cmd: Add caddy fmt command. (#3090)

This takes the config file as input and formats it.
Prints the result to stdout. Can write changes to
file if `--write` flag is passed.

Fixes #3020

Signed-off-by: Vaibhav <vrongmeal@gmail.com>

cmd/commandfuncs.go

@@ -34,6 +34,7 @@ import (
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
 	"github.com/mholt/certmagic"
 	"go.uber.org/zap"
 )
@@ -538,6 +539,35 @@ func cmdValidateConfig(fl Flags) (int, error) {
 	return caddy.ExitCodeSuccess, nil
 }
 
+func cmdFormatConfig(fl Flags) (int, error) {
+	// Default path of file is Caddyfile
+	formatCmdConfigFile := fl.Arg(0)
+	if formatCmdConfigFile == "" {
+		formatCmdConfigFile = "Caddyfile"
+	}
+
+	formatCmdWriteFlag := fl.Bool("write")
+
+	input, err := ioutil.ReadFile(formatCmdConfigFile)
+	if err != nil {
+		return caddy.ExitCodeFailedStartup,
+			fmt.Errorf("reading input file: %v", err)
+	}
+
+	output := caddyfile.Format(input)
+
+	if formatCmdWriteFlag {
+		err = ioutil.WriteFile(formatCmdConfigFile, output, 0644)
+		if err != nil {
+			return caddy.ExitCodeFailedStartup, nil
+		}
+	} else {
+		fmt.Print(string(output))
+	}
+
+	return caddy.ExitCodeSuccess, nil
+}
+
 func cmdHelp(fl Flags) (int, error) {
 	const fullDocs = `Full documentation is available at:
 https://caddyserver.com/docs/command-line`