Split plugin framework into its own package

Signed-off-by: Carlisia <carlisiac@vmware.com>

pkg/plugin/framework/logger.go

@@ -0,0 +1,59 @@
+/*
+Copyright 2017, 2019 the Velero contributors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package framework
+
+import (
+	"github.com/sirupsen/logrus"
+
+	"github.com/heptio/velero/pkg/util/logging"
+)
+
+// newLogger returns a logger that is suitable for use within an
+// Velero plugin.
+func newLogger() *logrus.Logger {
+	logger := logrus.New()
+	/*
+		!!!DO NOT SET THE OUTPUT TO STDOUT!!!
+
+		go-plugin uses stdout for a communications protocol between client and server.
+
+		stderr is used for log messages from server to client. The velero server makes sure they are logged to stdout.
+	*/
+
+	// we use the JSON formatter because go-plugin will parse incoming
+	// JSON on stderr and use it to create structured log entries.
+	logger.Formatter = &logrus.JSONFormatter{
+		FieldMap: logrus.FieldMap{
+			// this is the hclog-compatible message field
+			logrus.FieldKeyMsg: "@message",
+		},
+		// Velero server already adds timestamps when emitting logs, so
+		// don't do it within the plugin.
+		DisableTimestamp: true,
+	}
+
+	// set a logger name for the location hook which will signal to the Velero
+	// server logger that the location has been set within a hook.
+	logger.Hooks.Add((&logging.LogLocationHook{}).WithLoggerName("plugin"))
+
+	// this hook adjusts the string representation of WarnLevel to "warn"
+	// rather than "warning" to make it parseable by go-plugin within the
+	// Velero server code
+	logger.Hooks.Add(&logging.HcLogLevelHook{})
+
+	return logger
+}