In some cases, you need to store attachment in another system that the Odoo's
filestore. For example, when your deployment is based on a multi-server
architecture to ensure redundancy and scalability, your attachments must
be stored in a way that they are accessible from all the servers. In this
way, you can use a shared storage system like NFS or a cloud storage like
S3 compliant storage, or....

This addon extend the storage mechanism of Odoo's attachments to allow
you to store them in any storage filesystem supported by the Python
library `fsspec <https://filesystem-spec.readthedocs.io/en/latest/>`_ and made
available via the `fs_storage` addon.

In contrast to Odoo, when a file is stored into an external storage, this
addon ensures that the filename keeps its meaning (In odoo the filename
into the filestore is the file content checksum). Concretely the filename
is based on the pattern:
'<name-without-extension>-<attachment-id>-<version>.<extension>'

This addon also adds on the attachments 2 new fields to use
to retrieve the file content from a URL:

* ``Internal URL``: URL to retrieve the file content from the Odoo's
  filestore.
* ``Filesystem URL``: URL to retrieve the file content from the external
  storage.

.. note::

   The internal URL is always available, but the filesystem URL is only
   available when the attachment is stored in an external storage.
   Particular attention has been paid to limit as much as possible the consumption
   of resources necessary to serve via Odoo the content stored in an external
   filesystem. The implementation is based on an end-to-end streaming of content
   between the external filesystem and the Odoo client application by default.
   Nevertheless, if your content is available via a URL on the external filesystem,
   you can configure the storage to use the x-sendfile mechanism to serve the
   content if it's activated on your Odoo instance. In this case, the content
   served by Odoo at the internal URL will be proxied to the filesystem URL
   by nginx.

Last but not least, the addon adds a new method `open` on the attachment. This
method allows you to open the attachment as a file. For attachments stored into
the filestore or in an external filesystem, it allows you to directly read from
and write to the file and therefore minimize the memory consumption since data
are not kept into memory before being written into the database.