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Programming => Packages and Libraries => Topic started by: Borneq on January 09, 2020, 08:41:15 am

Title: [paszlib]How to make streaming compression?
Post by: Borneq on January 09, 2020, 08:41:15 am

I use paszlib library, in zCompres unit is

Code: Pascal  [Select][+][-]

1. function compress2 (dest : Pbyte;
2.                     var destLen : cardinal;
3.                     const source : array of byte;
4.                     sourceLen : cardinal;
5.                     level : integer) : integer;
6. var
7.   stream : z_stream;
8.   err : integer;
9. begin
10.   stream.next_in := Pbyte(@source);
11.   stream.avail_in := cardinal(sourceLen);
12.   stream.next_out := dest;
13.   stream.avail_out := cardinal(destLen);
14. .....
15.   err := deflateInit(stream, level);
16. .....
17.   err := deflate(stream, Z_FINISH);
18.   if (err <> Z_STREAM_END) then
19.   begin
20.     deflateEnd(stream);
21.     if err = Z_OK then
22.       compress2 := Z_BUF_ERROR
23.     else
24.       compress2 := err;
25.     exit;
26.   end;
27.   destLen := stream.total_out;
28.  
29.   err := deflateEnd(stream);
30.   compress2 := err;
31. end;

This compress one block at once, how to use TStream and compress/uncompress chunk by chunk. Unit gzIO has streaming but works on files given by path, I prefer TStream and maybe memory streams.
Is sggzip.pas but is not compatible with paszlib.
I want write method: at first it must deflateInit, at end deflateEnd, and in loop deflate(stream, ?); where "?" is not Z_FINISH and maybe one from list below:

Code: Pascal  [Select][+][-]

1.    Z_NO_FLUSH      = 0;
2.    Z_PARTIAL_FLUSH = 1;
3.    Z_SYNC_FLUSH    = 2;
4.    Z_FULL_FLUSH    = 3;
5.    Z_FINISH        = 4;

Title: Re: [paszlib]How to make streaming compression?
Post by: rvk on January 09, 2020, 10:17:48 am

Maybe using the ZStream unit.

You could use Tcompressionstream (create with a destination stream) and use Tcompressionstream.write() to write chunks to that compression stream.

Or something like CompressionStream.CopyFrom(YourPreferredStream); should also work (because Tcompressionstream is a TStream descendant).