Description

Following PR #4260, only BalancerForward was automatically setting the X-Real-IP header for IP spoofing protection. The Forward and DomainForward variants left the header untouched, creating a security inconsistency where migrating from BalancerForward to other Forward variants would lose spoofing protection.

This PR adds automatic X-Real-IP header setting to Forward and DomainForward, ensuring all three Forward variants consistently protect against IP spoofing attacks.

Changes introduced

• Security Fix: All Forward variants (Forward, DomainForward, BalancerForward) now automatically overwrite any incoming X-Real-IP header with the actual client IP from c.IP(). This prevents malicious clients from forging their IP address.

• Documentation Update:

  • Added Security section to /docs/middleware/proxy.md explaining the automatic X-Real-IP protection behavior
  • Documented which functions set X-Real-IP automatically vs. which require manual setting

• Tests: Added comprehensive tests for Forward and DomainForward X-Real-IP protection:

  • Test_Proxy_Forward_OverwritesXRealIP
  • Test_Proxy_DomainForward_OverwritesXRealIP

• Examples:

// Before: Forward didn't protect against IP spoofing
app.Use(proxy.Forward("http://backend:8080"))
// A malicious client could set X-Real-IP: 1.2.3.4 and it would be passed through

// After: Forward automatically protects against IP spoofing
app.Use(proxy.Forward("http://backend:8080"))
// Any spoofed X-Real-IP header is overwritten with the real client IP

Type of change

• Enhancement (improvement to existing features and functionality)
• Documentation update (changes to documentation)
• Code consistency (non-breaking change which improves code reliability and robustness)

Checklist

• Conducted a self-review of the code and provided comments for complex or critical parts.
• Updated the documentation in the /docs/ directory for Fiber's documentation.
• Added or updated unit tests to validate the effectiveness of the changes or new features.
• Ensured that new and existing unit tests pass locally with the changes.
• Verified that any new dependencies are essential and have been agreed upon by the maintainers/community.
• Aimed for optimal performance with minimal allocations in the new code.