cli: centralize command execution

Many commands have the same boilerplate code for setting up randomization and
logging. The new k8s.io/component-base/cli.Run method contains that common code
and simplifies the code of commands which are using it.

staging/src/k8s.io/component-base/cli/run.go

@@ -0,0 +1,74 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+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 cli
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"time"
+
+	"github.com/spf13/cobra"
+
+	"k8s.io/component-base/logs"
+)
+
+// Run provides the common boilerplate code around executing a cobra command.
+// For example, it ensures that logging is set up properly. Logging
+// flags get added to the command line if not added already.
+func Run(cmd *cobra.Command) int {
+	rand.Seed(time.Now().UnixNano())
+	defer logs.FlushLogs()
+
+	// This is idempotent.
+	logs.AddFlags(cmd.PersistentFlags())
+
+	// Inject logs.InitLogs after command line parsing into one of the
+	// PersistentPre* functions.
+	switch {
+	case cmd.PersistentPreRun != nil:
+		pre := cmd.PersistentPreRun
+		cmd.PersistentPreRun = func(cmd *cobra.Command, args []string) {
+			logs.InitLogs()
+			pre(cmd, args)
+		}
+	case cmd.PersistentPreRunE != nil:
+		pre := cmd.PersistentPreRunE
+		cmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
+			logs.InitLogs()
+			return pre(cmd, args)
+		}
+	default:
+		cmd.PersistentPreRun = func(cmd *cobra.Command, args []string) {
+			logs.InitLogs()
+		}
+	}
+
+	if err := cmd.Execute(); err != nil {
+		// The error may be about the command line ("unknown shorthand
+		// flag: 'e' in -elp" in kube-scheduler). Printing that without
+		// any decoration like the one that klog would add ("E0923
+		// 23:02:03.219216 4168816 run.go:61] unknown shorthand flag")
+		// is more readable.
+		//
+		// We also don't know in which state logging (configuration may
+		// have failed) is whereas os.Stderr always should be usable.
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		return 1
+	}
+	return 0
+}