;
                    break;
                case 'm':       /* Perloid synonym for n */
                case 'n':       /* \n affects ^ $ . [^ */
                    flags->cflags |= REG_NEWLINE;
                    break;
                case 'p':       /* ~Perl, \n affects . [^ */
                    flags->cflags |= REG_NLSTOP;
                    flags->cflags &= ~REG_NLANCH;
                    break;
                case 'q':       /* literal string */
                    flags->cflags |= REG_QUOTE;
                    flags->cflags &= ~(REG_ADVANCED | REG_EXTENDED);
                    break;
                case 's':       /* single line, \n ordinary */
                    flags->cflags &= ~REG_NEWLINE;
                    break;
                case 't':       /* tight syntax */
                    flags->cflags &= ~REG_EXPANDED;
                    break;
                case 'w':       /* weird, \n affects ^ $ only */
                    flags->cflags &= ~REG_NLSTOP;
                    flags->cflags |= REG_NLANCH;
                    break;
                case 'x':       /* expanded syntax */
                    flags->cflags |= REG_EXPANDED;
                    break;
                default:
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("invalid regexp option: \"%c\"",
                                    opt_p[i])));
                    break;
            }
        }
    }
}


/*
 *  interface routines called by the function manager
 */

Datum
nameregexeq(PG_FUNCTION_ARGS)
{
    Name        n = PG_GETARG_NAME(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(RE_compile_and_execute(p,
                                          NameStr(*n),
                                          strlen(NameStr(*n)),
                                          REG_ADVANCED,
                                          PG_GET_COLLATION(),
                                          0, NULL));
}

Datum
nameregexne(PG_FUNCTION_ARGS)
{
    Name        n = PG_GETARG_NAME(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(!RE_compile_and_execute(p,
                                           NameStr(*n),
                                           strlen(NameStr(*n)),
                                           REG_ADVANCED,
                                           PG_GET_COLLATION(),
                                           0, NULL));
}

Datum
textregexeq(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(RE_compile_and_execute(p,
                                          VARDATA_ANY(s),
                                          VARSIZE_ANY_EXHDR(s),
                                          REG_ADVANCED,
                                          PG_GET_COLLATION(),
                                          0, NULL));
}

Datum
textregexne(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(!RE_compile_and_execute(p,
                                           VARDATA_ANY(s),
                                           VARSIZE_ANY_EXHDR(s),
                                           REG_ADVANCED,
                                           PG_GET_COLLATION(),
                                           0, NULL));
}


/*
 *  routines that use the regexp stuff, but ignore the case.
 *  for this, we use the REG_ICASE flag to pg_regcomp
 */


Datum
nameicregexeq(PG_FUNCTION_ARGS)
{
    Name        n = PG_GETARG_NAME(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(RE_compile_and_execute(p,
                                          NameStr(*n),
                                          strlen(NameStr(*n)),
                                          REG_ADVANCED | REG_ICASE,
                                          PG_GET_COLLATION(),
                                          0, NULL));
}

Datum
nameicregexne(PG_FUNCTION_ARGS)
{
    Name        n = PG_GETARG_NAME(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(!RE_compile_and_execute(p,
                                           NameStr(*n),
                                           strlen(NameStr(*n)),
                                           REG_ADVANCED | REG_ICASE,
                                           PG_GET_COLLATION(),
                                           0, NULL));
}

Datum
texticregexeq(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(RE_compile_and_execute(p,
                                          VARDATA_ANY(s),
                                          VARSIZE_ANY_EXHDR(s),
                                          REG_ADVANCED | REG_ICASE,
                                          PG_GET_COLLATION(),
                                          0, NULL));
}

Datum
texticregexne(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);

    PG_RETURN_BOOL(!RE_compile_and_execute(p,
                                           VARDATA_ANY(s),
                                           VARSIZE_ANY_EXHDR(s),
                                           REG_ADVANCED | REG_ICASE,
                                           PG_GET_COLLATION(),
                                           0, NULL));
}


/*
 * textregexsubstr()
 *      Return a substring matched by a regular expression.
 */
Datum
textregexsubstr(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);
    regex_t    *re;
    regmatch_t  pmatch[2];
    int         so,
                eo;

