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tailscale/net/dns/config.go

107 lines
2.9 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package dns
import (
"sort"
"inet.af/netaddr"
"tailscale.com/util/dnsname"
)
// Config is a DNS configuration.
type Config struct {
// DefaultResolvers are the DNS resolvers to use for DNS names
// which aren't covered by more specific per-domain routes below.
// If empty, the OS's default resolvers (the ones that predate
// Tailscale altering the configuration) are used.
DefaultResolvers []netaddr.IPPort
// Routes maps a DNS suffix to the resolvers that should be used
// for queries that fall within that suffix.
// If a query doesn't match any entry in Routes, the
// DefaultResolvers are used.
// A Routes entry with no resolvers means the route should be
// authoritatively answered using the contents of Hosts.
Routes map[dnsname.FQDN][]netaddr.IPPort
// SearchDomains are DNS suffixes to try when expanding
// single-label queries.
SearchDomains []dnsname.FQDN
// Hosts maps DNS FQDNs to their IPs, which can be a mix of IPv4
// and IPv6.
// Queries matching entries in Hosts are resolved locally by
// 100.100.100.100 without leaving the machine.
// Adding an entry to Hosts merely creates the record. If you want
// it to resolve, you also need to add appropriate routes to
// Routes.
Hosts map[dnsname.FQDN][]netaddr.IP
}
// needsAnyResolvers reports whether c requires a resolver to be set
// at the OS level.
func (c Config) needsOSResolver() bool {
return c.hasDefaultResolvers() || c.hasRoutes()
}
func (c Config) hasRoutes() bool {
return len(c.Routes) > 0
}
// hasDefaultResolversOnly reports whether the only resolvers in c are
// DefaultResolvers.
func (c Config) hasDefaultResolversOnly() bool {
return c.hasDefaultResolvers() && !c.hasRoutes()
}
func (c Config) hasDefaultResolvers() bool {
return len(c.DefaultResolvers) > 0
}
// singleResolverSet returns the resolvers used by c.Routes if all
// routes use the same resolvers, or nil if multiple sets of resolvers
// are specified.
func (c Config) singleResolverSet() []netaddr.IPPort {
var (
prev []netaddr.IPPort
prevInitialized bool
)
for _, resolvers := range c.Routes {
if !prevInitialized {
prev = resolvers
prevInitialized = true
continue
}
if !sameIPPorts(prev, resolvers) {
return nil
}
}
return prev
}
// matchDomains returns the list of match suffixes needed by Routes.
func (c Config) matchDomains() []dnsname.FQDN {
ret := make([]dnsname.FQDN, 0, len(c.Routes))
for suffix := range c.Routes {
ret = append(ret, suffix)
}
sort.Slice(ret, func(i, j int) bool {
return ret[i].WithTrailingDot() < ret[j].WithTrailingDot()
})
return ret
}
func sameIPPorts(a, b []netaddr.IPPort) bool {
if len(a) != len(b) {
return false
}
for i := range a {
if a[i] != b[i] {
return false
}
}
return true
}