new S3 backup layout (#9830)

* DEV: new S3 backup layout

Currently, with $S3_BACKUP_BUCKET of "bucket/backups", multisite backups
end up in "bucket/backups/backups/dbname/" and single-site will be in
"bucket/backups/".

Both _should_ be in "bucket/backups/dbname/"

- remove MULTISITE_PREFIX,
- always include dbname,
- method to move to the new prefix
- job to call the method

* SPEC: add tests for `VacateLegacyPrefixBackups` onceoff job.

Co-authored-by: Vinoth Kannan <vinothkannan@vinkas.com>

lib/backup_restore/s3_backup_store.rb

@@ -3,12 +3,11 @@
 module BackupRestore
   class S3BackupStore < BackupStore
     UPLOAD_URL_EXPIRES_AFTER_SECONDS ||= 21_600 # 6 hours
-    MULTISITE_PREFIX = "backups"
 
     def initialize(opts = {})
-      s3_options = S3Helper.s3_options(SiteSetting)
-      s3_options.merge!(opts[:s3_options]) if opts[:s3_options]
-      @s3_helper = S3Helper.new(s3_bucket_name_with_prefix, '', s3_options)
+      @s3_options = S3Helper.s3_options(SiteSetting)
+      @s3_options.merge!(opts[:s3_options]) if opts[:s3_options]
+      @s3_helper = S3Helper.new(s3_bucket_name_with_prefix, '', @s3_options.clone)
     end
 
     def remote?
@@ -52,6 +51,20 @@ module BackupRestore
       raise StorageError
     end
 
+    def vacate_legacy_prefix
+      legacy_s3_helper = S3Helper.new(s3_bucket_name_with_legacy_prefix, '', @s3_options.clone)
+      legacy_keys = legacy_s3_helper.list.map { |o| o.key }
+      legacy_keys.each do |legacy_key|
+        bucket, prefix = s3_bucket_name_with_prefix.split('/', 2)
+        @s3_helper.s3_client.copy_object({
+          copy_source: File.join(bucket, legacy_key),
+          bucket: bucket,
+          key: File.join(prefix, legacy_key.split('/').last)
+        })
+        legacy_s3_helper.delete_object(legacy_key)
+      end
+    end
+
     private
 
     def unsorted_files
@@ -99,8 +112,12 @@ module BackupRestore
     end
 
     def s3_bucket_name_with_prefix
+      File.join(SiteSetting.s3_backup_bucket, RailsMultisite::ConnectionManagement.current_db)
+    end
+
+    def s3_bucket_name_with_legacy_prefix
       if Rails.configuration.multisite
-        File.join(SiteSetting.s3_backup_bucket, MULTISITE_PREFIX, RailsMultisite::ConnectionManagement.current_db)
+        File.join(SiteSetting.s3_backup_bucket, "backups", RailsMultisite::ConnectionManagement.current_db)
       else
         SiteSetting.s3_backup_bucket
       end