VpnHood.Net.Quic.Abstractions 9.1.864

VpnHood.Net.Quic.Abstractions

A minimal abstraction over the QUIC surface VpnHood actually uses, so the rest of the codebase does not depend on System.Net.Quic/MsQuic directly.

VpnHood uses QUIC purely as a transport (a custom protocol with the same binary framing as TCP — not HTTP/3; SslApplicationProtocol.Http3 is used only as the ALPN token). System.Net.Quic is a managed wrapper over the native MsQuic library and is only officially supported on Windows and Linux — on Android/iOS QuicConnection.IsSupported/QuicListener.IsSupported are false and the APIs throw. This abstraction keeps MsQuic as one implementation beside the platform-specific ones for iOS and Android.

This project is BCL-only (no VpnHood or native dependencies) so it is safe to reference from the low-level VpnHood.Net.Toolkit.

Surface

Everything else VpnHood needs is constant and is baked into the implementation, not exposed here: TLS 1.3, the Http3 ALPN token, EncryptionPolicy.RequireEncryption, X509RevocationMode.NoCheck, default stream/close error codes 0, and QuicStreamType.Bidirectional.

How it is wired into VpnHood

Implementations:

• VpnHood.Net.Quic.MsQuic (Windows / Linux) — MsQuicClient, MsQuicServer, MsQuicConnection, MsQuicListener, MsQuicSocketFactory. Owns the Microsoft.Native.Quic.MsQuic.OpenSSL native package. MsQuicClient.IsSupported / MsQuicServer.IsSupported report platform availability. Client and server.
• VpnHood.Net.Quic.Ios (iOS 15+) — IosQuicClient, IosQuicConnection, IosQuicStream, IosSocketFactory, built on Apple's Network.framework (NWMultiplexGroup / NWConnectionGroup / NWProtocolQuicOptions). Client only (iOS is never a server).
• VpnHood.Net.Quic.Android — AndroidQuicClient, AndroidQuicConnection, AndroidQuicStream, AndroidSocketFactory, over a libmsquic.so built for Android (see that project's README). Client only.

Client — through ISocketFactory

ISocketFactory (in VpnHood.Net.Toolkit) exposes QUIC capability:

bool IsQuicSupported { get; }
IQuicClient CreateQuicClient(); // throws NotSupportedException when !IsQuicSupported

The per-platform VpnService picks the socket factory, which is the seam that decides QUIC support:

• Windows / Linux VpnService → new MsQuicSocketFactory() (QUIC enabled).
• iOS VpnService → new IosSocketFactory(…) (QUIC enabled, iOS 15+).
• Android VpnService → new AndroidSocketFactory() (QUIC wherever the native library loads).

The socket factory flows VpnService → VpnHoodClient → ConnectorService, where QuicStreamConnectionFactory is built from socketFactory.CreateQuicClient() (only when IsQuicSupported). The decorators (ConfiguringSocketFactory, BindingSocketFactory, AdapterSocketFactory) forward IsQuicSupported/CreateQuicClient to their inner factory.

Server — explicit on VpnHoodServer

The server QUIC listener provider is passed explicitly (not via ISocketFactory): ServerOptions.QuicServer → VpnHoodServer → ServerHost → QuicListenerHost. ServerApp sets it to MsQuicServer.IsSupported ? new MsQuicServer() : null.

Adding another platform

1. Implement IQuicClient + IQuicConnection over the platform's QUIC, as VpnHood.Net.Quic.Ios does over Network.framework and VpnHood.Net.Quic.Android over a self-built libmsquic.so.
2. Expose it through an ISocketFactory whose IsQuicSupported is true and whose CreateQuicClient() returns your IQuicClient.
3. Have that platform's VpnService construct/use that socket factory instead of SystemSocketFactory.

No other VpnHood code needs to change — the abstraction is the single seam.