Move ext storage backends into their own apps

[DeepDiver1975]

I'd like to discuss the explicit steps to take in scope of 9.0 regarding out external storage implementations.

As soon as we touch any of these following steps are to be taken:

• convert the implementation to an app of its own
• setup travis unit testing - example https://github.com/icewind1991/files_external_ftp

In addtion we need to come up with a decision on if we want to continue to ship each of them - basically because of resource to be invested regarding the initial upgrade and future maintenance.

In case we decide to no longer ship any of these we can come up with a plan to move the code out to the community

Immediate action required:

• amazon s3
• dropbox
• google
• swift

Unclear:

• sftp

No action required

• ftp (already taken care of https://github.com/icewind1991/files_external_ftp)
• owncloud
• dav
• smb

@karlitschek @cmonteroluque @MTRichards @icewind1991 THX for your comments

@DeepDiver1975 thanks! My initial reaction is to continue to support what we have so far, under the new implementation. As many as possible in 9.0 and the rest afterwards. It is my default reaction, happy to talk more

[karlitschek]

thanks @DeepDiver1975

[icewind1991]

s3, dropdox and sftp have flysystem implementations which we could use

[DeepDiver1975]

s3, dropdox and sftp have flysystem implementations which we could use

no swift support? I missed that - THX

[DeepDiver1975]

ah rackspace - https://github.com/thephpleague/flysystem-rackspace - anyway

[PVince81]

First step would anyway moving the parts that aren't storage backends to core: #18160