I am making an app that creates multiple HTTP requests to different APIs, and would like to abstract the "sending" and "getting" portion of the data into a utility function that can be exported. It should be async. So far, I have created the following, but it won't work since request.end() needs to be declared somewhere, and I'm stuck here. Thanks!
Note: the resulting data should be able to be easily returned to some other function on order to do other work with it later on.
exports.handleHttpRequests = (url) => {
return new Promise((resolve, reject) => {
const request = http.request(url, response => {
let chunks = [];
res.on('data', chunk => {
chunks.push(chunk);
});
res.on('end', () => {
let body = Buffer.concat(chunks).toString();
resolve(body);
})
})
}).then(data => {
return data;
});
}
Hey you already done all, just call request.end() inside your new Promise callback & also handle error . And do what you want to do with resolve ,reject.
exports.handleHttpRequests = (url) => {
return new Promise((resolve, reject) => {
const request = http.request(url, res => {
let chunks = [];
res.on('data', chunk => {
chunks.push(chunk);
});
res.on('end', () => {
let body = Buffer.concat(chunks).toString();
resolve(body);
})
});
//handling error
request.on('error', (e) => {
reject('problem with request: ' + e.message);
});
//here you have to put request.end()
request.end();
})
};
Related
I am sending data to a Bluetooth device, and the responses are handled by a listener that's set up during the connection process:
device.connect().then(device => {
device.registerResponseListener((data) => {
// handle response
}
}
I have a separate function that sends data to the device:
const sendData = (device, data) => {
device.write(data);
}
My question is, how can I Promisify this code? I'd like to be able to do
const sendData = (device, data) => {
return new Promise((resolve, reject) => {
device.write(data);
// resolve...?
});
}
But how do I get the resolve into the Bluetooth response listener?
I don't know what API you're using but you can try BluetoothRemoteGATTCharacteristic API. It has writeValueWithResponse method which return Promise.
https://developer.mozilla.org/en-US/docs/Web/API/BluetoothRemoteGATTCharacteristic
If I understood you correctly then you can do it like this
const sendData = async (device, data) => {
const response = await device.write(data);
await Promise.all(device.responseListeners.map(listener => listener(response)))
}
The best possible solution in this case, while still not ideal, was to store the resolve function in variable at a higher scope:
var sendDataResolve;
device.connect().then(device => {
device.registerResponseListener((data) => {
sendDataResolve(data);
}
}
const sendData = (device, data) => {
return new Promise((resolve, reject) => {
sendDataResolve = resolve;
device.write(data);
});
}
...
sendData(device, "data")
.then(result => {
console.log("Got result",result);
});
The caveat is that Promise resolutions are NOT guaranteed to be tied correctly to the original request. This ONLY works with one request at a time.
I have this function
function getJsonObjectFromURL(url, onData) {
let chunks = [];
return require('https').get(url, res => {
res.setEncoding('utf8')
.on('data', (chunk) => {
chunks.push(chunk);
})
.on('end', () => {
onData(JSON.parse(chunks.join('')));
});
}).on('error', function(e) {
console.log("Got an error: ", e);
});
}
Also I have this script that converts url's data to json array.
url = https://pu.vk.com/c824502/upload.php?act=do_add&mid=213468131&aid=-14&gid=156603484&hash=7ab9a7e723425f4a6ca08709cbd5ebd0&rhash=ba8f0ec6580a6eafce38349b12ed3789&swfupload=1&api=1&wallphoto=1
getJsonObjectFromURL(url, data => {
console.log(data.server, data.photo, data.hash);
});
It goes well when console.log. But when I want to make from this script variable, it gives me huge collection
var xx = getJsonObjectFromURL(url, data => {
return data.server;
});
console.log(xx);
Your function getJsonObjectFromURL() doesn't return the object returned by the URL. It returns the object responsible for the https request code, which is something you don't want.
I see that you are using ES6, so the best solution for you is to probably create an async function that returns a promise, which will give you great flexibility. Here is an improved version of your code:
const https = require('https');
async function getJsonObjectFromURL(url) {
return new Promise((resolve, reject) => {
const chunks = [];
try {
https.get(url, res => {
res.setEncoding('utf8')
.on('data', (chunk) => {
chunks.push(chunk);
})
.on('end', () => {
resolve(JSON.parse(chunks.join('')));
});
}).on('error', e => reject(e));
} catch (err) {
reject(err);
}
});
};
This code allows you to retrieve the remote contents of the HTTPS url synchronously or asynchronously.
