regexport.c

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/*-------------------------------------------------------------------------
 *
 * regexport.c
 *    Functions for exporting info about a regex's NFA
 *
 * In this implementation, the NFA defines a necessary but not sufficient
 * condition for a string to match the regex: that is, there can be strings
 * that match the NFA but don't match the full regex, but not vice versa.
 * Thus, for example, it is okay for the functions below to treat lookaround
 * constraints as no-ops, since they merely constrain the string some more.
 *
 * Notice that these functions return info into caller-provided arrays
 * rather than doing their own malloc's.  This simplifies the APIs by
 * eliminating a class of error conditions, and in the case of colors
 * allows the caller to decide how big is too big to bother with.
 *
 *
 * Portions Copyright (c) 2013-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1998, 1999 Henry Spencer
 *
 * IDENTIFICATION
 *    src/backend/regex/regexport.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "regex/regguts.h"
 
#include "regex/regexport.h"
 
 
/*
 * Get total number of NFA states.
 */
int
pg_reg_getnumstates(const regex_t *regex)
{
    struct cnfa *cnfa;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    return cnfa->nstates;
}
 
/*
 * Get initial state of NFA.
 */
int
pg_reg_getinitialstate(const regex_t *regex)
{
    struct cnfa *cnfa;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    return cnfa->pre;
}
 
/*
 * Get final state of NFA.
 */
int
pg_reg_getfinalstate(const regex_t *regex)
{
    struct cnfa *cnfa;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    return cnfa->post;
}
 
/*
 * pg_reg_getnumoutarcs() and pg_reg_getoutarcs() mask the existence of LACON
 * arcs from the caller, treating any LACON as being automatically satisfied.
 * Since the output representation does not support arcs that consume no
 * character when traversed, we have to recursively traverse LACON arcs here,
 * and report whatever normal arcs are reachable by traversing LACON arcs.
 * Note that this wouldn't work if it were possible to reach the final state
 * via LACON traversal, but the regex library never builds NFAs that have
 * LACON arcs leading directly to the final state.  (This is because the
 * regex executor is designed to consume one character beyond the nominal
 * match end --- possibly an EOS indicator --- so there is always a set of
 * ordinary arcs leading to the final state.)
 *
 * traverse_lacons is a recursive subroutine used by both exported functions
 * to count and then emit the reachable regular arcs.  *arcs_count is
 * incremented by the number of reachable arcs, and as many as will fit in
 * arcs_len (possibly 0) are emitted into arcs[].
 */
static void
traverse_lacons(struct cnfa *cnfa, int st,
                int *arcs_count,
                regex_arc_t *arcs, int arcs_len)
{
    struct carc *ca;
 
    /*
     * Since this function recurses, it could theoretically be driven to stack
     * overflow.  In practice, this is mostly useful to backstop against a
     * failure of the regex compiler to remove a loop of LACON arcs.
     */
    check_stack_depth();
 
    for (ca = cnfa->states[st]; ca->co != COLORLESS; ca++)
    {
        if (ca->co < cnfa->ncolors)
        {
            /* Ordinary arc, so count and possibly emit it */
            int         ndx = (*arcs_count)++;
 
            if (ndx < arcs_len)
            {
                arcs[ndx].co = ca->co;
                arcs[ndx].to = ca->to;
            }
        }
        else
        {
            /* LACON arc --- assume it's satisfied and recurse... */
            /* ... but first, assert it doesn't lead directly to post state */
            Assert(ca->to != cnfa->post);
 
            traverse_lacons(cnfa, ca->to, arcs_count, arcs, arcs_len);
        }
    }
}
 
/*
 * Get number of outgoing NFA arcs of state number "st".
 */
int
pg_reg_getnumoutarcs(const regex_t *regex, int st)
{
    struct cnfa *cnfa;
    int         arcs_count;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    if (st < 0 || st >= cnfa->nstates)
        return 0;
    arcs_count = 0;
    traverse_lacons(cnfa, st, &arcs_count, NULL, 0);
    return arcs_count;
}
 
