Merge pull request #19 from picmonkey/handle-empty-list

Serialize data as an empty array in the response when it is a non-nil empty array

document.go

@@ -12,7 +12,7 @@ Refer to the JSON API Specification for a full descriptor
 of each attribute: http://jsonapi.org/format/#document-structure
 */
 type Document struct {
-	Data     List        `json:"data,omitempty"`
+	Data     List        `json:"data"`
 	Errors   ErrorList   `json:"errors,omitempty"`
 	Links    *Link       `json:"links,omitempty"`
 	Included []*Object   `json:"included,omitempty"`
@@ -89,10 +89,10 @@ func (d *Document) Validate(r *http.Request, response bool) *Error {
 		return nil
 	}
 
-	if !d.HasErrors() && !d.HasData() {
+	if !d.HasErrors() && d.Data == nil {
 		return ISE("Both `errors` and `data` cannot be blank for a JSON response")
 	}
-	if d.HasErrors() && d.HasData() {
+	if d.HasErrors() && d.Data != nil {
 		return ISE("Both `errors` and `data` cannot be set for a JSON response")
 	}
 	if !d.HasData() && d.Included != nil {

list.go

@@ -53,15 +53,23 @@ func (list *List) UnmarshalJSON(rawData []byte) error {
 
 /*
 MarshalJSON returns a top level object for the "data" attribute if a single object. In
-all other cases returns a JSON encoded list for "data".
+all other cases returns a JSON encoded list for "data". We use a pointer receiver here
+so we are able to distinguish between nil (don't serialize) and empty (serialize as []).
 */
-func (list List) MarshalJSON() ([]byte, error) {
+func (list *List) MarshalJSON() ([]byte, error) {
 	// avoid stack overflow by using this subtype for marshaling
 	type MarshalList List
-	marshalList := MarshalList(list)
+
+	if list == nil {
+		return nil, nil
+	}
+
+	marshalList := MarshalList(*list)
 	count := len(marshalList)
 
 	switch {
+	case count == 0:
+		return []byte("[]"), nil
 	case count == 1:
 		return json.Marshal(marshalList[0])
 	default:

list_test.go

@@ -51,6 +51,41 @@ func TestList(t *testing.T) {
 			})
 		})
 
+		Convey("->Send(empty list)", func() {
+
+			Convey("should send a properly formatted empty List response", func() {
+
+				writer := httptest.NewRecorder()
+				err := Send(writer, req, List([]*Object{}))
+				So(err, ShouldBeNil)
+				So(writer.Code, ShouldEqual, http.StatusOK)
+
+				contentLength, convErr := strconv.Atoi(writer.HeaderMap.Get("Content-Length"))
+				So(convErr, ShouldBeNil)
+				So(contentLength, ShouldBeGreaterThan, 0)
+				So(writer.HeaderMap.Get("Content-Type"), ShouldEqual, ContentType)
+
+				req, reqErr := testRequest(writer.Body.Bytes())
+				So(reqErr, ShouldBeNil)
+
+				responseList, parseErr := ParseList(req)
+				So(parseErr, ShouldBeNil)
+				So(len(responseList), ShouldEqual, 0)
+			})
+		})
+
+		Convey("->Send(nil list)", func() {
+
+			Convey("should fail with a 500 ISE", func() {
+
+				writer := httptest.NewRecorder()
+				var list []*Object
+				err := Send(writer, req, List(list))
+				So(err, ShouldNotBeNil)
+				So(writer.Code, ShouldEqual, http.StatusInternalServerError)
+			})
+		})
+
 		Convey("->UnmarshalJSON()", func() {
 
 			Convey("should handle a data object", func() {