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upstream_doh.go
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upstream_doh.go
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package upstream
import (
"context"
"crypto/tls"
"encoding/base64"
"fmt"
"io"
"net"
"net/http"
"net/url"
"runtime"
"sync"
"time"
"github.com/AdguardTeam/dnsproxy/internal/bootstrap"
"github.com/AdguardTeam/golibs/errors"
"github.com/AdguardTeam/golibs/log"
"github.com/miekg/dns"
"github.com/quic-go/quic-go"
"github.com/quic-go/quic-go/http3"
"golang.org/x/net/http2"
)
// Values to configure HTTP and HTTP/2 transport.
const (
// transportDefaultReadIdleTimeout is the default timeout for pinging
// idle connections in HTTP/2 transport.
transportDefaultReadIdleTimeout = 30 * time.Second
// transportDefaultIdleConnTimeout is the default timeout for idle
// connections in HTTP transport.
transportDefaultIdleConnTimeout = 5 * time.Minute
// dohMaxConnsPerHost controls the maximum number of connections for
// each host. Note, that setting it to 1 may cause issues with Go's http
// implementation, see https://github.com/AdguardTeam/dnsproxy/issues/278.
dohMaxConnsPerHost = 2
// dohMaxIdleConns controls the maximum number of connections being idle
// at the same time.
dohMaxIdleConns = 2
)
// dnsOverHTTPS is a struct that implements the Upstream interface for the
// DNS-over-HTTPS protocol.
type dnsOverHTTPS struct {
// getDialer either returns an initialized dial handler or creates a new
// one.
getDialer DialerInitializer
// addr is the DNS-over-HTTPS server URL.
addr *url.URL
// tlsConf is the configuration of TLS.
tlsConf *tls.Config
// The Client's Transport typically has internal state (cached TCP
// connections), so Clients should be reused instead of created as needed.
// Clients are safe for concurrent use by multiple goroutines.
client *http.Client
// quicConfig is the QUIC configuration that is used if HTTP/3 is enabled
// for this upstream.
quicConfig *quic.Config
// clientMu protects client.
clientMu sync.Mutex
// quicConfMu protects quicConfig.
quicConfMu sync.Mutex
// timeout is used in HTTP client and for H3 probes.
timeout time.Duration
}
// type check
var _ Upstream = (*dnsOverHTTPS)(nil)
// newDoH returns the DNS-over-HTTPS Upstream.
func newDoH(addr *url.URL, opts *Options) (u Upstream, err error) {
addPort(addr, defaultPortDoH)
var httpVersions []HTTPVersion
if addr.Scheme == "h3" {
addr.Scheme = "https"
httpVersions = []HTTPVersion{HTTPVersion3}
} else if httpVersions = opts.HTTPVersions; len(opts.HTTPVersions) == 0 {
httpVersions = DefaultHTTPVersions
}
getDialer, err := newDialerInitializer(addr, opts)
if err != nil {
// Don't wrap the error since it's informative enough as is.
return nil, err
}
ups := &dnsOverHTTPS{
getDialer: getDialer,
addr: addr,
quicConfig: &quic.Config{
KeepAlivePeriod: QUICKeepAlivePeriod,
TokenStore: newQUICTokenStore(),
Tracer: opts.QUICTracer,
},
tlsConf: &tls.Config{
ServerName: addr.Hostname(),
RootCAs: RootCAs,
CipherSuites: CipherSuites,
// Use the default capacity for the LRU cache. It may be useful to
// store several caches since the user may be routed to different
// servers in case there's load balancing on the server-side.
ClientSessionCache: tls.NewLRUClientSessionCache(0),
MinVersion: tls.VersionTLS12,
InsecureSkipVerify: opts.InsecureSkipVerify,
VerifyPeerCertificate: opts.VerifyServerCertificate,
VerifyConnection: opts.VerifyConnection,
},
timeout: opts.Timeout,
}
for _, v := range httpVersions {
ups.tlsConf.NextProtos = append(ups.tlsConf.NextProtos, string(v))
}
runtime.SetFinalizer(ups, (*dnsOverHTTPS).Close)
return ups, nil
}
// Address implements the [Upstream] interface for *dnsOverHTTPS.
func (p *dnsOverHTTPS) Address() string { return p.addr.String() }
// Exchange implements the Upstream interface for *dnsOverHTTPS.
func (p *dnsOverHTTPS) Exchange(m *dns.Msg) (resp *dns.Msg, err error) {
// In order to maximize HTTP cache friendliness, DoH clients using media
// formats that include the ID field from the DNS message header, such
// as "application/dns-message", SHOULD use a DNS ID of 0 in every DNS
// request.
