gofiber/fiber · error

failed to close interim response body: %w

Error message

failed to close interim response body: %w

What it means

Returned by App.Test (app.go:1505) when res.Body.Close() fails on a 1xx interim response body, immediately after discarding it. Like the discard error, it only occurs while Test walks interim responses; a Close failure indicates the underlying reader/connection rejected cleanup of the interim body.

Source

Thrown at app.go:1505

		if err != nil {
			if errors.Is(err, io.ErrUnexpectedEOF) {
				return nil, ErrTestGotEmptyResponse
			}
			return nil, fmt.Errorf("failed to read response: %w", err)
		}

		// Break if this response is non-1xx or there are no more responses
		if res.StatusCode >= http.StatusOK || buffer.Buffered() == 0 {
			break
		}

		// Discard interim response body before reading the next one
		if res.Body != nil {
			if _, errCopy := io.Copy(io.Discard, res.Body); errCopy != nil {
				return nil, fmt.Errorf("failed to discard interim response body: %w", errCopy)
			}
			if errClose := res.Body.Close(); errClose != nil {
				return nil, fmt.Errorf("failed to close interim response body: %w", errClose)
			}
		}
	}

	return res, nil
}

type disableLogger struct{}

// Printf implements the fasthttp Logger interface and discards log output.
func (*disableLogger) Printf(string, ...any) {
}

func (app *App) init() *App {
	func() {
		// lock application
		app.mutex.Lock()
		defer app.mutex.Unlock()

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Inspect the wrapped error to identify the close failure cause.
2. Ensure the handler writes interim responses without a body and transitions cleanly to the final response.
3. Increase TestConfig.Timeout if timing contributes to a torn connection.

resp, err := app.Test(req, fiber.TestConfig{Timeout: 5 * time.Second})
if err != nil && strings.Contains(err.Error(), "failed to close interim response body") {
    // interim body Close() failed — usually a torn connection
}

When it happens

Trigger: Same interim-response loop as error 73: the handler emits 1xx responses and closing the interim body fails — typically because the connection was already torn down or the body reader is in a bad state.

Common situations: Early-Hints/100-Continue tests with handlers that mismanage response bodies; connection resets between interim and final responses.

Related errors

• failed to discard interim response body: %w
• failed to dump request: %w
• failed to write: %w
• failed to read response: %w
• runtime.Goexit() called in handler or server panic

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/d0ddfa50fc1de09d.json. Report an issue: GitHub.