FileTransfer abstraction

[renatomassaro]

FileTransfer is an abstraction used by backends download, upload and pftp_download (downloading files from public FTP).

• [x] Interface
• [x] Events
• [x] Tests
  • [x] Handler
  • [x] Flow
  • [x] Public (for each backend)
  • [x] Action (copy/3)
  • [x] Internal (copy/3)
• [x] Docs
• [x] Event notifications (Mostly postponed until client is able to integrate with us)
• [x] ProcessViewable

TODO:

• Check file size before copying it to another storage. Postponed. See #279
• Log event handler on FileDownloaded, FileUploaded events. Postponed. See #278
• [x] Pending tests
  • [x] Rejects repeated transfers
  • Failure cases on FileTransferHandler. (Postponed above).
  • [x] (Driver) File being downloaded belongs to the given server
  • [x] (Driver) refuses to download from same server
• [x] Abort transfer
• Automatically abort transfer when file is deleted. Postponed. See #280
• [x] Doc Henforcers

Incidental:

• Event graph generator
• Move Software.Action.File.* to #Software.Action.Software.*
• Enhancement and standardization of Henforcers
• ProcessQuery.get_custom/3

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[sourcelevel-bot[bot]]

Ebert has finished reviewing this Pull Request and has found:

• 8 possible new issues (including those that may have been commented here).
• 8 fixed issues! 🎉

You can see more details about this review at https://ebertapp.io/github/HackerExperience/Helix/pulls/271.

[renatomassaro]

Reviewed 63 of 71 files at r1, 8 of 8 files at r2. Review status: all files reviewed at latest revision, all discussions resolved.

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