Go DNS Server

A fully functional DNS server implemented from scratch in Go. This project demonstrates building a DNS forwarding server that handles both UDP and TCP queries with complete DNS protocol parsing, EDNS support, and proper connection management.

Features

• Dual Protocol Support: UDP (port 8080) and TCP (port 8081) DNS server implementations
• DNS Forwarding: Forwards queries to upstream DNS servers (default: Google's 8.8.8.8)
• Complete DNS Protocol Parsing:
  • Header parsing with all flags and counters
  • Question section parsing with domain name decompression
  • Resource record parsing (Answers, Authorities, Additional)
  • DNS message compression/pointer support
• EDNS0 Support: Handles EDNS (Extension mechanisms for DNS) OPT records
• Robust TCP Handling:
  • TCP length prefix handling (RFC 1035)
  • Proper handling of partial reads and client disconnects
  • Connection timeouts to prevent stuck connections
• Graceful Shutdown: Context-based cancellation for clean server termination
• Type Safety: Well-structured types for DNS messages, headers, questions, and resource records

DNS Protocol Implementation

Supported Record Types

• A (1): IPv4 address
• NS (2): Name server
• CNAME (5): Canonical name
• SOA (6): Start of authority
• MX (15): Mail exchange
• TXT (16): Text record
• AAAA (28): IPv6 address
• OPT (41): EDNS0 option
• ANY (255): All records

Key Implementation Features

1. Domain Name Compression: Properly handles DNS compression pointers (0xC0 prefix)
2. TCP Length Prefix: Implements the 2-byte length prefix required for TCP DNS queries
3. EDNS Support: Forwards EDNS OPT records to upstream servers for modern DNS features
4. Concurrent Handling: Each TCP connection is handled in a separate goroutine
5. Error Recovery: Continues serving despite individual query failures