control/controlclient, tailcfg: add support for EarlyNoise payload before http/2

Not yet used, but skipped over, parsed, and tested.

Updates #5972

Change-Id: Icd00196959ce266ae16a6c9244bd5e458e2c2947
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlclient/noise.go

@@ -7,7 +7,10 @@ package controlclient
 import (
 	"bytes"
 	"context"
+	"encoding/binary"
 	"encoding/json"
+	"errors"
+	"io"
 	"math"
 	"net/http"
 	"net/url"
@@ -34,6 +37,77 @@ type noiseConn struct {
 	id   int
 	pool *noiseClient
 	h2cc *http2.ClientConn
+
+	readHeaderOnce    sync.Once     // guards init of reader field
+	reader            io.Reader     // (effectively Conn.Reader after header)
+	earlyPayloadReady chan struct{} // closed after earlyPayload is set (including set to nil)
+	earlyPayload      *tailcfg.EarlyNoise
+}
+
+func (c *noiseConn) RoundTrip(r *http.Request) (*http.Response, error) {
+	return c.h2cc.RoundTrip(r)
+}
+
+// The first 9 bytes from the server to client over Noise are either an HTTP/2
+// settings frame (a normal HTTP/2 setup) or, as we added later, an "early payload"
+// header that's also 9 bytes long: 5 bytes (earlyPayloadMagic) followed by 4 bytes
+// of length. Then that many bytes of JSON-encoded tailcfg.EarlyNoise.
+// The early payload is optional. Some servers may not send it.
+const (
+	hdrLen            = 9 // http2 frame header size; also size of our early payload size header
+	earlyPayloadMagic = "\xff\xff\xffTS"
+)
+
+// returnErrReader is an io.Reader that always returns an error.
+type returnErrReader struct {
+	err error // the error to return
+}
+
+func (r returnErrReader) Read([]byte) (int, error) { return 0, r.err }
+
+// Read is basically the same as controlbase.Conn.Read, but it first reads the
+// "early payload" header from the server which may or may not be present,
+// depending on the server.
+func (c *noiseConn) Read(p []byte) (n int, err error) {
+	c.readHeaderOnce.Do(c.readHeader)
+	return c.reader.Read(p)
+}
+
+// readHeader reads the optional "early payload" from the server that arrives
+// after the Noise handshake but before the HTTP/2 session begins.
+//
+// readHeader is responsible for reading the header (if present), initializing
+// c.earlyPayload, closing c.earlyPayloadReady, and initializing c.reader for
+// future reads.
+func (c *noiseConn) readHeader() {
+	var hdr [hdrLen]byte
+	if _, err := io.ReadFull(c.Conn, hdr[:]); err != nil {
+		c.reader = returnErrReader{err}
+		return
+	}
+	if string(hdr[:len(earlyPayloadMagic)]) != earlyPayloadMagic {
+		// No early payload. We have to return the 9 bytes read we already
+		// consumed.
+		close(c.earlyPayloadReady)
+		c.reader = io.MultiReader(bytes.NewReader(hdr[:]), c.Conn)
+		return
+	}
+	epLen := binary.BigEndian.Uint32(hdr[len(earlyPayloadMagic):])
+	if epLen > 10<<20 {
+		c.reader = returnErrReader{errors.New("invalid early payload length")}
+		return
+	}
+	payBuf := make([]byte, epLen)
+	if _, err := io.ReadFull(c.Conn, payBuf); err != nil {
+		c.reader = returnErrReader{err}
+		return
+	}
+	if err := json.Unmarshal(payBuf, &c.earlyPayload); err != nil {
+		c.reader = returnErrReader{err}
+		return
+	}
+	close(c.earlyPayloadReady)
+	c.reader = c.Conn
 }
 
 func (c *noiseConn) Close() error {
@@ -88,7 +162,7 @@ type noiseClient struct {
 // serverURL is of the form https://<host>:<port> (no trailing slash).
 //
 // dialPlan may be nil
-func newNoiseClient(priKey key.MachinePrivate, serverPubKey key.MachinePublic, serverURL string, dialer *tsdial.Dialer, dialPlan func() *tailcfg.ControlDialPlan) (*noiseClient, error) {
+func newNoiseClient(privKey key.MachinePrivate, serverPubKey key.MachinePublic, serverURL string, dialer *tsdial.Dialer, dialPlan func() *tailcfg.ControlDialPlan) (*noiseClient, error) {
 	u, err := url.Parse(serverURL)
 	if err != nil {
 		return nil, err
@@ -111,7 +185,7 @@ func newNoiseClient(priKey key.MachinePrivate, serverPubKey key.MachinePublic, s
 	}
 	np := &noiseClient{
 		serverPubKey: serverPubKey,
-		privKey:      priKey,
+		privKey:      privKey,
 		host:         u.Hostname(),
 		httpPort:     httpPort,
 		httpsPort:    httpsPort,
@@ -157,7 +231,7 @@ func (nc *noiseClient) RoundTrip(req *http.Request) (*http.Response, error) {
 	if err != nil {
 		return nil, err
 	}
-	return conn.h2cc.RoundTrip(req)
+	return conn.RoundTrip(req)
 }
 
 // connClosed removes the connection with the provided ID from the pool
@@ -262,11 +336,9 @@ func (nc *noiseClient) dial() (*noiseConn, error) {
 		Conn:              clientConn.Conn,
 		id:                connID,
 		pool:              nc,
+		earlyPayloadReady: make(chan struct{}),
 	}
 
