From 60fc4ebb599d82f5c7ddaca52f8aba74f0876381 Mon Sep 17 00:00:00 2001
From: simponic <simponic@hatecomputers.club>
Date: Thu, 28 Mar 2024 16:58:07 -0400
Subject: internal recursive dns server (#2)

Co-authored-by: Lizzy Hunt <lizzy.hunt@usu.edu>
Reviewed-on: https://git.hatecomputers.club/hatecomputers/hatecomputers.club/pulls/2
---
 dns/server.go | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 dns/server.go

(limited to 'dns/server.go')

diff --git a/dns/server.go b/dns/server.go
new file mode 100644
index 0000000..63bb067
--- /dev/null
+++ b/dns/server.go
@@ -0,0 +1,110 @@
+package dns
+
+import (
+	"database/sql"
+	"fmt"
+	"git.hatecomputers.club/hatecomputers/hatecomputers.club/args"
+	"git.hatecomputers.club/hatecomputers/hatecomputers.club/database"
+	"github.com/miekg/dns"
+	"log"
+)
+
+const MAX_RECURSION = 10
+
+func resolveRecursive(dbConn *sql.DB, dnsResolvers []string, domain string, qtype uint16, maxDepth int) ([]dns.RR, error) {
+	if maxDepth == 0 {
+		return nil, fmt.Errorf("too much recursion")
+	}
+
+	internalCnames, err := database.FindDNSRecords(dbConn, domain, "CNAME")
+	if err != nil {
+		return nil, err
+	}
+
+	answers := []dns.RR{}
+	for _, record := range internalCnames {
+		cnameRecursive, _ := resolveRecursive(dbConn, dnsResolvers, record.Content, qtype, maxDepth-1)
+		answers = append(answers, cnameRecursive...)
+	}
+
+	qtypeName := dns.TypeToString[qtype]
+	if qtypeName == "" {
+		return nil, fmt.Errorf("invalid query type %d", qtype)
+	}
+
+	typeDnsRecords, err := database.FindDNSRecords(dbConn, domain, qtypeName)
+	if err != nil {
+		return nil, err
+	}
+	for _, record := range typeDnsRecords {
+		answer, err := dns.NewRR(fmt.Sprintf("%s %d IN %s %s", record.Name, record.TTL, record.Type, record.Content))
+		if err != nil {
+			return nil, err
+		}
+		answers = append(answers, answer)
+	}
+
+	if len(answers) > 0 {
+		// base case; we found the answer
+		return answers, nil
+	}
+
+	message := new(dns.Msg)
+	message.SetQuestion(dns.Fqdn(domain), qtype)
+	message.RecursionDesired = true
+
+	client := new(dns.Client)
+
+	i := 0
+	in, _, err := client.Exchange(message, dnsResolvers[i])
+	for err != nil {
+		i += 1
+		if i == len(dnsResolvers) {
+			log.Println(err)
+			return nil, err
+		}
+		in, _, err = client.Exchange(message, dnsResolvers[i])
+	}
+
+	answers = append(answers, in.Answer...)
+	return answers, nil
+}
+
+type DnsHandler struct {
+	DnsResolvers []string
+	DbConn       *sql.DB
+}
+
+func (h *DnsHandler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
+	msg := new(dns.Msg)
+	msg.SetReply(r)
+	msg.Authoritative = true
+
+	for _, question := range r.Question {
+		answers, err := resolveRecursive(h.DbConn, h.DnsResolvers, question.Name, question.Qtype, MAX_RECURSION)
+		if err != nil {
+			fmt.Println(err)
+			continue
+		}
+		msg.Answer = append(msg.Answer, answers...)
+	}
+
+	log.Println(msg.Answer)
+	w.WriteMsg(msg)
+}
+
+func MakeServer(argv *args.Arguments, dbConn *sql.DB) *dns.Server {
+	handler := &DnsHandler{
+		DnsResolvers: argv.DnsRecursion,
+		DbConn:       dbConn,
+	}
+	addr := fmt.Sprintf(":%d", argv.DnsPort)
+
+	return &dns.Server{
+		Addr:      addr,
+		Net:       "udp",
+		Handler:   handler,
+		UDPSize:   65535,
+		ReusePort: true,
+	}
+}
-- 
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