TUN-3715: Only read config file once, right before invoking the command

cmd/cloudflared/cliutil/deprecated.go

@@ -9,12 +9,12 @@ import (
 func RemovedCommand(name string) *cli.Command {
 	return &cli.Command{
 		Name: name,
-		Action: ErrorHandler(func(context *cli.Context) error {
+		Action: func(context *cli.Context) error {
 			return cli.Exit(
 				fmt.Sprintf("%s command is no longer supported by cloudflared. Consult Argo Tunnel documentation for possible alternative solutions.", name),
 				-1,
 			)
-		}),
+		},
 		Description: fmt.Sprintf("%s is deprecated", name),
 		Hidden: true,
 	}

cmd/cloudflared/cliutil/errors.go

@@ -2,6 +2,7 @@ package cliutil
 
 import (
 	"fmt"
+
 	"github.com/urfave/cli/v2"
 )
 
@@ -21,7 +22,7 @@ func UsageError(format string, args ...interface{}) error {
 }
 
 // Ensures exit with error code if actionFunc returns an error
-func ErrorHandler(actionFunc cli.ActionFunc) cli.ActionFunc {
+func WithErrorHandler(actionFunc cli.ActionFunc) cli.ActionFunc {
 	return func(ctx *cli.Context) error {
 		err := actionFunc(ctx)
 		if err != nil {

cmd/cloudflared/cliutil/handler.go

@@ -0,0 +1,53 @@
+package cliutil
+
+import (
+	"github.com/urfave/cli/v2"
+	"github.com/urfave/cli/v2/altsrc"
+
+	"github.com/cloudflare/cloudflared/config"
+	"github.com/cloudflare/cloudflared/logger"
+)
+
+func Action(actionFunc cli.ActionFunc) cli.ActionFunc {
+	return WithErrorHandler(func(c *cli.Context) error {
+		if err := setFlagsFromConfigFile(c); err != nil {
+			return err
+		}
+		return actionFunc(c)
+	})
+}
+
+func setFlagsFromConfigFile(c *cli.Context) error {
+	const errorExitCode = 1
+	log := logger.CreateLoggerFromContext(c, logger.EnableTerminalLog)
+	inputSource, err := config.ReadConfigFile(c, log)
+	if err != nil {
+		if err == config.ErrNoConfigFile {
+			return nil
+		}
+		return cli.Exit(err, errorExitCode)
+	}
+
+	if err := applyConfig(c, inputSource); err != nil {
+		return cli.Exit(err, errorExitCode)
+	}
+	return nil
+}
+
+func applyConfig(c *cli.Context, inputSource altsrc.InputSourceContext) error {
+	for _, context := range c.Lineage() {
+		if context.Command == nil {
+			// we've reached the placeholder root context not associated with the app
+			break
+		}
+		targetFlags := context.Command.Flags
+		if context.Command.Name == "" {
+			// commands that define child subcommands are executed as if they were an app
+			targetFlags = c.App.Flags
+		}
+		if err := altsrc.ApplyInputSourceValues(context, inputSource, targetFlags); err != nil {
+			return err
+		}
+	}
+	return nil
+}