Bare Bones Node.js HTTP Proxy

index.js

const http = require('http')
const url = require('url')

const apiPort = 3000
const proxyPort = 3001

const apiResStatus = 200
const apiResBody = `"Hi, I'm the API!"`

const clientReqMethod = 'GET'
const clientReqPath = '/'

// Create API server
const api = http.createServer((apiReq, apiRes) => {
  apiReq.on('error', err => console.error('API Error:', err))
  const apiReqUrl = url.parse(apiReq.url)

  console.log('API Req:', apiPort, apiReq.method, apiReqUrl.path)

  apiRes.writeHead(apiResStatus)
  apiRes.end(apiResBody)

  console.log('API Res:', apiResStatus, apiResBody)
})

api.listen(apiPort, apiErr => {
  if (apiErr) throw apiErr
  console.log(`API listening on 'localhost:${apiPort}'`)

  // Create proxy server
  const proxy = http.createServer((proxyReq, proxyRes) => {
    proxyReq.on('error', err => console.error('Proxy Error:', err))

    const proxyReqUrl = url.parse(proxyReq.url)
    console.log('Proxy Req:', proxyPort, '->', apiPort, proxyReq.method, proxyReqUrl.path)
    const tunnelReq = http.request({
      method: proxyReq.method,
      path: proxyReqUrl.path,
      port: apiPort
    }, tunnelRes => {
      console.log('Proxy Res:', tunnelRes.statusCode, '(pipe)')
      proxyRes.writeHead(tunnelRes.statusCode)
      tunnelRes.pipe(proxyRes)
    })

    tunnelReq.on('error', err => console.error('Tunnel Error:', err))
    tunnelReq.end()
  })

  proxy.listen(proxyPort, proxyErr => {
    if (proxyErr) throw proxyErr
    console.log(`Proxy listening on 'localhost:${proxyPort}'`)

    // Make client request
    console.log('Client Req:', proxyPort, clientReqMethod, clientReqPath)
    const clientReq = http.request({
      port: proxyPort,
      path: clientReqPath,
      method: clientReqMethod
    }, clientRes => {
      const clientResBuffer = []
      clientRes.on('data', chunk => clientResBuffer.push(chunk))
      clientRes.on('end', () => {
        const clientResBody = Buffer.concat(clientResBuffer).toString()
        console.log('Client Res:', clientRes.statusCode, clientResBody)
      })
    })

    clientReq.on('error', err => console.error('Client Error:', err))
    clientReq.end()
  })
  proxy.unref()
})
api.unref()

$ node .
API listening on 'localhost:3000'
Proxy listening on 'localhost:3001'
Client Req: 3001 GET /
Proxy Req: 3001 -> 3000 GET /
API Req: 3000 GET /
API Res: 200 "Hi, I'm the API!"
Proxy Res: 200 (pipe)
Client Res: 200 "Hi, I'm the API!"