Escaped database error messages logged by `Q.check()`

[Natalia Bidart]

Q.check(), used by CheckConstraint.validate() and by UniqueConstraint.validate() with a condition, catches DatabaseError and logs it to the django.db.models logger:

logger.warning("Got a database error calling check() on %r: %s", self, e)

Database error messages can include the values being validated, which may originate from user input (for example through ModelForm validation). These messages are currently logged as-is. For defense in depth, and for consistency with other logging call sites, Q.check() should log the message through django.utils.log.log_message() so that its content is escaped, and trim it to a reasonable length.

The trimming logic for large values is currently duplicated in django/views/debug.py and django/contrib/gis/gdal/raster/source.py. A small trim_value() helper in django.utils.text could be shared by those two places and by Q.check().

Separately, the fact that BaseConstraint.validate() treats a constraint as satisfied when evaluating it raises a database error (logging a warning and leaving the error to surface on save()) is not documented. A short note in the constraints reference would help developers understand why a condition that can fail to evaluate does not act as validation.

[Natalia Bidart]

​PR

[nessita <124304+nessita@…>]

In 7d89d63:

Refs #37433 -- Added django.utils.text.trim_value() helper.

The debug page and the raster lookup check each trimmed large values
to 4096 characters with their own copy of the same code. The shared
helper also corrects the suffix, which reported characters as bytes
and showed the original length as if it were the amount trimmed.

The trimmed value and the suffix are returned separately so callers
can escape the value without escaping the suffix.

Refs #34746.

[nessita <124304+nessita@…>]

In 5190bbc3:

Fixed #37433 -- Escaped database error messages logged by Q.check().

Database error messages can include the values being validated, which
may originate from user input. Logging them through log_message()
escapes their content and keeps large values trimmed, consistent with
other logging call sites.

Thanks Jacob Walls for reviews.