//
// See https://www.rfc-editor.org/rfc/rfc8484.html.
id := m.Id
m.Id = 0
defer func() {
// Restore the original ID to not break compatibility with proxies.
m.Id = id
if resp != nil {
resp.Id = id
}
}()
// Check if there was already an active client before sending the request.
// We'll only attempt to re-connect if there was one.
client, isCached, err := p.getClient()
if err != nil {
return nil, fmt.Errorf("failed to init http client: %w", err)
}
// Make the first attempt to send the DNS query.
resp, err = p.exchangeHTTPS(client, m)
// Make up to 2 attempts to re-create the HTTP client and send the request
// again. There are several cases (mostly, with QUIC) where this workaround
// is necessary to make HTTP client usable. We need to make 2 attempts in
// the case when the connection was closed (due to inactivity for example)
// AND the server refuses to open a 0-RTT connection.
for i := 0; isCached && p.shouldRetry(err) && i < 2; i++ {
client, err = p.resetClient(err)
if err != nil {
return nil, fmt.Errorf("failed to reset http client: %w", err)
}
resp, err = p.exchangeHTTPS(client, m)
}
if err != nil {
// If the request failed anyway, make sure we don't use this client.
_, resErr := p.resetClient(err)
return nil, errors.WithDeferred(err, resErr)
}
return resp, err
}
// Close implements the Upstream interface for *dnsOverHTTPS.
func (p *dnsOverHTTPS) Close() (err error) {
p.clientMu.Lock()
defer p.clientMu.Unlock()
runtime.SetFinalizer(p, nil)
if p.client == nil {
return nil
}
return p.closeClient(p.client)
}
// closeClient cleans up resources used by client if necessary. Note, that at
// this point it should only be done for HTTP/3 as it may leak due to keep-alive
// connections.
func (p *dnsOverHTTPS) closeClient(client *http.Client) (err error) {
if isHTTP3(client) {
return client.Transport.(io.Closer).Close()
}
return nil
}
// exchangeHTTPS logs the request and its result and calls exchangeHTTPSClient.
func (p *dnsOverHTTPS) exchangeHTTPS(client *http.Client, req *dns.Msg) (resp *dns.Msg, err error) {
addr := p.Address()
n := networkTCP
if isHTTP3(client) {
n = networkUDP
}
logBegin(addr, n, req)
resp, err = p.exchangeHTTPSClient(client, req)
logFinish(addr, n, err)
return resp, err
}
// exchangeHTTPSClient sends the DNS query to a DoH resolver using the specified
// http.Client instance.
func (p *dnsOverHTTPS) exchangeHTTPSClient(
client *http.Client,
req *dns.Msg,
) (resp *dns.Msg, err error) {
buf, err := req.Pack()
if err != nil {
return nil, fmt.Errorf("packing message: %w", err)
}
// It appears, that GET requests are more memory-efficient with Golang
// implementation of HTTP/2.
method := http.MethodGet
if isHTTP3(client) {
// If we're using HTTP/3, use http3.MethodGet0RTT to force using 0-RTT.
method = http3.MethodGet0RTT
}
u := url.URL{
Scheme: p.addr.Scheme,
Host: p.addr.Host,
Path: p.addr.Path,
RawQuery: fmt.Sprintf("dns=%s", base64.RawURLEncoding.EncodeToString(buf)),
}
httpReq, err := http.NewRequest(method, u.String(), nil)
if err != nil {
return nil, fmt.Errorf("creating http request to %s: %w", p.addr, err)
}
httpReq.Header.Set("Accept", "application/dns-message")
httpReq.Header.Set("User-Agent", "")
httpResp, err := client.Do(httpReq)
if err != nil {
return nil, fmt.Errorf("requesting %s: %w", p.addr, err)
}
defer log.OnCloserError(httpResp.Body, log.DEBUG)
body, err := io.ReadAll(httpResp.Body)
if err != nil {
return nil, fmt.Errorf("reading %s: %w", p.addr, err)
}
if httpResp.StatusCode != http.StatusOK {
return nil,
fmt.Errorf(
"expected status %d, got %d from %s",
http.StatusOK,
httpResp.StatusCode,
p.addr,
)
}
resp = &dns.Msg{}
err = resp.Unpack(body)
if err != nil {
return nil, fmt.Errorf(
"unpacking response from %s: body is %s: %w",
p.addr,
body,
err,
)
}
if resp.Id != req.Id {
err = dns.ErrId
}
return resp, err
}
// shouldRetry checks what error we have received and returns true if we should
// re-create the HTTP client and retry the request.
