How do I set multiple http header fields with the same key in Node.js?

Question

I'm trying to set up server push with cloudflare, but they require multiple link header fields to push multiple files. However, I can't find any documented way to include multiple header fields with the same key in node.js. I tried providing an array, but that just concatenates them together as the value for a single header field.

Answer 1

express

You pass an array of values to res.header('HeaderName', arrayOfValues). Here's a working example and cURL output showing the duplicate response headers. This is not directly documented, but it does work (express@4.14.0).

const express = require('express')
const app = express()
app.get('/', (req, res, next) => {
  res.header('Link', ['Link1', 'Link2'])
  res.send()
})
app.listen(3000)

curl -v localhost:3000 output:

< HTTP/1.1 200 OK
< X-Powered-By: Express
< Link: Link1
< Link: Link2
< Date: Fri, 09 Sep 2016 01:44:22 GMT
< Connection: keep-alive
< Content-Length: 0

node core http

Use res.setHeader(name, arrayOfValues)

const http = require('http')

const server = http.createServer(function (req, res) {
  res.setHeader('Link', ['Link1b', 'Link2b'])
  res.end()
})
server.listen(3000)

curl output:

< HTTP/1.1 200 OK
< Link: Link1b
< Link: Link2b
< Date: Fri, 09 Sep 2016 01:52:53 GMT
< Connection: keep-alive
< Content-Length: 0