I am searching and searching since hours to create a valid .tar.gz file using streams in Delphi 10.
I was able to solve the tarball part using LibTar, which works well.
After some searching I also found examples to decompress gzip data using just System.ZLib. The secret lies in the WindowBits parameter:
// 31 bit wide window = gzip only mode
DecompStream:= TZDecompressionStream.Create(SourceStream, 15 + 16);
TarStream:= TTarArchive.Create(DecompStream);
TarStream.Reset;
while TarStream.FindNext(DirRec) do {...} TarStream.ReadFile(TargetStream);
Great! But is it really possible that System.ZLib is able to decompress gzip (I guess by just ignoring the gzip header by that +16?), but is not able to create such header by itself? Whatever I try, I only get a file that cannot be opened by 7zip or WinRar, because the header is missing.
Maybe it just can't work, because the gzip header contains a checksum, so it's not possible to write the header without knowing the following data. How to solve this? Edit: this is wrong, see comments: crc32 is in the trailer.
It seems, many others also have this problem - I found and tried multiple solutions to add this header, but nothing really worked and everything requires adding long units (not nice but acceptable) or even DLLs (not acceptable for me).
The secret lies in the WindowBits parameter - sounds familiar? :)
Believe it or not, compressing to gzip just works the same way! I couldn't find this anywhere using Google, or in the Embarcadero documentation/help. But have a look at this comment in the System.ZLib source of Delphi Tokyo:
Add 16 to windowBits to write a simple gzip header and trailer around the compressed data instead of a zlib wrapper. The gzip header will have no file name, no extra data, no comment, no modification time (set to zero), no header crc, and the operating system will be set to 255 (unknown).
It works:
TargetStream:= TFileStream.Create(TargetFilename, fmCreate);
CompressStream:= TZCompressionStream.Create(TargetStream, zcDefault, 15 + 16);
TarStream:= TTarWriter.Create(CompressStream);
TarStream.AddStream(SourceStream1, SourceFilename1, Now);
TarStream.AddString(SourceString2, SourceFilename2, Now);