    /* Compile RE */
    re = RE_compile_and_cache(p, REG_ADVANCED, PG_GET_COLLATION());

    /*
     * We pass two regmatch_t structs to get info about the overall match and
     * the match for the first parenthesized subexpression (if any). If there
     * is a parenthesized subexpression, we return what it matched; else
     * return what the whole regexp matched.
     */
    if (!RE_execute(re,
                    VARDATA_ANY(s), VARSIZE_ANY_EXHDR(s),
                    2, pmatch))
        PG_RETURN_NULL();       /* definitely no match */

    if (re->re_nsub > 0)
    {
        /* has parenthesized subexpressions, use the first one */
        so = pmatch[1].rm_so;
        eo = pmatch[1].rm_eo;
    }
    else
    {
        /* no parenthesized subexpression, use whole match */
        so = pmatch[0].rm_so;
        eo = pmatch[0].rm_eo;
    }

    /*
     * It is possible to have a match to the whole pattern but no match for a
     * subexpression; for example 'foo(bar)?' is considered to match 'foo' but
     * there is no subexpression match.  So this extra test for match failure
     * is not redundant.
     */
    if (so < 0 || eo < 0)
        PG_RETURN_NULL();

    return DirectFunctionCall3(text_substr,
                               PointerGetDatum(s),
                               Int32GetDatum(so + 1),
                               Int32GetDatum(eo - so));
}

/*
 * textregexreplace_noopt()
 *      Return a string matched by a regular expression, with replacement.
 *
 * This version doesn't have an option argument: we default to case
 * sensitive match, replace the first instance only.
 */
Datum
textregexreplace_noopt(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);
    text       *r = PG_GETARG_TEXT_PP(2);
    regex_t    *re;

    re = RE_compile_and_cache(p, REG_ADVANCED, PG_GET_COLLATION());

    PG_RETURN_TEXT_P(replace_text_regexp(s, (void *) re, r, false));
}

/*
 * textregexreplace()
 *      Return a string matched by a regular expression, with replacement.
 */
Datum
textregexreplace(PG_FUNCTION_ARGS)
{
    text       *s = PG_GETARG_TEXT_PP(0);
    text       *p = PG_GETARG_TEXT_PP(1);
    text       *r = PG_GETARG_TEXT_PP(2);
    text       *opt = PG_GETARG_TEXT_PP(3);
    regex_t    *re;
    pg_re_flags flags;

    parse_re_flags(&flags, opt);

    re = RE_compile_and_cache(p, flags.cflags, PG_GET_COLLATION());

    PG_RETURN_TEXT_P(replace_text_regexp(s, (void *) re, r, flags.glob));
}

/*
 * similar_escape()
 * Convert a SQL:2008 regexp pattern to POSIX style, so it can be used by
 * our regexp engine.
 */
Datum
similar_escape(PG_FUNCTION_ARGS)
{
    text       *pat_text;
    text       *esc_text;
    text       *result;
    char       *p,
               *e,
               *r;
    int         plen,
                elen;
    bool        afterescape = false;
    bool        incharclass = false;
    int         nquotes = 0;

    /* This function is not strict, so must test explicitly */
    if (PG_ARGISNULL(0))
        PG_RETURN_NULL();
    pat_text = PG_GETARG_TEXT_PP(0);
    p = VARDATA_ANY(pat_text);
    plen = VARSIZE_ANY_EXHDR(pat_text);
    if (PG_ARGISNULL(1))
    {
        /* No ESCAPE clause provided; default to backslash as escape */
        e = "\\";
        elen = 1;
    }
    else
    {
        esc_text = PG_GETARG_TEXT_PP(1);
        e = VARDATA_ANY(esc_text);
        elen = VARSIZE_ANY_EXHDR(esc_text);
        if (elen == 0)
            e = NULL;           /* no escape character */
        else if (elen != 1)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
                     errmsg("invalid escape string"),
                  errhint("Escape string must be empty or one character.")));
    }

