Report errors on writer close.

writer.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"net"
 	"sync"
@@ -576,6 +577,10 @@ func (w *Writer) Close() error {
 		w.transport.CloseIdleConnections()
 	}
 
+	errorsCount := w.stats().errors.snapshot()
+	if errorsCount > 0 {
+		return fmt.Errorf("failed to close gracefully, %d errors occurred", errorsCount)
+	}
 	return nil
 }
 

writer_test.go

@@ -106,6 +106,11 @@ func TestWriter(t *testing.T) {
 			function: testWriterClose,
 		},
 
+		{
+			scenario: "closing a writer with errors should return error",
+			function: testWriterCloseWithErrors,
+		},
+
 		{
 			scenario: "writing 1 message through a writer using round-robin balancing produces 1 message to the first partition",
 			function: testWriterRoundRobin1,
@@ -223,6 +228,15 @@ func testWriterClose(t *testing.T) {
 	}
 }
 
+func testWriterCloseWithErrors(t *testing.T) {
+	w := newTestWriter(WriterConfig{})
+	w.stats().errors.observe(1)
+
+	if err := w.Close(); err == nil {
+		t.Error("expected error, but got nil")
+	}
+}
+
 func testWriterRequiredAcksNone(t *testing.T) {
 	topic := makeTopic()
 	createTopic(t, topic, 1)