1 files changed, 293 insertions, 0 deletions
diff --git a/src/backend/regex/regexport.c b/src/backend/regex/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) 2013-2022, 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;
+		}
+	}
+}