eina: Adding API for base64 decode.

Summary:
Added eina_str_base64_decode API.

Signed-off-by: Srivardhan Hebbar <sri.hebbar@samsung.com>

Reviewers: cedric, jpeg

Reviewed By: jpeg

Subscribers: jpeg

Differential Revision: https://phab.enlightenment.org/D3381

@feature

src/lib/eina/eina_str.c

@@ -299,6 +299,11 @@ eina_str_split_full_helper(const char *str,
    return str_array;
 }
 
+static inline Eina_Bool is_base64(unsigned char c)
+{
+   return (isalnum(c) || (c == '+') || (c == '/'));
+}
+
 /**
  * @endcond
  */
@@ -779,3 +784,74 @@ eina_str_base64_encode(const unsigned char *src, unsigned int len)
 
    return dest;
 }
+
+EAPI
+unsigned char *eina_str_base64_decode(const char * src, int *decoded_str_len)
+{
+   unsigned char inarr[4], outarr[3];
+   int i = 0, j = 0, k = 0, l = 0;
+   int len;
+   unsigned char *dest;
+
+   if (!src)
+     goto error;
+
+   len = strlen(src);
+   /* The encoded string length should be a multiple of 4. Else it is not a
+    * valid encoded string.
+    */
+   if (len % 4)
+     goto error;
+
+   /* This is the max size the destination string can have.
+    */
+   dest = (unsigned char *)malloc(sizeof(unsigned char) * ((len * 3 / 4) + 1));
+   if (!dest)
+     goto error;
+
+   while (len-- && ( src[k] != '=') && is_base64(src[k]))
+     {
+       inarr[i++] = src[k++];
+       if (i ==4)
+         {
+           for (i = 0; i <4; i++)
+             inarr[i] = strchr(base64_table,(int) inarr[i]) - base64_table;
+
+           outarr[0] = (inarr[0] << 2) + ((inarr[1] & 0x30) >> 4);
+           outarr[1] = ((inarr[1] & 0xf) << 4) + ((inarr[2] & 0x3c) >> 2);
+           outarr[2] = ((inarr[2] & 0x3) << 6) + inarr[3];
+
+           for (i = 0; (i < 3); i++)
+             dest[l++] = outarr[i];
+           i = 0;
+         }
+     }
+
+   if (i)
+     {
+       for (j = i; j <4; j++)
+         inarr[j] = 0;
+
+       for (j = 0; j <4; j++)
+         inarr[j] = strchr(base64_table, (int) inarr[j]) - base64_table;
+
+       outarr[0] = (inarr[0] << 2) + ((inarr[1] & 0x30) >> 4);
+       outarr[1] = ((inarr[1] & 0xf) << 4) + ((inarr[2] & 0x3c) >> 2);
+       outarr[2] = ((inarr[2] & 0x3) << 6) + inarr[3];
+
+       for (j = 0; (j < i - 1); j++)
+         dest[l++] = outarr[j];
+     }
+
+   /* This is to prevent the applications from crashing. */
+   dest[l] = '\0';
+
+   if (decoded_str_len)
+     *decoded_str_len = l;
+   return dest;
+
+error:
+   if (decoded_str_len)
+     *decoded_str_len = 0;
+   return NULL;
+}

src/lib/eina/eina_str.h

@@ -395,6 +395,19 @@ EAPI char *eina_strftime(const char *format, const struct tm *tm);
  */
 EAPI char *eina_str_base64_encode(const unsigned char *src, unsigned int len);
 
+/**
+ * @brief base64 decoding function.
+ * @param src The string to be decoded.
+ * @param decoded_str_len The length of the decoded string.
+ * @return the base64 decoded string.
+ *
+ * This will create a NULL terminated string which is base64 decode of the src.
+ * The caller has to free the returned string using free().
+ *
+ * @since 1.17.0
+ */
+EAPI unsigned char * eina_str_base64_decode(const char * src, int *decoded_str_len);
+
 #include "eina_inline_str.x"
 
 /**