Base64 String throwing invalid character error

Question

I keep getting a Base64 invalid character error even though I shouldn t   The program takes an XML file and exports it to a document  If the user wants  it will compress the file as well  The compression works fine and returns a Base64 String which is encoded into UTF-8 and written to a file   When its time to reload the document into the program I have to check whether its compressed or not  the code is simply   byte   gzBuffer   System Convert FromBase64String text   return  1F-8B-08     BitConverter ToString new List lt Byte gt  gzBuffer  GetRange 4  3  ToArray       It checks the beginning of the string to see if it has GZips code in it   Now the thing is  all my tests work  I take a string  compress it  decompress it  and compare it to the original  The problem is when I get the string returned from an ADO Recordset  The string is exactly what was written to the file  with the addition of a   0  at the end  but I don t think that even does anything  even trimmed off it still throws   I even copy and pasted the entire string into a test method and compress decompress that  Works fine   The tests will pass but the code will fail using the exact same string  The only difference is instead of just declaring a regular string and passing it in I m getting one returned from a recordset   Any ideas on what am I doing wrong

User · Accepted Answer

You say

The string is exactly what was written to the file (with the addition of a "\0" at the end, but I don't think that even does anything).

In fact, it does do something (it causes your code to throw a FormatException:"Invalid character in a Base-64 string") because the Convert.FromBase64String does not consider "\0" to be a valid Base64 character.

  byte[] data1 = Convert.FromBase64String("AAAA\0"); // Throws exception
  byte[] data2 = Convert.FromBase64String("AAAA");   // Works

Solution: Get rid of the zero termination. (Maybe call .Trim("\0"))

Notes:

The MSDN docs for Convert.FromBase64String say it will throw a FormatException when

The length of s, ignoring white space characters, is not zero or a multiple of 4.

-or-

The format of s is invalid. s contains a non-base 64 character, more than two padding characters, or a non-white space character among the padding characters.

and that

The base 64 digits in ascending order from zero are the uppercase characters 'A' to 'Z', lowercase characters 'a' to 'z', numerals '0' to '9', and the symbols '+' and '/'.

User · Answer

One gotcha to do with converting Base64 from a string is that some conversion functions use the preceding  data image jpg base64   and others only accept the actual data

User · Answer

If removing  0 from the end of string is impossible  you can add your own character for each string you encode  and remove it on decode

User · Answer

string stringToDecrypt   HttpContext Current Request QueryString ToString       change to  string stringToDecrypt   HttpUtility UrlDecode HttpContext Current Request QueryString ToString

User · Answer

Whether null char is allowed or not really depends on base64 codec in question  Given vagueness of Base64 standard  there is no authoritative exact specification   many implementations would just ignore it as white space  And then others can flag it as a problem  And buggiest ones wouldn t notice and would happily try decoding it     -   But it sounds c  implementation does not like it  which is one valid approach  so if removing it helps  that should be done   One minor additional comment  UTF-8 is not a requirement  ISO-8859-x aka Latin-x  and 7-bit Ascii would work as well  This because Base64 was specifically designed to only use 7-bit subset which works with all 7-bit ascii compatible encodings

[c#] Base64 String throwing invalid character error

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