next start without next build logs an error and leaves the request hanging

[jamo]

When next start is run without running next build prior to it, the server logs the error below while keeping the socket open eternally.
Curl eventually logs: curl: (52) Empty reply from server

{ Error: Cannot find module <snip>/next-test/.next/dist/pages/_error
    at _callee$ (/usr/local/lib/node_modules/next/dist/server/resolve.js:153:19)
    at tryCatch (/usr/local/lib/node_modules/next/node_modules/regenerator-runtime/runtime.js:63:40)
    at Generator.invoke [as _invoke] (/usr/local/lib/node_modules/next/node_modules/regenerator-runtime/runtime.js:337:22)
    at Generator.prototype.(anonymous function) [as next] (/usr/local/lib/node_modules/next/node_modules/regenerator-runtime/runtime.js:96:21)
    at step (/usr/local/lib/node_modules/next/node_modules/babel-runtime/helpers/asyncToGenerator.js:17:30)
    at /usr/local/lib/node_modules/next/node_modules/babel-runtime/helpers/asyncToGenerator.js:28:20 code: 'ENOENT' }
(node:31466) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): TypeError: res.status is not a function
(node:31466) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Steps to reproduce:

mkdir next-test
cd next-test
next init
npm install
npm run start

and then curl -v 127.0.0.1:3000

$ curl -v 127.0.0.1:3000
* Rebuilt URL to: 127.0.0.1:3000/
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 3000 (#0)
> GET / HTTP/1.1
> Host: 127.0.0.1:3000
> User-Agent: curl/7.50.3
> Accept: */*
>
* Curl_http_done: called premature == 0
* Empty reply from server
* Connection #0 to host 127.0.0.1 left intact
curl: (52) Empty reply from server

[arunoda]

I think this is expected, you need to run next build before running next start.
Usually, you need to do next build while building the app and creating the runtime container (or similar)

Then you need to do next start.

Zeit's now runs npm run build inside it. For heroku you might need to do something like this.

[jamo]

I actually ran into this when "scripts.build": "next build" had a typo and the step was never run.

I mean, I wouldn't expect it to work, however, I wouldn't expect it fail like this (never responding anything).
Rather I would expect to have it returning a 500 error page.

[nkzawa]

I think we can check the existence of the .next directory and exit(1) if it's not there.

[rauchg]

We definitely need to improve error handling here… Thanks @jamo

[rauchg]

@nkzawa I would go further than that. We need to warn if you have a .next generated from development. Either that or we need to look for .next-prod ?

[timneutkens]

next start without a .next directory gives the following message in 2.0.0:

> Could not find the '.next' directory! Try building your app with 'next build' before starting the server.

[timneutkens]

As @rauchg stated it does pass when it's a dev generated .next. I'll have a look into fixing that.