aos/network/www/proxy.ts

import {Builder, ByteBuffer, Offset} from 'flatbuffers';
import {Channel as ChannelFb, Configuration} from 'org_frc971/aos/configuration_generated';
import {ChannelRequest as ChannelRequestFb, ChannelState, MessageHeader, Payload, SdpType, SubscriberRequest, TransferMethod, WebSocketIce, WebSocketMessage, WebSocketSdp} from 'org_frc971/aos/network/web_proxy_generated';
import {Schema} from 'flatbuffers_reflection/reflection_generated';

// There is one handler for each DataChannel, it maintains the state of
// multi-part messages and delegates to a callback when the message is fully
// assembled.
export class Handler {
  private dataBuffer: Uint8Array|null = null;
  private receivedMessageLength: number = 0;
  constructor(
      private readonly handlerFunc:
          (data: Uint8Array, sentTime: number) => void,
      private readonly channel: RTCDataChannel) {
    channel.addEventListener('message', (e) => this.handleMessage(e));
  }

  handleMessage(e: MessageEvent): void {
    const fbBuffer = new ByteBuffer(new Uint8Array(e.data));
    const messageHeader = MessageHeader.getRootAsMessageHeader(fbBuffer);
    const time = Number(messageHeader.monotonicSentTime()) * 1e-9;

    const stateBuilder = new Builder(512);
    ChannelState.startChannelState(stateBuilder);
    ChannelState.addQueueIndex(stateBuilder, messageHeader.queueIndex());
    ChannelState.addPacketIndex(stateBuilder, messageHeader.packetIndex());
    const state = ChannelState.endChannelState(stateBuilder);
    stateBuilder.finish(state);
    const stateArray = stateBuilder.asUint8Array();
    this.channel.send(stateArray);

    // Short circuit if only one packet
    if (messageHeader.packetCount() === 1) {
      this.handlerFunc(messageHeader.dataArray(), time);
      return;
    }

    if (messageHeader.packetIndex() === 0) {
      this.dataBuffer = new Uint8Array(messageHeader.length());
      this.receivedMessageLength = 0;
    }
    if (!messageHeader.dataLength()) {
      return;
    }
    this.dataBuffer.set(
        messageHeader.dataArray(),
        this.receivedMessageLength);
    this.receivedMessageLength += messageHeader.dataLength();

    if (messageHeader.packetIndex() === messageHeader.packetCount() - 1) {
      this.handlerFunc(this.dataBuffer, time);
    }
  }
}

class Channel {
  constructor(public readonly name: string, public readonly type: string) {}
  key(): string {
    return this.name + "/" + this.type;
  }
}

class ChannelRequest {
  constructor(
      public readonly channel: Channel,
      public readonly transferMethod: TransferMethod) {}
}

// Analogous to the Connection class in //aos/network/web_proxy.h. Because most
// of the apis are native in JS, it is much simpler.
export class Connection {
  private webSocketConnection: WebSocket|null = null;
  private rtcPeerConnection: RTCPeerConnection|null = null;
  private dataChannel: RTCDataChannel|null = null;
  private webSocketUrl: string;

  private configInternal: Configuration|null = null;
  // A set of functions that accept the config to handle.
  private readonly configHandlers = new Set<(config: Configuration) => void>();

  private readonly handlerFuncs =
      new Map<string, ((data: Uint8Array, sentTime: number) => void)[]>();
  private readonly handlers = new Set<Handler>();

  private subscribedChannels: ChannelRequest[] = [];

  constructor() {
    const server = location.host;
    this.webSocketUrl = `ws://${server}/ws`;
  }

  addConfigHandler(handler: (config: Configuration) => void): void {
    this.configHandlers.add(handler);
  }

  /**
   * Add a handler for a specific message type, with reliable delivery of all
   * messages.
   */
  addReliableHandler(
      name: string, type: string,
      handler: (data: Uint8Array, sentTime: number) => void): void {
    this.addHandlerImpl(
        name, type, TransferMethod.LOSSLESS, handler);
  }