Asynchronous Call
As you have already done in your code, you can use a lambda callback that handles the response when it is ready.
const url = 'https://pu.vk.com/c824502/upload.php?act=do_add&mid=213468131&aid=-14&gid=156603484&hash=7ab9a7e723425f4a6ca08709cbd5ebd0&rhash=ba8f0ec6580a6eafce38349b12ed3789&swfupload=1&api=1&wallphoto=1';
// here we use a lambda callback that handles the response
getJsonObjectFromURL(url)
.then(data => {
console.log(data.server, data.photo, data.hash);
})
.catch(err => console.error(err));
Synchronous Call
The synchronous call forces the function to wait for the result. This is how you can do it:
async function getSync() {
try {
// wait for the result
const data = await getJsonObjectFromURL(url);
console.log(data.server);
} catch(err) {
console.error(err);
}
}
getSync();
Please note that we can only use the await keyword when we are inside an async function. This is why I had to wrap the synchronous call with a function.
In my code I try to assign a value to json variable to return it after (because I can't return it from the anon. function).
As my function is async, because it sends requests (maybe someone knows how to make it sync? I didn't plan to make it asynchronous), I've added await before the request (https.get).
I've been trying to get value from the Promise, but it's always undefined, even though I've awaited the async function.
Here's a code:
async function get_users() {
const https = require('https');
var token = '...';
var json = undefined;
await https.get('...', (resp) => {
let data = '';
resp.on('data', (chunk) => {
data += chunk;
});
resp.on('end', () => {
json = JSON.parse(data)['response']['items'];
});
}).on("error", (err) => {
console.log("Error: " + err.message);
});
return json;
}
get_users().then(function(result) {
console.log(result);
});
Return a Promise and resolve it, when the end event is called, otherwise reject it in case of an error occurred:
async function get_users() {
const https = require('https');
const token = '...';
return new Promise((resolve, reject) => {
https.get('...', resp => {
let data = '';
resp.on('data', chunk => {
data += chunk;
});
resp.on('end', () => {
let json;
try {
json = JSON.parse(data)['response']['items'];
} catch (e) {
reject(e);
};
resolve(json);
});
}).on("error", err => reject(err));
});
}
get_users().then(result => console.log(result));
Please refer my below code.I had issues with getting responses from Promises too.But i finally got it to work.Here's the code:
var output;
var rp = require('request-promise-native');
var myJSONObject = {
"inputs": [{
"name": "<name>",
"value": < value >
}]
};
var orchName = 'TEST05';
postData = JSON.stringify(myJSONObject);
return networkCall(postData, orchName).then((response) => {
console.log('response is' + response)
}).catch((response) => {
console.log(`ERROR: ` + response);
});
function networkCall(postData, orchName) {
return new Promise((resolve, reject) => {
var options = {
method: 'post',
uri: '<URL>',
body: postData,
auth: {
'user': 'usr',
'pass': 'pwd'
},
json: true
};
return rp(options)
.then(body => {
var response = body;
resolve(response);
})
.catch(err => {
console.log('FAILED' + err);
reject(err);
});
});
}
This way your code can run in Synchronous Flow.If the return value is undefined,then,what might have probably happened is that the calling function would have finished executing even before the called function returns its response.But the above approach would work just fine.
I could get this function to work in one file, but I'd like to keep things clean by separating into multiple files.
// library.js file
module.exports = {
get: () =>{
return new Promise((reject, resolve) =>{
return resolve(https.get('https://api.instagram.com/v1/users/self/?access_token=' + cred.access_token, (res) =>{
res.setEncoding('utf8');
return res.on('data', (data) =>{
return data;
});
}));
});
}
}
I tried logging this but it didn't show anything?
// server.js file
igLib.get().then((data) => {
console.log("testing: " + data);
})
However, if I just do a simple log of..
// server.js file
console.log(igLib.get());
I somehow get the data without the res.setEncoding('utf8').
Any tips on what to do?
