This directory contains an example Unity native plugin for Windows OS.
The APIs use Platform Invoke (P/Invoke) technology as required by Unity native plugin.
This plugin dll can also be used by Windows C# applications other than Unity.

An example of wrapping native plugin into a C# managed class in Unity is given as following:

using System;
using System.Runtime.InteropServices;

namespace SimplePeerConnectionM {
  // This is a managed wrap up class for the native c style peer connection APIs.
  public class PeerConnectionM {
    //private const string dll_path = "SimplePeerConnection";
    private const string dll_path = "webrtc_unity_plugin";

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern int CreatePeerConnection();

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool ClosePeerConnection(int peer_connection_id);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool AddStream(int peer_connection_id, bool audio_only);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool AddDataChannel(int peer_connection_id);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool CreateOffer(int peer_connection_id);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool CreateAnswer(int peer_connection_id);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool SendDataViaDataChannel(int peer_connection_id, string data);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool SetAudioControl(int peer_connection_id, bool is_mute, bool is_record);

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void LocalDataChannelReadyInternalDelegate();
    public delegate void LocalDataChannelReadyDelegate(int id);
    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool RegisterOnLocalDataChannelReady(int peer_connection_id, LocalDataChannelReadyInternalDelegate callback);

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void DataFromDataChannelReadyInternalDelegate(string s);
    public delegate void DataFromDataChannelReadyDelegate(int id, string s);
    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool RegisterOnDataFromDataChannelReady(int peer_connection_id, DataFromDataChannelReadyInternalDelegate callback);

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void FailureMessageInternalDelegate(string msg);
    public delegate void FailureMessageDelegate(int id, string msg);
    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool RegisterOnFailure(int peer_connection_id, FailureMessageInternalDelegate callback);

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void AudioBusReadyInternalDelegate(IntPtr data, int bits_per_sample,
        int sample_rate, int number_of_channels, int number_of_frames);
    public delegate void AudioBusReadyDelegate(int id, IntPtr data, int bits_per_sample,
        int sample_rate, int number_of_channels, int number_of_frames);
    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool RegisterOnAudioBusReady(int peer_connection_id, AudioBusReadyInternalDelegate callback);

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void LocalSdpReadytoSendInternalDelegate(string s);
    public delegate void LocalSdpReadytoSendDelegate(int id, string s);
    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool RegisterOnLocalSdpReadytoSend(int peer_connection_id, LocalSdpReadytoSendInternalDelegate callback);

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void IceCandiateReadytoSendInternalDelegate(string s);
    public delegate void IceCandiateReadytoSendDelegate(int id, string s);
    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool RegisterOnIceCandiateReadytoSend(int peer_connection_id, IceCandiateReadytoSendInternalDelegate callback);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern int ReceivedSdp(int peer_connection_id, string sdp);

    [DllImport(dll_path, CallingConvention = CallingConvention.Cdecl)]
    private static extern bool ReceivedIceCandidate(int peer_connection_id, string ice_candidate);

    public void CreatePeerConnectionM() {
      peer_connection_id_ = CreatePeerConnection();
      RegisterCallbacks();
    }

    private void RegisterCallbacks() {
      localDataChannelReadyDelegate_ = new LocalDataChannelReadyInternalDelegate(RaiseLocalDataChannelReady);
      RegisterOnLocalDataChannelReady(peer_connection_id_, localDataChannelReadyDelegate_);

      dataFromDataChannelReadyDelegate_ = new DataFromDataChannelReadyInternalDelegate(RaiseDataFromDataChannelReady);
      RegisterOnDataFromDataChannelReady(peer_connection_id_, dataFromDataChannelReadyDelegate_);

      failureMessageDelegate_ = new FailureMessageInternalDelegate(RaiseFailureMessage);
      RegisterOnFailure(peer_connection_id_, failureMessageDelegate_);

      audioBusReadyDelegate_ = new AudioBusReadyInternalDelegate(RaiseAudioBusReady);
      RegisterOnAudioBusReady(peer_connection_id_, audioBusReadyDelegate_);

