nodejs - How to promisify http.request? reject got called two times

Question

I'm trying to wrap http.request into Promise:

 new Promise(function(resolve, reject) {     var req = http.request({         host: '127.0.0.1',         port: 4000,         method: 'GET',         path: '/api/v1/service'     }, function(res) {         if (res.statusCode < 200 || res.statusCode >= 300) {             // First reject             reject(new Error('statusCode=' + res.statusCode));             return;         }         var body = [];         res.on('data', function(chunk) {             body.push(chunk);         });         res.on('end', function() {             try {                 body = JSON.parse(Buffer.concat(body).toString());             } catch(e) {                 reject(e);                 return;             }             resolve(body);         });     });     req.on('error', function(err) {         // Second reject         reject(err);     });     req.write('test'); }).then(function(data) {     console.log(data); }).catch(function(err) {     console.log(err); }); 

If I recieve errornous statusCode from remote server it will call First reject and after a bit of time Second reject. How to make properly so it calls only single reject (I think First reject is proper one in this case)? I think I need to close res myself, but there is no close() method on ClientResponse object.

UPD: Second reject triggers very rarely - why?

Answer 1

Your code is almost fine. To restate a little, you want a function that wraps http.request with this form:

function httpRequest(params, postData) {     return new Promise(function(resolve, reject) {         var req = http.request(params, function(res) {             // on bad status, reject             // on response data, cumulate it             // on end, parse and resolve         });         // on request error, reject         // if there's post data, write it to the request         // important: end the request req.end()     }); } 

Notice the addition of params and postData so this can be used as a general purpose request. And notice the last line req.end() -- which must always be called -- was missing from the OP code.

Applying those couple changes to the OP code...

function httpRequest(params, postData) {     return new Promise(function(resolve, reject) {         var req = http.request(params, function(res) {             // reject on bad status             if (res.statusCode < 200 || res.statusCode >= 300) {                 return reject(new Error('statusCode=' + res.statusCode));             }             // cumulate data             var body = [];             res.on('data', function(chunk) {                 body.push(chunk);             });             // resolve on end             res.on('end', function() {                 try {                     body = JSON.parse(Buffer.concat(body).toString());                 } catch(e) {                     reject(e);                 }                 resolve(body);             });         });         // reject on request error         req.on('error', function(err) {             // This is not a "Second reject", just a different sort of failure             reject(err);         });         if (postData) {             req.write(postData);         }         // IMPORTANT         req.end();     }); } 

This is untested, but it should work fine...

var params = {     host: '127.0.0.1',     port: 4000,     method: 'GET',     path: '/api/v1/service' }; // this is a get, so there's no post data  httpRequest(params).then(function(body) {     console.log(body); }); 

And these promises can be chained, too...

httpRequest(params).then(function(body) {     console.log(body);     return httpRequest(otherParams); }).then(function(body) {     console.log(body);     // and so on });