Twilio Functionsを利用し、自前のDBに保存している転送設定で通話を転送する

/**
 *  Call Forward Template
 * 
 *  This Function will forward a call to another phone number. If the call isn't answered or the line is busy, 
 *  the call is optionally forwarded to a specified URL. You can optionally restrict which calling phones 
 *  will be forwarded.
 */

exports.handler = function(context, event, callback) {
  // set-up the variables that this Function will use to forward a phone call using TwiML

    var request = require('request');

    //ヘッダーを定義
    var headers = {
      'Content-Type':'application/json',
      'Cache-Control': 'no-cache',
      'Authorization': context.API_KEY
    }

    //GETパラメータ
    //event.Toで、コールされたTwilioの電話番号を取得できる
    param = "?twilio_number=" + encodeURIComponent(event.To)

    var options = {
        uri: context.HTTP_REQUEST_URL + param,
        method: 'GET',
        headers: headers,
        json: true
    };

    // 転送先の電話番号をhttp getで取得
    request(options, function(error, response, body){

        // 転送先電話番号
        let phoneNumber = body.forwarding_number;
        // 転送元番号（twilio の番号)
        let callerNumber = event.To;
        // タイムアウト時間
        let timeout = 10;
        // 録音
        let record = true;

        // OPTIONAL
        let allowedCallers = event.allowedCallers || [];


        // generate the TwiML to tell Twilio how to forward this call
        let twiml = new Twilio.twiml.VoiceResponse();

        let allowedThrough = true
        if (body.forwarding_number === undefined) {
            allowedThrough = false
        }

        let dialParams = {};
        if (callerNumber) {
            dialParams.callerId = callerNumber
        }
        if (timeout) {
            dialParams.timeout = timeout
        }
        if (record) {
            dialParams.record = record
        }

        let numberParams = {}

        console.log(allowedThrough)
        if (allowedThrough) {
          //転送用番号の取得に成功した場合は、転送先へダイヤルする
          const dial = twiml.dial(dialParams);
          dial.number(numberParams, phoneNumber);
        } else {
          //番号の取得に失敗した場合は、失敗用メッセージ（FAILED_VOICE_MESSAGE）を再生する
          twiml.say(
              {
                  voice: 'woman',
                  language: 'ja-JP',
                  loop: 2
              },
              context.FAILED_VOICE_MESSAGE
          );
        }

        // return the TwiML
        console.log(twiml.toString())
        callback(null, twiml);
    });
};