Compress with ZLIB to array of Bytes? - delphi

Question

Can I somehow compress with Delphi using ZLIB (Deflate with ZLIB headers) and get an array of Bytes?
Right now I am copying from TMemoryStream but it would be nice to not copy back to array (so it's faster overall)
PackedStream := TMemoryStream.Create;
ZLib := TZCompressionStream.Create(PackedStream);
ZLib.WriteBuffer(UnpackedArray[0], UnpackedArrayLen);
ZLib.Free;
PackedArrayLen := PackedStream.Size;
SetLength(PackedArray, PackedArrayLen);
PackedStream.Position := 0;
PackedStream.Read(PackedArray[0], PackedArrayLen);
PackedStream.Free;

Answer 1

Simply use TMemoryStream.Memory as the byte array, just don't free the stream until you are done using the bytes:
PackedStream := TMemoryStream.Create;
try
ZLib := TZCompressionStream.Create(PackedStream);
try
ZLib.WriteBuffer(UnpackedArray[0], UnpackedArrayLen);
finally
ZLib.Free;
end;
// use PackedStream.Memory up to PackedStream.Size bytes as needed...
finally
PackedStream.Free;
end;
Otherwise, you can use TBytesStream instead of TMemoryStream:
PackedStream := TBytesStream.Create;
try
ZLib := TZCompressionStream.Create(PackedStream);
try
ZLib.WriteBuffer(UnpackedArray[0], UnpackedArrayLen);
finally
ZLib.Free;
end;
// use PackedStream.Bytes up to PackedStream.Size bytes as needed...
finally
PackedStream.Free;
end;
Or, if you have a pre-allocated byte array, you can use TCustomMemoryStream giving it a pointer to that array so it will write directly into the array:
type
TMemoryBufferStream = class(TCustomMemoryStream)
public
constructor Create(APtr: Pointer; ASize: NativeInt);
function Write(const Buffer; Count: Longint): Longint; override;
end;
constructor TMemoryBufferStream.Create(APtr: Pointer; ASize: NativeInt);
begin
inherited Create;
SetPointer(APtr, ASize);
end;
function TMemoryBufferStream.Write(const Buffer; Count: Longint): Longint;
var
LAvailable: Int64;
LNumToCopy: Longint;
begin
Result := 0;
LAvailable := Size - Position;
if LAvailable > 0 then
begin
LNumToCopy := Count;
if Int64(LNumToCopy) > LAvailable then
LNumToCopy := Longint(LAvailable);
if LNumToCopy > 0 then
begin
Move(Buffer, (PByte(Memory) + Position)^, LNumToCopy);
Seek(LNumToCopy, soCurrent);
Result := LNumToCopy;
end;
end;
end;
PackedStream := TMemoryBufferStream.Create(SomeBuffer, MaxBufferSize);
try
ZLib := TZCompressionStream.Create(PackedStream);
try
ZLib.WriteBuffer(UnpackedArray[0], UnpackedArrayLen);
finally
ZLib.Free;
end;
// use SomeBuffer up to PackedStream.Size bytes as needed...
finally
PackedStream.Free;
end;