feat(metrics): import keypairreloader from a private project

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/metrics/keypairreloader.go

@@ -0,0 +1,81 @@
+package metrics
+
+import (
+	"crypto/tls"
+	"fmt"
+	"log/slog"
+	"os"
+	"sync"
+	"time"
+)
+
+type KeypairReloader struct {
+	certMu   sync.RWMutex
+	cert     *tls.Certificate
+	certPath string
+	keyPath  string
+	modTime  time.Time
+	lg       *slog.Logger
+}
+
+func NewKeypairReloader(certPath, keyPath string, lg *slog.Logger) (*KeypairReloader, error) {
+	result := &KeypairReloader{
+		certPath: certPath,
+		keyPath:  keyPath,
+		lg:       lg,
+	}
+	cert, err := tls.LoadX509KeyPair(certPath, keyPath)
+	if err != nil {
+		return nil, err
+	}
+	result.cert = &cert
+
+	st, err := os.Stat(certPath)
+	if err != nil {
+		return nil, err
+	}
+	result.modTime = st.ModTime()
+
+	return result, nil
+}
+
+func (kpr *KeypairReloader) maybeReload() error {
+	kpr.lg.Debug("loading new keypair", "cert", kpr.certPath, "key", kpr.keyPath)
+	newCert, err := tls.LoadX509KeyPair(kpr.certPath, kpr.keyPath)
+	if err != nil {
+		return err
+	}
+
+	st, err := os.Stat(kpr.certPath)
+	if err != nil {
+		return err
+	}
+
+	kpr.certMu.Lock()
+	defer kpr.certMu.Unlock()
+	kpr.cert = &newCert
+	kpr.modTime = st.ModTime()
+
+	return nil
+}
+
+func (kpr *KeypairReloader) GetCertificate(*tls.ClientHelloInfo) (*tls.Certificate, error) {
+	st, err := os.Stat(kpr.certPath)
+	if err != nil {
+		return nil, fmt.Errorf("stat(%q): %w", kpr.certPath, err)
+	}
+
+	kpr.certMu.RLock()
+	needsReload := st.ModTime().After(kpr.modTime)
+	kpr.certMu.RUnlock()
+
+	if needsReload {
+		if err := kpr.maybeReload(); err != nil {
+			return nil, fmt.Errorf("reload cert: %w", err)
+		}
+	}
+
+	kpr.certMu.RLock()
+	defer kpr.certMu.RUnlock()
+	return kpr.cert, nil
+}

