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Replace hardcoded 1.1.1.1 dns server with resolve.conf parsing #22

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Replace hardcoded 1.1.1.1 dns server with resolve.conf parsing #22

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31 changes: 26 additions & 5 deletions dns.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,11 @@ package main

import (
"context"
"errors"
"fmt"
"io"
"net"
"strings"

"github.com/miekg/dns"
)
Expand Down Expand Up @@ -236,8 +238,6 @@ func dnsTypeCode(t uint16) string {

// handleDNSQuery resolves IPv4 hostnames according to net.DefaultResolver
func handleDNSQuery(ctx context.Context, req *dns.Msg) ([]dns.RR, error) {
const upstreamDNS = "1.1.1.1:53" // TODO: get from resolv.conf and nsswitch.conf

if len(req.Question) == 0 {
return nil, nil // this means no answer, no error, which is fine
}
Expand Down Expand Up @@ -285,16 +285,37 @@ func handleDNSQuery(ctx context.Context, req *dns.Msg) ([]dns.RR, error) {

verbose("proxying non-A request to upstream DNS server...")

dnsClientConfig, err := dns.ClientConfigFromFile("/etc/resolv.conf")
if err != nil {
return nil, fmt.Errorf("could not parse /etc/resolv.conf: %w", err)
}

// proxy the request to another server
request := new(dns.Msg)
req.CopyTo(request)
request.Question = []dns.Question{question}

dnsClient := new(dns.Client)
dnsClient.Net = "udp"
response, _, err := dnsClient.Exchange(request, upstreamDNS)
if err != nil {
return nil, err
var (
response *dns.Msg
errs []error
)
for _, dnsServer := range dnsClientConfig.Servers {
response, _, err = dnsClient.Exchange(request, dnsServer)
if err != nil {
errs = append(errs, err)
continue
}
break
}

if len(errs) > 0 {
var errStr []string
for _, err := range errs {
errStr = append(errStr, err.Error())
}
return nil, errors.New(strings.Join(errStr, ", "))
}

verbosef("got answer from upstream dns server with %d answers", len(response.Answer))
Expand Down
32 changes: 26 additions & 6 deletions experiments/dns/dnsproxy.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,19 +2,18 @@ package main

import (
"context"
"errors"
"fmt"
"log"
"net"
"os"
"strings"

"github.com/alexflint/go-arg"
"github.com/miekg/dns"
)

const upstreamDNS = "1.1.1.1:53" // TODO: get from resolv.conf and nsswitch.conf

// handle resolves IPv4 hosts according to net.DefaultResolver

func handle(requestMsg *dns.Msg) ([]dns.RR, error) {
if len(requestMsg.Question) == 0 {
return nil, nil // this means no answer, no error, which is fine
Expand Down Expand Up @@ -47,16 +46,37 @@ func handle(requestMsg *dns.Msg) ([]dns.RR, error) {

log.Println("proxying the request...")

dnsClientConfig, err := dns.ClientConfigFromFile("/etc/resolv.conf")
if err != nil {
return nil, fmt.Errorf("could not parse /etc/resolv.conf: %w", err)
}

// proxy the request to another server
queryMsg := new(dns.Msg)
requestMsg.CopyTo(queryMsg)
queryMsg.Question = []dns.Question{question}

dnsClient := new(dns.Client)
dnsClient.Net = "udp"
response, _, err := dnsClient.Exchange(queryMsg, upstreamDNS)
if err != nil {
return nil, err
var (
response *dns.Msg
errs []error
)
for _, dnsServer := range dnsClientConfig.Servers {
response, _, err = dnsClient.Exchange(queryMsg, dnsServer)
if err != nil {
errs = append(errs, err)
continue
}
break
}

if len(errs) > 0 {
var errStr []string
for _, err := range errs {
errStr = append(errStr, err.Error())
}
return nil, errors.New(strings.Join(errStr, ", "))
}

log.Printf("got answer from upstream dns server with %d answers", len(response.Answer))
Expand Down