func (p *dnsOverHTTPS) shouldRetry(err error) (ok bool) {
if err == nil {
return false
}
var netErr net.Error
if errors.As(err, &netErr) && netErr.Timeout() {
// If this is a timeout error, trying to forcibly re-create the HTTP
// client instance. This is an attempt to fix an issue with DoH client
// stalling after a network change.
//
// See https://github.com/AdguardTeam/AdGuardHome/issues/3217.
return true
}
if isQUICRetryError(err) {
return true
}
return false
}
// resetClient triggers re-creation of the *http.Client that is used by this
// upstream. This method accepts the error that caused resetting client as
// depending on the error we may also reset the QUIC config.
func (p *dnsOverHTTPS) resetClient(resetErr error) (client *http.Client, err error) {
p.clientMu.Lock()
defer p.clientMu.Unlock()
if errors.Is(resetErr, quic.Err0RTTRejected) {
// Reset the TokenStore only if 0-RTT was rejected.
p.resetQUICConfig()
}
oldClient := p.client
if oldClient != nil {
closeErr := p.closeClient(oldClient)
if closeErr != nil {
log.Info("warning: failed to close the old http client: %v", closeErr)
}
}
log.Debug("re-creating the http client due to %v", resetErr)
p.client, err = p.createClient()
return p.client, err
}
// getQUICConfig returns the QUIC config in a thread-safe manner. Note, that
// this method returns a pointer, it is forbidden to change its properties.
func (p *dnsOverHTTPS) getQUICConfig() (c *quic.Config) {
p.quicConfMu.Lock()
defer p.quicConfMu.Unlock()
return p.quicConfig
}
// resetQUICConfig Re-create the token store to make sure we're not trying to
// use invalid for 0-RTT.
func (p *dnsOverHTTPS) resetQUICConfig() {
p.quicConfMu.Lock()
defer p.quicConfMu.Unlock()
p.quicConfig = p.quicConfig.Clone()
p.quicConfig.TokenStore = newQUICTokenStore()
}
// getClient gets or lazily initializes an HTTP client (and transport) that will
// be used for this DoH resolver.
func (p *dnsOverHTTPS) getClient() (c *http.Client, isCached bool, err error) {
startTime := time.Now()
p.clientMu.Lock()
defer p.clientMu.Unlock()
if p.client != nil {
return p.client, true, nil
}
// Timeout can be exceeded while waiting for the lock. This happens quite
// often on mobile devices.
elapsed := time.Since(startTime)
if p.timeout > 0 && elapsed > p.timeout {
return nil, false, fmt.Errorf("timeout exceeded: %s", elapsed)
}
log.Debug("creating a new http client")
p.client, err = p.createClient()
return p.client, false, err
}
// createClient creates a new *http.Client instance. The HTTP protocol version
// will depend on whether HTTP3 is allowed and provided by this upstream. Note,
// that we'll attempt to establish a QUIC connection when creating the client in
// order to check whether HTTP3 is supported.
func (p *dnsOverHTTPS) createClient() (*http.Client, error) {
transport, err := p.createTransport()
if err != nil {
return nil, fmt.Errorf("initializing http transport: %w", err)
}
client := &http.Client{
Transport: transport,
// TODO(ameshkov): p.timeout may appear zero that will disable the
// timeout for client, consider using the default.
Timeout: p.timeout,
Jar: nil,
}
p.client = client
return p.client, nil
}
// createTransport initializes an HTTP transport that will be used specifically
// for this DoH resolver. This HTTP transport ensures that the HTTP requests
// will be sent exactly to the IP address got from the bootstrap resolver. Note,
// that this function will first attempt to establish a QUIC connection (if
// HTTP3 is enabled in the upstream options). If this attempt is successful,
// it returns an HTTP3 transport, otherwise it returns the H1/H2 transport.
func (p *dnsOverHTTPS) createTransport() (t http.RoundTripper, err error) {
dialContext, err := p.getDialer()
if err != nil {
return nil, fmt.Errorf("bootstrapping %s: %w", p.addr, err)
}
// First, we attempt to create an HTTP3 transport. If the probe QUIC
// connection is established successfully, we'll be using HTTP3 for this
// upstream.
