add form data to context

When calling frontend.Fail pass the form data in the context.
In case of an error, returns the values back so they're not reset on the
page.

internal/frontend/account/login.go

@@ -14,8 +14,6 @@ import (
 
 func (srv server) loginForm(w http.ResponseWriter, r *http.Request) {
 	var (
-		ctx      = r.Context()
-		logger   = log.FromContext(ctx)
 		email    = r.FormValue("email")
 		password = r.FormValue("password")
 		data     = frontend.Data{
@@ -25,6 +23,8 @@ func (srv server) loginForm(w http.ResponseWriter, r *http.Request) {
 				"password": password,
 			},
 		}
+		ctx    = frontend.AddFormData(r.Context(), data)
+		logger = log.FromContext(ctx)
 	)
 
 	if r.Method == http.MethodGet {

internal/frontend/account/register.go

@@ -13,8 +13,6 @@ import (
 
 func (srv server) registerForm(w http.ResponseWriter, r *http.Request) {
 	var (
-		ctx      = r.Context()
-		logger   = log.FromContext(ctx)
 		username = r.FormValue("username")
 		email    = r.FormValue("email")
 		password = r.FormValue("password")
@@ -26,6 +24,8 @@ func (srv server) registerForm(w http.ResponseWriter, r *http.Request) {
 				"password": password,
 			},
 		}
+		ctx    = frontend.AddFormData(r.Context(), data)
+		logger = log.FromContext(ctx)
 	)
 
 	if r.Method == http.MethodGet {

pkg/frontend/context.go

@@ -0,0 +1,19 @@
+package frontend
+
+import "context"
+
+type key int
+
+const dataKey key = 0
+
+func AddFormData(ctx context.Context, data Data) context.Context {
+	return context.WithValue(ctx, dataKey, data)
+}
+
+func dataFromContext(ctx context.Context) Data {
+	v, ok := ctx.Value(dataKey).(Data)
+	if !ok {
+		return Data{}
+	}
+	return v
+}

pkg/frontend/frontend.go

@@ -174,7 +174,7 @@ func (srv *Server) Fail(ctx context.Context, w http.ResponseWriter, err error, k
 	}
 
 	if errors.As(err, &validationErr) {
-		srv.RenderTemplate(ctx, w, tpl, Data{}.
+		srv.RenderTemplate(ctx, w, tpl, dataFromContext(ctx).
 			FormErrors(validationErr.Invalid()).
 			WithLog(err, keyvals...).
 			WithCode(http.StatusBadRequest),