Add option to mc admin policy info to save policy JSON to file (#3914)

cmd/admin-policy-info.go

@@ -18,6 +18,8 @@
 package cmd
 
 import (
+	"os"
+
 	"github.com/fatih/color"
 	"github.com/minio/cli"
 	"github.com/minio/madmin-go"
@@ -25,18 +27,25 @@ import (
 	"github.com/minio/pkg/console"
 )
 
+var policyInfoFlags = []cli.Flag{
+	cli.StringFlag{
+		Name:  "policy-file, f",
+		Usage: "additionally (over-)write policy JSON to given file",
+	},
+}
+
 var adminPolicyInfoCmd = cli.Command{
 	Name:         "info",
 	Usage:        "show info on a policy",
 	Action:       mainAdminPolicyInfo,
 	OnUsageError: onUsageError,
 	Before:       setGlobalsFromContext,
-	Flags:        globalFlags,
+	Flags:        append(policyInfoFlags, globalFlags...),
 	CustomHelpTemplate: `NAME:
   {{.HelpName}} - {{.Usage}}
 
 USAGE:
-  {{.HelpName}} TARGET POLICYNAME
+  {{.HelpName}} TARGET POLICYNAME [OPTIONS...]
 
 POLICYNAME:
   Name of the policy on the MinIO server.
@@ -47,6 +56,9 @@ FLAGS:
 EXAMPLES:
   1. Show information on a given policy.
      {{.Prompt}} {{.HelpName}} myminio writeonly
+
+  2. Show information on a given policy and write the policy JSON content to /tmp/policy.json.
+     {{.Prompt}} {{.HelpName}} myminio writeonly --policy-file /tmp/policy.json
 `,
 }
 
@@ -93,6 +105,18 @@ func mainAdminPolicyInfo(ctx *cli.Context) error {
 	pinfo, e := getPolicyInfo(client, policyName)
 	fatalIf(probe.NewError(e).Trace(args...), "Unable to fetch policy")
 
+	policyFile := ctx.String("policy-file")
+	if policyFile != "" {
+		f, err := os.Create(policyFile)
+		if err != nil {
+			fatalIf(probe.NewError(err).Trace(args...), "Could not open given policy file")
+		}
+		_, err = f.Write(pinfo.Policy)
+		if err != nil {
+			fatalIf(probe.NewError(err).Trace(args...), "Could not write to given policy file")
+		}
+	}
+
 	printMsg(userPolicyMessage{
 		op:         "info",
 		Policy:     policyName,