    /*----------
     * We surround the transformed input string with
     *          ^(?: ... )$
     * which requires some explanation.  We need "^" and "$" to force
     * the pattern to match the entire input string as per SQL99 spec.
     * The "(?:" and ")" are a non-capturing set of parens; we have to have
     * parens in case the string contains "|", else the "^" and "$" will
     * be bound into the first and last alternatives which is not what we
     * want, and the parens must be non capturing because we don't want them
     * to count when selecting output for SUBSTRING.
     *----------
     */

    /*
     * We need room for the prefix/postfix plus as many as 3 output bytes per
     * input byte; since the input is at most 1GB this can't overflow
     */
    result = (text *) palloc(VARHDRSZ + 6 + 3 * plen);
    r = VARDATA(result);

    *r++ = '^';
    *r++ = '(';
    *r++ = '?';
    *r++ = ':';

    while (plen > 0)
    {
        char        pchar = *p;

        if (afterescape)
        {
            if (pchar == '"' && !incharclass)   /* for SUBSTRING patterns */
                *r++ = ((nquotes++ % 2) == 0) ? '(' : ')';
            else
            {
                *r++ = '\\';
                *r++ = pchar;
            }
            afterescape = false;
        }
        else if (e && pchar == *e)
        {
            /* SQL99 escape character; do not send to output */
            afterescape = true;
        }
        else if (incharclass)
        {
            if (pchar == '\\')
                *r++ = '\\';
            *r++ = pchar;
            if (pchar == ']')
                incharclass = false;
        }
        else if (pchar == '[')
        {
            *r++ = pchar;
            incharclass = true;
        }
        else if (pchar == '%')
        {
            *r++ = '.';
            *r++ = '*';
        }
        else if (pchar == '_')
            *r++ = '.';
        else if (pchar == '(')
        {
            /* convert to non-capturing parenthesis */
            *r++ = '(';
            *r++ = '?';
            *r++ = ':';
        }
        else if (pchar == '\\' || pchar == '.' ||
                 pchar == '^' || pchar == '$')
        {
            *r++ = '\\';
            *r++ = pchar;
        }
        else
            *r++ = pchar;
        p++, plen--;
    }

    *r++ = ')';
    *r++ = '$';

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

    PG_RETURN_TEXT_P(result);
}

/*
 * regexp_matches()
 *      Return a table of matches of a pattern within a string.
 */
Datum
regexp_matches(PG_FUNCTION_ARGS)
{
    FuncCallContext *funcctx;
    regexp_matches_ctx *matchctx;

    if (SRF_IS_FIRSTCALL())
    {
        text       *pattern = PG_GETARG_TEXT_PP(1);
        text       *flags = PG_GETARG_TEXT_PP_IF_EXISTS(2);
        MemoryContext oldcontext;

        funcctx = SRF_FIRSTCALL_INIT();
        oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

        /* be sure to copy the input string into the multi-call ctx */
        matchctx = setup_regexp_matches(PG_GETARG_TEXT_P_COPY(0), pattern,
                                        flags,
                                        PG_GET_COLLATION(),
                                        false, true, false);

        /* Pre-create workspace that build_regexp_matches_result needs */
        matchctx->elems = (Datum *) palloc(sizeof(Datum) * matchctx->npatterns);
        matchctx->nulls = (bool *) palloc(sizeof(bool) * matchctx->npatterns);

        MemoryContextSwitchTo(oldcontext);
        funcctx->user_fctx = (void *) matchctx;
    }

    funcctx = SRF_PERCALL_SETUP();
    matchctx = (regexp_matches_ctx *) funcctx->user_fctx;

    if (matchctx->next_match < matchctx->nmatches)
    {
        ArrayType  *result_ary;

        result_ary = build_regexp_matches_result(matchctx);
        matchctx->next_match++;
        SRF_RETURN_NEXT(funcctx, PointerGetDatum(result_ary));
    }

    /* release space in multi-call ctx to avoid intraquery memory leak */
    cleanup_regexp_matches(matchctx);

    SRF_RETURN_DONE(funcctx);
}

/* This is separate to keep the opr_sanity regression test from complaining */
Datum
regexp_matches_no_flags(PG_FUNCTION_ARGS)
{
    return regexp_matches(fcinfo);
}

/*
 * setup_regexp_matches --- do the initial matching for regexp_matches()
 *      or regexp_split()
 *
 * To avoid having to re-find the compiled pattern on each call, we do
 * all the matching in one swoop.  The returned regexp_matches_ctx contains
 * the locations of all the substrings matching the pattern.
 *
 * The three bool parameters have only two patterns (one for each caller)
 * but it seems clearer to distinguish the functionality this way than to
 * key it all off one "is_split" flag.
 */
static regexp_matches_ctx *
setup_regexp_matches(text *orig_str, text *pattern, text *flags,
                     Oid collation,
                     bool force_glob, bool use_subpatterns,
                     bool ignore_degenerate)
{
    regexp_matches_ctx *matchctx = palloc0(sizeof(regexp_matches_ctx));
    int         orig_len;
    pg_wchar   *wide_str;
    int         wide_len;
    pg_re_flags re_flags;
    regex_t    *cpattern;
    regmatch_t *pmatch;
    int         pmatch_len;
    int         array_len;
    int         array_idx;
    int         prev_match_end;
    int         start_search;

    /* save original string --- we'll extract result substrings from it */
    matchctx->orig_str = orig_str;

    /* convert string to pg_wchar form for matching */
    orig_len = VARSIZE_ANY_EXHDR(orig_str);
    wide_str = (pg_wchar *) palloc(sizeof(pg_wchar) * (orig_len + 1));
    wide_len = pg_mb2wchar_with_len(VARDATA_ANY(orig_str), wide_str, orig_len);

    /* determine options */
    parse_re_flags(&re_flags, flags);
    if (force_glob)
    {
        /* user mustn't specify 'g' for regexp_split */
        if (re_flags.glob)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("regexp_split does not support the global option")));
        /* but we find all the matches anyway */
        re_flags.glob = true;
    }

    /* set up the compiled pattern */
    cpattern = RE_compile_and_cache(pattern, re_flags.cflags, collation);

    /* do we want to remember subpatterns? */
    if (use_subpatterns && cpattern->re_nsub > 0)
    {
        matchctx->npatterns = cpattern->re_nsub;
        pmatch_len = cpattern->re_nsub + 1;
    }
    else
    {
        use_subpatterns = false;
        matchctx->npatterns = 1;
        pmatch_len = 1;
    }

    /* temporary output space for RE package */
    pmatch = palloc(sizeof(regmatch_t) * pmatch_len);

    /* the real output space (grown dynamically if needed) */
    array_len = re_flags.glob ? 256 : 32;
    matchctx->match_locs = (int *) palloc(sizeof(int) * array_len);
    array_idx = 0;

    /* search for the pattern, perhaps repeatedly */
    prev_match_end = 0;
    start_search = 0;
    while (RE_wchar_execute(cpattern, wide_str, wide_len, start_search,
                            pmatch_len, pmatch))
    {
        /*
         * If requested, ignore degenerate matches, which are zero-length
         * matches occurring at the start or end of a string or just after a
         * previous match.
         */
        if (!ignore_degenerate ||
            (pmatch[0].rm_so < wide_len &&
             pmatch[0].rm_eo > prev_match_end))
        {
            /* enlarge output space if needed */
            while (array_idx + matchctx->npatterns * 2 > array_len)
            {
                array_len *= 2;
                matchctx->match_locs = (int *) repalloc(matchctx->match_locs,
                                                    sizeof(int) * array_len);
            }

            /* save this match's locations */
            if (use_subpatterns)
            {
                int         i;

                for (i = 1; i <= matchctx->npatterns; i++)
                {
                    matchctx->match_locs[array_idx++] = pmatch[i].rm_so;
                    matchctx->match_locs[array_idx++] = pmatch[i].rm_eo;
                }
            }
            else
            {
                matchctx->match_locs[array_idx++] = pmatch[0].rm_so;
                matchctx->match_locs[array_idx++] = pmatch[0].rm_eo;
            }
            matchctx->nmatches++;
        }
        prev_match_end = pmatch[0].rm_eo;

