/_next/image can give empty body with /pages/api served images

[700software]

Bug report

Describe the bug

next.js/packages/next/next-server/server/image-optimizer.ts

Line 207 in 748bcb9

await server.getRequestHandler()(_req, mockRes, nodeUrl.parse(href, true))

• Looks like we need to wait for mockRes._final to be called — not await promise completion.
• (Also we need only implement mockRes._write, so we have no need to implement mockRes.write so we have no need to handle strings.)

To Reproduce

1. Create an API endpoint /pages/api/images.js that returns an image using .pipe

   export const config = { api: { bodyParser: false } }
   
   export default async function (req, res) {
   
     var downloadStream = // from an external API (or in your case test with just a file stream)
   
     res.setHeader('Content-Type', 'image/jpeg')
     res.setHeader('Content-Length', ...)
     downloadStream.pipe(res)
   }

2. Visit http://localhost:3000/_next/image?url=/api/image&w=3840&q=75
   (This is the endpoint normally generated by the new <Image> tags from next/image)

3. You will have a blank page caused by empty response. (Ctrl+S saves a file to your desktop with zero length)

Expected behavior

The compressed/resized version of image

Workaround

  await new Promise(function (resolve) {
    // Need to use promise because of https://github.com/vercel/next.js/issues/20110
    // Otherwise we could have just used a `pipe` line and no promise.
    downloadStream.pipe(res)
    downloadStream.on('end', resolve)
  })

System information

• OS: any, Browser: any
• Version of Next.js: [e.g. 10.0.3]
• Version of Node.js: [e.g. 14.3.0]
• Deployment: next run dev

Why does this matter?

Why can we not just wait for promise completion?

A blank page is very much not useful to the developer. Having to go line-by-line and debug a webpacked node_modules is not the experience we need to give to the developer.

Normally, if the developer tried to send a response from his/her API endpoint with res.write and res.end they would have gotten

API resolved without sending a response for /api/uploads/image, this may result in stalled requests.

which would totally make having a blank response no big deal because the clear problem statement is in the logs.

However, this log clue does not appear for pipe calls. So the developer, without us doing something on this issue, has no clear recourse.

[baptisteArno]

Hi @700software,

I have the same problem but with a different use case:

res.status(307)
console.log(signedUrl)
res.setHeader('Location', signedUrl)
res.end()

It logs a valid URL. But it says API resolved without sending a response and it doesn't have the location header. I don't understand why. Any idea?

[700software]

@baptisteArno, For your case use res.statusCode=.

.status() is calling .end() internally methinks. Probably from Express. It's not part of Node.js core.

Probably the reason for your issue is Express (or whatever framework .status() is from) is attached to res before Next.js adds it's override of .end(). This is normal.

[alexjpujol]

I've tried using res.statusCode = as well as res.status(...) and still get the API resolved without sending a response...

wondering if there's any insight or update here.

[700software]

Can you find my email address on my profile and send code of full file?

[github-actions]

Please verify that your issue can be recreated with next@canary.

Why was this issue marked with the please verify canary label?

We noticed the provided reproduction was using an older version of Next.js, instead of canary.

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[balazsorban44]

This issue has been automatically closed because it wasn't verified against next@canary. If you think it was closed by accident, please leave a comment. If you are running into a similar issue, please open a new issue with a reproduction. Thank you.