util/crypt: Add macro for max base64encode len

Maximum length of a base64 encoded string can be 33% over the actual
length of the input string. The formula to best cover all the edge cases
is mathematically
(4 * (input_length + 2) / 3) + 1

Add a macro to calculate this for a given input length.

src/util-crypt.h

@@ -29,6 +29,12 @@
 
 #include "suricata-common.h"
 
+/* Ratio of output bytes to input bytes for Base64 Encoding is 4:3, hence the
+ * required output bytes are 4 * ceil(input_len / 3) and an additional byte
+ * for storing the NULL pointer.
+ * */
+#define BASE64_BUFFER_SIZE(x)  ((4 * ((x) + 2) / 3) + 1)
+
 typedef enum {
     SC_SHA_1_OK,
     SC_SHA_1_NOK,