fix double write errors

main.go

@@ -28,6 +28,9 @@ func wrapHandler(h handler) http.Handler {
 		}()
 		err := h(w, r)
 		if err != nil {
+			if render.IsRendererError(err) {
+				return
+			}
 			fmt.Println(err)
 			utils.RenderError(w, r, 500, err.Error())
 		}

pages/media.go

@@ -84,6 +84,6 @@ func handleMedia(w http.ResponseWriter, r *http.Request, url string) error {
 		w.Header().Set("Content-Range", res.Header.Get("Content-Range"))
 	}
 
-	io.Copy(w, res.Body)
-	return nil // don't call RenderError after this point
+	_, err = io.Copy(w, res.Body)
+	return err
 }

render/render.go

@@ -2,6 +2,7 @@
 package render
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"io/fs"
@@ -63,14 +64,46 @@ func Initialize(views fs.FS) {
 func (r *renderer) Render(out io.Writer, name string, bind map[string]any) error {
 	tmpl := r.templates[name]
 	if tmpl == nil {
-		return fmt.Errorf("render: template %s does not exist", name)
+		return re(fmt.Errorf("render: template %s does not exist", name))
 	}
 	parsed, err := tmpl.Exec(bind)
 	if err != nil {
-		return fmt.Errorf("render: %w", err)
+		return re(fmt.Errorf("render: %w", err))
 	}
 	if _, err = out.Write([]byte(parsed)); err != nil {
-		return fmt.Errorf("render: %w", err)
+		return re(fmt.Errorf("render: %w", err))
 	}
-	return err
+	return re(err)
+}
+
+var reSentinel = &struct{}{}
+
+type RendererError struct {
+	u   *struct{}
+	err error
+}
+
+func re(err error) error {
+	if err == nil {
+		return nil
+	}
+	return RendererError{reSentinel, err}
+}
+func (re RendererError) Error() string {
+	return re.Error()
+}
+func (re RendererError) Unwrap() error {
+	e1, ok := re.err.(interface{ Unwrap() error })
+	if ok {
+		return e1.Unwrap()
+	}
+	e2, ok := re.err.(interface{ Unwrap() []error })
+	if ok {
+		return errors.Join(e2.Unwrap()...)
+	}
+	return nil
+}
+func IsRendererError(err error) bool {
+	re, ok := err.(RendererError)
+	return ok && re.u == reSentinel
 }