gofr-dev/gofr · error

, got

Error message

%w, got: %d

What it means

This is the wrapped form of errNegativeMaxIdleConns produced by (*ConnectionPoolConfig).Validate: fmt.Errorf("%w, got: %d", ...) so the sentinel remains checkable with errors.Is while including the offending MaxIdleConns value. It fires before the pool settings are applied to the HTTP transport.

Solutions

1. Correct the config value so MaxIdleConns >= 0
2. Clamp with max(0, v) before constructing ConnectionPoolConfig
3. Call Validate() right after loading config to fail fast at startup
4. Match with errors.Is(err, errNegativeMaxIdleConns) for precise field-level error messages

Example fix

// before
if err := pool.Validate(); err != nil { return err } // MaxIdleConns: -10
// after
pool.MaxIdleConns = max(pool.MaxIdleConns, 0)
if err := pool.Validate(); err != nil { return fmt.Errorf("invalid pool config: %w", err) }

pool := &ConnectionPoolConfig{MaxIdleConns: v}
if err := pool.Validate(); err != nil {
    if errors.Is(err, errNegativeMaxIdleConns) {
        return fmt.Errorf("config: MaxIdleConns invalid: %w", err)
    }
    return err
}

func isNegativeMaxIdleConnsErr(err error) bool { return errors.Is(err, errNegativeMaxIdleConns) }

if err := pool.Validate(); err != nil {
    if isNegativeMaxIdleConnsErr(err) {
        return fallbackWithDefaults()
    }
    return fmt.Errorf("connection pool config: %w", err)
}

When it happens

Trigger: Validate() (invoked directly or through AddOption when configuring AddHTTPService) sees c.MaxIdleConns < 0 and returns this wrapped error, e.g. ConnectionPoolConfig{MaxIdleConns: -5}.Validate().

Common situations: Environment-driven sizing producing negative numbers; negative values in YAML/JSON service config; arithmetic like maxConns - overhead underflowing to negative.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• IdleConnTimeout cannot be negative
• MaxIdleConns cannot be negative
• MaxIdleConnsPerHost cannot be negative
• , got
• invalid FTP configuration: host and port are required

AI-assisted analysis of gofr-dev/gofr@187eb24962 (2026-09-01). Data as JSON: /api/errors/a3dff2272e064e85. Report an issue: GitHub.

Appendix: source

Thrown at pkg/gofr/service/connection_pool.go:57

	// MaxIdleConnsPerHost controls the maximum idle (keep-alive) connections to keep per-host.
	// This is the critical setting for microservices making frequent requests to the same host.
	// If set to 0, Go's DefaultMaxIdleConnsPerHost (2) will be used.
	// Negative values will cause validation error.
	// Default Go value: 2 (which is often insufficient for microservices)
	// Recommended: 10-20 for typical microservices, higher for high-traffic services
	MaxIdleConnsPerHost int

	// IdleConnTimeout is the maximum amount of time an idle (keep-alive) connection will remain
	// idle before closing itself.
	// If not explicitly set (0), a default of 90 seconds will be used.
	// Negative values will cause validation error.
	IdleConnTimeout time.Duration
}

// Validate checks if the connection pool configuration values are valid.
func (c *ConnectionPoolConfig) Validate() error {
	if c.MaxIdleConns < 0 {
		return fmt.Errorf("%w, got: %d", errNegativeMaxIdleConns, c.MaxIdleConns)
	}

	if c.MaxIdleConnsPerHost < 0 {
		return fmt.Errorf("%w, got: %d", errNegativeMaxIdleConnsPerHost, c.MaxIdleConnsPerHost)
	}

	if c.IdleConnTimeout < 0 {
		return fmt.Errorf("%w, got: %v", errNegativeIdleConnTimeout, c.IdleConnTimeout)
	}

	return nil
}

// AddOption implements the Options interface to apply connection pool configuration to HTTP service.
// It modifies the underlying HTTP client's transport to use optimized connection pool settings.
func (c *ConnectionPoolConfig) AddOption(h HTTP) HTTP {
	// Extract the base httpService from any wrapped service
	httpSvc := extractHTTPService(h)

View on GitHub (pinned to 187eb24962)