lib/metrics/keypairreloader_test.go

@@ -0,0 +1,265 @@
+package metrics
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"errors"
+	"log/slog"
+	"math/big"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func discardLogger() *slog.Logger {
+	return slog.New(slog.DiscardHandler)
+}
+
+// writeKeypair generates a fresh self-signed cert + RSA key and writes them
+// as PEM files in dir. Returns the paths and the cert's DER bytes so callers
+// can identify which pair was loaded.
+func writeKeypair(t *testing.T, dir, prefix string) (certPath, keyPath string, certDER []byte) {
+	t.Helper()
+
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey: %v", err)
+	}
+
+	tmpl := &x509.Certificate{
+		SerialNumber:          big.NewInt(time.Now().UnixNano()),
+		Subject:               pkix.Name{CommonName: "keypairreloader-test"},
+		NotBefore:             time.Now().Add(-time.Hour),
+		NotAfter:              time.Now().Add(time.Hour),
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		BasicConstraintsValid: true,
+		DNSNames:              []string{"keypairreloader-test"},
+	}
+
+	der, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, &priv.PublicKey, priv)
+	if err != nil {
+		t.Fatalf("x509.CreateCertificate: %v", err)
+	}
+
+	certPath = filepath.Join(dir, prefix+"cert.pem")
+	keyPath = filepath.Join(dir, prefix+"key.pem")
+
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
+
+	if err := os.WriteFile(certPath, certPEM, 0o600); err != nil {
+		t.Fatalf("write cert: %v", err)
+	}
+	if err := os.WriteFile(keyPath, keyPEM, 0o600); err != nil {
+		t.Fatalf("write key: %v", err)
+	}
+
+	return certPath, keyPath, der
+}
+
+func TestNewKeypairReloader(t *testing.T) {
+	dir := t.TempDir()
+	goodCert, goodKey, _ := writeKeypair(t, dir, "good-")
+
+	garbagePath := filepath.Join(dir, "garbage.pem")
+	if err := os.WriteFile(garbagePath, []byte("not a pem file"), 0o600); err != nil {
+		t.Fatalf("write garbage: %v", err)
+	}
+
+	tests := []struct {
+		name     string
+		certPath string
+		keyPath  string
+		wantErr  error
+		wantNil  bool
+	}{
+		{
+			name:     "valid cert and key",
+			certPath: goodCert,
+			keyPath:  goodKey,
+		},
+		{
+			name:     "missing cert file",
+			certPath: filepath.Join(dir, "does-not-exist.pem"),
+			keyPath:  goodKey,
+			wantErr:  os.ErrNotExist,
+			wantNil:  true,
+		},
+		{
+			name:     "missing key file",
+			certPath: goodCert,
+			keyPath:  filepath.Join(dir, "does-not-exist-key.pem"),
+			wantErr:  os.ErrNotExist,
+			wantNil:  true,
+		},
+		{
+			name:     "cert file is garbage",
+			certPath: garbagePath,
+			keyPath:  goodKey,
+			wantNil:  true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			kpr, err := NewKeypairReloader(tt.certPath, tt.keyPath, discardLogger())
+
+			if tt.wantErr != nil && !errors.Is(err, tt.wantErr) {
+				t.Errorf("err = %v, want errors.Is(..., %v)", err, tt.wantErr)
+			}
+			if tt.wantErr == nil && !tt.wantNil && err != nil {
+				t.Errorf("unexpected err: %v", err)
+			}
+			if tt.wantNil && kpr != nil {
+				t.Errorf("kpr = %+v, want nil", kpr)
+			}
+			if !tt.wantNil && kpr == nil {
+				t.Errorf("kpr is nil, want non-nil")
+			}
+		})
+	}
+}
+
+func TestKeypairReloader_GetCertificate(t *testing.T) {
+	tests := []struct {
+		name string
+		run  func(t *testing.T)
+	}{
+		{
+			name: "returns loaded cert",
+			run: func(t *testing.T) {
+				dir := t.TempDir()
+				certPath, keyPath, wantDER := writeKeypair(t, dir, "a-")
+
+				kpr, err := NewKeypairReloader(certPath, keyPath, discardLogger())
+				if err != nil {
+					t.Fatalf("NewKeypairReloader: %v", err)
+				}
+
+				got, err := kpr.GetCertificate(nil)
+				if err != nil {
+					t.Fatalf("GetCertificate: %v", err)
+				}
+				if len(got.Certificate) == 0 || !bytes.Equal(got.Certificate[0], wantDER) {
+					t.Errorf("GetCertificate returned wrong cert bytes")
+				}
+			},
+		},
+		{
+			name: "reloads when mtime advances",
+			run: func(t *testing.T) {
+				dir := t.TempDir()
+				certPath, keyPath, _ := writeKeypair(t, dir, "a-")
+
+				kpr, err := NewKeypairReloader(certPath, keyPath, discardLogger())
+				if err != nil {
+					t.Fatalf("NewKeypairReloader: %v", err)
+				}
+
+				// Overwrite with a new pair at the same paths and bump mtime.
+				newCertPath, newKeyPath, newDER := writeKeypair(t, dir, "b-")
+				mustRename(t, newCertPath, certPath)
+				mustRename(t, newKeyPath, keyPath)
+				future := time.Now().Add(time.Hour)
+				if err := os.Chtimes(certPath, future, future); err != nil {
+					t.Fatalf("Chtimes: %v", err)
+				}
+
+				got, err := kpr.GetCertificate(nil)
+				if err != nil {
+					t.Fatalf("GetCertificate: %v", err)
+				}
+				if len(got.Certificate) == 0 || !bytes.Equal(got.Certificate[0], newDER) {
+					t.Errorf("GetCertificate did not return reloaded cert")
+				}
+			},
+		},
+		{
+			name: "does not reload when mtime unchanged",
+			run: func(t *testing.T) {
+				dir := t.TempDir()
+				certPath, keyPath, originalDER := writeKeypair(t, dir, "a-")
+
+				kpr, err := NewKeypairReloader(certPath, keyPath, discardLogger())
+				if err != nil {
+					t.Fatalf("NewKeypairReloader: %v", err)
+				}
+
+				// Overwrite the cert/key files with a *different* keypair, then
+				// rewind mtime so the reloader must not pick up the change.
+				newCertPath, newKeyPath, newDER := writeKeypair(t, dir, "b-")
+				mustRename(t, newCertPath, certPath)
+				mustRename(t, newKeyPath, keyPath)
+				past := time.Unix(0, 0)
+				if err := os.Chtimes(certPath, past, past); err != nil {
+					t.Fatalf("Chtimes: %v", err)
+				}
+
+				got, err := kpr.GetCertificate(nil)
+				if err != nil {
+					t.Fatalf("GetCertificate: %v", err)
+				}
+				if len(got.Certificate) == 0 {
+					t.Fatal("empty cert chain")
+				}
+				if bytes.Equal(got.Certificate[0], newDER) {
+					t.Errorf("GetCertificate reloaded despite unchanged mtime")
+				}
+				if !bytes.Equal(got.Certificate[0], originalDER) {
+					t.Errorf("GetCertificate did not return original cert")
+				}
+			},
+		},
+		{
+			name: "does not panic when reload fails after mtime bump",
+			run: func(t *testing.T) {
+				dir := t.TempDir()
+				certPath, keyPath, _ := writeKeypair(t, dir, "a-")
+
+				kpr, err := NewKeypairReloader(certPath, keyPath, discardLogger())
+				if err != nil {
+					t.Fatalf("NewKeypairReloader: %v", err)
+				}
+
+				// Corrupt the cert file and bump mtime. maybeReload will fail.
+				if err := os.WriteFile(certPath, []byte("not a pem file"), 0o600); err != nil {
+					t.Fatalf("corrupt cert: %v", err)
+				}
+				future := time.Now().Add(time.Hour)
+				if err := os.Chtimes(certPath, future, future); err != nil {
+					t.Fatalf("Chtimes: %v", err)
+				}
+
+				defer func() {
+					if r := recover(); r != nil {
+						t.Fatalf("GetCertificate panicked on reload failure: %v", r)
+					}
+				}()
+
+				got, err := kpr.GetCertificate(nil)
+				if err == nil {
+					t.Errorf("GetCertificate returned nil err for corrupt cert; got %+v", got)
+				}
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tt.run(t)
+		})
+	}
+}
+
+func mustRename(t *testing.T, from, to string) {
+	t.Helper()
+	if err := os.Rename(from, to); err != nil {
+		t.Fatalf("rename %q -> %q: %v", from, to, err)
+	}
+}

