Can I delay PUT upload in Express until my server finishes an operation? - http

Question

I have a server that receives files via PUT and in turn stores them in S3.
After a client PUTs files it will usually request them right in return for rendering. Unfortunately my server takes a bit of time to actually process the upload and store them in S3.
Here is the code I use in Express:
req.pipe(writeStream);
res.header('Access-Control-Allow-Origin', '*');
res.header('Access-Control-Allow-Methods', 'PUT, OPTIONS');
res.header('Access-Control-Allow-Headers', 'Content-Type');
if ('OPTIONS' === req.method) {
res.sendStatus(200);
res.end('OK!');
return;
}
if ('PUT' === req.method) {
writeStream.on('error', () => {
res.sendStatus(500);
});
writeStream.on('close', async () => {
// This might take 30s
await this.storage.store(fn, args.blobID);
// This does not seem to have any effect
// I would like to prevent the client from 'finishing' the
// PUT request before I say it is done.
res.end('OK!')
});
res.sendStatus(200);
}
Ideally I could 'stall' my client's PUT request for until storage.store() completed, making sure the file is actually available.
Is there any way how I could do this?
Also, I am not sure about the sendStatus() / end() calls, feel free to comment if I mixed something up.
P.S. I know, in an ideal world I would just hand out signed URLs and let the client upload to S3 directly, but I need AES256 encryption ...

Answer 1

I'm not familiar with S3 uploading, but I guess that there will be a callback(such as sending back a response(success or fail... etc) to you). (If not, please tell me)
S3.upload(data,function(response){ // something like this
// then, you can callback
// ...
// res.end() or res.sendStatus(...)
})
As I remember it, Express don't send timeout automatically, so you just put response in the S3's response function, so that your request should not end until your storing end.
From Must res.end() be called in express with node.js?
You don't have to call res.end() if you call res.send(). res.send() calls res.end() for you.
and res.sendStatus() equals to res.status(...).send(message or code) (via http://expressjs.com/en/api.html)
So, res.sendStatus() will call end().