Ensure default write concern is not appended

GODRIVER-667

Change-Id: Ia289f0a894ca7ce97025bc33ba324b6f9e86efd7

Author: skriptble

mongo/read_write_concern_spec_test.go

@@ -144,6 +144,14 @@ func runConnectionStringTest(t *testing.T, testName string, testCase *connection
 			}
 
 			wcBSON, err := wc.MarshalBSONElement()
+			if err == writeconcern.ErrEmptyWriteConcern {
+				if len(testCase.WriteConcern) == 0 {
+					return
+				}
+				if _, exists := testCase.WriteConcern["journal"]; exists && len(testCase.WriteConcern) == 1 {
+					return
+				}
+			}
 			require.NoError(t, err)
 
 			wcDoc := wcBSON.Value.Document()
@@ -227,6 +235,14 @@ func runDocumentTest(t *testing.T, testName string, testCase *documentTest) {
 				return
 			}
 
+			if err == writeconcern.ErrEmptyWriteConcern {
+				if len(testCase.WriteConcernDocument) == 0 {
+					return
+				}
+				if _, exists := testCase.WriteConcernDocument["j"]; exists && len(testCase.WriteConcernDocument) == 1 {
+					return
+				}
+			}
 			require.NoError(t, err)
 
 			wcBytes, _ := wcDoc.Value.Document().MarshalBSON()

mongo/writeconcern/writeconcern.go

@@ -18,6 +18,9 @@ import (
 // ErrInconsistent indicates that an inconsistent write concern was specified.
 var ErrInconsistent = errors.New("a write concern cannot have both w=0 and j=true")
 
+// ErrEmptyWriteConcern indicates that a write concern has no fields set.
+var ErrEmptyWriteConcern = errors.New("a write concern must have at least one field set")
+
 // ErrNegativeW indicates that a negative integer `w` field was specified.
 var ErrNegativeW = errors.New("write concern `w` field cannot be a negative number")
 
@@ -118,6 +121,9 @@ func (wc *WriteConcern) MarshalBSONElement() (bsonx.Elem, error) {
 		elems = append(elems, bsonx.Elem{"wtimeout", bsonx.Int64(int64(wc.wTimeout / time.Millisecond))})
 	}
 
+	if len(elems) == 0 {
+		return bsonx.Elem{}, ErrEmptyWriteConcern
+	}
 	return bsonx.Elem{"writeConcern", bsonx.Document(elems)}, nil
 }
 

x/network/command/command.go

@@ -12,6 +12,7 @@ import (
 	"context"
 
 	"fmt"
+
 	"github.com/mongodb/mongo-go-driver/bson"
 	"github.com/mongodb/mongo-go-driver/bson/bsontype"
 	"github.com/mongodb/mongo-go-driver/bson/primitive"
@@ -299,6 +300,9 @@ func addWriteConcern(cmd bsonx.Doc, wc *writeconcern.WriteConcern) (bsonx.Doc, e
 
 	element, err := wc.MarshalBSONElement()
 	if err != nil {
+		if err == writeconcern.ErrEmptyWriteConcern {
+			return cmd, nil
+		}
 		return cmd, err
 	}
 

x/network/command/write_test.go

@@ -0,0 +1,41 @@
+package command
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/mongodb/mongo-go-driver/mongo/writeconcern"
+	"github.com/mongodb/mongo-go-driver/x/bsonx"
+	"github.com/mongodb/mongo-go-driver/x/bsonx/bsoncore"
+	"github.com/mongodb/mongo-go-driver/x/network/description"
+	"github.com/mongodb/mongo-go-driver/x/network/wiremessage"
+)
+
+func TestWrite(t *testing.T) {
+	t.Run("Encode", func(t *testing.T) {
+		t.Run("should not encode empty write concern", func(t *testing.T) {
+			cmd := bsonx.Doc{{"fakeCommand", bsonx.Int32(1)}}
+			want, err := append(cmd, bsonx.Elem{"$db", bsonx.String("foobar")}).MarshalBSON()
+			noerr(t, err)
+			w := Write{
+				DB:           "foobar",
+				Command:      cmd,
+				WriteConcern: writeconcern.New(),
+			}
+			wm, err := w.Encode(description.SelectedServer{
+				Server: description.Server{
+					WireVersion: &description.VersionRange{Min: 0, Max: wiremessage.OpmsgWireVersion},
+				},
+			})
+			noerr(t, err)
+			msg, ok := wm.(wiremessage.Msg)
+			if !ok {
+				t.Errorf("Expected an OP_MSG wire message, but got something else. got %v", wm)
+			}
+			got := msg.Sections[0].(wiremessage.SectionBody).Document
+			if !bytes.Equal(got, want) {
+				t.Errorf("Command documents do not match. got %v; want %v", bsoncore.Document(got), bsoncore.Document(want))
+			}
+		})
+	})
+}