Node, how to send result back to client from nested HTTP request? - node.js

Question

I'm using ReactJS to run my front-end and using Express for my back-end. I want to make a get request to my back-end using the "/paas" path to get a listing of all of my pods that are running inside my namespace in Rancher(Kubernetes).
The back-end then needs to be able to make an https request to my Rancher API endpoint and return the result to the front-end. I can make the successful call to Rancher API and see the data print to the screen on my back-end but I get lost when trying to send this data to the front-end and console log it out inside the browser.
Due to "pre-flight" errors, I can't just make a direct call to the Rancher endpoint inside of my App.js file. More info on this here. So I need to go the custom back-end route. I any case, it seems like this should be pretty straightforward. Any guidance would be appreciated.
App.js:
import React, { useEffect } from "react"
import axios from "axios"
function App() {
useEffect(() => {
const fecthPods = async () => {
try {
const response = await axios.get(`http://localhost:3001/paas`)
console.log(response.data)
} catch (err) {
if (err.response) {
// Not in the 200 response range
console.log(err.response.data)
console.log(err.response.status)
console.log(err.response.headers)
} else {
console.log(`Error: ${err.message}`)
}
}
}
fecthPods()
},[])
return (
<div>
Hello World!
</div>
);
}
export default App;
Back-end server.js:
import express from "express"
import cors from "cors"
import https from "https"
import bodyParser from "body-parser";
const app = express()
app.use(cors())
app.use("/data", (req, res) => {
res.json({ name: "Minion", favFood: "pizza"})
})
app.get("/paas", bodyParser.json(), (req, res) => {
const options = {
hostname: "k8.fqdn.com",
port: 443,
path: "/k8s/clusters/c-wwfc/v1/pods/mynamespace",
method: "GET",
headers: {
Authorization: "Bearer token:12345"
}
}
const request = https.get(options, (res) => {
let responseBody = ""
res.setEncoding("UTF-8")
res.on("data", (chunk) => {
console.log("---chunk", chunk.length);
responseBody += chunk;
});
res.on("end", () => {
let json = JSON.parse(responseBody)
// console.log(responseBody)
console.log("Response finished");
res.json({data: responseBody})
});
});
request.end()
res.json({ status: "complete", data: request.data})
})
app.listen(3001)
console.log("backend up on 3001")

Answer 1

I see a couple of errors on your backend code.
First, you are naming the res variable for the express middleware and also for the response received by the https module. In this way, you lose the possibility to access to the express response object in the on.('end') callback.
Secondly, you are triyng to respond to the client multiple times (inside the on.('end') callback and also directly inside the express middleware with the instruction res.json({ status: "complete", data: request.data}). Also, consider that the code you wrote is repliyng to the client before the call to the k8s cluster is made. And the response will always be a JSON with this data: { "status": "complete", "data": undefined}.
To fix all, try with this code (I will try to comment all edits):
app.get("/paas", bodyParser.json(), (req, res) => {
const options = {
hostname: "k8.fqdn.com",
port: 443,
path: "/k8s/clusters/c-wwfc/v1/pods/mynamespace",
method: "GET",
headers: {
Authorization: "Bearer token:12345"
}
}
const k8sRequest = https.get(options, (k8sResponse ) => { // as you can see I renamed request and res to k8sRequest and k8sResponse, to avoid loosing the scope on req and res express middleware variables
let responseBody = ""
res.setEncoding("UTF-8")
k8sResponse.on("data", (chunk) => { // here use k8sResponse to collect chunks
console.log("---chunk", chunk.length);
responseBody += chunk;
});
k8sResponse.on("end", () => { // here use k8sResponse again
let json = JSON.parse(responseBody)
// console.log(responseBody)
console.log("Response finished");
res.json({ status: "complete", data: responseBody}) // here use the express res variable, to reply to the client.
});
});
k8sRequest.end() // here use the k8sRequest variable to make the https call to the k8s cluster
// here I deleted the res.json instruction
})
The above code should just works. Anyway, I suggest you using axios also with your backend service. You are already using it with React, so you know how to use it. The syntax is minimal and easier and you can use the async/await approach.
Axios solution:
import axios from "axios"
app.get("/paas", bodyParser.json(), async (req, res) => {
try {
const url = 'https://k8.fqdn.com/k8s/clusters/c-wwfc/v1/pods/mynamespace'
const k8sResponse = await axios.get(url, headers: {
Authorization: "Bearer token:12345"
})
res.json({ status: "complete", data: k8sResponse.data })
} catch (e) {
res.json({status: "error", data: e.response.data})
}
})
You should wrap your axios call inside a try/catch block to properly handle errors like you are doing with your React implementation. Error handling should be also implemented if you still want you the native node.js https module