File Exporter: fixes for simple configuration

exporters/filewriter/file_exporter.go

@@ -22,7 +22,7 @@ const exporterName = "filewriter"
 
 type fileExporter struct {
 	round             uint64
-	blockMetadataFile *os.File
+	blockMetadataFile string
 	blockMetadata     BlockMetaData
 	cfg               ExporterConfig
 	logger            *logrus.Logger
@@ -68,18 +68,26 @@ func (exp *fileExporter) Init(cfg plugins.PluginConfig, logger *logrus.Logger) e
 	}
 	// initialize block metadata
 	file := path.Join(exp.cfg.BlocksDir, "metadata.json")
-	if _, err = os.Stat(file); errors.Is(err, os.ErrNotExist) {
-		exp.blockMetadataFile, err = os.Create(file)
+	exp.blockMetadataFile = file
+	var stat os.FileInfo
+	if stat, err = os.Stat(file); errors.Is(err, os.ErrNotExist) || (stat != nil && stat.Size() == 0) {
+		if stat != nil && stat.Size() == 0 {
+			// somehow it did not finish initializing
+			err = os.Remove(file)
+			if err != nil {
+				return fmt.Errorf("Init(): error creating file: %w", err)
+			}
+		}
+		err = exp.encodeMetadataToFile()
 		if err != nil {
-			return fmt.Errorf("error creating file: %w", err)
+			return fmt.Errorf("Init(): error creating file: %w", err)
 		}
 		exp.blockMetadata = BlockMetaData{
 			GenesisHash: "",
 			Network:     "",
 			NextRound:   exp.round,
 		}
 	} else {
-		exp.blockMetadataFile, err = os.OpenFile(file, os.O_WRONLY, 0775)
 		if err != nil {
 			return fmt.Errorf("error opening file: %w", err)
 		}
@@ -102,37 +110,56 @@ func (exp *fileExporter) Config() plugins.PluginConfig {
 	return plugins.PluginConfig(ret)
 }
 
-func (exp *fileExporter) Close() error {
-	defer exp.blockMetadataFile.Close()
-	exp.logger.Infof("latest round on file: %d", exp.round)
-	err := json.NewEncoder(exp.blockMetadataFile).Encode(exp.blockMetadata)
+func (exp *fileExporter) encodeMetadataToFile() error {
+	tempFilename := fmt.Sprintf("%s.temp", exp.blockMetadataFile)
+	file, err := os.Create(tempFilename)
+	if err != nil {
+		return fmt.Errorf("encodeMetadataToFile(): failed to create temp metadata file: %w", err)
+	}
+	defer file.Close()
+	err = json.NewEncoder(file).Encode(exp.blockMetadata)
 	if err != nil {
-		return fmt.Errorf("Close() encoding err %w", err)
+		return fmt.Errorf("encodeMetadataToFile(): failed to write temp metadata: %w", err)
 	}
+
+	err = os.Rename(tempFilename, exp.blockMetadataFile)
+	if err != nil {
+		return fmt.Errorf("encodeMetadataToFile(): failed to replace metadata file: %w", err)
+	}
+
+	return nil
+}
+
+func (exp *fileExporter) Close() error {
+	exp.logger.Infof("latest round on file: %d", exp.round)
 	return nil
 }
 
 func (exp *fileExporter) Receive(exportData data.BlockData) error {
-	if exp.blockMetadataFile == nil {
+	if exp.blockMetadataFile == "" {
 		return fmt.Errorf("exporter not initialized")
 	}
 	if exportData.Round() != exp.round {
-		return fmt.Errorf("wrong block. received round %d, expected round %d", exportData.Round(), exp.round)
+		return fmt.Errorf("Receive(): wrong block: received round %d, expected round %d", exportData.Round(), exp.round)
 	}
 	//write block to file
 	blockFile := path.Join(exp.cfg.BlocksDir, fmt.Sprintf("block_%d.json", exportData.Round()))
 	file, err := os.OpenFile(blockFile, os.O_WRONLY|os.O_CREATE, 0755)
 	if err != nil {
-		return fmt.Errorf("error opening file %s, %w", blockFile, err)
+		return fmt.Errorf("Receive(): error opening file %s: %w", blockFile, err)
 	}
 	defer file.Close()
 	err = json.NewEncoder(file).Encode(exportData)
 	if err != nil {
-		return fmt.Errorf("error encoding exportData in Receive(), %w", err)
+		return fmt.Errorf("Receive(): error encoding exportData: %w", err)
 	}
 	exp.logger.Infof("Added block %d", exportData.Round())
 	exp.round++
 	exp.blockMetadata.NextRound = exp.round
+	err = exp.encodeMetadataToFile()
+	if err != nil {
+		return fmt.Errorf("Receive() metadata encoding err %w", err)
+	}
 	return nil
 }
 
@@ -142,9 +169,13 @@ func (exp *fileExporter) HandleGenesis(genesis bookkeeping.Genesis) error {
 	if exp.blockMetadata.GenesisHash == "" {
 		exp.blockMetadata.GenesisHash = gh
 		exp.blockMetadata.Network = string(genesis.Network)
+		err := exp.encodeMetadataToFile()
+		if err != nil {
+			return fmt.Errorf("HandleGenesis() metadata encoding err %w", err)
+		}
 	} else {
 		if exp.blockMetadata.GenesisHash != gh {
-			return fmt.Errorf("genesis hash in metadata does not match expected value. actual %s, expected %s ", gh, exp.blockMetadata.GenesisHash)
+			return fmt.Errorf("HandleGenesis() genesis hash in metadata does not match expected value: actual %s, expected %s", gh, exp.blockMetadata.GenesisHash)
 		}
 	}
 	return nil

exporters/filewriter/file_exporter_test.go

@@ -50,8 +50,17 @@ func TestExporterInit(t *testing.T) {
 	err = fileExp.Init(plugins.PluginConfig(config), logger)
 	assert.NoError(t, err)
 	fileExp.Close()
-
+	// re-initializes empty file
+	path := "/tmp/blocks/metadata.json"
+	assert.NoError(t, os.Remove(path))
+	f, err := os.Create(path)
+	f.Close()
+	assert.NoError(t, err)
+	err = fileExp.Init(plugins.PluginConfig(config), logger)
+	assert.NoError(t, err)
+	fileExp.Close()
 }
+
 func TestExporterHandleGenesis(t *testing.T) {
 	fileExp := fileCons.New()
 	fileExp.Init(plugins.PluginConfig(config), logger)