caddycmd: Add --skip-cleanup to upgrade commands

This is a partial fix for #4057, making it possible to retain the old build of Caddy, in case something went wrong.

cmd/commands.go

@@ -296,6 +296,11 @@ is always printed to stdout.`,
 		Long: `
 Downloads an updated Caddy binary with the same modules/plugins at the
 latest versions. EXPERIMENTAL: May be changed or removed.`,
+		Flags: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("upgrade", flag.ExitOnError)
+			fs.Bool("skip-cleanup", false, "Skips removing the backed up binary")
+			return fs
+		}(),
 	})
 
 	RegisterCommand(Command{
@@ -308,6 +313,11 @@ Downloads an updated Caddy binary with the specified packages (module/plugin)
 added. Retains existing packages. Returns an error if the any of packages are 
 already included. EXPERIMENTAL: May be changed or removed.
 `,
+		Flags: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("add-package", flag.ExitOnError)
+			fs.Bool("skip-cleanup", false, "Skips removing the backed up binary")
+			return fs
+		}(),
 	})
 
 	RegisterCommand(Command{
@@ -320,6 +330,11 @@ Downloads an updated Caddy binaries without the specified packages (module/plugi
 Returns an error if any of the packages are not included. 
 EXPERIMENTAL: May be changed or removed.
 `,
+		Flags: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("remove-package", flag.ExitOnError)
+			fs.Bool("skip-cleanup", false, "Skips removing the backed up binary")
+			return fs
+		}(),
 	})
 
 }

cmd/packagesfuncs.go

@@ -31,7 +31,7 @@ import (
 	"go.uber.org/zap"
 )
 
-func cmdUpgrade(_ Flags) (int, error) {
+func cmdUpgrade(fl Flags) (int, error) {
 	_, nonstandard, _, err := getModules()
 	if err != nil {
 		return caddy.ExitCodeFailedStartup, fmt.Errorf("unable to enumerate installed plugins: %v", err)
@@ -41,7 +41,7 @@ func cmdUpgrade(_ Flags) (int, error) {
 		return caddy.ExitCodeFailedStartup, err
 	}
 
-	return upgradeBuild(pluginPkgs)
+	return upgradeBuild(pluginPkgs, fl)
 }
 
 func cmdAddPackage(fl Flags) (int, error) {
@@ -64,7 +64,7 @@ func cmdAddPackage(fl Flags) (int, error) {
 		pluginPkgs[arg] = struct{}{}
 	}
 
-	return upgradeBuild(pluginPkgs)
+	return upgradeBuild(pluginPkgs, fl)
 }
 
 func cmdRemovePackage(fl Flags) (int, error) {
@@ -88,10 +88,10 @@ func cmdRemovePackage(fl Flags) (int, error) {
 		delete(pluginPkgs, arg)
 	}
 
-	return upgradeBuild(pluginPkgs)
+	return upgradeBuild(pluginPkgs, fl)
 }
 
-func upgradeBuild(pluginPkgs map[string]struct{}) (int, error) {
+func upgradeBuild(pluginPkgs map[string]struct{}, fl Flags) (int, error) {
 	l := caddy.Log()
 
 	thisExecPath, err := os.Executable()
@@ -161,9 +161,14 @@ func upgradeBuild(pluginPkgs map[string]struct{}) (int, error) {
 	fmt.Println()
 
 	// clean up the backup file
-	if err = os.Remove(backupExecPath); err != nil {
-		return caddy.ExitCodeFailedStartup, fmt.Errorf("download succeeded, but unable to clean up backup binary: %v", err)
+	if !fl.Bool("skip-cleanup") {
+		if err = os.Remove(backupExecPath); err != nil {
+			return caddy.ExitCodeFailedStartup, fmt.Errorf("download succeeded, but unable to clean up backup binary: %v", err)
+		}
+	} else {
+		l.Info("skipped cleaning up the backup file", zap.String("backup_path", backupExecPath))
 	}
+
 	l.Info("upgrade successful; please restart any running Caddy instances", zap.String("executable", thisExecPath))
 
 	return caddy.ExitCodeSuccess, nil