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39ffa16853
This is enough to handle the DNS queries as generated by Go's net package (which our HTTP/SOCKS client uses), and the responses generated by the ExitDNS DoH server. This isn't yet suitable for putting on 100.100.100.100 where a number of different DNS clients would hit it, as this doesn't yet do EDNS0. It might work, but it's untested and likely incomplete. Likewise, this doesn't handle anything about truncation, as the exchanges are entirely in memory between Go or DoH. That would also need to be handled later, if/when it's hooked up to 100.100.100.100. Updates #3507 Change-Id: I1736b0ad31eea85ea853b310c52c5e6bf65c6e2a Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
102 lines
2.5 KiB
Go
102 lines
2.5 KiB
Go
// Copyright (c) 2021 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 tsdial
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import (
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"bytes"
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"context"
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"errors"
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"fmt"
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"io"
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"net"
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"net/http"
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"time"
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"tailscale.com/net/dnscache"
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)
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// dohConn is a net.PacketConn suitable for returning from
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// net.Dialer.Dial to send DNS queries over PeerAPI to exit nodes'
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// ExitDNS DoH proxy service.
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type dohConn struct {
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ctx context.Context
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baseURL string
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hc *http.Client // if nil, default is used
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dnsCache *dnscache.MessageCache
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rbuf bytes.Buffer
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}
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var (
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_ net.Conn = (*dohConn)(nil)
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_ net.PacketConn = (*dohConn)(nil) // be a PacketConn to change net.Resolver semantics
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)
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func (*dohConn) Close() error { return nil }
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func (*dohConn) LocalAddr() net.Addr { return todoAddr{} }
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func (*dohConn) RemoteAddr() net.Addr { return todoAddr{} }
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func (*dohConn) SetDeadline(t time.Time) error { return nil }
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func (*dohConn) SetReadDeadline(t time.Time) error { return nil }
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func (*dohConn) SetWriteDeadline(t time.Time) error { return nil }
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func (c *dohConn) WriteTo(p []byte, addr net.Addr) (n int, err error) {
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return c.Write(p)
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}
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func (c *dohConn) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
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n, err = c.Read(p)
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return n, todoAddr{}, err
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}
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func (c *dohConn) Read(p []byte) (n int, err error) {
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return c.rbuf.Read(p)
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}
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func (c *dohConn) Write(packet []byte) (n int, err error) {
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if c.dnsCache != nil {
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err := c.dnsCache.ReplyFromCache(&c.rbuf, packet)
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if err == nil {
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// Cache hit.
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// TODO(bradfitz): add clientmetric
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return len(packet), nil
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}
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c.rbuf.Reset()
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}
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req, err := http.NewRequestWithContext(c.ctx, "POST", c.baseURL, bytes.NewReader(packet))
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if err != nil {
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return 0, err
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}
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const dohType = "application/dns-message"
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req.Header.Set("Content-Type", dohType)
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hc := c.hc
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if hc == nil {
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hc = http.DefaultClient
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}
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hres, err := hc.Do(req)
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if err != nil {
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return 0, err
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}
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defer hres.Body.Close()
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if hres.StatusCode != 200 {
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return 0, errors.New(hres.Status)
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}
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if ct := hres.Header.Get("Content-Type"); ct != dohType {
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return 0, fmt.Errorf("unexpected response Content-Type %q", ct)
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}
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_, err = io.Copy(&c.rbuf, hres.Body)
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if err != nil {
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return 0, err
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}
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if c.dnsCache != nil {
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c.dnsCache.AddCacheEntry(packet, c.rbuf.Bytes())
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}
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return len(packet), nil
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}
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type todoAddr struct{}
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func (todoAddr) Network() string { return "unused" }
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func (todoAddr) String() string { return "unused-todoAddr" }
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