From d1a74a7b9514a7ae1ba31eaa88ab85deaf822f2c Mon Sep 17 00:00:00 2001
From: Tim Beatham <tcb1@st-andrews.ac.uk>
Date: Fri, 24 Nov 2023 15:04:07 +0000
Subject: [PATCH] 32-incorporate-dns

Incorporated a DNS server. A DNS server can be run to resolve host
names.
---
 cmd/dns/main.go              |  18 ++++++
 pkg/ctrlserver/ctrlserver.go |   2 +-
 pkg/dns/dns.go               | 114 +++++++++++++++++++++++++++++++++++
 pkg/lib/id.go                |  13 +++-
 pkg/lib/regex.go             |  19 ++++++
 5 files changed, 164 insertions(+), 2 deletions(-)
 create mode 100644 cmd/dns/main.go
 create mode 100644 pkg/dns/dns.go
 create mode 100644 pkg/lib/regex.go

diff --git a/cmd/dns/main.go b/cmd/dns/main.go
new file mode 100644
index 0000000..7d45f8f
--- /dev/null
+++ b/cmd/dns/main.go
@@ -0,0 +1,18 @@
+package main
+
+import (
+	"log"
+
+	smegdns "github.com/tim-beatham/wgmesh/pkg/dns"
+)
+
+func main() {
+	server, err := smegdns.NewDns(53)
+
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+
+	defer server.Close()
+	server.Listen()
+}
diff --git a/pkg/ctrlserver/ctrlserver.go b/pkg/ctrlserver/ctrlserver.go
index fe779ee..6708956 100644
--- a/pkg/ctrlserver/ctrlserver.go
+++ b/pkg/ctrlserver/ctrlserver.go
@@ -31,7 +31,7 @@ func NewCtrlServer(params *NewCtrlServerParams) (*MeshCtrlServer, error) {
 	nodeFactory := crdt.MeshNodeFactory{
 		Config: *params.Conf,
 	}
-	idGenerator := &lib.UUIDGenerator{}
+	idGenerator := &lib.IDNameGenerator{}
 	ipAllocator := &ip.ULABuilder{}
 	interfaceManipulator := wg.NewWgInterfaceManipulator(params.Client)
 
diff --git a/pkg/dns/dns.go b/pkg/dns/dns.go
new file mode 100644
index 0000000..dab9143
--- /dev/null
+++ b/pkg/dns/dns.go
@@ -0,0 +1,114 @@
+package smegdns
+
+import (
+	"encoding/json"
+	"fmt"
+	"net"
+	"net/rpc"
+
+	"github.com/miekg/dns"
+	"github.com/tim-beatham/wgmesh/pkg/ipc"
+	"github.com/tim-beatham/wgmesh/pkg/lib"
+	logging "github.com/tim-beatham/wgmesh/pkg/log"
+	"github.com/tim-beatham/wgmesh/pkg/query"
+)
+
+const SockAddr = "/tmp/wgmesh_ipc.sock"
+
+const MeshRegularExpression = `(?P<meshId>.+)\.(?P<alias>.+)\.smeg\.`
+
+type DNSHandler struct {
+	client *rpc.Client
+	server *dns.Server
+}
+
+// queryMesh: queries the mesh network for the given meshId and node
+// with alias
+func (d *DNSHandler) queryMesh(meshId, alias string) net.IP {
+	var reply string
+
+	err := d.client.Call("IpcHandler.Query", &ipc.QueryMesh{
+		MeshId: meshId,
+		Query:  "[?alias == 'tim'] | [0]",
+	}, &reply)
+
+	if err != nil {
+		return nil
+	}
+
+	var node *query.QueryNode
+
+	err = json.Unmarshal([]byte(reply), &node)
+
+	if err != nil || node == nil {
+		return nil
+	}
+
+	ip, _, _ := net.ParseCIDR(node.WgHost)
+	return ip
+}
+
+func (d *DNSHandler) handleQuery(m *dns.Msg) {
+	for _, q := range m.Question {
+		switch q.Qtype {
+		case dns.TypeAAAA:
+			logging.Log.WriteInfof("Query for %s", q.Name)
+
+			groups := lib.MatchCaptureGroup(MeshRegularExpression, q.Name)
+
+			if len(groups) == 0 {
+				continue
+			}
+
+			ip := d.queryMesh(groups["meshId"], groups["alias"])
+
+			rr, err := dns.NewRR(fmt.Sprintf("%s AAAA %s", q.Name, ip))
+
+			if err != nil {
+				logging.Log.WriteErrorf(err.Error())
+			}
+
+			if err == nil {
+				m.Answer = append(m.Answer, rr)
+			}
+		}
+	}
+}
+
+func (h *DNSHandler) handleDnsRequest(w dns.ResponseWriter, r *dns.Msg) {
+	msg := new(dns.Msg)
+	msg.SetReply(r)
+	msg.Authoritative = true
+
+	switch r.Opcode {
+	case dns.OpcodeQuery:
+		h.handleQuery(msg)
+	}
+
+	w.WriteMsg(msg)
+}
+
+func (h *DNSHandler) Listen() error {
+	return h.server.ListenAndServe()
+}
+
+func (h *DNSHandler) Close() error {
+	return h.server.Shutdown()
+}
+
+func NewDns(udpPort int) (*DNSHandler, error) {
+	client, err := rpc.DialHTTP("unix", SockAddr)
+
+	if err != nil {
+		return nil, err
+	}
+
+	dnsHander := DNSHandler{
+		client: client,
+	}
+
+	dns.HandleFunc("smeg.", dnsHander.handleDnsRequest)
+
+	dnsHander.server = &dns.Server{Addr: fmt.Sprintf(":%d", udpPort), Net: "udp"}
+	return &dnsHander, nil
+}
diff --git a/pkg/lib/id.go b/pkg/lib/id.go
index ff486a4..d1b85ec 100644
--- a/pkg/lib/id.go
+++ b/pkg/lib/id.go
@@ -1,6 +1,9 @@
 package lib
 
-import "github.com/google/uuid"
+import (
+	"github.com/anandvarma/namegen"
+	"github.com/google/uuid"
+)
 
 // IdGenerator generates unique ids
 type IdGenerator interface {
@@ -15,3 +18,11 @@ func (g *UUIDGenerator) GetId() (string, error) {
 	id := uuid.New()
 	return id.String(), nil
 }
+
+type IDNameGenerator struct {
+}
+
+func (i *IDNameGenerator) GetId() (string, error) {
+	name_schema := namegen.New()
+	return name_schema.Get(), nil
+}
diff --git a/pkg/lib/regex.go b/pkg/lib/regex.go
new file mode 100644
index 0000000..6188fe6
--- /dev/null
+++ b/pkg/lib/regex.go
@@ -0,0 +1,19 @@
+package lib
+
+import "regexp"
+
+func MatchCaptureGroup(pattern, payload string) map[string]string {
+	patterns := make(map[string]string)
+
+	expr := regexp.MustCompile(pattern)
+
+	match := expr.FindStringSubmatch(payload)
+
+	for i, name := range expr.SubexpNames() {
+		if i != 0 && name != "" {
+			patterns[name] = match[i]
+		}
+	}
+
+	return patterns
+}