gofiber/fiber · error

failed to discard interim response body: %w

Error message

failed to discard interim response body: %w

What it means

Returned by App.Test (app.go:1502) when discarding the body of a 1xx interim response fails before reading the next response in the loop. Test loops over interim responses (100 Continue, 102 Processing, 103 Early Hints) and discards each body; if io.Copy(io.Discard, res.Body) errors, the interim body could not be drained.

Source

Thrown at app.go:1502

	for {
		// Convert raw http response to *http.Response
		res, err = httpReadResponse(buffer, req)
		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() {

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Inspect the wrapped error (usually io.ErrUnexpectedEOF or a read on a closed conn).
2. Ensure interim responses in the handler carry no body (or a validly framed one) per RFC 2516.
3. Increase TestConfig.Timeout if the handler is slow to produce the final response after interim ones.

resp, err := app.Test(req, fiber.TestConfig{Timeout: 5 * time.Second})
if err != nil && strings.Contains(err.Error(), "failed to discard interim response body") {
    // 1xx interim response body could not be drained — inspect handler's interim writes
}

When it happens

Trigger: A handler under test emits 1xx interim responses with a body that errors on read (broken/short body), or the testConn is closed mid-interim-response. Occurs specifically when exercising interim-response code paths.

Common situations: Testing Early Hints (103) / 100-Continue flows; handlers that write interim status then reset the connection; compression/streaming edge cases on interim responses.

Related errors

• failed to close 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/3b12e5745bb2978a.json. Report an issue: GitHub.