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232 lines
8.3 KiB
Go
232 lines
8.3 KiB
Go
// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package publicdns contains mapping and helpers for working with
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// public DNS providers.
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package publicdns
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import (
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"bytes"
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"encoding/hex"
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"fmt"
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"net/netip"
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"sort"
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"strings"
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"sync"
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"tailscale.com/util/strs"
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)
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// dohOfIP maps from public DNS IPs to their DoH base URL.
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//
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// This does not include NextDNS which is handled specially.
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var dohOfIP = map[netip.Addr]string{} // 8.8.8.8 => "https://..."
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var dohIPsOfBase = map[string][]netip.Addr{}
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var populateOnce sync.Once
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// DoHEndpointFromIP returns the DNS-over-HTTPS base URL for a given IP
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// and whether it's DoH-only (not speaking DNS on port 53).
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//
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// The ok result is whether the IP is a known DNS server.
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func DoHEndpointFromIP(ip netip.Addr) (dohBase string, dohOnly bool, ok bool) {
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populateOnce.Do(populate)
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if b, ok := dohOfIP[ip]; ok {
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return b, false, true
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}
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// NextDNS DoH URLs are of the form "https://dns.nextdns.io/c3a884"
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// where the path component is the lower 8 bytes of the IPv6 address
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// in lowercase hex without any zero padding.
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if nextDNSv6RangeA.Contains(ip) || nextDNSv6RangeB.Contains(ip) {
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a := ip.As16()
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var sb strings.Builder
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const base = "https://dns.nextdns.io/"
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sb.Grow(len(base) + 8)
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sb.WriteString(base)
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for _, b := range bytes.TrimLeft(a[8:], "\x00") {
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fmt.Fprintf(&sb, "%02x", b)
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}
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return sb.String(), true, true
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}
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return "", false, false
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}
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// KnownDoHPrefixes returns the list of DoH base URLs.
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//
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// It returns a new copy each time, sorted. It's meant for tests.
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//
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// It does not include providers that have customer-specific DoH URLs like
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// NextDNS.
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func KnownDoHPrefixes() []string {
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populateOnce.Do(populate)
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ret := make([]string, 0, len(dohIPsOfBase))
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for b := range dohIPsOfBase {
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ret = append(ret, b)
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}
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sort.Strings(ret)
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return ret
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}
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func isSlashOrQuestionMark(r rune) bool {
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return r == '/' || r == '?'
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}
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// DoHIPsOfBase returns the IP addresses to use to dial the provided DoH base
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// URL.
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//
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// It is basically the inverse of DoHEndpointFromIP with the exception that for
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// NextDNS it returns IPv4 addresses that DoHEndpointFromIP doesn't map back.
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func DoHIPsOfBase(dohBase string) []netip.Addr {
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populateOnce.Do(populate)
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if s := dohIPsOfBase[dohBase]; len(s) > 0 {
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return s
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}
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if hexStr, ok := strs.CutPrefix(dohBase, "https://dns.nextdns.io/"); ok {
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// The path is of the form /<profile-hex>[/<hostname>/<model>/<device id>...]
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// or /<profile-hex>?<query params>
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// but only the <profile-hex> is required. Ignore the rest:
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if i := strings.IndexFunc(hexStr, isSlashOrQuestionMark); i != -1 {
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hexStr = hexStr[:i]
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}
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// TODO(bradfitz): using the NextDNS anycast addresses works but is not
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// ideal. Some of their regions have better latency via a non-anycast IP
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// which we could get by first resolving A/AAAA "dns.nextdns.io" over
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// DoH using their anycast address. For now we only use the anycast
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// addresses. The IPv4 IPs we use are just the first one in their ranges.
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// For IPv6 we put the profile ID in the lower bytes, but that seems just
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// conventional for them and not required (it'll already be in the DoH path).
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// (Really we shouldn't use either IPv4 or IPv6 anycast for DoH once we
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// resolve "dns.nextdns.io".)
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if b, err := hex.DecodeString(hexStr); err == nil && len(b) <= 8 && len(b) > 0 {
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return []netip.Addr{
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nextDNSv4One,
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nextDNSv4Two,
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nextDNSv6Gen(nextDNSv6RangeA.Addr(), b),
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nextDNSv6Gen(nextDNSv6RangeB.Addr(), b),
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}
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}
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}
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return nil
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}
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// DoHV6 returns the first IPv6 DNS address from a given public DNS provider
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// if found, along with a boolean indicating success.
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func DoHV6(base string) (ip netip.Addr, ok bool) {
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populateOnce.Do(populate)
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for _, ip := range dohIPsOfBase[base] {
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if ip.Is6() {
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return ip, true
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}
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}
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return ip, false
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}
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// addDoH parses a given well-formed ip string into a netip.Addr type and
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// adds it to both knownDoH and dohIPsOFBase maps.
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func addDoH(ipStr, base string) {
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ip := netip.MustParseAddr(ipStr)
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dohOfIP[ip] = base
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dohIPsOfBase[base] = append(dohIPsOfBase[base], ip)
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}
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// populate is called once to initialize the knownDoH and dohIPsOfBase maps.