        /* if not glob, stop after one match */
        if (!re_flags.glob)
            break;

        /*
         * Advance search position.  Normally we start the next search at the
         * end of the previous match; but if the match was of zero length, we
         * have to advance by one character, or we'd just find the same match
         * again.
         */
        start_search = prev_match_end;
        if (pmatch[0].rm_so == pmatch[0].rm_eo)
            start_search++;
        if (start_search > wide_len)
            break;
    }

    /* Clean up temp storage */
    pfree(wide_str);
    pfree(pmatch);

    return matchctx;
}

/*
 * cleanup_regexp_matches - release memory of a regexp_matches_ctx
 */
static void
cleanup_regexp_matches(regexp_matches_ctx *matchctx)
{
    pfree(matchctx->orig_str);
    pfree(matchctx->match_locs);
    if (matchctx->elems)
        pfree(matchctx->elems);
    if (matchctx->nulls)
        pfree(matchctx->nulls);
    pfree(matchctx);
}

/*
 * build_regexp_matches_result - build output array for current match
 */
static ArrayType *
build_regexp_matches_result(regexp_matches_ctx *matchctx)
{
    Datum      *elems = matchctx->elems;
    bool       *nulls = matchctx->nulls;
    int         dims[1];
    int         lbs[1];
    int         loc;
    int         i;

    /* Extract matching substrings from the original string */
    loc = matchctx->next_match * matchctx->npatterns * 2;
    for (i = 0; i < matchctx->npatterns; i++)
    {
        int         so = matchctx->match_locs[loc++];
        int         eo = matchctx->match_locs[loc++];

        if (so < 0 || eo < 0)
        {
            elems[i] = (Datum) 0;
            nulls[i] = true;
        }
        else
        {
            elems[i] = DirectFunctionCall3(text_substr,
                                         PointerGetDatum(matchctx->orig_str),
                                           Int32GetDatum(so + 1),
                                           Int32GetDatum(eo - so));
            nulls[i] = false;
        }
    }

    /* And form an array */
    dims[0] = matchctx->npatterns;
    lbs[0] = 1;
    /* XXX: this hardcodes assumptions about the text type */
    return construct_md_array(elems, nulls, 1, dims, lbs,
                              TEXTOID, -1, false, 'i');
}

/*
 * regexp_split_to_table()
 *      Split the string at matches of the pattern, returning the
 *      split-out substrings as a table.
 */
Datum
regexp_split_to_table(PG_FUNCTION_ARGS)
{
    FuncCallContext *funcctx;
    regexp_matches_ctx *splitctx;

    if (SRF_IS_FIRSTCALL())
    {
        text       *pattern = PG_GETARG_TEXT_PP(1);
        text       *flags = PG_GETARG_TEXT_PP_IF_EXISTS(2);
        MemoryContext oldcontext;

        funcctx = SRF_FIRSTCALL_INIT();
        oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

        /* be sure to copy the input string into the multi-call ctx */
        splitctx = setup_regexp_matches(PG_GETARG_TEXT_P_COPY(0), pattern,
                                        flags,
                                        PG_GET_COLLATION(),
                                        true, false, true);

        MemoryContextSwitchTo(oldcontext);
        funcctx->user_fctx = (void *) splitctx;
    }

    funcctx = SRF_PERCALL_SETUP();
    splitctx = (regexp_matches_ctx *) funcctx->user_fctx;

    if (splitctx->next_match <= splitctx->nmatches)
    {
        Datum       result = build_regexp_split_result(splitctx);

        splitctx->next_match++;
        SRF_RETURN_NEXT(funcctx, result);
    }

    /* release space in multi-call ctx to avoid intraquery memory leak */
    cleanup_regexp_matches(splitctx);

    SRF_RETURN_DONE(funcctx);
}

/* This is separate to keep the opr_sanity regression test from complaining */
Datum
regexp_split_to_table_no_flags(PG_FUNCTION_ARGS)
{
    return regexp_split_to_table(fcinfo);
}

