Revert ndpi_strnstr() optimization introduced in a813121e0

example/ndpiReader.c

@@ -5691,6 +5691,16 @@ void strnstrUnitTest(void) {
 
   /* Test 10: substring equal to the string */
   assert(strcmp(ndpi_strnstr("string", "string", 6), "string") == 0);
+
+  /* Test 11a,b: max_length bigger that string length */
+  assert(strcmp(ndpi_strnstr("string", "string", 66), "string") == 0);
+  assert(ndpi_strnstr("string", "a", 66) == NULL);
+
+  /* Test 12: substring longer than the string */
+  assert(ndpi_strnstr("string", "stringA", 6) == NULL);
+
+  /* Test 13 */
+  assert(ndpi_strnstr("abcdef", "abc", 2) == NULL);
 }
 
 /* *********************************************** */

src/lib/ndpi_main.c

@@ -9687,42 +9687,27 @@ void ndpi_dump_risks_score(FILE *risk_out) {
  * first slen characters of s.
  */
 char *ndpi_strnstr(const char *s, const char *find, size_t slen) {
-  if (s == NULL || find == NULL || slen == 0) {
-    return NULL;
-  }
-
-  char c = *find;
-
-  if (c == '\0') {
-    return (char *)s;
-  }
-
-  if (*(find + 1) == '\0') {
-    return (char *)memchr(s, c, slen);
-  }
-
-  size_t find_len = strnlen(find, slen);
+  char c;
+  size_t len;
 
-  if (find_len > slen) {
+  if(s == NULL || find == NULL || slen == 0)
     return NULL;
-  }
 
-  const char *end = s + slen - find_len;
-
-  while (s <= end) {
-    if (memcmp(s, find, find_len) == 0) {
-      return (char *)s;
-    }
-
-    size_t remaining_length = end - s;
-    s = (char *)memchr(s + 1, c, remaining_length);
-
-    if (s == NULL || s > end) {
-      return NULL;
-    }
-  }
-
-  return NULL;
+  if((c = *find++) != '\0') {
+    len = strnlen(find, slen);
+    do {
+      char sc;
+
+      do {
+	if(slen-- < 1 || (sc = *s++) == '\0')
+	  return(NULL);
+      } while(sc != c);
+      if(len > slen)
+	return(NULL);
+    } while(strncmp(s, find, len) != 0);
+    s--;
+  }
+  return((char *) s);
 }
 
 /* ****************************************************** */