Optimize performance of ndpi_strnstr()

Author: 0xA50C1A1

src/include/ndpi_api.h

@@ -115,17 +115,17 @@ extern "C" {
   u_int32_t ndpi_get_tot_allocated_memory(void);
 
   /**
-   * Search the first occurrence of substring -find- in -s-
-   * The search is limited to the first -slen- characters of the string
+   * Finds the first occurrence of the substring 'needle' in the string 'haystack'.
    *
-   * @par    s     = string to parse
-   * @par    find  = string to match with -s-
-   * @par    slen  = max length to match between -s- and -find-
-   * @return a pointer to the beginning of the located substring;
-   *         NULL if the substring is not found
+   * This function is similar to the standard `strstr()` function, but it has an additional parameter `len` that
+   * specifies the maximum length of the search.
    *
+   * @param haystack The string to search in.
+   * @param needle The substring to search for.
+   * @param len The maximum length of the search.
+   * @return Pointer to the first occurrence of 'needle' in 'haystack', or NULL if no match is found.
    */
-  char* ndpi_strnstr(const char *s, const char *find, size_t slen);
+  char *ndpi_strnstr(const char *haystack, const char *needle, size_t len);
 
   /**
    * Same as ndpi_strnstr but case insensitive

src/lib/ndpi_main.c

@@ -9685,32 +9685,55 @@ void ndpi_dump_risks_score(FILE *risk_out) {
 
 /* ****************************************************** */
 
-/*
- * Find the first occurrence of find in s, where the search is limited to the
- * first slen characters of s.
- */
-char *ndpi_strnstr(const char *s, const char *find, size_t slen) {
-  char c;
-  size_t len;
+char *ndpi_strnstr(const char *haystack, const char *needle, size_t len)
+{
+  if (!haystack || !needle)
+  {
+    return NULL;
+  }
+
+  size_t needle_len = strlen(needle);
+  size_t hs_real_len = strnlen(haystack, len);
 
-  if(s == NULL || find == NULL || slen == 0)
+  if (needle_len == 0)
+  {
+    return (char *)haystack;
+  }
+
+  if (needle_len > hs_real_len)
+  {
     return NULL;
+  }
+
+  if (needle_len == 1)
+  {
+    return (char *)memchr(haystack, (int)*needle, hs_real_len);
+  }
 
-  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);
+  const char *current = haystack;
+  const char *haystack_end = haystack + hs_real_len;
+
+  while (current <= haystack_end - needle_len)
+  {
+    /* Find the first occurrence of the first character from the needle */
+    current = (const char *)memchr(current, *needle, haystack_end - current);
+
+    if (!current)
+    {
+      return NULL;
+    }
+
+     /* Check the rest of the needle for a match */
+    if ((current + needle_len <= haystack_end) && (memcmp(current, needle, needle_len) == 0))
+    {
+      return (char *)current;
+    }
+
+    /* Shift one character to the right for the next search */
+    current++;
+  }
+
+  return NULL;
 }
 
 /* ****************************************************** */

tests/performance/strnstr.cpp

@@ -30,40 +30,57 @@ char *ndpi_strnstr(const char *s, const char *find, size_t slen) {
   return ((char *)s);
 }
 
-char *ndpi_strnstr_opt(const char *s, const char *find, size_t slen) {
-  if (s == NULL || find == NULL || slen == 0) {
+char *ndpi_strnstr_opt(const char *haystack, const char *needle, size_t len)
+{
+  if (!haystack || !needle)
+  {
     return NULL;
   }
 
-  char c = *find;
+  size_t needle_len = strlen(needle);
+  size_t hs_real_len = strnlen(haystack, len);
 
-  if (c == '\0') {
-    return (char *)s;
+  if (!haystack || !needle)
+  {
+    return NULL;
   }
 
-  if (*(find + 1) == '\0') {
-    return (char *)memchr(s, c, slen);
+  if (needle_len == 0)
+  {
+    return (char *)haystack;
   }
 
-  size_t find_len = strnlen(find, slen);
-
-  if (find_len > slen) {
+  if (needle_len > hs_real_len)
+  {
     return NULL;
   }
 
-  const char *end = s + slen - find_len;
+  if (needle_len == 1)
+  {
+    return (char *)memchr(haystack, (int)*needle, hs_real_len);
+  }
 
-  while (s <= end) {
-    if (memcmp(s, find, find_len) == 0) {
-      return (char *)s;
-    }
+  const char *current = haystack;
+  const char *haystack_end = haystack + hs_real_len;
 
-    size_t remaining_length = end - s;
-    s = (char *)memchr(s + 1, c, remaining_length);
+  while (current <= haystack_end - needle_len)
+  {
+    /* Find the first occurrence of the first character from the needle */
+    current = (const char *)memchr(current, *needle, haystack_end - current);
 
-    if (s == NULL || s > end) {
+    if (!current)
+    {
       return NULL;
     }
+
+     /* Check the rest of the needle for a match */
+    if ((current + needle_len <= haystack_end) && (memcmp(current, needle, needle_len) == 0))
+    {
+      return (char *)current;
+    }
+
+    /* Shift one character to the right for the next search */
+    current++;
   }
 
   return NULL;