Merge pull request #4898 from aws/fix-restxml-emptyheaderlist

fix header serialization of empty enum lists in restxml

Author: lucix-aws

CHANGELOG_PENDING.md

@@ -3,3 +3,5 @@
 ### SDK Enhancements
 
 ### SDK Bugs
+* `private/protocol`: Fix header serialization of empty enum lists in restxml.
+  * Header was serialized as the empty string if list was nil/empty.

private/protocol/rest/build.go

@@ -287,6 +287,10 @@ func convertType(v reflect.Value, tag reflect.StructTag) (str string, err error)
 		if tag.Get("location") != "header" || tag.Get("enum") == "" {
 			return "", fmt.Errorf("%T is only supported with location header and enum shapes", value)
 		}
+		if len(value) == 0 {
+			return "", errValueNotSet
+		}
+
 		buff := &bytes.Buffer{}
 		for i, sv := range value {
 			if sv == nil || len(*sv) == 0 {

private/protocol/rest/build_test.go

@@ -147,6 +147,28 @@ func TestListOfEnums(t *testing.T) {
 				"X-Amz-Test-Header": {`"f,o,o","\"bar\""`},
 			},
 		},
+		{
+			Input: func() interface{} {
+				type v struct {
+					List []*string `type:"list" location:"header" locationName:"x-amz-test-header" enum:"FooBar"`
+				}
+				return &v{
+					List: nil,
+				}
+			}(),
+			Expected: http.Header{},
+		},
+		{
+			Input: func() interface{} {
+				type v struct {
+					List []*string `type:"list" location:"header" locationName:"x-amz-test-header" enum:"FooBar"`
+				}
+				return &v{
+					List: []*string{},
+				}
+			}(),
+			Expected: http.Header{},
+		},
 	}
 
 	for i, tt := range cases {