gofiber/fiber · error

failed to execute: %w

Error message

failed to execute: %w

What it means

In Render's fallback path, after parsing, executing the template against bind failed. This is a template runtime error: referencing a field/method that doesn't exist on the bind, a nil pointer in a pipeline, a bad type assertion, or an index out of range in a {{range}}.

Source

Thrown at res.go:797

			}
		}
	}

	if !rendered {
		// Render raw template using 'name' as filepath if no engine is set
		var tmpl *template.Template
		if _, err := readContent(buf, name); err != nil {
			return err
		}
		// Parse template
		tmpl, err := template.New("").Parse(rootApp.toString(buf.Bytes()))
		if err != nil {
			return fmt.Errorf("failed to parse: %w", err)
		}
		buf.Reset()
		// Render template
		if err := tmpl.Execute(buf, bind); err != nil {
			return fmt.Errorf("failed to execute: %w", err)
		}
	}

	response := &r.c.fasthttp.Response

	// Set Content-Type to text/html
	response.Header.SetContentType(MIMETextHTMLCharsetUTF8)
	// Set rendered template to body
	response.SetBody(buf.Bytes())

	return nil
}

func (r *DefaultRes) renderExtensions(bind any) {
	r.c.renderExtensions(bind)
}

// Send sets the HTTP response body without copying it.

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Ensure the bind value exposes every field/method the template references.
2. Guard optional values in the template with {{ if .User }}...{{ end }}.
3. Keep the bind type and the template in sync; add a render test.

Example fix

// before: bind = fiber.Map{"title": "Hi"}  template: {{ .User.Name }}
//   -> failed to execute: nil has no fields

// after:  bind = fiber.Map{"title": "Hi", "user": u}
//   template: {{ if .User }}{{ .User.Name }}{{ end }}

// render into a buffer in a test to surface execution errors early
func TestRender(t *testing.T) {
    app := fiber.New()
    c := app.AcquireCtx(&fasthttp.RequestCtx{})
    defer app.ReleaseCtx(c)
    if err := c.Render("tpl", bind); err != nil { t.Fatal(err) }
}

if err := c.Render(name, bind); err != nil {
    log.Errorf("execute %q failed: %v", name, err)
    return c.Status(fiber.StatusInternalServerError).
        SendString("template error")
}

When it happens

Trigger: Template references {{ .User.Name }} but bind (or .User) is nil or missing the field; calling a method not defined on the bind type; {{ index .Arr 5 }} with too few elements.

Common situations: Bind struct changed but template not updated; nil nested fields; passing a Map missing expected keys; type mismatches after refactors.

Related errors

• logtemplate: unknown tag
• failed to render: %w
• failed to parse: %w
• min constraint requires an argument
• max constraint requires an argument

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/2c2d12ea6bc8c11d.json. Report an issue: GitHub.