Redirect REST API response to UI/Browser NodeJs/Express/Request

Question

Not able to send response of a REST api callout to browser page using NodeJs server with Express and Request module.

I understand that due to asynchronous nature of callback method, response of api callout cannot be returned in typical style.

I have tried res.send method, but it gives error res.send is not a function.

Below is sample piece of that I have tried.

        const options = {
            url: endPoint,
            method: 'POST',
            headers: {
                'Authorization': 'Basic',
                'Accept': 'application/json',
                'Content-Type': 'application/json',
                'Accept-Charset': 'UTF-8'
            }
        };
        request(options, (err, res, body) => {
            if (err) { return console.log(err); }
            //want to send this body to the page.
            console.log(JSON.stringify(body));
            res.send(body);
        });

It gives this error message,

res.send(body);
TypeError: res.send is not a function
at Request.request [as _callback]

Answer 1

Figured the issue. First problem was as @vipul pointed above. res was response of callout and not instance of global HttpResponse object, so send method was not available on that object. I changed the method,

    request(options, (err, response, body) => {
        if (err) { return console.log(err); }
        //want to send this body to the page.
        console.log(JSON.stringify(response.body));
        // using the HttpResponse in global context.
        this.res.send(JSON.parse(body));
    });

Then I faced below error,

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client]

Problem was while making the callout, I was returning the response right after callout method.

  .get('/authorize', (req, res) => {
      console.log('Authorize Hit! '+req.query.code);
      try {
          //TODO: Need to utilize state to the current flow in action.
          let flowDetails = flow.flowMap.get('wsf');
          if(flowDetails) {
            //this method makes REST API call
            flowDetails.refreshToken(req, res);
            //this line was the problem!! Removed it to fix the error.
            res.send('Refresh Token Completed!');
          }
      } catch (error) {
          (Object.keys(error).length === 0)?res.send(error.message):res.send(error);
      }
  })

But due to asynchronous nature of callback function, by the time callout response was received, actual request/response was already returned and request was completed. So removed the res.send right after callout to fix the issue.

Hopefully it will be helpful for others as well:)