Compress Base64 string with zlib - delphi

Question

I need to send from Windows to mobile devices, iOS and Android, by TCP protocol, a big Base64 string.
I have no problem to send and receive, but the strings size are too big, about 24000 characters, and I'm looking at method to compress an decompress these strings.
Looking I see, that the best way is using the Zlib, and I found these link Delphi XE and ZLib Problems (II) in which explains how to do it.
The functions work with normal text string, but compressing base64 strings make they more big.
An example of a very small string that i would send, would be this:
cEJNYkpCSThLVEh6QjNFWC9wSGhXQ3lHWUlBcGNURS83TFdDNVUwUURxRnJvZlRVUWd4WEFWcFJBNUZSSE9JRXlsaWgzcEJvTGo5anQwTlEyd1pBTEtVQVlPbXdkKzJ6N3J5ZUd4SmU2bDNBWjFEd3lVZmZTR1FwNXRqWTVFOFd2SHRwakhDOU9JUEZRM00wMWhnU0p3MWxxNFRVdmdEU2pwekhwV2thS0JFNG9WYXRDUHhTdnp4blU5Vis2ZzJQYnRIdllubzhKSFhZeUlpckNtTGtUZHVHOTFncHVUWC9FSTdOK3JEUDBOVzlaTngrcEdxcXhpRWJ1ZXNUMmdxOXpJa0ZEak1ORHBFenFVSTlCdytHTy==
I don't know if is posible to compress this types of strings. I need help.
The functions that I use are this:
uses
SysUtils, Classes, ZLib, EncdDecd;
function CompressAndEncodeString(const Str: string): string;
var
Utf8Stream: TStringStream;
Compressed: TMemoryStream;
Base64Stream: TStringStream;
begin
Utf8Stream := TStringStream.Create(Str, TEncoding.UTF8);
try
Compressed := TMemoryStream.Create;
try
ZCompressStream(Utf8Stream, Compressed);
Compressed.Position := 0;
Base64Stream := TStringStream.Create('', TEncoding.ASCII);
try
EncodeStream(Compressed, Base64Stream);
Result := Base64Stream.DataString;
finally
Base64Stream.Free;
end;
finally
Compressed.Free;
end;
finally
Utf8Stream.Free;
end;
end;
function DecodeAndDecompressString(const Str: string): string;
var
Utf8Stream: TStringStream;
Compressed: TMemoryStream;
Base64Stream: TStringStream;
begin
Base64Stream := TStringStream.Create(Str, TEncoding.ASCII);
try
Compressed := TMemoryStream.Create;
try
DecodeStream(Base64Stream, Compressed);
Compressed.Position := 0;
Utf8Stream := TStringStream.Create('', TEncoding.UTF8);
try
ZDecompressStream(Compressed, Utf8Stream);
Result := Utf8Stream.DataString;
finally
Utf8Stream.Free;
end;
finally
Compressed.Free;
end;
finally
Base64Stream.Free;
end;
end;

Answer 1

As I understand the question you have done the following:
Encoding a string as UTF-8 bytes.
Compressed those bytes using zlib.
Base64 encoded the compressed bytes.
You then attempt to compress the output of step 3 and find that the result is no smaller. That is to be expected. You have already compressed the data, and further attempts to compress it cannot be expected to reduce the size significantly, especially not if you have base64 encoded in the meantime. If you could repeatedly compress data and have it get smaller each time, then eventually there would be nothing left. That is obviously not possible.
I think you are already doing a good job. You convert to UTF-8 which for most text is the most space effective of the Unicode encodings. If you worked with Chinese text then you'd be better off with UTF-16. You then compress the UTF-8 which is also reasonable. And finally for transmission you encode with base64, also reasonable.
The most obvious way for you to reduce the size of data to be transmitted is for you to omit the base64 step. If you can transmit the compressed bytes that are produced in step 2 then you will be transmitting less. Base64 uses 4 bytes to encode 3 bytes so the size of base64 encoded data is a third larger than the input data.
Another way could be to use a better compression algorithm than zlib, but again there are limits to what can be achieved. And usually better compression is achieved at the cost of increased computational time.