      localSdpReadytoSendDelegate_ = new LocalSdpReadytoSendInternalDelegate(RaiseLocalSdpReadytoSend);
      RegisterOnLocalSdpReadytoSend(peer_connection_id_, localSdpReadytoSendDelegate_);

      iceCandiateReadytoSendDelegate_ = new IceCandiateReadytoSendInternalDelegate(RaiseIceCandiateReadytoSend);
      RegisterOnIceCandiateReadytoSend(peer_connection_id_, iceCandiateReadytoSendDelegate_);
    }

    public void ClosePeerConnectionM() {
      ClosePeerConnection(peer_connection_id_);
      peer_connection_id_ = -1;
    }

    // Return -1 if Peerconnection is not available.
    public int GetUniqueId() {
      return peer_connection_id_;
    }

    public void AddStreamM(bool audio_only) {
      AddStream(peer_connection_id_, audio_only);
    }

    public void AddDataChannelM() {
      AddDataChannel(peer_connection_id_);
    }

    public void CreateOfferM() {
      CreateOffer(peer_connection_id_);
    }

    public void CreateAnswerM() {
      CreateAnswer(peer_connection_id_);
    }

    public void SendDataViaDataChannelM(string data) {
      SendDataViaDataChannel(peer_connection_id_, data);
    }

    public void SetAudioControl(bool is_mute, bool is_record) {
      SetAudioControl(peer_connection_id_, is_mute, is_record);
    }

    public void ReceivedSdpM(string sdp) {
      peer_connection_id_ = ReceivedSdp(peer_connection_id_, sdp);
      RegisterCallbacks();
    }

    public void ReceivedIceCandidateM(string ice_candidate) {
      ReceivedIceCandidate(peer_connection_id_, ice_candidate);
    }

    private void RaiseLocalDataChannelReady() {
      if (OnLocalDataChannelReady != null)
        OnLocalDataChannelReady(peer_connection_id_);
    }

    private void RaiseDataFromDataChannelReady(string data) {
      if (OnDataFromDataChannelReady != null)
        OnDataFromDataChannelReady(peer_connection_id_, data);
    }

    private void RaiseFailureMessage(string msg) {
      if (OnFailureMessage != null)
        OnFailureMessage(peer_connection_id_, msg);
    }

    private void RaiseAudioBusReady(IntPtr data, int bits_per_sample,
      int sample_rate, int number_of_channels, int number_of_frames) {
      if (OnAudioBusReady != null)
        OnAudioBusReady(peer_connection_id_, data, bits_per_sample, sample_rate,
            number_of_channels, number_of_frames);
    }

    private void RaiseLocalSdpReadytoSend(string msg) {
      if (OnLocalSdpReadytoSend != null)
        OnLocalSdpReadytoSend(peer_connection_id_, msg);
    }

    private void RaiseIceCandiateReadytoSend(string msg) {
      if (OnIceCandiateReadytoSend != null)
        OnIceCandiateReadytoSend(peer_connection_id_, msg);
    }

    private LocalDataChannelReadyInternalDelegate localDataChannelReadyDelegate_ = null;
    public event LocalDataChannelReadyDelegate OnLocalDataChannelReady;

    private DataFromDataChannelReadyInternalDelegate dataFromDataChannelReadyDelegate_ = null;
    public event DataFromDataChannelReadyDelegate OnDataFromDataChannelReady;

    private FailureMessageInternalDelegate failureMessageDelegate_ = null;
    public event FailureMessageDelegate OnFailureMessage;

    private AudioBusReadyInternalDelegate audioBusReadyDelegate_ = null;
    public event AudioBusReadyDelegate OnAudioBusReady;

    private LocalSdpReadytoSendInternalDelegate localSdpReadytoSendDelegate_ = null;
    public event LocalSdpReadytoSendDelegate OnLocalSdpReadytoSend;

    private IceCandiateReadytoSendInternalDelegate iceCandiateReadytoSendDelegate_ = null;
    public event IceCandiateReadytoSendDelegate OnIceCandiateReadytoSend;

    private int peer_connection_id_ = -1;
  }
}