Fix output-file flag. (#1264)

The writer was getting closed prematurely in the PreRun command. We need to save
this as a temp variable at the command level and close the writer in PostRun.

Signed-off-by: Dan Lorenc <lorenc.d@gmail.com>

cmd/cosign/cli/commands.go

@@ -30,21 +30,22 @@ var (
 )
 
 func New() *cobra.Command {
+	var (
+		out, stdout *os.File
+	)
+
 	cmd := &cobra.Command{
 		Use:               "cosign",
 		DisableAutoGenTag: true,
 		SilenceUsage:      true, // Don't show usage on errors
 		PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
 			if ro.OutputFile != "" {
-				out, err := os.Create(ro.OutputFile)
+				var err error
+				out, err = os.Create(ro.OutputFile)
 				if err != nil {
 					return errors.Wrapf(err, "Error creating output file %s", ro.OutputFile)
 				}
-				stdout := os.Stdout
-				defer func() {
-					os.Stdout = stdout
-					_ = out.Close()
-				}()
+				stdout = os.Stdout
 				os.Stdout = out // TODO: don't do this.
 				cmd.SetOut(out)
 			}
@@ -54,6 +55,12 @@ func New() *cobra.Command {
 			}
 			return nil
 		},
+		PersistentPostRun: func(cmd *cobra.Command, args []string) {
+			if out != nil {
+				_ = out.Close()
+			}
+			os.Stdout = stdout
+		},
 	}
 	ro.AddFlags(cmd)
 

test/e2e_test_secrets.sh

@@ -51,6 +51,11 @@ crane cp gcr.io/distroless/base $multiarch_img
 # `initialize`
 ./cosign initialize
 
+## Generate (also test output redirection
+./cosign generate $img > payload1
+./cosign generate --output-file=payload2 $img
+diff payload1 payload2
+
 ## sign/verify
 ./cosign sign --key ${signing_key} $img
 ./cosign verify --key ${verification_key} $img