System.IO.Compression: Exposing Remaining number of Input buffer bytes to support mixed data blocks.

[jnix-abk]

I am working with data that has packed objects that contain header bytes and then a ZLib blob. The DeflateStream class has an internal buffer that advances the BaseStream to fetch data. The problem is that the underlying Stream is then advanced past where the ZLib blob ends. Currently, I have to use reflection to reach down into the object model to get the number of bytes that were not consumed in the buffer so I can re-wind the BaseStream to where the ZLib data ended.
Like so:

//Get the Available Bytes in the internal buffer
//Reflection Path = deflateStream -> _inflater / inflater -> _zlibStream -> AvailIn
var flags = BindingFlags.NonPublic | BindingFlags.Instance;
var inflater = deflateStream
    .GetType()
    .GetFields(flags)
    .ToList()
    .Find(x => x.Name == "inflater" || x.Name == "_inflater");
var inflaterInstance = inflater.GetValue(deflateStream);
var zlibStream = inflaterInstance.GetType().GetField("_zlibStream", flags);
var zlibStreamInstance = zlibStream.GetValue(inflaterInstance);
var availIn = zlibStreamInstance.GetType().GetProperty("AvailIn");
var availInValue = availIn.GetValue(zlibStreamInstance);

//Rewind the BaseStream
deflateStream.BaseStream.Seek(-1 * (uint)availInValue, SeekOrigin.Current);

Can you add public int AvailableInput => (int)_zlibStream.AvailIn; to this:

runtime/src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/Inflater.cs

Line 43 in a3fb0d3

public int AvailableOutput => (int)_zlibStream.AvailOut;

And then add

        public int RemainingBufferBytes
        {
            get
            {
                if (_inflater != null)
                    return _inflater.AvailableInput;
                else
                    return -1;
            }
        }

to this:

runtime/src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

Line 120 in a3fb0d3

And then add

        public int RemainingBufferBytes { get { throw null; } }

to this:

runtime/src/libraries/System.IO.Compression/ref/System.IO.Compression.cs

Line 27 in a3fb0d3

public System.IO.Stream BaseStream { get { throw null; } }

I pulled down the runtime-6.0.8 release and added those snippets. I am able to build and use the new method and it works properly.

[jnix-abk]

@stephentoub, @adamsitnik, @danmoseley
, what are your thoughts on this? I'd like to be able to do this without Reflection / building this code on my own.

[jnix-abk]

I've moved this to an API proposal.