ProtocolStackApiDemo.cs

using System;
using System.Net;

/// <summary>Readonly stream of bytes</summary>
interface iReadStream
{
	/// <summary>Read bytes from the stream.</summary>
	/// <remarks>Blocks indefinitely until the entire buffer is filled, throws exceptions when things fail.</remarks>
	void read( Span<byte> buffer );
}

static class Factories
{
	/// <summary>Open a TCP connection to remote host, return object to read bytes from that socket</summary>
	/// <remarks>The state of the stream is the TCP socket</remarks>
	public static iReadStream connect( IPEndPoint address )
	{
		// TODO: write a class that wraps TcpClient from standard library
		throw new NotImplementedException();
	}

	/// <summary>Create a stream that decrypts data from another stream on the fly, with the specified symmetric key</summary>
	/// <remarks>The mutable state of the stream is the source stream being wrapped, plus state of AES stream cypher, plus up to 16 bytes of the data (size of AES block)</remarks>
	public static iReadStream decrypt( iReadStream encrypted, ReadOnlySpan<byte> key )
	{
		// TODO: write a class that wraps AesManaged from standard library
		throw new NotImplementedException();
	}

	/// <summary>Create a stream that decompresses GZip from another stream on the fly</summary>
	/// <remarks>The mutable state of the stream is the source stream, plus GZip decompressor state</remarks>
	public static iReadStream decompressGzip( iReadStream compressed )
	{
		// TODO: write a class that wraps GZipStream from standard library
		throw new NotImplementedException();
	}

	/// <summary>Create a stream that decompresses LZ4 from another stream on the fly</summary>
	/// <remarks>The mutable state of the stream is the source stream, plus LZ4 decompressor state</remarks>
	public static iReadStream decompressLz4( iReadStream compressed )
	{
		// TODO: write a class that uses [DllImport] to call lz4.dll on Windows, or liblz4.so.1 on Linux: https://packages.debian.org/buster/liblz4-1
		throw new NotImplementedException();
	}
}

enum eCompression: byte
{
	None,
	GZip,
	LZ4,
}

static class Connect
{
	public static iReadStream setupConnection( IPEndPoint address, byte[] decryptionKey, eCompression compression )
	{
		// Here the magic happens: building protocol stack in runtime, based on the arguments.
		iReadStream sess = Factories.connect( address );

		if( null != decryptionKey )
		{
			// Encryption was configured, wrap socket into the decryptor
			sess = Factories.decrypt( sess, decryptionKey );
		}
		// Optionally, wrap the session into decompressor
		switch( compression )
		{
			case eCompression.None:
				return sess;
			case eCompression.GZip:
				return Factories.decompressGzip( sess );
			case eCompression.LZ4:
				return Factories.decompressLz4( sess );
			default:
				throw new ArgumentException( $"Invalid compression algorithm { compression }" );
		}
	}
}