Automate deployment with this Node.js script and GitHub webhooks

webhook.js

const http = require('http')
const crypto = require('crypto')
const cp = require('child_process')

// Configuration variables

// secret you set in github settings
const secret = process.env.SECRET 

// port to listen for requests
const port = process.env.PORT || 4000

// directory of your project
const dir = process.env.DIR

// branch to pull (optional)
const branch = process.env.BRANCH 

// command executed before pull
const postPull = process.env.POST_PULL_CMD

http.createServer((req, res) => {
    // Read request body
    let body = ''
    req.on('data', chunk => {
        body += chunk.toString()
    })

    req.on('end', () => {
        // Verify signature of request
        let signature = 'sha1=' + crypto.createHmac('sha1', secret).update(body).digest('hex')

        if (req.headers['x-hub-signature'] !== signature) {
            res.statusCode = 500
            res.end('Signature verification failed')
            return
        }

        // Parse body
        let payload = JSON.parse(body)

        // Check branch 
        if (branch) {
            if (!payload.ref.endsWith(branch)) {
                console.log(`${payload.ref} of ${payload.repository.name} will not be deployed`)

                res.statusCode = 202
                res.end(`${payload.ref} will not be deployed`)
                return
            }
        }

        console.log(`Deploying ${payload.ref} of ${payload.repository.name}`)
        deploy()
        res.end(`${payload.ref} will be deployed`)
    })
}).listen(port)

function deploy() {
    // Pull
    cp.exec(`cd ${dir} && git pull`, (err, stdout, stderr) => {
        logExec(err, stdout, stderr)
        
        // Execute post pull command
        if (postPull) {
            cp.exec(`cd ${dir} && ${postPull}`, logExec)
        }
    })
}

// Function for logging child_process.exec() callback
function logExec(err, stdout, stderr) {
    if (err) {
        return console.error(err)
    }
    if (stdout) {
        return console.log(stdout)
    }
    if (stderr) {
        return console.error(stderr)
    }
}