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Merge pull request #409 from CHTJonas/master

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Make internal DNS resolution opt-in
This commit is contained in:
Zack 2021-08-16 12:27:57 -07:00 • committed by GitHub
commit 9ce2321d01
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2 changed files with 32 additions and 29 deletions
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1
src/cli/cli.go
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@ -80,6 +80,7 @@ func Run() (err error) {
},
}
app.Flags = []cli.Flag{
&cli.BoolFlag{Name: "internal-dns", Usage: "use a built-in DNS stub resolver rather than the host operating system"},
&cli.BoolFlag{Name: "remember", Usage: "save these settings to reuse next time"},
&cli.BoolFlag{Name: "debug", Usage: "toggle debug mode"},
&cli.BoolFlag{Name: "yes", Usage: "automatically agree to all prompts"},

60
src/models/constants.go
View file

@ -4,7 +4,7 @@ import (
"context"
"fmt"
"net"
"time"
"os"
)
// TCP_BUFFER_SIZE is the maximum packet size
@ -16,25 +16,38 @@ var (
DEFAULT_RELAY6 = "croc6.schollz.com"
DEFAULT_PORT = "9009"
DEFAULT_PASSPHRASE = "pass123"
INTERNAL_DNS = false
)
// lookupTimeout for DNS requests
const lookupTimeout = time.Second
// publicDns are servers to be queried if a local lookup fails
var publicDns = []string{
"1.0.0.1", // Cloudflare
"1.1.1.1", // Cloudflare
"[2606:4700:4700::1111]", // Cloudflare
"[2606:4700:4700::1001]", // Cloudflare
"8.8.4.4", // Google
"8.8.8.8", // Google
"8.26.56.26", // Comodo
"208.67.220.220", // Cisco OpenDNS
"208.67.222.222", // Cisco OpenDNS
"[2001:4860:4860::8844]", // Google
"[2001:4860:4860::8888]", // Google
"9.9.9.9", // Quad9
"149.112.112.112", // Quad9
"[2620:fe::fe]", // Quad9
"[2620:fe::fe:9]", // Quad9
"8.26.56.26", // Comodo
"8.20.247.20", // Comodo
"208.67.220.220", // Cisco OpenDNS
"208.67.222.222", // Cisco OpenDNS
"[2620:119:35::35]", // Cisco OpenDNS
"[2620:119:53::53]", // Cisco OpenDNS
}
func init() {
for _, flag := range os.Args {
if flag == "--internal-dns" {
INTERNAL_DNS = true
break
}
}
var err error
DEFAULT_RELAY, err = lookup(DEFAULT_RELAY)
if err == nil {
@ -50,42 +63,33 @@ func init() {
}
}
// lookup an IP address.
//
// Priority is given to local queries, and the system falls back to a list of
// public DNS servers.
// Resolve a hostname to an IP address using DNS.
func lookup(address string) (ipaddress string, err error) {
ipaddress, err = localLookupIP(address)
if err == nil {
return
if !INTERNAL_DNS {
return localLookupIP(address)
}
err = nil
result := make(chan string, len(publicDns))
for _, dns := range publicDns {
go func(dns string) {
s, _ := remoteLookupIP(address, dns)
result <- s
s, err := remoteLookupIP(address, dns)
if err == nil {
result <- s
}
}(dns)
}
for i := 0; i < len(publicDns); i++ {
ipaddress = <-result
if ipaddress != "" {
return
}
}
err = fmt.Errorf("failed to lookup %s at any DNS server", address)
err = fmt.Errorf("failed to resolve %s: all DNS servers exhausted", address)
return
}
// localLookupIP returns a host's IP address based on the local resolver.
func localLookupIP(address string) (ipaddress string, err error) {
ctx, cancel := context.WithTimeout(context.Background(), lookupTimeout)
defer cancel()
ip, err := net.DefaultResolver.LookupHost(ctx, address)
ip, err := net.LookupHost(address)
if err != nil {
return
}
@ -98,10 +102,8 @@ func remoteLookupIP(address, dns string) (ipaddress string, err error) {
r := &net.Resolver{
PreferGo: true,
Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
d := net.Dialer{
Timeout: lookupTimeout,
}
return d.DialContext(ctx, "udp", dns+":53")
d := new(net.Dialer)
return d.DialContext(ctx, network, dns+":53")
},
}
ip, err := r.LookupHost(context.Background(), address)