URL Protocol-Relative Regex for Go

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching url protocol-relative, ported and verified for Go. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

// URL Protocol-Relative
// ReDoS-safe | RegexVault — Web & Network > URL

package validation

import "regexp"

var urlProtocolrelativeRe = regexp.MustCompile(`^//(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,63}(?::(?:6553[0-5]|655[0-2][0-9]|65[0-4][0-9]{2}|6[0-4][0-9]{3}|[1-5][0-9]{4}|[1-9][0-9]{0,3}))?(?:/[^\s]*)?$`)

func ValidateUrlProtocolrelative(s string) bool {
    return urlProtocolrelativeRe.MatchString(s)
}

// Example
// fmt.Println(ValidateUrlProtocolrelative("//example.com")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > URL category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Protocol-relative URLs are deprecated in modern development. Prefer explicit https:// to avoid downgrade attacks when embedded in mixed-content pages.