fix(validator): reload Web3Signer keys after same-size file updates

changelog/questfever_fix-web3signer-same-size-reload.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- Reload Web3Signer validator public keys when the configured key file changes without changing size.

validator/keymanager/remote-web3signer/keymanager.go

@@ -309,11 +309,9 @@ func (km *Keymanager) refreshRemoteKeysFromFileChanges(ctx context.Context, mark
 			log.WithError(err).Error("Could not close file watcher")
 		}
 	}()
-	initialFileInfo, err := os.Stat(km.keyFilePath)
-	if err != nil {
+	if _, err := os.Stat(km.keyFilePath); err != nil {
 		return errors.Wrap(err, "could not stat remote signer public key file")
 	}
-	initialFileSize := initialFileInfo.Size()
 	if err := watcher.Add(km.keyFilePath); err != nil {
 		return errors.Wrap(err, "could not add file to file watcher")
 	}
@@ -352,29 +350,22 @@ func (km *Keymanager) refreshRemoteKeysFromFileChanges(ctx context.Context, mark
 			if e.Has(fsnotify.Remove) {
 				return errors.New("remote signer key file was removed")
 			}
-			currentFileInfo, err := os.Stat(km.keyFilePath)
+			fileKeys, _, err := km.readKeyFile()
+			if err != nil {
+				return errors.New("could not read key file")
+			}
+			// prioritize file keys over flag keys
+			if len(fileKeys) == 0 {
+				log.Warnln("Remote signer key file no longer has keys, defaulting to flag provided keys")
+				fileKeys = slices.Collect(maps.Values(km.flagLoadedKeysMap))
+			}
+			currentKeys, err := km.FetchValidatingPublicKeys(ctx)
 			if err != nil {
-				return errors.Wrap(err, "could not stat remote signer public key file")
+				return errors.Wrap(err, "could not fetch current keys")
 			}
-			if currentFileInfo.Size() != initialFileSize {
+			if !slices.Equal(currentKeys, fileKeys) {
 				log.Info("Remote signer key file updated")
-				fileKeys, _, err := km.readKeyFile()
-				if err != nil {
-					return errors.New("could not read key file")
-				}
-				// prioritize file keys over flag keys
-				if len(fileKeys) == 0 {
-					log.Warnln("Remote signer key file no longer has keys, defaulting to flag provided keys")
-					fileKeys = slices.Collect(maps.Values(km.flagLoadedKeysMap))
-				}
-				currentKeys, err := km.FetchValidatingPublicKeys(ctx)
-				if err != nil {
-					return errors.Wrap(err, "could not fetch current keys")
-				}
-				if !slices.Equal(currentKeys, fileKeys) {
-					km.updatePublicKeys(fileKeys)
-				}
-				initialFileSize = currentFileInfo.Size()
+				km.updatePublicKeys(fileKeys)
 			}
 		case err, ok := <-watcher.Errors:
 			if !ok { // Channel was closed (i.e. Watcher.Close() was called).

validator/keymanager/remote-web3signer/keymanager_test.go

@@ -253,6 +253,53 @@ func TestNewKeyManager_ChangingFileCreated(t *testing.T) {
 	}
 }
 
+func TestNewKeyManager_ReloadsSameSizeKeyFileUpdate(t *testing.T) {
+	ctx, cancel := context.WithCancel(t.Context())
+	defer cancel()
+
+	const keyA = "0x800077e04f8d7496099b3d30ac5430aea64873a45e5bcfe004d2095babcbf55e21138ff0d5691abc29da190aa32755c6"
+	const keyB = "0x8000a9a6d3f5e22d783eefaadbcf0298146adb5d95b04db910a0d4e16976b30229d0b1e7b9cda6c7e0bfa11f72efe055"
+	keyFilePath := filepath.Join(t.TempDir(), "keyfile.txt")
+	require.NoError(t, file.WriteFile(keyFilePath, []byte(keyA+"\n")))
+
+	root, err := hexutil.Decode("0x270d43e74ce340de4bca2b1936beca0f4f5408d9e78aec4850920baf659d5b69")
+	require.NoError(t, err)
+	km, err := NewKeymanager(ctx, &SetupConfig{
+		BaseEndpoint:          "http://example.com",
+		GenesisValidatorsRoot: root,
+		KeyFilePath:           keyFilePath,
+	})
+	require.NoError(t, err)
+
+	before, err := os.Stat(keyFilePath)
+	require.NoError(t, err)
+	pubKeysChan := make(chan [][fieldparams.BLSPubkeyLength]byte, 1)
+	sub := km.SubscribeAccountChanges(pubKeysChan)
+	defer sub.Unsubscribe()
+
+	// Do not truncate the file: overwrite it in place so its size never changes.
+	f, err := os.OpenFile(keyFilePath, os.O_WRONLY, 0600)
+	require.NoError(t, err)
+	_, err = f.WriteString(keyB + "\n")
+	require.NoError(t, err)
+	require.NoError(t, f.Sync())
+	require.NoError(t, f.Close())
+
+	after, err := os.Stat(keyFilePath)
+	require.NoError(t, err)
+	require.Equal(t, before.Size(), after.Size())
+
+	timer := time.NewTimer(5 * time.Second)
+	defer timer.Stop()
+	select {
+	case updatedKeys := <-pubKeysChan:
+		require.Equal(t, 1, len(updatedKeys))
+		require.Equal(t, keyB, hexutil.Encode(updatedKeys[0][:]))
+	case <-timer.C:
+		t.Fatal("timed out waiting for the same-size key file update")
+	}
+}
+
 func TestNewKeyManager_FileAndFlagsWithDifferentKeys(t *testing.T) {
 	ctx, cancel := context.WithCancel(t.Context())
 	defer cancel()