dns-resolution

name	dns-resolution
description	Use when working with the Resolver interface in pkg/resolver — custom resolvers, DNS caching/TTL, retries, hostname validation, or resolution error handling for the proxy frontends.

DNS Resolution

Expertise in implementing DNS resolution interfaces and custom resolver patterns for hostname-to-IP translation in the NanoProxy project.

When to use this skill

• Implementing custom DNS resolvers
• Adding DNS caching functionality
• Debugging hostname resolution issues
• Integrating with different DNS backends
• Optimizing DNS lookup performance

Expertise areas

• DNS resolver interface design
• Custom DNS implementation
• DNS caching strategies
• Error handling for DNS failures
• Performance optimization
• Testing DNS resolution

Key files

• pkg/resolver/resolver.go - DNS resolver interface
• pkg/resolver/resolver_test.go - Resolver tests

Common tasks

Creating a custom resolver

Implement the resolver interface with a Resolve method that takes a hostname and returns an IP address.

Adding caching

Implement a caching layer to reduce DNS lookups, with TTL support.

Error handling

Properly handle NXDOMAIN, timeout, and other DNS errors.

Example patterns

Implementing the resolver interface

type Resolver interface {
    Resolve(hostname string) (string, error)
}

type DNSResolver struct {
    cache map[string]cachedResult
    ttl   time.Duration
}

func (r *DNSResolver) Resolve(hostname string) (string, error) {
    // Check cache
    if cached, ok := r.cache[hostname]; ok {
        if time.Now().Before(cached.expiry) {
            return cached.ip, nil
        }
    }

    // Resolve using system DNS
    addrs, err := net.LookupHost(hostname)
    if err != nil {
        return "", err
    }

    // Cache result
    r.cache[hostname] = cachedResult{
        ip:     addrs[0],
        expiry: time.Now().Add(r.ttl),
    }

    return addrs[0], nil
}

Custom resolver with retry

func (r *DNSResolver) ResolveWithRetry(hostname string, retries int) (string, error) {
    var lastErr error

    for i := 0; i < retries; i++ {
        ip, err := r.Resolve(hostname)
        if err == nil {
            return ip, nil
        }

        lastErr = err
        time.Sleep(time.Duration(i+1) * 100 * time.Millisecond)
    }

    return "", lastErr
}

Testing approach

• Test with valid hostnames
• Test with invalid hostnames (NXDOMAIN)
• Test with localhost
• Test with IP addresses
• Test cache hit/miss
• Test TTL expiration
• Test concurrent resolution
• Test timeout scenarios

Performance considerations

• Implement caching to reduce lookups
• Set appropriate TTL values
• Batch DNS queries when possible
• Monitor DNS lookup latency
• Profile resolver performance

Security considerations

• Validate hostnames
• Prevent DNS poisoning
• Implement timeout to prevent hanging
• Consider DNSSEC validation
• Log DNS failures appropriately

References

• RFC 1035: Domain Names - Implementation and Specification
• Go net package documentation

Related skills

• socks5-protocol - Uses DNS resolution
• http-proxy - Uses DNS resolution
• go-concurrency - For concurrent DNS lookups