perf: avoid array allocation in _onMethod

[Samuron]

One more small optimization. This method may also benefit in using switch statement, I can give it a try if you want

[Samuron]

It will look like this:

/** @internal */
  _onMethod(methodFrame: MethodFrame): void {
    if (this._state.incoming != null) {
      throw new AMQPConnectionError('UNEXPECTED_FRAME',
        'unexpected method frame, already awaiting header/body; this is a bug')
    }
    switch(methodFrame.methodId) {
      case Cmd.BasicDeliver:
      case Cmd.BasicReturn:
      case Cmd.BasicGetOK:
        this._state.incoming = {methodFrame, headerFrame: undefined, chunks: undefined, received: 0}
        break;
      case Cmd.BasicGetEmpty:
        this._handleRPC(Cmd.BasicGetOK, undefined)
        break;
      case Cmd.BasicAck:
        if (this._state.mode === CH_MODE.CONFIRM) {
          const params = methodFrame.params as Required<MethodParams[Cmd.BasicAck]>
          if (params.multiple) {
            for (const [tag, dfd] of this._state.unconfirmed.entries()) {
              if (tag > params.deliveryTag)
                break
              dfd.resolve()
              this._state.unconfirmed.delete(tag)
            }
          } else {
            const dfd = this._state.unconfirmed.get(params.deliveryTag)
            if (dfd) {
              dfd.resolve()
              this._state.unconfirmed.delete(params.deliveryTag)
            } else {
              //TODO channel error; PRECONDITION_FAILED, unexpected ack
            }
          }
        }
        break;
      case Cmd.BasicNack:
        if (this._state.mode === CH_MODE.CONFIRM) {
          const params = methodFrame.params as Required<MethodParams[Cmd.BasicNack]>
          if (params.multiple) {
            for (const [tag, dfd] of this._state.unconfirmed.entries()) {
              if (tag > params.deliveryTag)
                break
              dfd.reject(new AMQPError('NACK', 'message rejected by server'))
              this._state.unconfirmed.delete(tag)
            }
          } else {
            const dfd = this._state.unconfirmed.get(params.deliveryTag)
            if (dfd) {
              dfd.reject(new AMQPError('NACK', 'message rejected by server'))
              this._state.unconfirmed.delete(params.deliveryTag)
            } else {
              //TODO channel error; PRECONDITION_FAILED, unexpected nack
            }
          }
        }
        break;
      case Cmd.BasicCancel:
        const params = methodFrame.params as Required<MethodParams[Cmd.BasicCancel]>
        this._state.consumers.delete(params.consumerTag)
        setImmediate(() => {
          this.emit('basic.cancel', params.consumerTag, new AMQPError('CANCEL_FORCED', 'cancelled by server'))
        })
        break;
      default:
        this._handleRPC(methodFrame.methodId, methodFrame.params)
    }
  }