Update:
I couldn't get the promise to work and I'm sorry to the folks who provided me good answers to my problem, but I went ahead and used the request-promise module instead. This is how it looks like:
// library.js file
var instagramSelfUrl = 'https://api.instagram.com/v1/users/self/?access_token=' + cred.access_token;
module.exports = {
get: () =>{
return rp(instagramSelfUrl).then((res) =>{
return res;
});
}
}
And here is where I console.log:
// server.js file
igLib.get().then((data) =>{
console.log(data);
});
It's simpler and it works. If there's a solution to the problem other than using a module for this to work, please let it be known and post! Thank you all to who posted and helped out!
The promise you create should resolve with the data from the response.
// library.js file
const https = require('https');
const instagramSelfUrl = 'https://api.instagram.com/v1/users/self/?access_token=' + cred.access_token;
module.exports = {
get: () => new Promise(function (resolve, reject) {
https.get(instagramSelfUrl, res => {
var chunks = [];
res.setEncoding('utf8');
res.on('data', chunk => chunks.push(chunk));
res.on('end', () => resolve(chunks.join('')));
});
})
};
In fact, the above is incomplete and brittle. For example, request errors or response status 500 should reject the promise, but there is no error handling. Or when the response is not really UTF-8 it will decode the data improperly. And those are only the two most obvious issues here.
The promisification of HTTP requests is a solved problem. I strongly suggest that you use one of the available libraries instead of rolling your own code that makes all the mistakes all over again.
const request = require('request-promise');
const instagramSelfUrl = 'https://api.instagram.com/v1/users/self/?access_token=' + cred.access_token;
module.exports = {
get: () => request(instagramSelfUrl)
};
Now the function is complete and behaves properly, even in corner cases. It also is so short that it hardly justifies writing a separate function at all.
It seems you aren't return the data correctly try this:
// library.js file
module.exports = {
get: () =>{
return new Promise((reject, resolve) =>{
https.get('https://api.instagram.com/v1/users/self/?access_token=' + cred.access_token, (res) =>{
res.setEncoding('utf8');
return res.on('data', (data) =>{
return resolve(data);
});
});
});
}
}
You can do something like this
module.exports = {
get: () =>{
return new Promise((resolve, reject) =>{
https.get('https://api.instagram.com/v1/users/self/?access_token=' + cred.access_token, (res) =>{
res.setEncoding('utf8');
res.on('data', (data) =>{
resolve(data);
});
}).on('error', (e) => reject(e))
});
}
}
For more on promise you can visit https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise
I am learning Node. I have a console app that must make requests to web services in order. Specifically, I need to make three requests in order. In an attempt to make these requests, I'm using the built-in HTTPS module. I have one request successfully executing. But, I need to make three in succession. I'm not sure how to do this. Right now, I have:
console.log('Running Request #1...');
var options = {
host: 'example.com',
path: '/api/service',
port: 443,
method: 'GET',
headers: {
'api-key': '[Hidden]'
}
};
var req = https.request(options, (res) => {
res.on('data', (d) => {});
});
req.end();
req.on('error', (e) => {
console.error(e);
});
I'm not sure how to call my three requests in order. Yet, at the same time, gracefully handling an error. If I had promises, I would know how to chain them together and just use the catch handler. But, I'm not sure how to chain together requests since the HTTPS module uses the Arrow function syntax.
Any help is appreciated it.
Try this:
var https = require('https');
var urls = ['url1', 'url2', 'url3'];
var request = function(url) {
console.log(url);
return new Promise((resolve, reject) => {
https.get(url, (res) => {
res.on('end', () => {
resolve('what');
});
res.on('data', data =>{
});
}).on('error', e => {
reject(e);
});
});
};
var promise = request(urls.shift());
while(urls.length > 0) {
let url = urls.shift();
promise = promise.then(function() {
return request(url);
});
}
promise.catch(e => console.log);
consider use promise with reduce,something like this
var urls=['u1','u2','u3'];
var er=0
function getPromise(url) {
return new Promise(function (resolve,reject) {
setTimeout(function () {
console.log(url+ " is resolved in 2 sec")
er++
if(er==1)
{
reject(url)
}else{
resolve(url)
}
},2000)
})
}
urls.reduce(function (pre,cur) {
return pre.then(function () {
return getPromise(cur)
})
},new Promise(function (resolve,reject) {
resolve(null)
}))
.then(function (result) {
console.log("final result is "+result)
},function (e) {
console.log("something wrong happens : "+e)
})
Play with the code,I think it is want you want