Remove StorageManager::SFTP.

Remove the SFTP file storage backend. Downstream users can use either
sshfs (which is what Danbooru now uses in production) or rclone instead.
The Ruby SFTP gem was much slower than sshfs.

app/logical/storage_manager.rb

@@ -9,7 +9,6 @@
 # @see StorageManager::Local
 # @see StorageManager::Mirror
 # @see StorageManager::Rclone
-# @see StorageManager::SFTP
 class StorageManager
   class Error < StandardError; end
 

app/logical/storage_manager/sftp.rb

@@ -1,81 +0,0 @@
-# A StorageManager that stores files on a remote filesystem using SFTP.
-class StorageManager::SFTP < StorageManager
-  DEFAULT_PERMISSIONS = 0o644
-
-  # http://net-ssh.github.io/net-ssh/Net/SSH.html#method-c-start
-  DEFAULT_SSH_OPTIONS = {
-    timeout: 10,
-    logger: Rails.logger,
-    verbose: :fatal,
-    non_interactive: true
-  }
-
-  attr_reader :hosts, :ssh_options, :base_dir
-
-  def initialize(*hosts, base_dir: nil, ssh_options: {}, **options)
-    @hosts = hosts
-    @base_dir = base_dir.to_s
-    @ssh_options = DEFAULT_SSH_OPTIONS.merge(ssh_options)
-    super(**options)
-  end
-
-  def store(file, dest_path)
-    dest_path = full_path(dest_path)
-    temp_upload_path = dest_path + "-" + SecureRandom.uuid + ".tmp"
-    dest_backup_path = dest_path + "-" + SecureRandom.uuid + ".bak"
-
-    each_host do |_host, sftp|
-      sftp.upload!(file.path, temp_upload_path)
-      sftp.setstat!(temp_upload_path, permissions: DEFAULT_PERMISSIONS)
-
-      # `rename!` can't overwrite existing files, so if a file already exists
-      # at dest_path we move it out of the way first.
-      force { sftp.rename!(dest_path, dest_backup_path) }
-      force { sftp.rename!(temp_upload_path, dest_path) }
-    rescue StandardError => e
-      # if anything fails, try to move the original file back in place (if it was moved).
-      force { sftp.rename!(dest_backup_path, dest_path) }
-      raise Error, e
-    ensure
-      force { sftp.remove!(temp_upload_path) }
-      force { sftp.remove!(dest_backup_path) }
-    end
-  end
-
-  def delete(dest_path)
-    each_host do |_host, sftp|
-      force { sftp.remove!(full_path(dest_path)) }
-    end
-  end
-
-  def open(dest_path)
-    file = Tempfile.new(binmode: true)
-
-    Net::SFTP.start(hosts.first, nil, ssh_options) do |sftp|
-      sftp.download!(full_path(dest_path), file.path)
-    end
-
-    file
-  end
-
-  protected
-
-  # Ignore "no such file" exceptions for the given operation.
-  def force
-    yield
-  rescue Net::SFTP::StatusException => e
-    raise Error, e unless e.description == "no such file"
-  end
-
-  def each_host
-    hosts.each do |host|
-      Net::SFTP.start(host, nil, ssh_options) do |sftp|
-        yield host, sftp
-      end
-    end
-  end
-
-  def full_path(path)
-    File.join(base_dir, path)
-  end
-end