nextjs-custom-server.js is a patch for urlencode problem on cloudrun.

nextjs-custom-server.js

const { createServer } = require('http')
const { parse } = require('url')
const next = require('next')

const dev = process.env.NODE_ENV !== 'production'
const hostname = '0.0.0.0'
const port = process.env.PORT || 8000

// Initialize Next.js app
const app = next({ dev, hostname, port })
const handle = app.getRequestHandler()

app.prepare().then(() => {
    createServer(async (req, res) => {
        try {
            // Parse the URL
            const parsedUrl = parse(req.url, true)
            let { pathname } = parsedUrl

            // Fix for Cloud Run encoded characters in static files
            // Cloud Run/GFE passes encoded URLs (e.g. %5BcountryCode%5D) which Next.js static handler doesn't decode automatically
            if (pathname && pathname.startsWith('/_next/static/')) {
                try {
                    // Decode the entire pathname to handle %5B, %5D, %40 etc.
                    const decodedPath = decodeURIComponent(pathname)

                    if (decodedPath !== pathname) {
                        // Update the parsedUrl object with the decoded path
                        parsedUrl.pathname = decodedPath
                        parsedUrl.path = parsedUrl.path.replace(pathname, decodedPath)
                        parsedUrl.href = parsedUrl.href.replace(pathname, decodedPath)

                        console.log(`> Rewrote encoded path: ${pathname} -> ${decodedPath}`)
                    }
                } catch (e) {
                    console.error('Failed to decode pathname', e)
                }
            }

            await handle(req, res, parsedUrl)
        } catch (err) {
            console.error('Error occurred handling', req.url, err)
            res.statusCode = 500
            res.end('internal server error')
        }
    })
        .once('error', (err) => {
            console.error(err)
            process.exit(1)
        })
        .listen(port, () => {
            console.log(`> Ready on http://${hostname}:${port}`)
        })
})