Util: Reinstate item.Body after it is consumed in BulkIndexer

To allow accessing the item body in success/error callbacks,
reinstate it when the callbacks are defined.

Closes #161

(cherry picked from commit 55d65cdfc77a15b545e12339d613f9a7270fef2f)

esutil/bulk_indexer.go

@@ -10,6 +10,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"net/http"
 	"runtime"
 	"strconv"
@@ -354,7 +355,7 @@ func (w *worker) run() {
 				continue
 			}
 
-			if err := w.writeBody(item); err != nil {
+			if err := w.writeBody(&item); err != nil {
 				if item.OnFailure != nil {
 					item.OnFailure(ctx, item, BulkIndexerResponseItem{}, err)
 				}
@@ -410,15 +411,32 @@ func (w *worker) writeMeta(item BulkIndexerItem) error {
 
 // writeBody writes the item body to the buffer; it must be called under a lock.
 //
-func (w *worker) writeBody(item BulkIndexerItem) error {
+func (w *worker) writeBody(item *BulkIndexerItem) error {
 	if item.Body != nil {
+
+		var getBody func() io.Reader
+
+		if item.OnSuccess != nil || item.OnFailure != nil {
+			var buf bytes.Buffer
+			buf.ReadFrom(item.Body)
+			getBody = func() io.Reader {
+				r := buf
+				return ioutil.NopCloser(&r)
+			}
+			item.Body = getBody()
+		}
+
 		if _, err := w.buf.ReadFrom(item.Body); err != nil {
 			if w.bi.config.OnError != nil {
 				w.bi.config.OnError(context.Background(), err)
 			}
 			return err
 		}
 		w.buf.WriteRune('\n')
+
+		if getBody != nil && (item.OnSuccess != nil || item.OnFailure != nil) {
+			item.Body = getBody()
+		}
 	}
 	return nil
 }

esutil/bulk_indexer_internal_test.go

@@ -232,9 +232,11 @@ func TestBulkIndexer(t *testing.T) {
 
 	t.Run("Item Callbacks", func(t *testing.T) {
 		var (
-			countSuccessful uint64
-			countFailed     uint64
-			failedIDs       []string
+			countSuccessful      uint64
+			countFailed          uint64
+			failedIDs            []string
+			successfulItemBodies []string
+			failedItemBodies     []string
 
 			numItems       = 4
 			numFailed      = 2
@@ -256,10 +258,22 @@ func TestBulkIndexer(t *testing.T) {
 
 		successFunc := func(ctx context.Context, item BulkIndexerItem, res BulkIndexerResponseItem) {
 			atomic.AddUint64(&countSuccessful, 1)
+
+			buf, err := ioutil.ReadAll(item.Body)
+			if err != nil {
+				t.Fatalf("Unexpected error: %s", err)
+			}
+			successfulItemBodies = append(successfulItemBodies, string(buf))
 		}
 		failureFunc := func(ctx context.Context, item BulkIndexerItem, res BulkIndexerResponseItem, err error) {
 			atomic.AddUint64(&countFailed, 1)
 			failedIDs = append(failedIDs, item.DocumentID)
+
+			buf, err := ioutil.ReadAll(item.Body)
+			if err != nil {
+				t.Fatalf("Unexpected error: %s", err)
+			}
+			failedItemBodies = append(failedItemBodies, string(buf))
 		}
 
 		if err := bi.Add(context.Background(), BulkIndexerItem{
@@ -285,6 +299,7 @@ func TestBulkIndexer(t *testing.T) {
 		if err := bi.Add(context.Background(), BulkIndexerItem{
 			Action:     "delete",
 			DocumentID: "2",
+			Body:       strings.NewReader(`{"title":"baz"}`),
 			OnSuccess:  successFunc,
 			OnFailure:  failureFunc,
 		}); err != nil {
@@ -343,6 +358,14 @@ func TestBulkIndexer(t *testing.T) {
 		if !reflect.DeepEqual(failedIDs, []string{"1", "2"}) {
 			t.Errorf("Unexpected failedIDs: %#v", failedIDs)
 		}
+
+		if !reflect.DeepEqual(successfulItemBodies, []string{`{"title":"foo"}`, `{"doc":{"title":"qux"}}`}) {
+			t.Errorf("Unexpected successfulItemBodies: %#v", successfulItemBodies)
+		}
+
+		if !reflect.DeepEqual(failedItemBodies, []string{`{"title":"bar"}`, `{"title":"baz"}`}) {
+			t.Errorf("Unexpected failedItemBodies: %#v", failedItemBodies)
+		}
 	})
 
 	t.Run("OnFlush callbacks", func(t *testing.T) {