Fetch Http Response NodeJS

Question

Trying to execute a AWS Lambda in NodeJS (newbie to nodeJs) in which I make a http request. At the end of Lambda execution, I wish to return response code and response message of http request.

Making the http request call:

var executeRequest = function(request, callback) {

const req = https.request(request, (res) => {

  console.log('statusCode:', res.statusCode);
  console.log('headers:', res.headers);

  res.on('data', (d) => {
     process.stdout.write(d);
  });
  callback(res);
});

req.on('error', (e) => {
  console.error(e);
});

req.end(request.body);

};

Lambda Code:

    exports.handler = (event, context, callback) => {

    // Formulate request 

    var result = executeRequest(request, function(response) {
         console.log("Response Code: ", response.statusCode);
         console.log("Response Message: ", response.statusMessage);
         // Successfully able to print the response above

        return response;
     });
     console.log("Result Response Code: ", result);
     console.log("Result Response Message: ", result);
     }

I wish to return the response.statusCode and response.statusMessage as response from Lambda

return{
    statusCode: <the code>,
    body: <the message>,
};

However, the result is populated as undefined. How to extract the required response parameter so they can be returned correctly?

** Edit: ** Snippet after changes suggested: Code using Promise:

var executeRequest = function(request, callback) {

    return new Promise((resolve, reject) => {
        https.request(request, function(res) {
            if(res.statusCode==200 || res.statusCode==404) {
                resolve(res);
            }
            else {
                console.error(res);
                reject(res.statusCode);
            }
        }).end(request.body || '');
    });
};


exports.handler = (event, context, callback) => {

    // Formulate request 

    var value = executeRequest(request).then(function(result) {
  console.log("Result ", result);
  const response = { statusCode: 200, body: JSON.stringify('Hello from Lambda!') }; 
  return response;
 });

    console.log(value);
}

@ Kannaiyan : Result Response Code: undefined Result Response Message: undefined — alwaysAStudent
– alwaysAStudent, Commented May 23, 2019 at 20:55
Move your console.log lines inside the "result" function, otherwise they will always be undefined (place them before return response) — Deiv
– Deiv, Commented May 23, 2019 at 21:01

alwaysAStudent · Accepted Answer · 2019-05-24 05:50:11Z

3

Problem is that your executeRequest is asynchronous and your lambda doesn't know about that so it will simply return right away.

Instead of returning the response, pass it to callback as the second argument (first is error object)

callback(null, response)

This part is executed and without waiting for the executeRequest response, the rest of the code is executed

var result = executeRequest(request, function(response) {
     console.log("Response Code: ", response.statusCode);
     console.log("Response Message: ", response.statusMessage);
     // Successfully able to print the response above

    return response;
 });

So at this point

console.log("Result Response Code: ", result);
console.log("Result Response Message: ", result);

The result is still empty.

So you should instead do something like this.

var result = executeRequest(request, function(response) {
     console.log("Response Code: ", response.statusCode);
     console.log("Response Message: ", response.statusMessage);
     // Successfully able to print the response above

     callback(null, response);
 });

edited May 24, 2019 at 5:50

alwaysAStudent

2,3146 gold badges36 silver badges59 bronze badges

answered May 23, 2019 at 20:56

Matus Dubrava

14.6k3 gold badges44 silver badges60 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

alwaysAStudent Over a year ago

Getting response: ReferenceError: callback is not defined

Matus Dubrava Over a year ago

You need to place the above code into the exports.handler body where the callback is defined, I will update the code snippet

alwaysAStudent Over a year ago

Probably miinterpretating your comment. :( ... I have edited my question to include code based on suggested answer along with log statement being printed.

Hans-Eric Lippke Over a year ago

Asynchronous is the issue. Try using promises.

alwaysAStudent Over a year ago

@Hans-Eric Lippke: Do you have code snippet I can reference? I have edited the question section to include using Promises. I however get INFO Promise { <pending> } in the logs

|

Hans-Eric Lippke · Accepted Answer · 2019-05-25 20:29:57Z

Try something like this.

exports.handler = function( event, context, callback ) { 
 //this is to allow function to return as soon as result is shown
 context.callbackWaitsForEmptyEventLoop = false;
 var request = ...//I expect request is a predefined value or define the request here.

 executeRequest(request).then( function( result ) { 


  //keep all console log before return.
  console.log("Result ", result);

  const response = { statusCode: 200, body: JSON.stringify('Hello from Lambda!') }; 

  callback(null, response);
  return;
 });
}
function executeRequest(request){
   return new Promise( ( resolve, reject ) => {

    https.request(request, function(res) {

     if(res.statusCode==200 || res.statusCode==404) {
        resolve(res);
     }else {
        console.error(res);
        reject(res.statusCode);
        return;
     }
    }).end(request.body || '');
  });
}

Kannaiyan · Accepted Answer · 2019-05-23 21:02:28Z

0

Change your Lambda code to the following,

exports.handler = (event, context, callback) => {

    // Formulate request 

    var result = executeRequest(request, function(response) {
         console.log("Response Code: ", response.statusCode);
         console.log("Response Message: ", response.statusMessage);
         // Successfully able to print the response above

        callback(null, response);
     });

     }

Hope it helps.

answered May 23, 2019 at 21:02

Kannaiyan

13.1k4 gold badges52 silver badges91 bronze badges

4 Comments

alwaysAStudent Over a year ago

Getting error: ReferenceError: callback is not defined

Kannaiyan Over a year ago

You might have typed it, instead of copy paste. You can see it is defined with the arrow function.

alwaysAStudent Over a year ago

@Kanniyan: Probably miinterpretating your comment. :( ... I have edited my question to include code based on suggested answer along with log statement being printed.

Kannaiyan Over a year ago

console.log("Test response1: ", result); console.log("Test response2: ", callback); Since the function is not a synchronous call. You cannot print the variable outside of the function. You can try to use async and await.

Collectives™ on Stack Overflow

Fetch Http Response NodeJS

3 Answers 3

6 Comments

Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

6 Comments

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related