"Precondition failed" should provide more info

[htgoebel]

I just spent more then one hour tracking down a "Precondition failed" issue. The cause tracked down to "Creation asked but item found: item can't be replaced".

Expected behaviour

If "Precondition failed",

• report the exact reason to the logger (I suggest using level warning)
• depending on the security level/policy of this project:
  • report the exact reason in the message body returned
  • report a message without too much details in the message body returned

[pbiering]

Makes sense, will add some log statements

[pbiering]

@htgoebel - log statements added, but what is expected as error message (content/format)? Is a client able to display it?

[pbiering]

closing now as implemented in log and unclear how to display error message to client in which format. As support is needed for the 2nd one has to create a PR in case.

[htgoebel]

Thanks for fixing.

but what is expected as error message (content/format)?

Instead of returning httputils.PRECONDITION_FAILED, one could return something like

types.WSGIResponse = (
    client.PRECONDITION_FAILED,
    (("Content-Type", "text/plain"),), f"Precondition failed: {error_details}")```

If you like the idea, I will provide a pull-request which implements a wrapper creating the response (depending on whether there error_details are given.

Is a client able to display it?

Clients would show it in the error log at least.

[pbiering]

PR is welcome, question is what should be disclosed?

Case 1
Precondition failed on PUT request for %r (HTTP_IF_MATCH: %s, item not existing) -> something like item not exist but requested to update?

Case 2
Precondition failed on PUT request for %r (HTTP_IF_MATCH: %s, item has different etag: %s) -> ??? the item IDs are not really helpful to the user, has then anyhow contact server admin to lookup the item

Case 3
Precondition failed on PUT request for %r (HTTP_IF_NONE_MATCH: *, creation requested but item found with etag: %s) -> something like item already found?

Anyhow, user can only resync collection and try to update then what is still existing.