doggo/pkg/resolve/resolver.go

86 lines
2.1 KiB
Go

package resolve
import (
"fmt"
"net"
"github.com/miekg/dns"
)
// Resolver holds the configuration for a dns.Client
type Resolver 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{}
return &Resolver{
client: client,
servers: servers,
}
}
// 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 &Resolver{
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 (r *Resolver) 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 r.servers {
in, rtt, err := r.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
}