Prevent duplicate creation via Direct Transfer

Scope

Before uploading anything, a check has to be done to prevent duplicates.

• By default, if the document does not exist: create a new document.
• If a document with the same name already exists on the server:
  • if the document has a blob stored into the file:content xpath, asks the user for:
    • upload cancellation;
    • blob replacement.
  • If the document has no attached blob (in case of a previous failure at the upload step):
    • upload and attach the blob.

Possible Issue

Note about possible duplicate creation via a race condition client <-> server.
Given the local file with the path "$HOME/some-folder/subfolder/file.odt", the file name is "file.odt".

Scenario:

• Step 1: local, check for a doc with the path name "file.odt" => nothing returned, continuing;
• Step 2: server, a document with a path name set to "file.odt" is created;
• Step 3: local, create the document with the path name "file.odt".

Even if the elapsed time between steps 1 and 3 is really short, it may happen.

What can be done to prevent such scenario is not on the Nuxeo Drive side but on the server one.
For now, 2 options are possible but not qualified to be done in a near future:

• NXP-22959;
• create a new operation Document.GetOrCreate that ensures atomicity.