Related D2082

Daniele Serafini authored 5 years ago and Stefano Zacchiroli committed 5 years ago

... from test_persistent_identifier.

Closes T1986

It is now possible to install swh-model without dulwich (and Click, FWIW).

Users who want to use "swh identify" should "pip install swh-model[cli]".

make mypy 0.730 pass cleanly again

Needed by the replayer in swh-journal.

It kind of matches the current state of the postgresql storage, which
does not support it.

But keep support for deserializing from str, like
swh-storage does.

Code manipulating a Content object may want to access a hash
of configurable name; this method allows it to do that
without using getattr directly.

It denotes files whose length is unknown.

Loaders use it, but it is ignored by the pg storage.
However, as the Cassandra storage uses swh-model to validate
its input, it refuses this input from the loaders (and journal).