private/protocol/xml/xmlutil: Fix SDK marshaling of empty types (aws#…

…2081)

Fixes the SDK's marshaling of types without members. This corrects the
issue where the SDK would not marshal an XML tag for a type, if that
type did not have any exported members.

Fix aws#2015

CHANGELOG_PENDING.md

@@ -7,3 +7,6 @@
   * Adds workaround to correct the endpoint for Application Autoscaling running in AWS China. This will allow your application to make API calls to Application Autoscaling service in AWS China.
   * Fixes [#2079](https://github.com/aws/aws-sdk-go/issues/2079)
   * Fixes [#1957](https://github.com/aws/aws-sdk-go/issues/1957)
+* `private/protocol/xml/xmlutil`: Fix SDK marshaling of empty types ([#2081](https://github.com/aws/aws-sdk-go/pull/2081))
+  * Fixes the SDK's marshaling of types without members. This corrects the issue where the SDK would not marshal an XML tag for a type, if that type did not have any exported members.
+  * Fixes [#2015](https://github.com/aws/aws-sdk-go/issues/2015)

private/protocol/xml/xmlutil/build.go

@@ -94,8 +94,6 @@ func (b *xmlBuilder) buildStruct(value reflect.Value, current *XMLNode, tag refl
 		return nil
 	}
 
-	fieldAdded := false
-
 	// unwrap payloads
 	if payload := tag.Get("payload"); payload != "" {
 		field, _ := value.Type().FieldByName(payload)
@@ -123,6 +121,8 @@ func (b *xmlBuilder) buildStruct(value reflect.Value, current *XMLNode, tag refl
 		child.Attr = append(child.Attr, ns)
 	}
 
+	var payloadFields, nonPayloadFields int
+
 	t := value.Type()
 	for i := 0; i < value.NumField(); i++ {
 		member := elemOf(value.Field(i))
@@ -137,8 +137,10 @@ func (b *xmlBuilder) buildStruct(value reflect.Value, current *XMLNode, tag refl
 
 		mTag := field.Tag
 		if mTag.Get("location") != "" { // skip non-body members
+			nonPayloadFields++
 			continue
 		}
+		payloadFields++
 
 		if protocol.CanSetIdempotencyToken(value.Field(i), field) {
 			token := protocol.GetIdempotencyToken()
@@ -153,11 +155,11 @@ func (b *xmlBuilder) buildStruct(value reflect.Value, current *XMLNode, tag refl
 		if err := b.buildValue(member, child, mTag); err != nil {
 			return err
 		}
-
-		fieldAdded = true
 	}
 
-	if fieldAdded { // only append this child if we have one ore more valid members
+	// Only case where the child shape is not added is if the shape only contains
+	// non-payload fields, e.g headers/query.
+	if !(payloadFields == 0 && nonPayloadFields > 0) {
 		current.AddChild(child)
 	}
 

private/protocol/xml/xmlutil/build_test.go

@@ -32,13 +32,44 @@ type explicitPayload struct {
 	Second *nestedType `type:"structure" locationName:"Second"`
 }
 
+type useEmptyNested struct {
+	_ struct{} `type:"structure" locationName:"useEmptyNested"`
+
+	StrVal *string    `type:"string"`
+	Empty  *emptyType `type:"structure"`
+}
+
+type useIgnoreNested struct {
+	_      struct{}      `type:"structure" locationName:"useIgnoreNested"`
+	StrVal *string       `type:"string"`
+	Ignore *ignoreNested `type:"structure"`
+}
+
+type skipNonPayload struct {
+	_     struct{} `type:"structure" locationName:"skipNonPayload"`
+	Field *string  `type:"string" location:"header"`
+}
+type namedEmptyPayload struct {
+	_ struct{} `type:"structure" locationName:"namedEmptyPayload"`
+}
+
 type nestedType struct {
 	_ struct{} `type:"structure"`
 
 	IntVal *int64  `type:"integer"`
 	StrVal *string `type:"string"`
 }
 
+type emptyType struct {
+	_ struct{} `type:"structure"`
+}
+
+type ignoreNested struct {
+	_ struct{} `type:"structure"`
+
+	IgnoreMe *string `type:"string" ignore:"true"`
+}
+
 func TestBuildXML(t *testing.T) {
 	cases := map[string]struct {
 		Input  interface{}
@@ -81,7 +112,7 @@ func TestBuildXML(t *testing.T) {
 			},
 			Expect: `<namedPayload><Second><IntVal>1111</IntVal><StrVal>second string</StrVal></Second><StrVal>string value</StrVal><Third><IntVal>2222</IntVal><StrVal>third string</StrVal></Third></namedPayload>`,
 		},
-		"empty nested type": {
+		"empty with fields nested type": {
 			Input: &namedImplicitPayload{
 				StrVal: aws.String("string value"),
 				Second: &nestedType{},
@@ -92,6 +123,36 @@ func TestBuildXML(t *testing.T) {
 			},
 			Expect: `<namedPayload><Second></Second><StrVal>string value</StrVal><Third><IntVal>2222</IntVal><StrVal>third string</StrVal></Third></namedPayload>`,
 		},
+		"empty no fields nested type": {
+			Input: &useEmptyNested{
+				StrVal: aws.String("string value"),
+				Empty:  &emptyType{},
+			},
+			Expect: `<useEmptyNested><Empty></Empty><StrVal>string value</StrVal></useEmptyNested>`,
+		},
+		"ignored nested field": {
+			Input: &useIgnoreNested{
+				StrVal: aws.String("string value"),
+				Ignore: &ignoreNested{
+					IgnoreMe: aws.String("abc123"),
+				},
+			},
+			Expect: `<useIgnoreNested><Ignore></Ignore><StrVal>string value</StrVal></useIgnoreNested>`,
+		},
+		"skip non payload root": {
+			Input: &skipNonPayload{
+				Field: aws.String("value"),
+			},
+			Expect: "",
+		},
+		"skip empty root": {
+			Input:  &emptyType{},
+			Expect: "",
+		},
+		"named empty payload": {
+			Input:  &namedEmptyPayload{},
+			Expect: "<namedEmptyPayload></namedEmptyPayload>",
+		},
 	}
 
 	for name, c := range cases {