Problem

When generating route regular expressions for data routes, some code paths appear to not escape the . in .json. This causes routing to be slightly slower, prevents some optimizations related to static postfixes, and potentially allows for unintended request paths to be accepted as value.

Solution

After much tracing and digging, I found a code path writing regular expressions directly without escaping. In this case the solution is to escape the . using \\. when generating static data routes.

A simple next app was made to exercise this path with a route pages/server-time.tsx that contains a simple getServerSideProps.

import type { InferGetServerSidePropsType, GetServerSideProps } from 'next'
 
type TimeDate = {
  timestamp: number
}
 
export const getServerSideProps = (async () => {
  return { props: { timestamp: Date.now() } }
}) satisfies GetServerSideProps<TimeDate>
 
export default function Page({
  timestamp,
}: InferGetServerSidePropsType<typeof getServerSideProps>) {
  return (
    <main>
      <p>{new Date(timestamp).toUTCString()}</p>
    </main>
  )
}

Before the change, the generated route regexp was "^/_next/data/[build_id]/server-time.json$", but after then change it becomes "^/_next/data/[build_id]/server-time\\.json$"

The related tests were updated to expect properly escaped \\.json$ endings to the regexps.