/*
 * regexp_split_to_array()
 *      Split the string at matches of the pattern, returning the
 *      split-out substrings as an array.
 */
Datum
regexp_split_to_array(PG_FUNCTION_ARGS)
{
    ArrayBuildState *astate = NULL;
    regexp_matches_ctx *splitctx;

    splitctx = setup_regexp_matches(PG_GETARG_TEXT_PP(0),
                                    PG_GETARG_TEXT_PP(1),
                                    PG_GETARG_TEXT_PP_IF_EXISTS(2),
                                    PG_GET_COLLATION(),
                                    true, false, true);

    while (splitctx->next_match <= splitctx->nmatches)
    {
        astate = accumArrayResult(astate,
                                  build_regexp_split_result(splitctx),
                                  false,
                                  TEXTOID,
                                  CurrentMemoryContext);
        splitctx->next_match++;
    }

    /*
     * We don't call cleanup_regexp_matches here; it would try to pfree the
     * input string, which we didn't copy.  The space is not in a long-lived
     * memory context anyway.
     */

    PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, CurrentMemoryContext));
}

/* This is separate to keep the opr_sanity regression test from complaining */
Datum
regexp_split_to_array_no_flags(PG_FUNCTION_ARGS)
{
    return regexp_split_to_array(fcinfo);
}

/*
 * build_regexp_split_result - build output string for current match
 *
 * We return the string between the current match and the previous one,
 * or the string after the last match when next_match == nmatches.
 */
static Datum
build_regexp_split_result(regexp_matches_ctx *splitctx)
{
    int         startpos;
    int         endpos;

    if (splitctx->next_match > 0)
        startpos = splitctx->match_locs[splitctx->next_match * 2 - 1];
    else
        startpos = 0;
    if (startpos < 0)
        elog(ERROR, "invalid match ending position");

    if (splitctx->next_match < splitctx->nmatches)
    {
        endpos = splitctx->match_locs[splitctx->next_match * 2];
        if (endpos < startpos)
            elog(ERROR, "invalid match starting position");
        return DirectFunctionCall3(text_substr,
                                   PointerGetDatum(splitctx->orig_str),
                                   Int32GetDatum(startpos + 1),
                                   Int32GetDatum(endpos - startpos));
    }
    else
    {
        /* no more matches, return rest of string */
        return DirectFunctionCall2(text_substr_no_len,
                                   PointerGetDatum(splitctx->orig_str),
                                   Int32GetDatum(startpos + 1));
    }
}

/*
 * regexp_fixed_prefix - extract fixed prefix, if any, for a regexp
 *
 * The result is NULL if there is no fixed prefix, else a palloc'd string.
 * If it is an exact match, not just a prefix, *exact is returned as TRUE.
 */
char *
regexp_fixed_prefix(text *text_re, bool case_insensitive, Oid collation,
                    bool *exact)
{
    char       *result;
    regex_t    *re;
    int         cflags;
    int         re_result;
    pg_wchar   *str;
    size_t      slen;
    size_t      maxlen;
    char        errMsg[100];

    *exact = false;             /* default result */

    /* Compile RE */
    cflags = REG_ADVANCED;
    if (case_insensitive)
        cflags |= REG_ICASE;

    re = RE_compile_and_cache(text_re, cflags, collation);

    /* Examine it to see if there's a fixed prefix */
    re_result = pg_regprefix(re, &str, &slen);

    switch (re_result)
    {
        case REG_NOMATCH:
            return NULL;

        case REG_PREFIX:
            /* continue with wchar conversion */
            break;

        case REG_EXACT:
            *exact = true;
            /* continue with wchar conversion */
            break;

        default:
            /* re failed??? */
            pg_regerror(re_result, re, errMsg, sizeof(errMsg));
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_REGULAR_EXPRESSION),
                     errmsg("regular expression failed: %s", errMsg)));
            break;
    }

    /* Convert pg_wchar result back to database encoding */
    maxlen = pg_database_encoding_max_length() * slen + 1;
    result = (char *) palloc(maxlen);
    slen = pg_wchar2mb_with_len(str, result, slen);
    Assert(slen < maxlen);

    free(str);

    return result;
}