cloudflared-mirror/edgediscovery/allregions/discovery.go

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package allregions
import (
"context"
"crypto/tls"
"fmt"
"net"
"time"
"github.com/cloudflare/cloudflared/logger"
"github.com/pkg/errors"
)
const (
// Used to discover HA origintunneld servers
srvService = "origintunneld"
srvProto = "tcp"
srvName = "argotunnel.com"
// Used to fallback to DoT when we can't use the default resolver to
// discover HA origintunneld servers (GitHub issue #75).
dotServerName = "cloudflare-dns.com"
dotServerAddr = "1.1.1.1:853"
dotTimeout = time.Duration(15 * time.Second)
// SRV record resolution TTL
resolveEdgeAddrTTL = 1 * time.Hour
subsystemEdgeAddrResolver = "edgeAddrResolver"
)
// Redeclare network functions so they can be overridden in tests.
var (
netLookupSRV = net.LookupSRV
netLookupIP = net.LookupIP
)
// If the call to net.LookupSRV fails, try to fall back to DoT from Cloudflare directly.
//
// Note: Instead of DoT, we could also have used DoH. Either of these:
// - directly via the JSON API (https://1.1.1.1/dns-query?ct=application/dns-json&name=_origintunneld._tcp.argotunnel.com&type=srv)
// - indirectly via `tunneldns.NewUpstreamHTTPS()`
// But both of these cases miss out on a key feature from the stdlib:
// "The returned records are sorted by priority and randomized by weight within a priority."
// (https://golang.org/pkg/net/#Resolver.LookupSRV)
// Does this matter? I don't know. It may someday. Let's use DoT so we don't need to worry about it.
// See also: Go feature request for stdlib-supported DoH: https://github.com/golang/go/issues/27552
var fallbackLookupSRV = lookupSRVWithDOT
var friendlyDNSErrorLines = []string{
`Please try the following things to diagnose this issue:`,
` 1. ensure that argotunnel.com is returning "origintunneld" service records.`,
` Run your system's equivalent of: dig srv _origintunneld._tcp.argotunnel.com`,
` 2. ensure that your DNS resolver is not returning compressed SRV records.`,
` See GitHub issue https://github.com/golang/go/issues/27546`,
` For example, you could use Cloudflare's 1.1.1.1 as your resolver:`,
` https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/`,
}
// EdgeDiscovery implements HA service discovery lookup.
func edgeDiscovery(logger logger.Service) ([][]*net.TCPAddr, error) {
_, addrs, err := netLookupSRV(srvService, srvProto, srvName)
if err != nil {
_, fallbackAddrs, fallbackErr := fallbackLookupSRV(srvService, srvProto, srvName)
if fallbackErr != nil || len(fallbackAddrs) == 0 {
// use the original DNS error `err` in messages, not `fallbackErr`
logger.Errorf("Error looking up Cloudflare edge IPs: the DNS query failed: %s", err)
for _, s := range friendlyDNSErrorLines {
logger.Error(s)
}
return nil, errors.Wrapf(err, "Could not lookup srv records on _%v._%v.%v", srvService, srvProto, srvName)
}
// Accept the fallback results and keep going
addrs = fallbackAddrs
}
var resolvedIPsPerCNAME [][]*net.TCPAddr
for _, addr := range addrs {
ips, err := resolveSRVToTCP(addr)
if err != nil {
return nil, err
}
resolvedIPsPerCNAME = append(resolvedIPsPerCNAME, ips)
}
return resolvedIPsPerCNAME, nil
}
func lookupSRVWithDOT(service, proto, name string) (cname string, addrs []*net.SRV, err error) {
// Inspiration: https://github.com/artyom/dot/blob/master/dot.go
r := &net.Resolver{
PreferGo: true,
Dial: func(ctx context.Context, _ string, _ string) (net.Conn, error) {
var dialer net.Dialer
conn, err := dialer.DialContext(ctx, "tcp", dotServerAddr)
if err != nil {
return nil, err
}
tlsConfig := &tls.Config{ServerName: dotServerName}
return tls.Client(conn, tlsConfig), nil
},
}
ctx, cancel := context.WithTimeout(context.Background(), dotTimeout)
defer cancel()
return r.LookupSRV(ctx, srvService, srvProto, srvName)
}
func resolveSRVToTCP(srv *net.SRV) ([]*net.TCPAddr, error) {
ips, err := netLookupIP(srv.Target)
if err != nil {
return nil, errors.Wrapf(err, "Couldn't resolve SRV record %v", srv)
}
if len(ips) == 0 {
return nil, fmt.Errorf("SRV record %v had no IPs", srv)
}
addrs := make([]*net.TCPAddr, len(ips))
for i, ip := range ips {
addrs[i] = &net.TCPAddr{IP: ip, Port: int(srv.Port)}
}
return addrs, nil
}
// ResolveAddrs resolves TCP address given a list of addresses. Address can be a hostname, however, it will return at most one
// of the hostname's IP addresses.
func ResolveAddrs(addrs []string, logger logger.Service) (resolved []*net.TCPAddr) {
for _, addr := range addrs {
tcpAddr, err := net.ResolveTCPAddr("tcp", addr)
if err != nil {
logger.Errorf("Failed to resolve %s, err: %v", addr, err)
} else {
resolved = append(resolved, tcpAddr)
}
}
return
}