ms/packages/websocket/src/engine.io-client/transport.ts

// import { decodePacket, Packet, RawData } from "engine.io-parser"
import { decodePacket, Packet, RawData } from "../engine.io-parser"
import { Emitter } from "@socket.io/component-emitter"
import { installTimerFunctions } from "./util"
// import debugModule from "debug"; // debug()
import { SocketOptions } from "./socket"

// const debug = debugModule("engine.io-client:transport"); // debug()
const debug = require('../debug')("engine.io-client:transport") // debug()

class TransportError extends Error {
    public readonly type = "TransportError";

    constructor(
        reason: string,
        readonly description: any,
        readonly context: any
    ) {
        super(reason)
    }
}

export interface CloseDetails {
    description: string
    context?: unknown // context should be typed as CloseEvent | XMLHttpRequest, but these types are not available on non-browser platforms
}

interface TransportReservedEvents {
    open: () => void
    error: (err: TransportError) => void
    packet: (packet: Packet) => void
    close: (details?: CloseDetails) => void
    poll: () => void
    pollComplete: () => void
    drain: () => void
}

type TransportState = "opening" | "open" | "closed" | "pausing" | "paused"

export abstract class Transport extends Emitter<
    Record<never, never>,
    Record<never, never>,
    TransportReservedEvents
> {
    public query: Record<string, string>
    public writable: boolean = false;

    protected opts: SocketOptions
    protected supportsBinary: boolean
    protected readyState: TransportState
    protected socket: any
    protected setTimeoutFn: typeof setTimeout

    /**
      * Transport abstract constructor.
      *
      * @param {Object} opts - options
      * @protected
      */
    constructor(opts) {
        super()
        installTimerFunctions(this, opts)

        this.opts = opts
        this.query = opts.query
        this.socket = opts.socket
    }

    /**
     * Emits an error.
     *
     * @param {String} reason
     * @param description
     * @param context - the error context
     * @return {Transport} for chaining
     * @protected
     */
    protected onError(reason: string, description: any, context?: any) {
        super.emitReserved(
            "error",
            new TransportError(reason, description, context)
        )
        return this
    }

    /**
     * Opens the transport.
     */
    public open() {
        this.readyState = "opening"
        this.doOpen()

        return this
    }

    /**
     * Closes the transport.
     */
    public close() {
        if (this.readyState === "opening" || this.readyState === "open") {
            this.doClose()
            this.onClose()
        }

        return this
    }

    /**
     * Sends multiple packets.
     *
     * @param {Array} packets
     */
    public send(packets) {
        if (this.readyState === "open") {
            this.write(packets)
        } else {
            // this might happen if the transport was silently closed in the beforeunload event handler
            debug("transport is not open, discarding packets")
        }
    }

    /**
     * Called upon open
     *
     * @protected
     */
    protected onOpen() {
        this.readyState = "open"
        this.writable = true
        super.emitReserved("open")
    }

    /**
     * Called with data.
     *
     * @param {String} data
     * @protected
     */
    protected onData(data: RawData) {
        const packet = decodePacket(data, this.socket.binaryType)
        this.onPacket(packet)
    }


    /**
     * Called with a decoded packet.
     *
     * @protected
     */
    protected onPacket(packet: Packet) {
        super.emitReserved("packet", packet)
    }

    /**
     * Called upon close.
     *
     * @protected
     */
    protected onClose(details?: CloseDetails) {
        this.readyState = "closed"
        super.emitReserved("close", details)
    }

    /**
     * The name of the transport
     */
    public abstract get name(): string

    /**
     * Pauses the transport, in order not to lose packets during an upgrade.
     *
     * @param onPause
     */
    public pause(onPause: () => void) { }

    protected abstract doOpen()
    protected abstract doClose()
    protected abstract write(packets: Packet[])
}