Consider links when marshaling

document.go

@@ -159,12 +159,22 @@ func MarshalDocument(doc *Document, url *URL) ([]byte, error) {
 		plMap["meta"] = doc.Meta
 	}
 
+	links := doc.Links
+
 	if url != nil {
-		plMap["links"] = map[string]string{
-			"self": doc.PrePath + url.String(),
+		if links == nil {
+			links = map[string]Link{}
+		}
+
+		links["self"] = Link{
+			HRef: doc.PrePath + url.String(),
 		}
 	}
 
+	if links != nil {
+		plMap["links"] = links
+	}
+
 	plMap["jsonapi"] = map[string]string{"version": "1.0"}
 
 	return json.Marshal(plMap)

document_test.go

@@ -256,6 +256,21 @@ func TestMarshalDocument(t *testing.T) {
 					return []Error{err1, err2}
 				}(),
 			},
+		}, {
+			name: "links",
+			doc: &Document{
+				Links: map[string]Link{
+					"self":      {HRef: "http://example.com"},
+					"some_link": {HRef: "http://example.org"},
+					"other_link": {
+						HRef: "http://example.com/other/path",
+						Meta: map[string]interface{}{
+							"field1": "value1",
+							"field2": 123,
+						},
+					},
+				},
+			},
 		},
 	}
 

testdata/goldenfiles/marshaling/links.json

@@ -0,0 +1,17 @@
+{
+	"data": null,
+	"jsonapi": {
+		"version": "1.0"
+	},
+	"links": {
+		"other_link": {
+			"href": "http://example.com/other/path",
+			"meta": {
+				"field1": "value1",
+				"field2": 123
+			}
+		},
+		"self": "/fake/path?fields%5Bmocktype%",
+		"some_link": "http://example.org"
+	}
+}