tlsConf := p.tlsConf.Clone()
transportH3, err := p.createTransportH3(tlsConf, dialContext)
if err == nil {
log.Debug("using HTTP/3 for this upstream: QUIC was faster")
return transportH3, nil
}
log.Debug("using HTTP/2 for this upstream: %v", err)
if !p.supportsHTTP() {
return nil, errors.Error("HTTP1/1 and HTTP2 are not supported by this upstream")
}
transport := &http.Transport{
TLSClientConfig: tlsConf,
DisableCompression: true,
DialContext: dialContext,
IdleConnTimeout: transportDefaultIdleConnTimeout,
MaxConnsPerHost: dohMaxConnsPerHost,
MaxIdleConns: dohMaxIdleConns,
// Since we have a custom DialContext, we need to use this field to make
// golang http.Client attempt to use HTTP/2. Otherwise, it would only be
// used when negotiated on the TLS level.
ForceAttemptHTTP2: true,
}
// Explicitly configure transport to use HTTP/2.
//
// See https://github.com/AdguardTeam/dnsproxy/issues/11.
var transportH2 *http2.Transport
transportH2, err = http2.ConfigureTransports(transport)
if err != nil {
return nil, err
}
// Enable HTTP/2 pings on idle connections.
transportH2.ReadIdleTimeout = transportDefaultReadIdleTimeout
return transport, nil
}
// http3Transport is a wrapper over *http3.RoundTripper that tries to optimize
// its behavior. The main thing that it does is trying to force use a single
// connection to a host instead of creating a new one all the time. It also
// helps mitigate race issues with quic-go.
type http3Transport struct {
baseTransport *http3.RoundTripper
closed bool
mu sync.RWMutex
}
// type check
var _ http.RoundTripper = (*http3Transport)(nil)
// RoundTrip implements the http.RoundTripper interface for *http3Transport.
func (h *http3Transport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
h.mu.RLock()
defer h.mu.RUnlock()
if h.closed {
return nil, net.ErrClosed
}
// Try to use cached connection to the target host if it's available.
resp, err = h.baseTransport.RoundTripOpt(req, http3.RoundTripOpt{OnlyCachedConn: true})
if errors.Is(err, http3.ErrNoCachedConn) {
// If there are no cached connection, trigger creating a new one.
resp, err = h.baseTransport.RoundTrip(req)
}
return resp, err
}
// type check
var _ io.Closer = (*http3Transport)(nil)
// Close implements the io.Closer interface for *http3Transport.
func (h *http3Transport) Close() (err error) {
h.mu.Lock()
defer h.mu.Unlock()
h.closed = true
return h.baseTransport.Close()
}
// createTransportH3 tries to create an HTTP/3 transport for this upstream.
// We should be able to fall back to H1/H2 in case if HTTP/3 is unavailable or
// if it is too slow. In order to do that, this method will run two probes
// in parallel (one for TLS, the other one for QUIC) and if QUIC is faster it
// will create the *http3.RoundTripper instance.
func (p *dnsOverHTTPS) createTransportH3(
tlsConfig *tls.Config,
dialContext bootstrap.DialHandler,
) (roundTripper http.RoundTripper, err error) {
if !p.supportsH3() {
return nil, errors.Error("HTTP3 support is not enabled")
}
addr, err := p.probeH3(tlsConfig, dialContext)
if err != nil {
return nil, err
}
rt := &http3.RoundTripper{
Dial: func(
ctx context.Context,
// Ignore the address and always connect to the one that we got
// from the bootstrapper.
_ string,
tlsCfg *tls.Config,
cfg *quic.Config,
) (c quic.EarlyConnection, err error) {
c, err = quic.DialAddrEarly(ctx, addr, tlsCfg, cfg)
return c, err
},
DisableCompression: true,
TLSClientConfig: tlsConfig,
QuicConfig: p.getQUICConfig(),
}
return &http3Transport{baseTransport: rt}, nil
}
// probeH3 runs a test to check whether QUIC is faster than TLS for this
// upstream. If the test is successful it will return the address that we
// should use to establish the QUIC connections.
func (p *dnsOverHTTPS) probeH3(
tlsConfig *tls.Config,
dialContext bootstrap.DialHandler,
) (addr string, err error) {
// We're using bootstrapped address instead of what's passed to the function
// it does not create an actual connection, but it helps us determine
// what IP is actually reachable (when there are v4/v6 addresses).
rawConn, err := dialContext(context.Background(), "udp", "")
if err != nil {
return "", fmt.Errorf("failed to dial: %w", err)
}
// It's never actually used.
