GoLookup

A DNS client and server implemented in Go.

Supports A, MX, CNAME, TXT, and NS record types.

Compliant with RFC 1035.

Architecture

graph TD
    A[CLI Input] -->|Client Mode| E[Generate New DNS Query]
    C[External DNS Client e.g. dig] --> D[UDP Listener :port]
    
    D -->|Server Mode| F[Parse Incoming Query]
    F -->|Get Domain and Type| E
    
    E -->|Root Server 198.41.0.4| I[Send DNS Query]
    I --> J[Parse Response Packet]
    J --> K{Answer Found?}
    
    K -->|Yes| V[Display Result to CLI]
    V -->|Server Mode| W[Send Response to Client]

    K -->|No| L[Extract TLD/Authortative <br>Name Server domain]
    L --> M{Its IP Found?}
    M -->|Yes| I
    M -->|No| E
    
    style A fill:#e1f5fe
    style C fill:#e1f5fe
    style I fill:#fff3e0
    style V fill:#e8f5e8
    style W fill:#e8f5e8

Loading

Example Usage

$ go run ./cmd -h
usage:
    golookup [domain] [A|NS|MX|CNAME|TXT]
    golookup serve --port=<port-number>

$ go run ./cmd serve --port=9999 &
[1] 25685
$ dig @127.0.0.1 -p 9999 example.com NS

Querying: 198.41.0.4
Received Name Server for "com": "l.gtld-servers.net"
Received "l.gtld-servers.net" IP: "192.41.162.30"
Querying: 192.41.162.30
Received Name Server for "example.com": "b.iana-servers.net"
name server IP not found in packet
starting new query for: b.iana-servers.net
Querying: 198.41.0.4
Received Name Server for "net": "m.gtld-servers.net"
Received "m.gtld-servers.net" IP: "192.55.83.30"
Querying: 192.55.83.30
Received Name Server for "iana-servers.net": "a.iana-servers.net"
Received "a.iana-servers.net" IP: "199.43.135.53"
Querying: 199.43.135.53
new query done, found "b.iana-servers.net" IP: "199.43.133.53"
Querying: 199.43.133.53

; <<>> DiG 9.18.30-0ubuntu0.24.04.2-Ubuntu <<>> @127.0.0.1 -p 9999 example.com ns
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55664
;; flags: qr; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;example.com.                   IN      NS

;; ANSWER SECTION:
example.com.            86400   IN      NS      a.iana-servers.net.
example.com.            86400   IN      NS      b.iana-servers.net.

;; Query time: 909 msec
;; SERVER: 127.0.0.1#9999(127.0.0.1) (UDP)
;; WHEN: Fri Sep 12 15:57:06 EEST 2025
;; MSG SIZE  rcvd: 115

TODO

• Add inverse queries support.
• Improve error handling.
• Support TXT records in server mode.