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func populate() {
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// Cloudflare
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addDoH("1.1.1.1", "https://cloudflare-dns.com/dns-query")
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addDoH("1.0.0.1", "https://cloudflare-dns.com/dns-query")
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addDoH("2606:4700:4700::1111", "https://cloudflare-dns.com/dns-query")
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addDoH("2606:4700:4700::1001", "https://cloudflare-dns.com/dns-query")
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// Cloudflare -Malware
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addDoH("1.1.1.2", "https://security.cloudflare-dns.com/dns-query")
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addDoH("1.0.0.2", "https://security.cloudflare-dns.com/dns-query")
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addDoH("2606:4700:4700::1112", "https://security.cloudflare-dns.com/dns-query")
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addDoH("2606:4700:4700::1002", "https://security.cloudflare-dns.com/dns-query")
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// Cloudflare -Malware -Adult
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addDoH("1.1.1.3", "https://family.cloudflare-dns.com/dns-query")
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addDoH("1.0.0.3", "https://family.cloudflare-dns.com/dns-query")
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addDoH("2606:4700:4700::1113", "https://family.cloudflare-dns.com/dns-query")
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addDoH("2606:4700:4700::1003", "https://family.cloudflare-dns.com/dns-query")
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// Google
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addDoH("8.8.8.8", "https://dns.google/dns-query")
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addDoH("8.8.4.4", "https://dns.google/dns-query")
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addDoH("2001:4860:4860::8888", "https://dns.google/dns-query")
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addDoH("2001:4860:4860::8844", "https://dns.google/dns-query")
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// OpenDNS
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// TODO(bradfitz): OpenDNS is unique amongst this current set in that
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// its DoH DNS names resolve to different IPs than its normal DNS
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// IPs. Support that later. For now we assume that they're the same.
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// addDoH("208.67.222.222", "https://doh.opendns.com/dns-query")
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// addDoH("208.67.220.220", "https://doh.opendns.com/dns-query")
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// addDoH("208.67.222.123", "https://doh.familyshield.opendns.com/dns-query")
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// addDoH("208.67.220.123", "https://doh.familyshield.opendns.com/dns-query")
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// Quad9
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addDoH("9.9.9.9", "https://dns.quad9.net/dns-query")
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addDoH("149.112.112.112", "https://dns.quad9.net/dns-query")
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addDoH("2620:fe::fe", "https://dns.quad9.net/dns-query")
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addDoH("2620:fe::fe:9", "https://dns.quad9.net/dns-query")
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// Quad9 -DNSSEC
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addDoH("9.9.9.10", "https://dns10.quad9.net/dns-query")
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addDoH("149.112.112.10", "https://dns10.quad9.net/dns-query")
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addDoH("2620:fe::10", "https://dns10.quad9.net/dns-query")
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addDoH("2620:fe::fe:10", "https://dns10.quad9.net/dns-query")
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// Mullvad
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addDoH("194.242.2.2", "https://doh.mullvad.net/dns-query")
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addDoH("193.19.108.2", "https://doh.mullvad.net/dns-query")
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addDoH("2a07:e340::2", "https://doh.mullvad.net/dns-query")
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// Mullvad -Ads
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addDoH("194.242.2.3", "https://adblock.doh.mullvad.net/dns-query")
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addDoH("193.19.108.3", "https://adblock.doh.mullvad.net/dns-query")
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addDoH("2a07:e340::3", "https://adblock.doh.mullvad.net/dns-query")
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}
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var (
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// The NextDNS IPv6 ranges (primary and secondary). The customer ID is
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// encoded in the lower bytes and is used (in hex form) as the DoH query
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// path.
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nextDNSv6RangeA = netip.MustParsePrefix("2a07:a8c0::/33")
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nextDNSv6RangeB = netip.MustParsePrefix("2a07:a8c1::/33")
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// The first two IPs in the /24 v4 ranges can be used for DoH to NextDNS.
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//
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// They're Anycast and usually okay, but NextDNS has some locations that
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// don't do BGP and can get results for querying them over DoH to find the
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// IPv4 address of "dns.mynextdns.io" and find an even better result.
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//
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// Note that the Tailscale DNS client does not do any of the "IP address
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// linking" that NextDNS can do with its IPv4 addresses. These addresses
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// are only used for DoH.
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nextDNSv4RangeA = netip.MustParsePrefix("45.90.28.0/24")
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nextDNSv4RangeB = netip.MustParsePrefix("45.90.30.0/24")
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nextDNSv4One = nextDNSv4RangeA.Addr()
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nextDNSv4Two = nextDNSv4RangeB.Addr()
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)
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// nextDNSv6Gen generates a NextDNS IPv6 address from the upper 8 bytes in the
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// provided ip and using id as the lowest 0-8 bytes.
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func nextDNSv6Gen(ip netip.Addr, id []byte) netip.Addr {
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if len(id) > 8 {
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return netip.Addr{}
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}
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a := ip.As16()
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copy(a[16-len(id):], id)
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return netip.AddrFrom16(a)
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}
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// IPIsDoHOnlyServer reports whether ip is a DNS server that should only use
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// DNS-over-HTTPS (not regular port 53 DNS).
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func IPIsDoHOnlyServer(ip netip.Addr) bool {
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return nextDNSv6RangeA.Contains(ip) || nextDNSv6RangeB.Contains(ip) ||
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nextDNSv4RangeA.Contains(ip) || nextDNSv4RangeB.Contains(ip)
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}
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