added memstr and extract_token_str helper functions

src/libstrongswan/utils.h

@@ -224,6 +224,12 @@ void *clalloc(void *pointer, size_t size);
  */
 void memxor(u_int8_t dest[], u_int8_t src[], size_t n);
 
+/**
+ * A variant of strstr with the characteristics of memchr, where haystack is not
+ * a null-terminated string but simply a memory area of length n.
+ */
+void *memstr(const void *haystack, const char *needle, size_t n);
+
 /**
  * Creates a directory and all required parent directories. 
  *