  /**
   * Add a handler for a specific message type.
   */
  addHandler(
      name: string, type: string,
      handler: (data: Uint8Array, sentTime: number) => void): void {
    this.addHandlerImpl(name, type, TransferMethod.SUBSAMPLE, handler);
  }

  addHandlerImpl(
      name: string, type: string, method: TransferMethod,
      handler: (data: Uint8Array, sentTime: number) => void): void {
    const channel = new Channel(name, type);
    const request = new ChannelRequest(channel, method);
    if (!this.handlerFuncs.has(channel.key())) {
      this.handlerFuncs.set(channel.key(), []);
    } else {
      if (method == TransferMethod.LOSSLESS) {
        console.warn(
            'Behavior of multiple reliable handlers is currently poorly ' +
            'defined and may not actually deliver all of the messages.');
      }
    }
    this.handlerFuncs.get(channel.key()).push(handler);
    this.subscribeToChannel(request);
  }

  getSchema(typeName: string): Schema {
    let schema = null;
    const config = this.getConfig();
    for (let ii = 0; ii < config.channelsLength(); ++ii) {
      if (config.channels(ii).type() === typeName) {
        schema = config.channels(ii).schema();
      }
    }
    if (schema === null) {
      throw new Error('Unable to find schema for ' + typeName);
    }
    return schema;
  }

  subscribeToChannel(channel: ChannelRequest): void {
    this.subscribedChannels.push(channel);
    if (this.configInternal === null) {
      throw new Error(
          'Must call subscribeToChannel after we\'ve received the config.');
    }
    const builder = new Builder(512);
    const channels: Offset[] = [];
    for (const channel of this.subscribedChannels) {
      const nameFb = builder.createString(channel.channel.name);
      const typeFb = builder.createString(channel.channel.type);
      ChannelFb.startChannel(builder);
      ChannelFb.addName(builder, nameFb);
      ChannelFb.addType(builder, typeFb);
      const channelFb = ChannelFb.endChannel(builder);
      ChannelRequestFb.startChannelRequest(builder);
      ChannelRequestFb.addChannel(builder, channelFb);
      ChannelRequestFb.addMethod(builder, channel.transferMethod);
      channels.push(ChannelRequestFb.endChannelRequest(builder));
    }

    const channelsFb =
        SubscriberRequest.createChannelsToTransferVector(builder, channels);
    SubscriberRequest.startSubscriberRequest(builder);
    SubscriberRequest.addChannelsToTransfer(builder, channelsFb);
    const connect = SubscriberRequest.endSubscriberRequest(builder);
    builder.finish(connect);
    this.sendConnectMessage(builder);
  }

  connect(): void {
    this.webSocketConnection = new WebSocket(this.webSocketUrl);
    this.webSocketConnection.binaryType = 'arraybuffer';
    this.webSocketConnection.addEventListener(
        'open', () => this.onWebSocketOpen());
    this.webSocketConnection.addEventListener(
        'message', (e) => this.onWebSocketMessage(e));
  }

  getConfig() {
    return this.configInternal;
  }

  // Handle messages on the DataChannel. Handles the Configuration message as
  // all other messages are sent on specific DataChannels.
  onConfigMessage(data: Uint8Array): void {
    const fbBuffer = new ByteBuffer(data);
    this.configInternal = Configuration.getRootAsConfiguration(fbBuffer);
    for (const handler of Array.from(this.configHandlers)) {
      handler(this.configInternal);
    }
  }

  onDataChannel(ev: RTCDataChannelEvent): void {
    const channel = ev.channel;
    const name = channel.label;
    const handlers = this.handlerFuncs.get(name);
    for (const handler of handlers) {
      this.handlers.add(new Handler(handler, channel));
    }
  }

  onIceCandidate(e: RTCPeerConnectionIceEvent): void {
    if (!e.candidate) {
      return;
    }
    const candidate = e.candidate;
    const builder = new Builder(512);
    const candidateString = builder.createString(candidate.candidate);
    const sdpMidString = builder.createString(candidate.sdpMid);

