chore: Create a resolver package

pkg/resolvers/classic.go

@@ -0,0 +1,97 @@
+package resolvers
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/miekg/dns"
+)
+
+// Manager represents the config options for setting up a Resolver.
+type Manager struct {
+	client  *dns.Client
+	servers []string
+}
+
+//DefaultResolvConfPath specifies path to default resolv config file on UNIX.
+const DefaultResolvConfPath = "/etc/resolv.conf"
+
+// NewResolver accepts a list of nameservers and configures a DNS resolver.
+func NewResolver(servers []string) Resolver {
+	client := &dns.Client{}
+	var nameservers []string
+	for _, srv := range servers {
+		if i := net.ParseIP(srv); i != nil {
+			nameservers = append(nameservers, net.JoinHostPort(srv, "53"))
+		} else {
+			nameservers = append(nameservers, dns.Fqdn(srv)+":"+"53")
+		}
+	}
+	return &Manager{
+		client:  client,
+		servers: nameservers,
+	}
+}
+
+// NewResolverFromResolvFile loads the configuration from resolv config file
+// and initialises a DNS resolver.
+func NewResolverFromResolvFile(resolvFilePath string) (Resolver, error) {
+	if resolvFilePath == "" {
+		resolvFilePath = DefaultResolvConfPath
+	}
+	cfg, err := dns.ClientConfigFromFile(resolvFilePath)
+	if err != nil {
+		return nil, err
+	}
+
+	servers := make([]string, 0, len(cfg.Servers))
+	for _, s := range cfg.Servers {
+		ip := net.ParseIP(s)
+		// handle IPv6
+		if ip != nil && ip.To4() != nil {
+			servers = append(servers, fmt.Sprintf("%s:%s", s, cfg.Port))
+		} else {
+			servers = append(servers, fmt.Sprintf("[%s]:%s", s, cfg.Port))
+		}
+	}
+
+	client := &dns.Client{}
+	return &Manager{
+		client:  client,
+		servers: servers,
+	}, nil
+}
+
+// Lookup prepare a list of DNS messages to be sent to the server.
+// It's possible to send multiple question in one message
+// but some nameservers are not able to
+func (m *Manager) Lookup(questions []dns.Question) error {
+	var messages = make([]dns.Msg, 0, len(questions))
+	for _, q := range questions {
+		msg := dns.Msg{}
+		msg.Id = dns.Id()
+		msg.RecursionDesired = true
+		// It's recommended to only send 1 question for 1 DNS message.
+		msg.Question = []dns.Question{q}
+		messages = append(messages, msg)
+	}
+	for _, msg := range messages {
+		for _, srv := range m.servers {
+			in, rtt, err := m.client.Exchange(&msg, srv)
+			if err != nil {
+				return err
+			}
+			for _, ans := range in.Answer {
+				if t, ok := ans.(*dns.A); ok {
+					fmt.Println(t.String())
+				}
+			}
+			fmt.Println("rtt is", rtt)
+		}
+	}
+	return nil
+}
+
+func (m *Manager) Name() string {
+	return "classic"
+}

pkg/resolvers/doh.go

@@ -0,0 +1 @@
+package resolvers

pkg/resolvers/dot.go

@@ -0,0 +1 @@
+package resolvers

pkg/resolvers/resolver.go

@@ -0,0 +1,8 @@
+package resolvers
+
+import "github.com/miekg/dns"
+
+type Resolver interface {
+	Name() string
+	Lookup([]dns.Question) error
+}