Support links with null values (#313)

* Support links with null values

Author: ryanuber

jsonapi/data_structs.go

@@ -58,6 +58,12 @@ type Link struct {
 // UnmarshalJSON marshals a string value into the Href field or marshals an
 // object value into the whole struct.
 func (l *Link) UnmarshalJSON(payload []byte) error {
+	// Links may be null in certain cases, mainly noted in the JSONAPI spec
+	// with pagination links (http://jsonapi.org/format/#fetching-pagination).
+	if len(payload) == 4 && string(payload) == "null" {
+		return nil
+	}
+
 	if bytes.HasPrefix(payload, stringSuffix) {
 		return json.Unmarshal(payload, &l.Href)
 	}
@@ -84,6 +90,9 @@ func (l *Link) UnmarshalJSON(payload []byte) error {
 // MarshalJSON returns the JSON encoding of only the Href field if the Meta
 // field is empty, otherwise it marshals the whole struct.
 func (l Link) MarshalJSON() ([]byte, error) {
+	if l.Empty() {
+		return json.Marshal(nil)
+	}
 	if len(l.Meta) == 0 {
 		return json.Marshal(l.Href)
 	}
@@ -93,6 +102,11 @@ func (l Link) MarshalJSON() ([]byte, error) {
 	})
 }
 
+// Empty returns true if the link has no href and no metadata.
+func (l Link) Empty() bool {
+	return len(l.Meta) == 0 && l.Href == ""
+}
+
 // Links contains a map of custom Link objects as given by an element.
 type Links map[string]Link
 

jsonapi/data_structs_test.go

@@ -208,6 +208,14 @@ var _ = Describe("JSONAPI Struct tests", func() {
 			Expect(target).To(Equal(expected))
 		})
 
+		It("unmarshals from null", func() {
+			expected := Link{}
+			target := Link{}
+			err := json.Unmarshal([]byte(`null`), &target)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(target).To(Equal(expected))
+		})
+
 		It("unmarshals with an error when href is missing", func() {
 			err := json.Unmarshal([]byte(`{}`), &Link{})
 			Expect(err).To(HaveOccurred())
@@ -224,7 +232,7 @@ var _ = Describe("JSONAPI Struct tests", func() {
 		})
 
 		It("unmarshals with an error for wrong types", func() {
-			badPayloads := []string{`null`, `13`, `[]`}
+			badPayloads := []string{`13`, `[]`}
 			for _, payload := range badPayloads {
 				err := json.Unmarshal([]byte(payload), &Link{})
 				Expect(err).To(HaveOccurred())

jsonapi/fixtures_test.go

@@ -489,7 +489,8 @@ func (n CustomLinksPost) GetName() string {
 
 func (n CustomLinksPost) GetCustomLinks(base string) Links {
 	return Links{
-		"someLink": Link{Href: base + `/someLink`},
+		"nothingInHere": Link{},
+		"someLink":      Link{Href: base + `/someLink`},
 		"otherLink": Link{
 			Href: base + `/otherLink`,
 			Meta: Meta{

jsonapi/marshal_test.go

@@ -232,6 +232,7 @@ var _ = Describe("Marshalling", func() {
 					"id": "someID",
 					"attributes": {},
 					"links": {
+						"nothingInHere": null,
 						"someLink": "http://my.domain/v1/posts/someID/someLink",
 						"otherLink": {
 							"href": "http://my.domain/v1/posts/someID/otherLink",