net/http: allow Handlers to handle http2 upgrade PRI requests

The http2 spec defines a magic string which initates an http2 session:

    "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"

It was intentionally chosen to kinda look like an HTTP request, but
just different enough to break things not ready for it. This change
makes Go ready for it.

Notably: Go now accepts the request header (the prefix "PRI *
HTTP/2.0\r\n\r\n") as a valid request, even though it doesn't have a
Host header. But we now mark it as "Connection: close" and teach the
Server to never read a second request from the connection once that's
seen. If the http.Handler wants to deal with the upgrade, it has to
hijack the request, read out the "body", compare it against
"SM\r\n\r\n", and then speak http2. One of the new tests demonstrates
that hijacking.

Fixes #14451
Updates #14141 (h2c)

Change-Id: Ib46142f31c55be7d00c56fa2624ec8a232e00c43
Reviewed-on: https://go-review.googlesource.com/21327Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/readrequest_test.go

@@ -380,6 +380,27 @@ var reqTests = []reqTest{
 		noTrailer,
 		noError,
 	},
+
+	// http2 client preface:
+	{
+		"PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n",
+		&Request{
+			Method: "PRI",
+			URL: &url.URL{
+				Path: "*",
+			},
+			Header:        Header{},
+			Proto:         "HTTP/2.0",
+			ProtoMajor:    2,
+			ProtoMinor:    0,
+			RequestURI:    "*",
+			ContentLength: -1,
+			Close:         true,
+		},
+		noBody,
+		noTrailer,
+		noError,
+	},
 }
 
 func TestReadRequest(t *testing.T) {

src/net/http/request.go

@@ -343,6 +343,12 @@ func (r *Request) multipartReader() (*multipart.Reader, error) {
 	return multipart.NewReader(r.Body, boundary), nil
 }
 
+// isH2Upgrade reports whether r represents the http2 "client preface"
+// magic string.
+func (r *Request) isH2Upgrade() bool {
+	return r.Method == "PRI" && len(r.Header) == 0 && r.URL.Path == "*" && r.Proto == "HTTP/2.0"
+}
+
 // Return value if nonempty, def otherwise.
 func valueOrDefault(value, def string) string {
 	if value != "" {
@@ -794,6 +800,16 @@ func readRequest(b *bufio.Reader, deleteHostHeader bool) (req *Request, err erro
 		return nil, err
 	}
 
+	if req.isH2Upgrade() {
+		// Because it's neither chunked, nor declared:
+		req.ContentLength = -1
+
+		// We want to give handlers a chance to hijack the
+		// connection, but we need to prevent the Server from
+		// dealing with the connection further if it's not
+		// hijacked. Set Close to ensure that:
+		req.Close = true
+	}
 	return req, nil
 }
 

src/net/http/serve_test.go

@@ -741,6 +741,13 @@ func TestHandlersCanSetConnectionClose10(t *testing.T) {
 	}))
 }
 
+func TestHTTP2UpgradeClosesConnection(t *testing.T) {
+	testTCPConnectionCloses(t, "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n", HandlerFunc(func(w ResponseWriter, r *Request) {
+		// Nothing. (if not hijacked, the server should close the connection
+		// afterwards)
+	}))
+}
+
 func TestSetsRemoteAddr_h1(t *testing.T) { testSetsRemoteAddr(t, h1Mode) }
 func TestSetsRemoteAddr_h2(t *testing.T) { testSetsRemoteAddr(t, h2Mode) }
 
@@ -3877,10 +3884,17 @@ func TestServerValidatesHostHeader(t *testing.T) {
 		{"HTTP/1.0", "", 200},
 		{"HTTP/1.0", "Host: first\r\nHost: second\r\n", 400},
 		{"HTTP/1.0", "Host: \xff\r\n", 400},
+
+		// Make an exception for HTTP upgrade requests:
+		{"PRI * HTTP/2.0", "", 200},
 	}
 	for _, tt := range tests {
 		conn := &testConn{closec: make(chan bool, 1)}
-		io.WriteString(&conn.readBuf, "GET / "+tt.proto+"\r\n"+tt.host+"\r\n")
+		methodTarget := "GET / "
+		if !strings.HasPrefix(tt.proto, "HTTP/") {
+			methodTarget = ""
+		}
+		io.WriteString(&conn.readBuf, methodTarget+tt.proto+"\r\n"+tt.host+"\r\n")
 
 		ln := &oneConnListener{conn}
 		go Serve(ln, HandlerFunc(func(ResponseWriter, *Request) {}))
@@ -3896,6 +3910,45 @@ func TestServerValidatesHostHeader(t *testing.T) {
 	}
 }
 
+func TestServerHandlersCanHandleH2PRI(t *testing.T) {
+	const upgradeResponse = "upgrade here"
+	defer afterTest(t)
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		conn, br, err := w.(Hijacker).Hijack()
+		defer conn.Close()
+		if r.Method != "PRI" || r.RequestURI != "*" {
+			t.Errorf("Got method/target %q %q; want PRI *", r.Method, r.RequestURI)
+			return
+		}
+		if !r.Close {
+			t.Errorf("Request.Close = true; want false")
+		}
+		const want = "SM\r\n\r\n"
+		buf := make([]byte, len(want))
+		n, err := io.ReadFull(br, buf)
+		if err != nil || string(buf[:n]) != want {
+			t.Errorf("Read = %v, %v (%q), want %q", n, err, buf[:n], want)
+			return
+		}
+		io.WriteString(conn, upgradeResponse)
+	}))
+	defer ts.Close()
+
+	c, err := net.Dial("tcp", ts.Listener.Addr().String())
+	if err != nil {
+		t.Fatalf("Dial: %v", err)
+	}
+	defer c.Close()
+	io.WriteString(c, "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n")
+	slurp, err := ioutil.ReadAll(c)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(slurp) != upgradeResponse {
+		t.Errorf("Handler response = %q; want %q", slurp, upgradeResponse)
+	}
+}
+
 // Test that we validate the valid bytes in HTTP/1 headers.
 // Issue 11207.
 func TestServerValidatesHeaders(t *testing.T) {

src/net/http/server.go

@@ -714,7 +714,8 @@ func (c *conn) readRequest() (w *response, err error) {
 	c.r.setInfiniteReadLimit()
 
 	hosts, haveHost := req.Header["Host"]
-	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) {
+	isH2Upgrade := req.isH2Upgrade()
+	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade {
 		return nil, badRequestError("missing required Host header")
 	}
 	if len(hosts) > 1 {
@@ -748,6 +749,9 @@ func (c *conn) readRequest() (w *response, err error) {
 		handlerHeader: make(Header),
 		contentLength: -1,
 	}
+	if isH2Upgrade {
+		w.closeAfterReply = true
+	}
 	w.cw.res = w
 	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
 	return w, nil