fix: gracefully handle empty request body (#174)

input/elasticapm/processor.go

@@ -39,6 +39,8 @@ import (
 var (
 	errUnrecognizedObject = errors.New("did not recognize object type")
 
+	errEmptyBody = errors.New("empty body")
+
 	// ErrQueueFull may be returned by HandleStream when the internal
 	// queue is full.
 	ErrQueueFull = errors.New("queue is full")
@@ -114,6 +116,9 @@ func (p *Processor) readMetadata(reader *streamReader, out *modelpb.APMEvent) er
 	body, err := reader.ReadAhead()
 	if err != nil {
 		if err == io.EOF {
+			if len(reader.LatestLine()) == 0 {
+				return errEmptyBody
+			}
 			return &InvalidInputError{
 				Message:  "EOF while reading metadata",
 				Document: string(reader.LatestLine()),
@@ -274,6 +279,9 @@ func (p *Processor) HandleStream(
 
 	// The first item is the metadata object.
 	if err := p.readMetadata(sr, baseEvent); err != nil {
+		if err == errEmptyBody {
+			return nil
+		}
 		// no point in continuing if we couldn't read the metadata
 		if _, ok := err.(*InvalidInputError); ok {
 			return err

input/elasticapm/processor_test.go

@@ -169,6 +169,8 @@ func TestHandleStreamErrors(t *testing.T) {
 				Document: invalidEventType,
 			},
 		},
+	}, {
+		name: "EmptyEvent",
 	}, {
 		name:     "TooLargeEvent",
 		payload:  validMetadata + "\n" + tooLargeEvent + "\n",