not getting full body with npm request package - json

Question

I have the following function which returns a promise to get data. I am using the request npm module.
let getData = function (user) {
return new Promise(function (resolve, reject) {
let url = 'https://someurl.com/' + user;
request(url, function (error, res, body) {
if (error) reject(error);
try{
resolve(cleanData(JSON.parse(body).items))
}catch(e){
console.log(body)
console.log(url)
console.log(e);
}
})
})
}
When I resolve my promise, I sometimes get something like this:
SyntaxError: Unexpected token u in JSON at position 0
That happens when my body is returned as undefined. But other times I also get something like this:
SyntaxError: Unexpected token f in JSON at position 11203
And other times (most of the times), it goes through perfectly.
I've been able to double check this while debugging and it seems that there are times when I get an incomplete body. I know for a fact that the body from the source url is not incomplete. I checked this by going to the url directly with my browser and making sure the json was complete and valid.
What is going on? It is my understanding that the callback on the request function is only called when the response is ready to be consumed.

Answer 1

No - the callback is triggered as soon as there is a response - see
HTTP request API documentation. You will need to implement a response listener as:
res.on('data', (chunk) => {
// do the data accumulation here
});
res.on('end', () => {
// do the resolve here
});

Answer 2

In request module if you expect binary data from response, then set encoding: null in request options.
Excerpt from:
encoding - encoding to be used on setEncoding of response data. If null, the body is returned as a Buffer. Anything else (including the default value of undefined) will be passed as the encoding parameter to toString() (meaning this is effectively utf8 by default). (Note: if you expect binary data, you should set encoding: null.)
https://www.npmjs.com/package/request