Add storage managers (local, sftp, s3, hybrid).

app/logical/storage_manager/sftp.rb

@@ -0,0 +1,76 @@
+class StorageManager::SFTP < StorageManager
+  DEFAULT_PERMISSIONS = 0644
+
+  # 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
+
+  def initialize(*hosts, ssh_options: {}, **options)
+    @hosts = hosts
+    @ssh_options = DEFAULT_SSH_OPTIONS.merge(ssh_options)
+    super(**options)
+  end
+
+  def store(file, dest_path)
+    temp_upload_path = dest_path + "-" + SecureRandom.uuid + ".tmp"
+    dest_backup_path = dest_path + "-" + SecureRandom.uuid + ".bak"
+
+    each_host do |host, sftp|
+      begin
+        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
+  end
+
+  def delete(dest_path)
+    each_host do |host, sftp|
+      force { sftp.remove!(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!(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
+end