/*
 * Write array of outgoing NFA arcs of state number "st" into arcs[],
 * whose length arcs_len must be at least as long as indicated by
 * pg_reg_getnumoutarcs(), else not all arcs will be returned.
 */
void
pg_reg_getoutarcs(const regex_t *regex, int st,
                  regex_arc_t *arcs, int arcs_len)
{
    struct cnfa *cnfa;
    int         arcs_count;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    if (st < 0 || st >= cnfa->nstates || arcs_len <= 0)
        return;
    arcs_count = 0;
    traverse_lacons(cnfa, st, &arcs_count, arcs, arcs_len);
}
 
/*
 * Get total number of colors.
 */
int
pg_reg_getnumcolors(const regex_t *regex)
{
    struct colormap *cm;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cm = &((struct guts *) regex->re_guts)->cmap;
 
    return cm->max + 1;
}
 
/*
 * Check if color is beginning of line/string.
 *
 * (We might at some point need to offer more refined handling of pseudocolors,
 * but this will do for now.)
 */
int
pg_reg_colorisbegin(const regex_t *regex, int co)
{
    struct cnfa *cnfa;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    if (co == cnfa->bos[0] || co == cnfa->bos[1])
        return true;
    else
        return false;
}
 
/*
 * Check if color is end of line/string.
 */
int
pg_reg_colorisend(const regex_t *regex, int co)
{
    struct cnfa *cnfa;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cnfa = &((struct guts *) regex->re_guts)->search;
 
    if (co == cnfa->eos[0] || co == cnfa->eos[1])
        return true;
    else
        return false;
}
 
/*
 * Get number of member chrs of color number "co".
 *
 * Note: we return -1 if the color number is invalid, or if it is a special
 * color (WHITE, RAINBOW, or a pseudocolor), or if the number of members is
 * uncertain.
 * Callers should not try to extract the members if -1 is returned.
 */
int
pg_reg_getnumcharacters(const regex_t *regex, int co)
{
    struct colormap *cm;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cm = &((struct guts *) regex->re_guts)->cmap;
 
    if (co <= 0 || co > cm->max)    /* <= 0 rejects WHITE and RAINBOW */
        return -1;
    if (cm->cd[co].flags & PSEUDO)  /* also pseudocolors (BOS etc) */
        return -1;
 
    /*
     * If the color appears anywhere in the high colormap, treat its number of
     * members as uncertain.  In principle we could determine all the specific
     * chrs corresponding to each such entry, but it would be expensive
     * (particularly if character class tests are required) and it doesn't
     * seem worth it.
     */
    if (cm->cd[co].nuchrs != 0)
        return -1;
 
    /* OK, return the known number of member chrs */
    return cm->cd[co].nschrs;
}
 
/*
 * Write array of member chrs of color number "co" into chars[],
 * whose length chars_len must be at least as long as indicated by
 * pg_reg_getnumcharacters(), else not all chars will be returned.
 *
 * Fetching the members of WHITE, RAINBOW, or a pseudocolor is not supported.
 *
 * Caution: this is a relatively expensive operation.
 */
void
pg_reg_getcharacters(const regex_t *regex, int co,
                     pg_wchar *chars, int chars_len)
{
    struct colormap *cm;
    chr         c;
 
    assert(regex != NULL && regex->re_magic == REMAGIC);
    cm = &((struct guts *) regex->re_guts)->cmap;
 
    if (co <= 0 || co > cm->max || chars_len <= 0)
        return;
    if (cm->cd[co].flags & PSEUDO)
        return;
 
    /*
     * We need only examine the low character map; there should not be any
     * matching entries in the high map.
     */
    for (c = CHR_MIN; c <= MAX_SIMPLE_CHR; c++)
    {
        if (cm->locolormap[c - CHR_MIN] == co)
        {
            *chars++ = c;
            if (--chars_len == 0)
                break;
        }
    }
}