Now rendering json on request instead of html

web/handlers.go

@@ -19,8 +19,8 @@ func MakeIndexHandler(templ *template.Template, model *todo.List) http.Handler {
  http.Error(w, "Not found", http.StatusNotFound)
  return
  }
- data := viewModel(model, r)
- executeTemplate(w, templ, data)
+ vm := viewModel(model, r)
+ render(w, r, templ, vm)
  })
 }
 
@@ -32,8 +32,8 @@ func MakeNewItemHandler(templ *template.Template, model *todo.List) http.Handler
  return
  }
  model.Add(r.Form.Get("new-todo"))
- data := viewModel(model, r)
- executeTemplate(w, templ, data)
+ vm := viewModel(model, r)
+ render(w, r, templ, vm)
  })
 }
 
@@ -61,8 +61,8 @@ func MakeToggleHandler(templ *template.Template, model *todo.List) http.Handler
  return
  }
 
- data := viewModel(model, r)
- executeTemplate(w, templ, data)
+ vm := viewModel(model, r)
+ render(w, r, templ, vm)
  })
 }
 
@@ -94,8 +94,8 @@ func MakeEditHandler(templ *template.Template, model *todo.List) http.Handler {
  }
  }
 
- data := viewModel(model, r)
- executeTemplate(w, templ, data)
+ vm := viewModel(model, r)
+ render(w, r, templ, vm)
  })
 }
 
@@ -113,19 +113,11 @@ func MakeDestroyHandler(templ *template.Template, model *todo.List) http.Handler
  }
  model.Destroy(id)
 
- data := viewModel(model, r)
- executeTemplate(w, templ, data)
+ vm := viewModel(model, r)
+ render(w, r, templ, vm)
  })
 }
 
 func badRequest(w http.ResponseWriter, err error) {
  http.Error(w, err.Error(), http.StatusBadRequest)
 }
-
-func executeTemplate(w http.ResponseWriter, templ *template.Template, data map[string]interface{}) {
- err := templ.Execute(w, data)
- if err != nil {
- http.Error(w, "Error rendering template", http.StatusInternalServerError)
- return
- }
-}

web/render.go

@@ -0,0 +1,38 @@
+package web
+
+import (
+ "encoding/json"
+ "html/template"
+ "net/http"
+)
+
+const (
+ headerKeyAccept = "accept"
+)
+
+func render(w http.ResponseWriter, r *http.Request, templ *template.Template, model ViewModel) {
+ if acceptsJson(r) {
+ w.Header().Add("content-type", "application/json")
+ err := json.NewEncoder(w).Encode(model)
+ if err != nil {
+ panic(err.Error())
+ }
+ return
+ }
+ err := templ.Execute(w, model)
+ if err != nil {
+ http.Error(w, "Error rendering template", http.StatusInternalServerError)
+ }
+}
+
+func acceptsJson(r *http.Request) bool {
+ accept := r.Header.Get(headerKeyAccept)
+
+ return startsWith("application/json", accept)
+}
+
+func startsWith(prefix string, s string) bool {
+ lenPrefix := len(prefix)
+
+ return lenPrefix <= len(s) && s[:lenPrefix] == prefix
+}

web/render_test.go

@@ -0,0 +1,50 @@
+package web
+
+import (
+ "github.com/stretchr/testify/assert"
+ "html/template"
+ "net/http"
+ "net/http/httptest"
+ "testing"
+)
+
+func Test_rendersJson(t *testing.T) {
+ w, r := httptest.NewRecorder(), httptest.NewRequest(http.MethodGet, "/", nil)
+ r.Header.Set(headerKeyAccept, "application/json, */*")
+ vm := ViewModel{"Foo": 123}
+
+ render(w, r, nil, vm)
+
+ assert := assert.New(t)
+ assert.Equal("application/json", w.Header().Get("content-type"))
+ assert.Equal("{\"Foo\":123}\n", w.Body.String())
+}
+
+func Test_rendersHtml(t *testing.T) {
+ w, r := httptest.NewRecorder(), httptest.NewRequest(http.MethodGet, "/", nil)
+ vm := ViewModel{"Foo": 123}
+ var templFoo = template.Must(template.New("index").Parse("<p>{{.Foo}}</p>"))
+
+ render(w, r, templFoo, vm)
+
+ assert := assert.New(t)
+ assert.Equal("text/html; charset=utf-8", w.Header().Get("content-type"))
+ assert.Equal("<p>123</p>", w.Body.String())
+}
+
+func Test_failsRenderingTemplate(t *testing.T) {
+ w, r := httptest.NewRecorder(), httptest.NewRequest(http.MethodGet, "/", nil)
+ vm := ViewModel{"Foo": 123}
+ var templFoo = template.Must(template.New("broken").Parse("{{ len .Foo }}"))
+
+ render(w, r, templFoo, vm)
+
+ assert.Equal(t, 500, w.Code)
+}
+
+func Test_startsWith(t *testing.T) {
+ assert := assert.New(t)
+ assert.True(startsWith("ab", "abc"))
+ assert.False(startsWith("xx", "abc"))
+ assert.False(startsWith("abc", "ab"))
+}

web/viewModel.go

@@ -6,15 +6,17 @@ import (
  "net/http"
 )
 
-func viewModel(model *todo.List, r *http.Request) map[string]interface{} {
+type ViewModel map[string]interface{}
+
+func viewModel(model *todo.List, r *http.Request) ViewModel {
  items := model.AllItems()
  path := determinePath(r)
  if path == pathCompleted {
  items = model.CompletedItems()
  } else if path == pathActive {
  items = model.ActiveItems()
  }
- return map[string]interface{}{
+ return ViewModel{
  "Items": items,
  "Path": path,
  "ItemsCount": len(model.Items),