Use a custom template function for csrf protection

controllers/static.go

@@ -4,7 +4,6 @@ import (
 	"git.kealoha.me/lks/lenslocked/templates"
 	"git.kealoha.me/lks/lenslocked/views"
 	"net/http"
-	"strings"
 )
 
 type Template interface {
@@ -14,8 +13,7 @@ type Template interface {
 func StaticController(templatePath ...string) http.HandlerFunc {
 	tpl := views.Must(views.FromFS(templates.FS, templatePath...))
 
-	var testWriter strings.Builder
+	err := tpl.TestTemplate(nil)
-	err := tpl.ExecuteWriter(&testWriter, nil)
 	if err != nil {
 		panic(err)
 	}
@@ -40,8 +38,7 @@ func FAQ(templatePath ...string) http.HandlerFunc {
 
 	tpl := views.Must(views.FromFS(templates.FS, templatePath...))
 
-	var testWriter strings.Builder
+	err := tpl.TestTemplate(nil)
-	err := tpl.ExecuteWriter(&testWriter, nil)
 	if err != nil {
 		panic(err)
 	}

controllers/users.go

@@ -2,14 +2,11 @@ package controllers
 
 import (
 	"fmt"
-	"html/template"
 	"net/http"
-	"strings"
 
 	"git.kealoha.me/lks/lenslocked/models"
 	"git.kealoha.me/lks/lenslocked/templates"
 	"git.kealoha.me/lks/lenslocked/views"
-	"github.com/gorilla/csrf"
 )
 
 type Users struct {
@@ -23,10 +20,8 @@ type Users struct {
 func (u Users) GetSignup(w http.ResponseWriter, r *http.Request) {
 	var data struct {
 		Email string
-		CSRFField template.HTML
 	}
 	data.Email = r.FormValue("email")
-	data.CSRFField = csrf.TemplateField(r)
 	u.Templates.Signup.Execute(w, r, data)
 }
 
@@ -45,10 +40,8 @@ func (u Users) PostSignup(w http.ResponseWriter, r *http.Request) {
 func (u Users) GetSignin(w http.ResponseWriter, r *http.Request) {
 	var data struct {
 		Email string
-		CSRFField template.HTML
 	}
 	data.Email = r.FormValue("email")
-	data.CSRFField = csrf.TemplateField(r)
 	u.Templates.Signin.Execute(w, r, data)
 }
 func (u Users) PostSignin(w http.ResponseWriter, r *http.Request) {
@@ -97,12 +90,11 @@ func Default(user_service *models.UserService, templatePath ...string) Users {
 	signup_tpl := views.Must(views.FromFS(templates.FS, "signup.gohtml", "tailwind.gohtml"))
 	signin_tpl := views.Must(views.FromFS(templates.FS, "signin.gohtml", "tailwind.gohtml"))
 
-	var testWriter strings.Builder
+	err := signup_tpl.TestTemplate(nil)
-	err := signup_tpl.ExecuteWriter(&testWriter, nil)
 	if err != nil {
 		panic(err)
 	}
-	err = signin_tpl.ExecuteWriter(&testWriter, nil)
+	err = signin_tpl.TestTemplate(nil)
 	if err != nil {
 		panic(err)
 	}

templates/signin.gohtml

@@ -9,7 +9,7 @@
           Welcome back!
         </h1>
         <form action="/signin" method="post">
-          {{.CSRFField}}
+          {{csrfField}}
           <div class="py-2">
             <label for="email" class="text-sm font-semibold text-gray-800">
               Email Address

templates/signup.gohtml

@@ -10,7 +10,7 @@
             Sign Up!
           </h1>
           <form action="/signup" method="post">
-            {{.CSRFField}}
+            {{csrfField}}
             <div>
               <label for="signupEmail" class="text-sm font-semibold text-gray-800">Email Address</label>
               <input name="email" id="signupEmail" type="email" placeholder="Email address" required autocomplete="email" 

views/template.go

@@ -3,11 +3,13 @@ package views
 import (
 	"fmt"
 	"html/template"
-	"io"
 	"io/fs"
 	"log"
 	"net/http"
 	"os"
+	"strings"
+
+	"github.com/gorilla/csrf"
 )
 
 type Template struct {
@@ -15,16 +17,32 @@ type Template struct {
 }
 
 func (t Template) Execute(w http.ResponseWriter, r *http.Request, data interface{}) {
+	tpl, err := t.htmlTpl.Clone()
+	if err != nil {
+		log.Printf("Template Clone Error: %v", err)
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return
+	}
+
+	tpl = tpl.Funcs(template.FuncMap{
+		"csrfField": func() template.HTML { return csrf.TemplateField(r) },
+	})
+
 	w.Header().Set("Content-Type", "text/html; charset=utf8")
-	err := t.htmlTpl.Execute(w, data)
+	err = tpl.Execute(w, data)
 	if err != nil {
 		log.Printf("Error executing template: %v", err)
 		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
 		return
 	}
 }
-func (t Template) ExecuteWriter(w io.Writer, data interface{}) error {
+func (t Template) TestTemplate(data interface{}) error {
-	return t.htmlTpl.Execute(w, data)
+	var testWriter strings.Builder
+	tpl, err := t.htmlTpl.Clone()
+	if err != nil {
+		return err
+	}
+	return tpl.Execute(&testWriter, data)
 }
 
 func FromFile(pattern ...string) (Template, error) {
@@ -32,7 +50,13 @@ func FromFile(pattern ...string) (Template, error) {
 	return FromFS(fs, pattern...)
 }
 func FromFS(fs fs.FS, pattern ...string) (Template, error) {
-	tpl, err := template.ParseFS(fs, pattern...)
+	tpl := template.New(pattern[0])
+	tpl = tpl.Funcs(template.FuncMap{
+		"csrfField": func() template.HTML {
+			return `<div class="hidden">STUB: PLACEHOLDER</div>`
+		},
+	})
+	tpl, err := tpl.ParseFS(fs, pattern...)
 	if err != nil {
 		return Template{}, fmt.Errorf("Error parsing template: %v", err)
 	}