compression level support

[dmitrip]

It seems that different compression levels are not supported (although level is passed to the ccall of ZSTD_initCStream in libzstd.jl):

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.4.0 (2020-03-21)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> using Pkg; Pkg.status("CodecZstd")
Status `~/.julia/environments/v1.4/Project.toml`
  [6b39b394] CodecZstd v0.7.0

julia> using CodecZstd

julia> data = rand(0xa:0xb, 10^6); # something compressible

julia> unique(length(transcode(ZstdCompressor(level=level), data)) for level in 1:22)
# returns a 1-element array, so the compressed length is independent of level

Tips for debugging or understanding this?

[milankl]

Maybe the initialization is not properly set up? If I do

julia> using TranscodingStreams, CodecZstd
julia> A = sort(rand(UInt8,1000));

julia> ZstdCompressorL3 = ZstdCompressor(level=3)
julia> ZstdCompressorL22 = ZstdCompressor(level=22)
julia> TranscodingStreams.initialize(ZstdCompressorL3)
julia> TranscodingStreams.initialize(ZstdCompressorL22)

julia> sizeof(A)/sizeof(transcode(ZstdCompressorL3,A))
1.6207455429497568

julia> sizeof(A)/sizeof(transcode(ZstdCompressorL22,A))
1.9083969465648856

choosing the level does indeed have an effect.

[dmitrip]

You're right that the initialize call fixes this, and I now realize that this is intended behavior as documented in the transcode(codec::Codec, data::Vector{UInt8}) method in TranscodingStreams.jl.