Add memmem() implementation (#2378)

* Add memmem() implementation

* Fix build

* Add fix to avoid too many memcmp calls

2 files changed, 41 insertions, 0 deletions

diff --git a/src/include/ndpi_api.h b/src/include/ndpi_api.h
index 38fac3add..00d15bbda 100644
--- a/src/include/ndpi_api.h
+++ b/src/include/ndpi_api.h
@@ -2219,6 +2219,19 @@ extern "C" {
 
   const char *ndpi_lru_cache_idx_to_name(lru_cache_type idx);
 
+  /**
+   * Searches for a subsequence ('needle') within a block of memory ('haystack').
+   *
+   * @par haystack     = pointer to the block of memory where the search is performed
+   * @par haystack_len = length of the haystack block of memory
+   * @par needle       = pointer to the memory block representing the needle to search for
+   * @par needle_len   = length of the needle memory block
+   * 
+   * @return Pointer to the beginning of the needle within the haystack if found;
+   * otherwise, NULL.
+   */
+  void* ndpi_memmem(const void* haystack, size_t haystack_len, const void* needle,
+                    size_t needle_len);
 
 #ifdef __cplusplus
 }
diff --git a/src/lib/ndpi_main.c b/src/lib/ndpi_main.c
index 9bb5010fd..67eff0e99 100644
--- a/src/lib/ndpi_main.c
+++ b/src/lib/ndpi_main.c
@@ -11447,3 +11447,31 @@ char *ndpi_dump_config(struct ndpi_detection_module_struct *ndpi_str,
   }
   return NULL;
 }
+
+void* ndpi_memmem(const void* haystack, size_t haystack_len, const void* needle, size_t needle_len)
+{
+  if (!haystack || !needle) {
+    return NULL;
+  }
+
+  if (needle_len > haystack_len) {
+    return NULL;
+  }
+
+  if ((size_t)(const u_int8_t*)haystack+haystack_len < haystack_len) {
+    return NULL;
+  }
+
+  if (needle_len == 1) {
+    return memchr(haystack, *(int*)needle, haystack_len);
+  }
+
+  const u_int8_t* h = NULL;
+  const u_int8_t* n = (const u_int8_t*)needle;
+  for (h = haystack; h <= (const u_int8_t*)haystack+haystack_len-needle_len; ++h) {
+    if (*h == n[0] && !memcmp(h, needle, needle_len))
+      return (void*)h;
+  }
+
+  return NULL;
+}