labstack/echo · critical

invalid gzip level

Error message

invalid gzip level

What it means

Returned by GzipConfig.ToMiddleware when config.Level is outside the valid gzip level range [-2, 9], then converted to a panic by toMiddlewareOrPanic. gzip levels: -2 (HuffmanOnly), -1 (Default), 0 (no compression, remapped to -1), 1 (BestSpeed) through 9 (BestCompression). Any value outside this range is invalid.

Source

Thrown at middleware/compress.go:74

}

// Gzip returns a middleware which compresses HTTP response using gzip compression scheme.
func Gzip() echo.MiddlewareFunc {
	return GzipWithConfig(GzipConfig{})
}

// GzipWithConfig returns a middleware which compresses HTTP response using gzip compression scheme.
func GzipWithConfig(config GzipConfig) echo.MiddlewareFunc {
	return toMiddlewareOrPanic(config)
}

// ToMiddleware converts GzipConfig to middleware or returns an error for invalid configuration
func (config GzipConfig) ToMiddleware() (echo.MiddlewareFunc, error) {
	if config.Skipper == nil {
		config.Skipper = DefaultSkipper
	}
	if config.Level < -2 || config.Level > 9 { // these are consts: gzip.HuffmanOnly and gzip.BestCompression
		return nil, errors.New("invalid gzip level")
	}
	if config.Level == 0 {
		config.Level = -1
	}
	if config.MinLength < 0 {
		config.MinLength = 0
	}

	pool := gzipCompressPool(config)
	bpool := bufferPool()

	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c *echo.Context) error {
			if config.Skipper(c) {
				return next(c)
			}

			res := c.Response()

View on GitHub (pinned to 05489dc173)

Solutions

1. Use a valid level: -1 (default), 1-9 (speed to compression tradeoff), -2 (HuffmanOnly)
2. Omit Level to accept the default (-1), or use middleware.Gzip() which uses defaults
3. Use config.ToMiddleware() to get an error instead of a panic for graceful handling

Example fix

// before
mw := middleware.GzipWithConfig(middleware.GzipConfig{Level: 10}) // panic

// after
mw := middleware.GzipWithConfig(middleware.GzipConfig{Level: 6}) // ok

func validGzipLevel(level int) bool {
    return level >= -2 && level <= 9
}
if !validGzipLevel(cfg.Level) {
    return fmt.Errorf("invalid gzip level %d: must be -2..9", cfg.Level)
}

defer func() {
    if r := recover(); r != nil {
        log.Fatal("middleware setup failed:", r)
    }
}()
mw := middleware.GzipWithConfig(cfg)

When it happens

Trigger: Calling middleware.GzipWithConfig(middleware.GzipConfig{Level: 10}) or Level: -3 or any other out-of-range integer. The panic occurs at middleware chain construction time before the server starts.

Common situations: Typo or magic number for the level. Reading level from config file/env without validation. Confusing the level with MinLength or another setting.

Related errors

• echo basic-auth middleware requires a validator function
• echo body-dump middleware requires a handler function
• panic: err from config.ToMiddleware() in RequestLoggerWithCo
• timeout must be set
• at least one AllowOrigins is required or UnsafeAllowOriginFu

AI-assisted analysis of labstack/echo@05489dc173 (2026-08-04). Data as JSON: /data/errors/d4f4cc00b8fe01cf.json. Report an issue: GitHub.