-	// TODO(bradfitz): wrap clientConn in a type that sniffs the leading bytes
-	// from the server to see if it has early post-Noise, pre-H2 data for us.
-
 	h2cc, err := nc.h2t.NewClientConn(ncc)
 	if err != nil {
 		return nil, err

control/controlclient/noise_test.go

@@ -13,6 +13,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
+	"time"
 
 	"golang.org/x/net/http2"
 	"tailscale.com/control/controlhttp"
@@ -38,15 +39,32 @@ func TestNoiseVersion(t *testing.T) {
 	}
 }
 
+type noiseClientTest struct {
+	sendEarlyPayload bool
+}
+
 func TestNoiseClientHTTP2Upgrade(t *testing.T) {
+	noiseClientTest{}.run(t)
+}
+
+func TestNoiseClientHTTP2Upgrade_earlyPayload(t *testing.T) {
+	noiseClientTest{
+		sendEarlyPayload: true,
+	}.run(t)
+}
+
+func (tt noiseClientTest) run(t *testing.T) {
 	serverPrivate := key.NewMachine()
 	clientPrivate := key.NewMachine()
+	chalPrivate := key.NewChallenge()
 
 	const msg = "Hello, client"
 	h2 := &http2.Server{}
 	hs := httptest.NewServer(&Upgrader{
 		h2srv:            h2,
 		noiseKeyPriv:     serverPrivate,
+		sendEarlyPayload: tt.sendEarlyPayload,
+		challenge:        chalPrivate,
 		httpBaseConfig: &http.Server{
 			Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 				w.Header().Set("Content-Type", "text/plain")
@@ -61,10 +79,33 @@ func TestNoiseClientHTTP2Upgrade(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	res, err := nc.post(context.Background(), "/", nil)
+
+	// Get a conn and verify it read its early payload before the http/2
+	// handshake.
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	c, err := nc.getConn(ctx)
 	if err != nil {
 		t.Fatal(err)
 	}
+	select {
+	case <-c.earlyPayloadReady:
+		gotNonNil := c.earlyPayload != nil
+		if gotNonNil != tt.sendEarlyPayload {
+			t.Errorf("sendEarlyPayload = %v but got earlyPayload = %T", tt.sendEarlyPayload, c.earlyPayload)
+		}
+		if c.earlyPayload != nil {
+			if c.earlyPayload.NodeKeyChallenge != chalPrivate.Public() {
+				t.Errorf("earlyPayload.NodeKeyChallenge = %v; want %v", c.earlyPayload.NodeKeyChallenge, chalPrivate.Public())
+			}
+		}
+
+	case <-ctx.Done():
+		t.Fatal("timed out waiting for didReadHeaderCh")
+	}
+
+	checkRes := func(t *testing.T, res *http.Response) {
+		t.Helper()
 		defer res.Body.Close()
 		all, err := io.ReadAll(res.Body)
 		if err != nil {
@@ -73,7 +114,21 @@ func TestNoiseClientHTTP2Upgrade(t *testing.T) {
 		if string(all) != msg {
 			t.Errorf("got response %q; want %q", all, msg)
 		}
+	}
 
+	// And verify we can do HTTP/2 against that conn.
+	res, err := (&http.Client{Transport: c}).Get("https://unused.example/")
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkRes(t, res)
+
+	// And try using the high-level nc.post API as well.
+	res, err = nc.post(context.Background(), "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkRes(t, res)
 }
 
 // Upgrader is an http.Handler that hijacks and upgrades POST-with-Upgrade
@@ -91,6 +146,7 @@ type Upgrader struct {
 	logf logger.Logf
 
 	noiseKeyPriv key.MachinePrivate
+	challenge    key.ChallengePrivate
 
 	sendEarlyPayload bool
 }
@@ -109,21 +165,21 @@ func (up *Upgrader) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	chalPub := key.NewChallenge()
 	earlyWriteFn := func(protocolVersion int, w io.Writer) error {
 		if !up.sendEarlyPayload {
 			return nil
 		}
-		earlyJSON, err := json.Marshal(struct {
-			NodeKeyOwnershipChallenge string
-		}{chalPub.Public().String()})
+		earlyJSON, err := json.Marshal(&tailcfg.EarlyNoise{
+			NodeKeyChallenge: up.challenge.Public(),
+		})
 		if err != nil {
 			return err
 		}
 		// 5 bytes that won't be mistaken for an HTTP/2 frame:
 		// https://httpwg.org/specs/rfc7540.html#rfc.section.4.1 (Especially not
 		// an HTTP/2 settings frame, which isn't of type 'T')
-		var notH2Frame = [5]byte{0xff, 0xff, 0xff, 'T', 'S'}
+		var notH2Frame [5]byte
+		copy(notH2Frame[:], earlyPayloadMagic)
 		var lenBuf [4]byte
 		binary.BigEndian.PutUint32(lenBuf[:], uint32(len(earlyJSON)))
 		// These writes are all buffered by caller, so fine to do them

tailcfg/tailcfg.go

@@ -1946,3 +1946,15 @@ type PeerChange struct {
 //
 // Mnemonic: 3.3.40 are numbers above the keys D, E, R, P.
 const DerpMagicIP = "127.3.3.40"
+
+// EarlyNoise is the early payload that's sent over Noise but before the HTTP/2
+// handshake when connecting to the coordination server.
+//
+// This exists to let the server push some early info to client for that
+// stateful HTTP/2+Noise connection without incurring an extra round trip. (This
+// would've used HTTP/2 server push, had Go's client-side APIs been available)
+type EarlyNoise struct {
+	// NodeKeyChallenge is a random per-connection public key to be used by
+	// the client to prove possession of a wireguard private key.
+	NodeKeyChallenge key.ChallengePublic `json:"nodeKeyChallenge"`
+}