adds binding.Bindable interface (#1613)

binding/bindable.go

@@ -0,0 +1,10 @@
+package binding
+
+import "net/http"
+
+// Bindable when implemented, on a type
+// will override any Binders that have been
+// configured when using buffalo#Context.Bind
+type Bindable interface {
+	Bind(*http.Request) error
+}

binding/bindable_test.go

@@ -0,0 +1,28 @@
+package binding
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type orbison struct {
+	bound bool
+}
+
+func (o *orbison) Bind(req *http.Request) error {
+	o.bound = true
+	return nil
+}
+
+func Test_Bindable(t *testing.T) {
+	r := require.New(t)
+
+	req := httptest.NewRequest("GET", "/", nil)
+	o := &orbison{}
+	r.False(o.bound)
+	r.NoError(Exec(req, o))
+	r.True(o.bound)
+}

binding/binding.go

@@ -74,6 +74,10 @@ func Register(contentType string, fn Binder) {
 // is "application/xml" it will use "xml.NewDecoder". The default
 // binder is "https://github.com/monoculum/formam".
 func Exec(req *http.Request, value interface{}) error {
+	if ba, ok := value.(Bindable); ok {
+		return ba.Bind(req)
+	}
+
 	ct := httpx.ContentType(req)
 	if ct == "" {
 		return errors.New("blank content type")