Decoding base64 adds extra spaces

I am working in Delphi XE2 I am converting base64 byte array to string using this

TEncoding.UTF7.GetString(byte1)

Then decoding string into byte array using this function

function Base64Decode(const EncodedText: string): TBytes;
var
  DecodedStm: TBytesStream;
  Decoder: TIdDecoderMIME;
begin
  Decoder := TIdDecoderMIME.Create(nil);
  try
    DecodedStm := TBytesStream.Create;
    try
      Decoder.DecodeBegin(DecodedStm);
      Decoder.Decode(EncodedText);
      Decoder.DecodeEnd;
      Result := DecodedStm.Bytes;
    finally
      DecodedStm.Free;
    end;
  finally
    Decoder.Free;
  end;
end;

But input string length is 400 and after decode its byte array length is 8192.

Somewhere it is adding extra spaces... any suggestion as what I'm doing wrong?

Edit...

this is base64 of my data send from c# through tcp to delphi XE2 app string length = 400

TVpQAAIAAAAEAA8A//8AALgAAAAAAAAAQAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAALoQAA4ftAnNIbgBTM0hkJBUaGlzIHByb2dyYW0gbXVzdCBiZSBydW4gdW5kZXIgV2luMzINCiQ3AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFBFAABMAQgAGV5CKgAAAAAAAAAA4ACOgQsBAhkArAoAAMQCAAAAAAAwugoA

i receive TBytes in my delphi app when i convert TBytes to string following comes

Tbytes to UTF-7 string string length = 401

TVpQAAIAAAAEAA8A//8AALgAAAAAAAAAQAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAALoQAA4ftAnNIbgBTM0hkJBUaGlzIHByb2dyYW0gbXVzdCBiZSBydW4gdW5kZXIgV2luMzINCiQ3AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA‘AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFBFAABMAQgAGV5CKgAAAAAAAAAA4ACOgQsBAhkArAoAAMQCAAAAAAAwugoA

TByte to UTF-8 String string length= 0 ( ZERO)

TByte to ANSI String string length= 401

TVpQAAIAAAAEAA8A//8AALgAAAAAAAAAQAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAALoQAA4ftAnNIbgBTM0hkJBUaGlzIHByb2dyYW0gbXVzdCBiZSBydW4gdW5kZXIgV2luMzINCiQ3AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA‘AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFBFAABMAQgAGV5CKgAAAAAAAAAA4ACOgQsBAhkArAoAAMQCAAAAAAAwugoA

there is 1 extra bit is comming in between but i dont know why it is comming.

kindly advice am i doing any thing wrong.

You can add one line to get the length you are expecting:

function Base64Decode(const EncodedText: string): TBytes;
var
  DecodedStm: TBytesStream;
  Decoder: TIdDecoderMIME;
begin
  Decoder := TIdDecoderMIME.Create(nil);
  try
    DecodedStm := TBytesStream.Create;
    try
      Decoder.DecodeBegin(DecodedStm);
      Decoder.Decode(EncodedText);
      Decoder.DecodeEnd;
      Result := DecodedStm.Bytes;
      SetLength(Result, DecodedStm.Size);  // add this line
    finally
      DecodedStm.Free;
    end;
  finally
    Decoder.Free;
  end;
end;

While it is a very bad idea to mix UTF7 encoding with Base64 decoding, you should use the built-in functions EncodeBase64 and DecodeBase64 found in Soap.EncdDecd.pas.

First and foremost, why are you involving UTF-7 at all? Base64 is a 7-bit encoding that uses only ASCII characters. Converting base64 to/from UTF-7 is an unnecessary operation. If you have a TBytes that contains base64-encoded character octets, then you can simply copy the TBytes directly into an AnsiString without doing any decoding at all:

var
  byte1: TBytes;
  s: AnsiString;

SetString(s, PAnsiChar(byte1), Length(byte));

Or use Indy's BytesToStringRaw() function:

var
  byte1: TBytes;
  s: String;

s := BytesToStringRaw(byte1);

Either way, once you have a base64-encoded string, you can eliminate your custom Base64Decode() function completely by using the TIdDecoderMIME.DecodeBytes() method instead:

var
  decoded: TBytes;

decoded := TIdDecoderMIME.DecodeBytes(s);