feat: IPv6 support (#192)

* 🐛 fix(server.go): validate IP address before starting server
✨ feat(server.go): add support for IPv6 addresses

* ✨ feat(cli): add support for IPv6 addresses in the `--listen` flag

* 🐛 fix(server.go): add nolint comment to ignore magic number warning in ipv6 check

* 🐛 fix(server.go): use fmt.Sprintf to format IP and port instead of strconv.Itoa and string concatenation

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to this package will be documented in this file.
 
 The format is based on [Keep a Changelog][keepachangelog] and this project adheres to [Semantic Versioning][semver].
 
+## v2.24.0
+
+### Added
+
+- Support for IPv6 addresses in the `--listen` flag [#191]
+
+[#191]:https://github.com/tarampampam/error-pages/issues/191
+
 ## v2.23.0
 
 ### Added

internal/cli/shared/flags.go

@@ -17,7 +17,7 @@ var ConfigFileFlag = &cli.StringFlag{ //nolint:gochecknoglobals
 var ListenAddrFlag = &cli.StringFlag{ //nolint:gochecknoglobals
 	Name:    "listen",
 	Aliases: []string{"l"},
-	Usage:   "IP address to Listen on",
+	Usage:   "IP (v4 or v6) address to Listen on",
 	Value:   "0.0.0.0",
 	EnvVars: []string{env.ListenAddr.String()},
 }

internal/http/server.go

@@ -1,7 +1,10 @@
 package http
 
 import (
-	"strconv"
+	"errors"
+	"fmt"
+	"net"
+	"strings"
 	"time"
 
 	"github.com/fasthttp/router"
@@ -57,8 +60,24 @@ func NewServer(log *zap.Logger) Server {
 }
 
 // Start server.
-func (s *Server) Start(ip string, port uint16) error {
-	return s.fast.ListenAndServe(ip + ":" + strconv.Itoa(int(port)))
+func (s *Server) Start(ip string, port uint16) (err error) {
+	if net.ParseIP(ip) == nil {
+		return errors.New("invalid IP address")
+	}
+
+	var ln net.Listener
+
+	if strings.Count(ip, ":") >= 2 { //nolint:gomnd // ipv6
+		if ln, err = net.Listen("tcp6", fmt.Sprintf("[%s]:%d", ip, port)); err != nil {
+			return err
+		}
+	} else { // ipv4
+		if ln, err = net.Listen("tcp4", fmt.Sprintf("%s:%d", ip, port)); err != nil {
+			return err
+		}
+	}
+
+	return s.fast.Serve(ln)
 }
 
 type templatePicker interface {