add google cloud storage support in addition to S3

[nergdron]

I see S3 support for shared media storage across multiple linked Mastodon instances. This is great! but it'd be nice to also have Google Cloud Storage support for running on their cloud / Kubernetes.

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• I searched or browsed the repo’s other issues to ensure this is not a duplicate.

[Gargron]

Doesn't Google Cloud Storage have a S3-compatible API? In that case you simply need to specify S3_ENDPOINT

[nergdron]

Ah, you're right! I didn't realize that! Should work fine, thank you!

[jviide]

Sorry to resurrect an already closed issue, but it appears that Google Cloud Storage is having hard time with the "Expires" header set in config/initializers/paperclip.rb. Otherwise Google's S3 compatibility layer seems fine - changing the line

Paperclip::Attachment.default_options[:s3_headers]     = { 'Cache-Control' => 'max-age=315576000', 'Expires' => 10.years.from_now.httpdate }

to

Paperclip::Attachment.default_options[:s3_headers]     = { 'Cache-Control' => 'max-age=315576000' }

was enough to convince Google Cloud Storage to cooperate.

I created pull request #1886 for this, just in case if it's ok to drop the header.