    const iceFb = WebSocketIce.createWebSocketIce(
        builder, candidateString, sdpMidString, candidate.sdpMLineIndex);
    const messageFb = WebSocketMessage.createWebSocketMessage(
        builder, Payload.WebSocketIce, iceFb);
    builder.finish(messageFb);
    const array = builder.asUint8Array();
    this.webSocketConnection.send(array.buffer.slice(array.byteOffset));
  }

  onIceCandidateError(e: Event): void {
    console.warn(e);
  }

  // Called for new SDPs. Make sure to set it locally and remotely.
  onOfferCreated(description: RTCSessionDescriptionInit): void {
    this.rtcPeerConnection.setLocalDescription(description);
    const builder = new Builder(512);
    const offerString = builder.createString(description.sdp);

    const webSocketSdp = WebSocketSdp.createWebSocketSdp(
        builder, SdpType.OFFER, offerString);
    const message = WebSocketMessage.createWebSocketMessage(
        builder, Payload.WebSocketSdp,
        webSocketSdp);
    builder.finish(message);
    const array = builder.asUint8Array();
    this.webSocketConnection.send(array.buffer.slice(array.byteOffset));
  }

  // We now have a websocket, so start setting up the peer connection. We only
  // want a DataChannel, so create it and then create an offer to send.
  onWebSocketOpen(): void {
    this.rtcPeerConnection = new RTCPeerConnection(
        {'iceServers': [{'urls': ['stun:stun.l.google.com:19302']}]});
    this.rtcPeerConnection.addEventListener(
        'datachannel', (e) => this.onDataChannel(e));
    this.dataChannel = this.rtcPeerConnection.createDataChannel('signalling');
    this.handlers.add(
        new Handler((data) => this.onConfigMessage(data), this.dataChannel));
    this.rtcPeerConnection.addEventListener(
        'icecandidate', (e) => this.onIceCandidate(e));
    this.rtcPeerConnection.addEventListener(
        'icecandidateerror', (e) => this.onIceCandidateError(e));
    this.rtcPeerConnection.createOffer().then(
        (offer) => this.onOfferCreated(offer));
  }

  // When we receive a websocket message, we need to determine what type it is
  // and handle appropriately. Either by setting the remote description or
  // adding the remote ice candidate.
  onWebSocketMessage(e: MessageEvent): void {
    const buffer = new Uint8Array(e.data)
    const fbBuffer = new ByteBuffer(buffer);
    const message = WebSocketMessage.getRootAsWebSocketMessage(fbBuffer);
    switch (message.payloadType()) {
      case Payload.WebSocketSdp:
        const sdpFb = message.payload(new WebSocketSdp());
        if (sdpFb.type() !== SdpType.ANSWER) {
          console.log('got something other than an answer back');
          break;
        }
        this.rtcPeerConnection.setRemoteDescription(new RTCSessionDescription(
            {'type': 'answer', 'sdp': sdpFb.payload()}));
        break;
      case Payload.WebSocketIce:
        const iceFb = message.payload(new WebSocketIce());
        const candidate = {} as RTCIceCandidateInit;
        candidate.candidate = iceFb.candidate();
        candidate.sdpMid = iceFb.sdpMid();
        candidate.sdpMLineIndex = iceFb.sdpMLineIndex();
        this.rtcPeerConnection.addIceCandidate(candidate);
        break;
      default:
        console.log('got an unknown message');
        break;
    }
  }

  /**
   * Subscribes to messages. Only the most recent connect message is in use. Any
   * channels not specified in the message are implicitely unsubscribed.
   * @param a Finished flatbuffer.Builder containing a Connect message to send.
   */
  sendConnectMessage(builder: any) {
    const array = builder.asUint8Array();
    this.dataChannel.send(array.buffer.slice(array.byteOffset));
  }
}