_ = rawConn.Close()
udpConn, ok := rawConn.(*net.UDPConn)
if !ok {
return "", fmt.Errorf("not a UDP connection to %s", p.addr)
}
addr = udpConn.RemoteAddr().String()
// Avoid spending time on probing if this upstream only supports HTTP/3.
if p.supportsH3() && !p.supportsHTTP() {
return addr, nil
}
// Use a new *tls.Config with empty session cache for probe connections.
// Surprisingly, this is really important since otherwise it invalidates
// the existing cache.
// TODO(ameshkov): figure out why the sessions cache invalidates here.
probeTLSCfg := tlsConfig.Clone()
probeTLSCfg.ClientSessionCache = nil
// Do not expose probe connections to the callbacks that are passed to
// the bootstrap options to avoid side-effects.
// TODO(ameshkov): consider exposing, somehow mark that this is a probe.
probeTLSCfg.VerifyPeerCertificate = nil
probeTLSCfg.VerifyConnection = nil
// Run probeQUIC and probeTLS in parallel and see which one is faster.
chQuic := make(chan error, 1)
chTLS := make(chan error, 1)
go p.probeQUIC(addr, probeTLSCfg, chQuic)
go p.probeTLS(dialContext, probeTLSCfg, chTLS)
select {
case quicErr := <-chQuic:
if quicErr != nil {
// QUIC failed, return error since HTTP3 was not preferred.
return "", quicErr
}
// Return immediately, QUIC was faster.
return addr, quicErr
case tlsErr := <-chTLS:
if tlsErr != nil {
// Return immediately, TLS failed.
log.Debug("probing TLS: %v", tlsErr)
return addr, nil
}
return "", errors.Error("TLS was faster than QUIC, prefer it")
}
}
// probeQUIC attempts to establish a QUIC connection to the specified address.
// We run probeQUIC and probeTLS in parallel and see which one is faster.
func (p *dnsOverHTTPS) probeQUIC(addr string, tlsConfig *tls.Config, ch chan error) {
startTime := time.Now()
timeout := p.timeout
if timeout == 0 {
timeout = dialTimeout
}
ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(timeout))
defer cancel()
conn, err := quic.DialAddrEarly(ctx, addr, tlsConfig, p.getQUICConfig())
if err != nil {
ch <- fmt.Errorf("opening QUIC connection to %s: %w", p.addr, err)
return
}
// Ignore the error since there's no way we can use it for anything useful.
_ = conn.CloseWithError(QUICCodeNoError, "")
ch <- nil
elapsed := time.Since(startTime)
log.Debug("elapsed on establishing a QUIC connection: %s", elapsed)
}
// probeTLS attempts to establish a TLS connection to the specified address. We
// run probeQUIC and probeTLS in parallel and see which one is faster.
func (p *dnsOverHTTPS) probeTLS(dialContext bootstrap.DialHandler, tlsConfig *tls.Config, ch chan error) {
startTime := time.Now()
conn, err := tlsDial(dialContext, tlsConfig)
if err != nil {
ch <- fmt.Errorf("opening TLS connection: %w", err)
return
}
// Ignore the error since there's no way we can use it for anything useful.
_ = conn.Close()
ch <- nil
elapsed := time.Since(startTime)
log.Debug("elapsed on establishing a TLS connection: %s", elapsed)
}
// supportsH3 returns true if HTTP/3 is supported by this upstream.
func (p *dnsOverHTTPS) supportsH3() (ok bool) {
for _, v := range p.tlsConf.NextProtos {
if v == string(HTTPVersion3) {
return true
}
}
return false
}
// supportsHTTP returns true if HTTP/1.1 or HTTP2 is supported by this upstream.
func (p *dnsOverHTTPS) supportsHTTP() (ok bool) {
for _, v := range p.tlsConf.NextProtos {
if v == string(HTTPVersion11) || v == string(HTTPVersion2) {
return true
}
}
return false
}
// isHTTP3 checks if the *http.Client is an HTTP/3 client.
func isHTTP3(client *http.Client) (ok bool) {
_, ok = client.Transport.(*http3Transport)
return ok
}