Disallow empty update documents.

GODRIVER-743

Change-Id: I57ef34e7ce9368128c560fef056eff1ccede9e3b

Author: Divjot Arora

mongo/collection.go

@@ -1189,8 +1189,11 @@ func (coll *Collection) FindOneAndUpdate(ctx context.Context, filter interface{}
 		return &SingleResult{err: err}
 	}
 
-	if len(u) > 0 && !strings.HasPrefix(u[0].Key, "$") {
-		return &SingleResult{err: errors.New("update document must contain key beginning with '$")}
+	err = ensureDollarKey(u)
+	if err != nil {
+		return &SingleResult{
+			err: err,
+		}
 	}
 
 	sess := sessionFromContext(ctx)

mongo/collection_internal_test.go

@@ -817,6 +817,12 @@ func TestCollection_DeleteOne_WriteConcernError(t *testing.T) {
 	}
 }
 
+func TestCollection_UpdateOne_EmptyUpdate(t *testing.T) {
+	coll := createTestCollection(t, nil, nil)
+	_, err := coll.UpdateOne(ctx, bsonx.Doc{}, bsonx.Doc{})
+	require.NotNil(t, err)
+}
+
 func TestCollection_UpdateOne_found(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping integration test in short mode")
@@ -933,6 +939,12 @@ func TestCollection_UpdateOne_WriteConcernError(t *testing.T) {
 	}
 }
 
+func TestCollection_UpdateMany_EmptyUpdate(t *testing.T) {
+	coll := createTestCollection(t, nil, nil)
+	_, err := coll.UpdateMany(ctx, bsonx.Doc{}, bsonx.Doc{})
+	require.NotNil(t, err)
+}
+
 func TestCollection_UpdateMany_found(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping integration test in short mode")
@@ -1790,6 +1802,12 @@ func TestCollection_FindOneAndUpdate_found(t *testing.T) {
 	require.Equal(t, int(elem.Int32()), 3)
 }
 
+func TestCollection_FindOneAndUpdate_EmptyUpdate(t *testing.T) {
+	coll := createTestCollection(t, nil, nil)
+	res := coll.FindOneAndUpdate(context.Background(), bsonx.Doc{}, bsonx.Doc{})
+	require.NotNil(t, res.Err())
+}
+
 func TestCollection_FindOneAndUpdate_found_ignoreResult(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping integration test in short mode")

mongo/mongo.go

@@ -170,7 +170,10 @@ func ensureID(d bsonx.Doc) (bsonx.Doc, interface{}) {
 }
 
 func ensureDollarKey(doc bsonx.Doc) error {
-	if len(doc) > 0 && !strings.HasPrefix(doc[0].Key, "$") {
+	if len(doc) == 0 {
+		return errors.New("update document must have at least one element")
+	}
+	if !strings.HasPrefix(doc[0].Key, "$") {
 		return errors.New("update document must contain key beginning with '$'")
 	}
 	return nil