From 63b147c2879c3110d1ad3d960013c1df7442e64d Mon Sep 17 00:00:00 2001
From: 9seconds <nineseconds@yandex.ru>
Date: Mon, 23 Mar 2026 14:45:10 +0100
Subject: [PATCH] Add doctor command for deprecated config values

---
 internal/cli/cli.go    |   1 +
 internal/cli/doctor.go | 105 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 internal/cli/doctor.go

diff --git a/internal/cli/cli.go b/internal/cli/cli.go
index f287ad8..ec25fac 100644
--- a/internal/cli/cli.go
+++ b/internal/cli/cli.go
@@ -4,6 +4,7 @@ import "github.com/alecthomas/kong"
 
 type CLI struct {
 	GenerateSecret GenerateSecret   `kong:"cmd,help='Generate new proxy secret'"`
+	Doctor         Doctor           `kong:"cmd,help='Check that proxy can run correctly'"`
 	Access         Access           `kong:"cmd,help='Print access information.'"`
 	Run            Run              `kong:"cmd,help='Run proxy.'"`
 	SimpleRun      SimpleRun        `kong:"cmd,help='Run proxy without config file.'"`
diff --git a/internal/cli/doctor.go b/internal/cli/doctor.go
new file mode 100644
index 0000000..a66a693
--- /dev/null
+++ b/internal/cli/doctor.go
@@ -0,0 +1,105 @@
+package cli
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"text/template"
+
+	"github.com/9seconds/mtg/v2/internal/config"
+	"github.com/9seconds/mtg/v2/internal/utils"
+)
+
+var (
+	tplWDeprecatedConfig = template.Must(
+		template.New("deprecated-config").
+			Parse(`  ⚠️ Option {{ .old | printf "%q" }}{{ if .old_section }} from section [{{ .old_section }}]{{ end }} is deprecated and will be removed in v{{ .when }}. Please use {{ .new | printf "%q" }}{{ if .new_section }} in [{{ .new_section }}] section{{ end }} instead.`),
+	)
+)
+
+type Doctor struct {
+	conf *config.Config
+
+	ConfigPath string `kong:"arg,required,type='existingfile',help='Path to the configuration file.',name='config-path'"` //nolint: lll
+}
+
+func (d *Doctor) Run(cli *CLI, version string) error {
+	conf, err := utils.ReadConfig(d.ConfigPath)
+	if err != nil {
+		return fmt.Errorf("cannot init config: %w", err)
+	}
+
+	d.conf = conf
+	everythingOK := true
+
+	fmt.Println("Deprecated options")
+	if errs := d.checkDeprecatedConfig(); len(errs) > 0 {
+		for _, err := range errs {
+			fmt.Println(err)
+			everythingOK = false
+		}
+	} else {
+		fmt.Println("  ✅ All good")
+	}
+
+	if !everythingOK {
+		os.Exit(1)
+	}
+
+	return nil
+}
+
+func (d *Doctor) checkDeprecatedConfig() []string {
+	errors := []string{}
+
+	if d.conf.DomainFrontingIP.Value != nil {
+		errors = d.addError(errors, tplWDeprecatedConfig, map[string]string{
+			"when":        "2.3.0",
+			"old":         "domain-fronting-ip",
+			"old_section": "",
+			"new":         "ip",
+			"new_section": "domain-fronting",
+		})
+	}
+
+	if d.conf.DomainFrontingPort.Value != 0 {
+		errors = d.addError(errors, tplWDeprecatedConfig, map[string]string{
+			"when":        "2.3.0",
+			"old":         "domain-fronting-port",
+			"old_section": "",
+			"new":         "port",
+			"new_section": "domain-fronting",
+		})
+	}
+
+	if d.conf.DomainFrontingProxyProtocol.Value {
+		errors = d.addError(errors, tplWDeprecatedConfig, map[string]string{
+			"when":        "2.3.0",
+			"old":         "domain-fronting-proxy-protocol",
+			"old_section": "",
+			"new":         "proxy-protocol",
+			"new_section": "domain-fronting",
+		})
+	}
+
+	if d.conf.Network.DOHIP.Value != nil {
+		errors = d.addError(errors, tplWDeprecatedConfig, map[string]string{
+			"when":        "2.3.0",
+			"old":         "doh-ip",
+			"old_section": "network",
+			"new":         "dns",
+			"new_section": "network",
+		})
+	}
+
+	return errors
+}
+
+func (d *Doctor) addError(messages []string, tpl *template.Template, context map[string]string) []string {
+	value := &strings.Builder{}
+	if err := tpl.Execute(value, context); err != nil {
+		panic(err)
+	}
+
+	return append(messages, value.String())
+}