lib/metrics/metrics.go

@@ -2,6 +2,7 @@ package metrics
 
 import (
 	"context"
+	"crypto/tls"
 	"errors"
 	"fmt"
 	"log/slog"
@@ -62,6 +63,17 @@ func (s *Server) Run(ctx context.Context, done func()) error {
 
 	defer ln.Close()
 
+	if s.Config.TLS != nil {
+		kpr, err := NewKeypairReloader(s.Config.TLS.Certificate, s.Config.TLS.Key, lg)
+		if err != nil {
+			return fmt.Errorf("can't setup keypair reloader: %w", err)
+		}
+
+		srv.TLSConfig = &tls.Config{
+			GetCertificate: kpr.GetCertificate,
+		}
+	}
+
 	lg.Debug("listening for metrics", "url", metricsURL)
 
 	go func() {
@@ -75,7 +87,7 @@ func (s *Server) Run(ctx context.Context, done func()) error {
 
 	switch s.Config.TLS != nil {
 	case true:
-		if err := srv.ServeTLS(ln, s.Config.TLS.Certificate, s.Config.TLS.Key); !errors.Is(err, http.ErrServerClosed) {
+		if err := srv.ServeTLS(ln, "", ""); !errors.Is(err, http.ErrServerClosed) {
 			return fmt.Errorf("can't serve TLS metrics server: %w", err)
 		}
 	case false: