Add caseless version of rabin-karp substring search

src/libutil/str_util.c

@@ -1118,6 +1118,46 @@ rspamd_substring_search (const gchar *in, gsize inlen,
 	return -1;
 }
 
+goffset
+rspamd_substring_search_caseless (const gchar *in, gsize inlen,
+		const gchar *srch, gsize srchlen)
+{
+	gint d, hash_srch, hash_in;
+	gsize i, j;
+	gchar c1, c2;
+
+	if (inlen < srchlen) {
+		return -1;
+	}
+
+	/* Preprocessing */
+	for (d = i = 1; i < srchlen; ++i) {
+		/* computes d = 2^(m-1) with the left-shift operator */
+		d = (d << 1);
+	}
+
+	for (hash_in = hash_srch = i = 0; i < srchlen; ++i) {
+		hash_srch = ((hash_srch << 1) + g_ascii_tolower (srch[i]));
+		hash_in = ((hash_in << 1) + g_ascii_tolower (in[i]));
+	}
+
+	/* Searching */
+	j = 0;
+	while (j <= inlen - srchlen) {
+
+		if (hash_srch == hash_in && g_ascii_strncasecmp (srch, in + j, srchlen) == 0) {
+			return (goffset) j;
+		}
+
+		c1 = g_ascii_tolower (in[j]);
+		c2 = g_ascii_tolower (in[j + srchlen]);
+		hash_in = RKHASH (c1, c2, hash_in);
+		++j;
+	}
+
+	return -1;
+}
+
 goffset
 rspamd_string_find_eoh (GString *input)
 {

src/libutil/str_util.h

@@ -189,6 +189,17 @@ GString *rspamd_header_value_fold (const gchar *name,
 goffset rspamd_substring_search (const gchar *in, gsize inlen,
 	const gchar *srch, gsize srchlen);
 
+/**
+ * Search for a substring `srch` in the text `in` using Karp-Rabin algorithm in caseless matter (ASCII only)
+ * @param in input
+ * @param inlen input len
+ * @param srch search string
+ * @param srchlen length of the search string
+ * @return position of the first substring match or (-1) if not found
+ */
+goffset rspamd_substring_search_caseless (const gchar *in, gsize inlen,
+		const gchar *srch, gsize srchlen);
+
 
 /**
  * Search for end-of-headers mark in the input string. Returns position just after