[BUG] Etag verification fails if force_auth_field_projection=True

[yuregir]

On put requests to replace existing objects, I am getting “412 - Client and server etags don't match”, even if-match header is correctly set.
I tried to debug the root cause of the problem.
Wanted to explain my findings.

This happens only on endpoints which auth_field is enabled.

My findings:

On put.py line 138;

original = get_document(
        resource,
        concurrency_check,
        check_auth_value=False,
        force_auth_field_projection=True,
        **lookup
    )

When force_auth_field_projection=True -> get_document() function forces to add projection ={ ‘auth_field’ :1} to pymongo query (it is exact added at io/base.py line 511: if force_auth_field_projection: fields[auth_field] = 1). This causes pymongo to return original item, only with fields _id and auth_field.

On common.py line 120;

etag = document.get(
             config.ETAG, document_etag(document, ignore_fields=ignore_fields))

Object before document.get() in common.py line 120; (Original object has 10+ fields including _etag, but it contains only id and auth field because of force_auth_field_projection=True)

{
  '_id': ObjectId('6092e319f17d74634b081df2'), 
  ‘auth_field': ObjectId('5f401f37917546325003ba46’),
   '_updated': datetime.datetime(1970, 1, 1, 0, 0), 
  '_created': datetime.datetime(1970, 1, 1, 0, 0)
}

As I mentioned on top, returned item only have _id and auth_field and not _etag;
.get() cant find current _etag value in document item and tries to calculate it from document_etag() function, but document item doesnt have all fields, causes_etag value to be calculated incorrectly,
Then I get error 412 etag values doesnt match.

When debugging I manually override force_auth_field_projection=True to False, PUT request runs without any error.

---

Expected Behavior

PUT requests with auth_field enabled endpoints, should be successful, if _etag value is correctly set in IF-Match header.

Actual Behavior

Getting “412 - Client and server etags don't match” on endpoints which auth_field is enabled, even if-match header is correct.

Environment

• Python version: 3.8
• Eve version: 1.1.5

[stale]

Is this still relevant? If so, what is blocking it? Is there anything you can do to help move it forward?

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