Respect nil slices, maps in bson encoder

bson/bson_test.go

@@ -1933,3 +1933,59 @@ func (s *S) BenchmarkNewObjectId(c *C) {
 		bson.NewObjectId()
 	}
 }
+
+func (s *S) TestMarshalRespectNil(c *C) {
+	type T struct {
+		Slice    []int
+		SlicePtr *[]int
+		Ptr      *int
+		Map      map[string]interface{}
+		MapPtr   *map[string]interface{}
+	}
+
+	bson.SetRespectNilValues(true)
+	defer bson.SetRespectNilValues(false)
+
+	testStruct1 := T{}
+
+	c.Assert(testStruct1.Slice, IsNil)
+	c.Assert(testStruct1.SlicePtr, IsNil)
+	c.Assert(testStruct1.Map, IsNil)
+	c.Assert(testStruct1.MapPtr, IsNil)
+	c.Assert(testStruct1.Ptr, IsNil)
+
+	b, _ := bson.Marshal(testStruct1)
+
+	testStruct2 := T{}
+
+	bson.Unmarshal(b, &testStruct2)
+
+	c.Assert(testStruct2.Slice, IsNil)
+	c.Assert(testStruct2.SlicePtr, IsNil)
+	c.Assert(testStruct2.Map, IsNil)
+	c.Assert(testStruct2.MapPtr, IsNil)
+	c.Assert(testStruct2.Ptr, IsNil)
+
+	testStruct1 = T{
+		Slice:    []int{},
+		SlicePtr: &[]int{},
+		Map:      map[string]interface{}{},
+		MapPtr:   &map[string]interface{}{},
+	}
+
+	c.Assert(testStruct1.Slice, NotNil)
+	c.Assert(testStruct1.SlicePtr, NotNil)
+	c.Assert(testStruct1.Map, NotNil)
+	c.Assert(testStruct1.MapPtr, NotNil)
+
+	b, _ = bson.Marshal(testStruct1)
+
+	testStruct2 = T{}
+
+	bson.Unmarshal(b, &testStruct2)
+
+	c.Assert(testStruct2.Slice, NotNil)
+	c.Assert(testStruct2.SlicePtr, NotNil)
+	c.Assert(testStruct2.Map, NotNil)
+	c.Assert(testStruct2.MapPtr, NotNil)
+}

bson/compatibility.go

@@ -1,7 +1,8 @@
 package bson
 
-// Current state of the JSON tag fallback option. 
+// Current state of the JSON tag fallback option.
 var useJSONTagFallback = false
+var useRespectNilValues = false
 
 // SetJSONTagFallback enables or disables the JSON-tag fallback for structure tagging. When this is enabled, structures
 // without BSON tags on a field will fall-back to using the JSON tag (if present).
@@ -14,3 +15,15 @@ func SetJSONTagFallback(state bool) {
 func JSONTagFallbackState() bool {
 	return useJSONTagFallback
 }
+
+// SetRespectNilValues enables or disables serializing nil slices or maps to `null` values.
+// In other words it enables `encoding/json` compatible behaviour.
+func SetRespectNilValues(state bool) {
+	useRespectNilValues = state
+}
+
+// RespectNilValuesState returns the current status of the JSON nil slices and maps fallback compatibility option.
+// See SetRespectNilValues for more information.
+func RespectNilValuesState() bool {
+	return useRespectNilValues
+}

bson/encode.go

@@ -245,6 +245,12 @@ func (e *encoder) addStruct(v reflect.Value) {
 		if info.OmitEmpty && isZero(value) {
 			continue
 		}
+		if useRespectNilValues &&
+			(value.Kind() == reflect.Slice || value.Kind() == reflect.Map) &&
+			value.IsNil() {
+			e.addElem(info.Key, reflect.ValueOf(nil), info.MinSize)
+			continue
+		}
 		e.addElem(info.Key, value, info.MinSize)
 	}
 }

internal/sasl/sasl.go

@@ -127,6 +127,7 @@ func (ss *saslSession) Step(serverData []byte) (clientData []byte, done bool, er
 	if rc == C.SASL_CONTINUE {
 		return clientData, false, nil
 	}
+
 	return nil, false, saslError(rc, ss.conn, "cannot establish SASL session")
 }
 

internal/scram/scram.go

@@ -91,7 +91,7 @@ func NewClient(newHash func() hash.Hash, user, pass string) *Client {
 // Out returns the data to be sent to the server in the current step.
 func (c *Client) Out() []byte {
 	if c.out.Len() == 0 {
-		return nil
+		return []byte{}
 	}
 	return c.out.Bytes()
 }