Add function "string_decode_base64" in plugin API

src/core/wee-string.c

@@ -1333,3 +1333,80 @@ string_encode_base64 (const char *from, int length, char *to)
     else
         ptr_to[0] = '\0';
 }
+
+/*
+ * string_convbase64_6x4_to_8x3 : convert 4 bytes of 6 bits to 3 bytes of 8 bits
+ */
+
+void
+string_convbase64_6x4_to_8x3 (const unsigned char *from, unsigned char *to)
+{
+    to[0] = from[0] << 2 | from[1] >> 4;
+    to[1] = from[1] << 4 | from[2] >> 2;
+    to[2] = ((from[2] << 6) & 0xc0) | from[3];
+}
+
+/*
+ * string_decode_base64: decode a base64 string
+ *                       return length of string in *to
+ *                       (does not count final \0)
+ */
+
+int
+string_decode_base64 (const char *from, char *to)
+{
+    const char *ptr_from;
+    int length, to_length, i;
+    char *ptr_to;
+    unsigned char c, in[4], out[3];
+    unsigned char base64_table[]="|$$$}rstuvwxyz{$$$$$$$>?"
+        "@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[\\]^_`abcdefghijklmnopq";
+    
+    ptr_from = from;
+    ptr_to = to;
+    
+    ptr_to[0] = '\0';
+    to_length = 0;
+    
+    while (ptr_from && ptr_from[0])
+    {
+        length = 0;
+        for (i = 0; i < 4; i++)
+        {
+            c = 0;
+            while (ptr_from[0] && (c == 0))
+            {
+                c = (unsigned char) ptr_from[0];
+                ptr_from++;
+                c = ((c < 43) || (c > 122)) ? 0 : base64_table[c - 43];
+                if (c)
+                    c = (c == '$') ? 0 : c - 61;
+            }
+            if (ptr_from[0])
+            {
+                length++;
+                if (c)
+                    in[i] = c - 1;
+            }
+            else
+            {
+                in[i] = '\0';
+                break;
+            }
+        }
+        if (length)
+        {
+            string_convbase64_6x4_to_8x3 (in, out);
+            for (i = 0; i < length - 1; i++)
+            {
+                ptr_to[0] = out[i];
+                ptr_to++;
+                to_length++;
+            }
+        }
+    }
+    
+    ptr_to[0] = '\0';
+    
+    return to_length;
+}

src/core/wee-string.h

@@ -57,5 +57,6 @@ extern char *string_iconv_from_internal (const char *charset,
 extern void string_iconv_fprintf (FILE *file, const char *data, ...);
 extern char *string_format_size (unsigned long size);
 extern void string_encode_base64 (const char *from, int length, char *to);
+extern int string_decode_base64 (const char *from, char *to);
 
 #endif /* wee-string.h */