add WriterOperator::WriteBatch and Operator::ProcessBatch methods

The File input's `emitBatch` function now calls `ProcessBatch` instead of `Process`.

The added `ProcessBatch` method will make each Stanza operator
capable of accepting a batch of entries.

pkg/stanza/operator/helper/emitter.go

@@ -94,7 +94,7 @@ func (e *LogEmitter) Stop() error {
 	return nil
 }
 
-// Process will emit an entry to the output channel
+// Process emits an entry to the consumerFunc
 func (e *LogEmitter) Process(ctx context.Context, ent *entry.Entry) error {
 	if oldBatch := e.appendEntry(ent); len(oldBatch) > 0 {
 		e.consumerFunc(ctx, oldBatch)
@@ -103,6 +103,15 @@ func (e *LogEmitter) Process(ctx context.Context, ent *entry.Entry) error {
 	return nil
 }
 
+// ProcessBatch emits the entries to the consumerFunc
+func (e *LogEmitter) ProcessBatch(ctx context.Context, entries []entry.Entry) error {
+	for _, entry := range entries {
+		e.Process(ctx, &entry)
+	}
+
+	return nil
+}
+
 // appendEntry appends the entry to the current batch. If maxBatchSize is reached, a new batch will be made, and the old batch
 // (which should be flushed) will be returned
 func (e *LogEmitter) appendEntry(ent *entry.Entry) []*entry.Entry {

pkg/stanza/operator/helper/input.go

@@ -90,3 +90,12 @@ func (i *InputOperator) Process(_ context.Context, _ *entry.Entry) error {
 		"Ensure that operator is not configured to receive logs from other operators",
 	)
 }
+
+// ProcessBatch will always return an error if called.
+func (i *InputOperator) ProcessBatch(_ context.Context, _ []entry.Entry) error {
+	i.Logger().Error("Operator received a batch of entries, but can not process")
+	return errors.NewError(
+		"Operator can not process logs.",
+		"Ensure that operator is not configured to receive logs from other operators",
+	)
+}

pkg/stanza/operator/helper/writer.go

@@ -61,6 +61,25 @@ func (w *WriterOperator) Write(ctx context.Context, e *entry.Entry) error {
 	return nil
 }
 
+// Write writes a batch of entries to the outputs of the operator.
+// A batch is a collection of entries that are sent in one go.
+func (w *WriterOperator) WriteBatch(ctx context.Context, entries []entry.Entry) error {
+	for i, op := range w.OutputOperators {
+		if i == len(w.OutputOperators)-1 {
+			return op.ProcessBatch(ctx, entries)
+		}
+		copyOfEntries := make([]entry.Entry, 0, len(entries))
+		for _, entry := range entries {
+			copyOfEntries = append(copyOfEntries, *entry.Copy())
+		}
+		err := op.ProcessBatch(ctx, copyOfEntries)
+		if err != nil {
+			w.Logger().Error("Failed to process entries", zap.Error(err))
+		}
+	}
+	return nil
+}
+
 // CanOutput always returns true for a writer operator.
 func (w *WriterOperator) CanOutput() bool {
 	return true

pkg/stanza/operator/input/file/input.go

@@ -39,33 +39,46 @@ func (i *Input) Stop() error {
 }
 
 func (i *Input) emitBatch(ctx context.Context, tokens []emit.Token) error {
+	entries, conversionError := i.convertTokens(tokens)
+	if conversionError != nil {
+		conversionError = fmt.Errorf("convert tokens: %w", conversionError)
+	}
+
+	consumeError := i.WriteBatch(ctx, entries)
+	if consumeError != nil {
+		consumeError = fmt.Errorf("consume entries: %w", consumeError)
+	}
+
+	return errors.Join(conversionError, consumeError)
+}
+
+func (i *Input) convertTokens(tokens []emit.Token) ([]entry.Entry, error) {
+	entries := make([]entry.Entry, 0, len(tokens))
 	var errs []error
 	for _, token := range tokens {
-		err := i.emit(ctx, token)
+		if len(token.Body) == 0 {
+			continue
+		}
+		entry, err := i.convertToken(token)
 		if err != nil {
 			errs = append(errs, err)
+			continue
 		}
+		entries = append(entries, *entry)
 	}
-	if len(errs) > 0 {
-		return errors.Join(errs...)
-	}
-	return nil
+	return entries, errors.Join(errs...)
 }
 
-func (i *Input) emit(ctx context.Context, token emit.Token) error {
-	if len(token.Body) == 0 {
-		return nil
-	}
-
+func (i *Input) convertToken(token emit.Token) (*entry.Entry, error) {
 	ent, err := i.NewEntry(i.toBody(token.Body))
 	if err != nil {
-		return fmt.Errorf("create entry: %w", err)
+		return nil, fmt.Errorf("create entry: %w", err)
 	}
 
 	for k, v := range token.Attributes {
 		if err := ent.Set(entry.NewAttributeField(k), v); err != nil {
 			i.Logger().Error("set attribute", zap.Error(err))
 		}
 	}
-	return i.Write(ctx, ent)
+	return ent, nil
 }

pkg/stanza/operator/operator.go

@@ -38,6 +38,8 @@ type Operator interface {
 	CanProcess() bool
 	// Process will process an entry from an operator.
 	Process(context.Context, *entry.Entry) error
+	// Process processes a batch of entries from an operator.
+	ProcessBatch(context.Context, []entry.Entry) error
 	// Logger returns the operator's logger
 	Logger() *zap.Logger
 }