From ad2c7ca67102d21c72406406ab7c4da548f80c3c Mon Sep 17 00:00:00 2001
From: Denis Kirillov <denis@nspcc.ru>
Date: Fri, 9 Sep 2022 19:00:04 +0300
Subject: [PATCH] [#200] Reload certs on SIGHUP

Signed-off-by: Denis Kirillov <denis@nspcc.ru>
---
 app.go | 89 ++++++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 74 insertions(+), 15 deletions(-)

diff --git a/app.go b/app.go
index 39dfa9f..9b34267 100644
--- a/app.go
+++ b/app.go
@@ -3,7 +3,10 @@ package main
 import (
 	"context"
 	"crypto/ecdsa"
+	"crypto/tls"
+	"errors"
 	"fmt"
+	"net"
 	"os"
 	"os/signal"
 	"strconv"
@@ -45,8 +48,9 @@ type (
 	}
 
 	appSettings struct {
-		Uploader   *uploader.Settings
-		Downloader *downloader.Settings
+		Uploader    *uploader.Settings
+		Downloader  *downloader.Settings
+		TLSProvider *certProvider
 	}
 
 	// App is an interface for the main gateway function.
@@ -174,8 +178,9 @@ func newApp(ctx context.Context, opt ...Option) App {
 
 func (a *app) initAppSettings() {
 	a.settings = &appSettings{
-		Uploader:   &uploader.Settings{},
-		Downloader: &downloader.Settings{},
+		Uploader:    &uploader.Settings{},
+		Downloader:  &downloader.Settings{},
+		TLSProvider: &certProvider{Enabled: a.cfg.IsSet(cfgTLSCertificate) || a.cfg.IsSet(cfgTLSKey)},
 	}
 
 	a.updateSettings()
@@ -335,6 +340,43 @@ func (a *app) setHealthStatus() {
 	a.metrics.SetHealth(1)
 }
 
+type certProvider struct {
+	Enabled bool
+
+	mu       sync.RWMutex
+	certPath string
+	keyPath  string
+	cert     *tls.Certificate
+}
+
+func (p *certProvider) GetCertificate(*tls.ClientHelloInfo) (*tls.Certificate, error) {
+	if !p.Enabled {
+		return nil, errors.New("cert provider: disabled")
+	}
+
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+	return p.cert, nil
+}
+
+func (p *certProvider) UpdateCert(certPath, keyPath string) error {
+	if !p.Enabled {
+		return fmt.Errorf("tls disabled")
+	}
+
+	cert, err := tls.LoadX509KeyPair(certPath, keyPath)
+	if err != nil {
+		return fmt.Errorf("cannot load TLS key pair from certFile '%s' and keyFile '%s': %w", certPath, keyPath, err)
+	}
+
+	p.mu.Lock()
+	p.certPath = certPath
+	p.keyPath = keyPath
+	p.cert = &cert
+	p.mu.Unlock()
+	return nil
+}
+
 func (a *app) Serve(ctx context.Context) {
 	uploadRoutes := uploader.New(ctx, a.AppParams(), a.settings.Uploader)
 	downloadRoutes := downloader.New(ctx, a.AppParams(), a.settings.Downloader)
@@ -344,21 +386,34 @@ func (a *app) Serve(ctx context.Context) {
 
 	a.startServices()
 
-	bind := a.cfg.GetString(cfgListenAddress)
-	tlsCertPath := a.cfg.GetString(cfgTLSCertificate)
-	tlsKeyPath := a.cfg.GetString(cfgTLSKey)
-
 	go func() {
 		var err error
-		if tlsCertPath == "" && tlsKeyPath == "" {
+		defer func() {
+			if err != nil {
+				a.log.Fatal("could not start server", zap.Error(err))
+			}
+		}()
+
+		bind := a.cfg.GetString(cfgListenAddress)
+
+		if a.settings.TLSProvider.Enabled {
+			if err = a.settings.TLSProvider.UpdateCert(a.cfg.GetString(cfgTLSCertificate), a.cfg.GetString(cfgTLSKey)); err != nil {
+				return
+			}
+
+			var ln net.Listener
+			if ln, err = net.Listen("tcp4", bind); err != nil {
+				return
+			}
+			lnTLS := tls.NewListener(ln, &tls.Config{
+				GetCertificate: a.settings.TLSProvider.GetCertificate,
+			})
+
+			a.log.Info("running web server (TLS-enabled)", zap.String("address", bind))
+			err = a.webServer.Serve(lnTLS)
+		} else {
 			a.log.Info("running web server", zap.String("address", bind))
 			err = a.webServer.ListenAndServe(bind)
-		} else {
-			a.log.Info("running web server (TLS-enabled)", zap.String("address", bind))
-			err = a.webServer.ListenAndServeTLS(bind, tlsCertPath, tlsKeyPath)
-		}
-		if err != nil {
-			a.log.Fatal("could not start server", zap.Error(err))
 		}
 	}()
 
@@ -417,6 +472,10 @@ func (a *app) configReload() {
 func (a *app) updateSettings() {
 	a.settings.Uploader.SetDefaultTimestamp(a.cfg.GetBool(cfgUploaderHeaderEnableDefaultTimestamp))
 	a.settings.Downloader.SetZipCompression(a.cfg.GetBool(cfgZipCompression))
+
+	if err := a.settings.TLSProvider.UpdateCert(a.cfg.GetString(cfgTLSCertificate), a.cfg.GetString(cfgTLSKey)); err != nil {
+		a.log.Warn("failed to reload TLS certs", zap.Error(err))
+	}
 }
 
 func (a *app) startServices() {