From c5cd71fb720df53bd625075d3e7016a7b016c287 Mon Sep 17 00:00:00 2001
From: Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
Date: Thu, 17 Jan 2019 10:56:24 +0100
Subject: [PATCH] sys/base64: Add size estimation macros

---
 sys/base64/base64.c  |  4 ++--
 sys/include/base64.h | 28 ++++++++++++++++++++++++++--
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/sys/base64/base64.c b/sys/base64/base64.c
index d43f1b5f8a..a0d28df4a2 100644
--- a/sys/base64/base64.c
+++ b/sys/base64/base64.c
@@ -60,7 +60,7 @@ int base64_encode(const void *data_in, size_t data_in_size,
                   unsigned char *base64_out, size_t *base64_out_size)
 {
     const unsigned char *in = data_in;
-    size_t required_size = 4 * ((data_in_size + 2) / 3);
+    size_t required_size = base64_estimate_encode_size(data_in_size);
 
     if (data_in == NULL) {
         return BASE64_ERROR_DATA_IN;
@@ -164,7 +164,7 @@ int base64_decode(const unsigned char *base64_in, size_t base64_in_size,
                   void *data_out, size_t *data_out_size)
 {
     unsigned char *out = data_out;
-    size_t required_size = ((base64_in_size / 4) * 3);
+    size_t required_size = base64_estimate_decode_size(base64_in_size);
 
     if (base64_in == NULL) {
         return BASE64_ERROR_DATA_IN;
diff --git a/sys/include/base64.h b/sys/include/base64.h
index e4a039cd8d..84c9655f91 100644
--- a/sys/include/base64.h
+++ b/sys/include/base64.h
@@ -32,6 +32,30 @@ extern "C" {
 #define BASE64_ERROR_DATA_IN          (-3) /**< error value for invalid input buffer           */
 #define BASE64_ERROR_DATA_IN_SIZE     (-4) /**< error value for invalid input buffer size      */
 
+/**
+ * @brief Estimates the amount of bytes needed for decoding @p base64_in_size
+ * characters from base64.
+ *
+ * @param[in] base64_in_size Size of the string to be decoded
+ * @return Amount of bytes estimated to be used after decoding
+ */
+static inline size_t base64_estimate_decode_size(size_t base64_in_size)
+{
+    return ((base64_in_size / 4) * 3);
+}
+
+/**
+ * @brief Estimates the length of the resulting string after encoding
+ * @p data_in_size bytes into base64.
+ *
+ * @param[in] data_in_size Amount of bytes to be encoded
+ * @return Amount of characters the output string is estimated to have
+ */
+static inline size_t base64_estimate_encode_size(size_t data_in_size)
+{
+    return (4 * ((data_in_size + 2) / 3));
+}
+
 /**
  * @brief           Encodes a given datum to base64 and save the result to the given destination.
  * @param[in]       data_in           pointer to the datum to encode
@@ -48,7 +72,7 @@ extern "C" {
             BASE64_ERROR_BUFFER_OUT if `base64_out` equals NULL
                                     but the `base64_out_size` is sufficient,
             BASE64_ERROR_DATA_IN if `data_in` equals NULL,
-            BASE64_ERROR_DATA_IN_SIZE if `data_in_size` is less then 1.
+            BASE64_ERROR_DATA_IN_SIZE if `data_in_size` is less than 1.
  */
 int base64_encode(const void *data_in, size_t data_in_size,
                   unsigned char *base64_out, size_t *base64_out_size);
@@ -69,7 +93,7 @@ int base64_encode(const void *data_in, size_t data_in_size,
             BASE64_ERROR_BUFFER_OUT if `data_out` equals NULL
                                     but the size for `data_out_size` is sufficient,
             BASE64_ERROR_DATA_IN if `base64_in` equals NULL,
-            BASE64_ERROR_DATA_IN_SIZE if `base64_in_size` is less then 4.
+            BASE64_ERROR_DATA_IN_SIZE if `base64_in_size` is less than 4.
  */
 int base64_decode(const unsigned char *base64_in, size_t base64_in_size,
                   void *data_out, size_t *data_out_size);