File looks like it can be copied from received share and exceed quota

[phil-davis]

Steps to reproduce

1. Alice has some storage quota, Brian has zero or low quota
2. Alice shares a file with Brian, or a folder containing a file
3. Brian copies the received file to his own home storage

Expected behaviour

The API copy request should fail with a suitable HTTP response status like 507 "insufficient storage".

Actual behaviour

The HTTP status is 201 - to the client it seems that the copy was successful.
But actually the copied file does not exist. It seems that the copy did not really happen.

Server configuration

Current core master - see demonstration test scenarios

[phil-davis]

Demonstration tests are added in PR #40141

[phil-davis]

The same problem happens in the reverse direction:

Steps to reproduce

1. Alice has zero or low storage quota, Brian has enough quota
2. Alice shares a file or folder with Brian
3. Brian copies a file from his own home storage to the share received from Alice

Expected behaviour

The API copy request should fail with a suitable HTTP response status like 507 "insufficient storage".

Actual behaviour

The HTTP status is 201 or 204 - to the client it seems that the copy was successful.
But actually the copied file does not exist. It seems that the copy did not really happen.

Server configuration

Current core master - see demonstration test scenarios

[phil-davis]

Note: when the encryption app is enabled and encryption is happening, it seems that, as well as getting a success HTTP 2xx status, the file content actually gets written to storage and the quota is exceeded. See test scenarios added by encryption PR owncloud/encryption#346