🐛 [Bug]: Logger middleware default Format isn't the format that's used

[daenney]

Bug Description

I'm filing this as a bug since I think the behaviour is counter-intuitive.

The logger middleware has a configuration with a default format:

fiber/middleware/logger/config.go

Line 89 in 2374cad

Format: "[${time}] ${status} - ${latency} ${method} ${path}\n",

However, when the logger proceeds to print this, it ignores the actual format:

fiber/middleware/logger/logger.go

Lines 141 to 174 in 2374cad

	if cfg.Format == ConfigDefault.Format {
	// Format error if exist
	formatErr := ""
	if cfg.enableColors {
	if chainErr != nil {
	formatErr = colors.Red + " | " + chainErr.Error() + colors.Reset
	}
	_, _ = buf.WriteString( //nolint:errcheck // This will never fail
	fmt.Sprintf("%s |%s %3d %s| %13v | %15s |%s %-7s %s| %-"+errPaddingStr+"s %s\n",
	timestamp.Load().(string),
	statusColor(c.Response().StatusCode(), colors), c.Response().StatusCode(), colors.Reset,
	data.Stop.Sub(data.Start),
	c.IP(),
	methodColor(c.Method(), colors), c.Method(), colors.Reset,
	c.Path(),
	formatErr,
	),
	)
	} else {
	if chainErr != nil {
	formatErr = " | " + chainErr.Error()
	}
	_, _ = buf.WriteString( //nolint:errcheck // This will never fail
	fmt.Sprintf("%s | %3d | %13v | %15s | %-7s | %-"+errPaddingStr+"s %s\n",
	timestamp.Load().(string),
	c.Response().StatusCode(),
	data.Stop.Sub(data.Start),
	c.IP(),
	c.Method(),
	c.Path(),
	formatErr,
	),
	)
	}

Despite it checking for if it should use the default format, it then uses a different format string in the fmt.Sprintf() calls.

How to Reproduce

• Add the logging middleware without overriding the Format
• Do a request and observe the log output

Expected Behavior

Logged line should use the ConfigDefault.Format for output, as shown in the configuration: https://docs.gofiber.io/api/middleware/logger#default-config

Fiber Version

v2.50.0

Code Snippet (optional)

No response

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my problem prior to opening this one.
• I understand that improperly formatted bug reports may be closed without explanation.

[brunodmartins]

I want to work on this issue!

[brunodmartins]

@ReneWerner87 I opened a draft PR! I explained the problem and a proposed solution.

[triadmoko]

i found the same bug