net/http: accept HEAD requests with a body

RFC 7231 permits HEAD requests to contain a body, although it does
state there are no defined semantics for payloads of HEAD requests
and that some servers may reject HEAD requests with a payload.

Accept HEAD requests with a body.

Fix a bug where a HEAD request with a chunked body would interpret
the body as the headers for the next request on the connection.

For #53960.

Change-Id: I83f7112fdedabd6d6291cd956151d718ee6942cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/418614
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/net/http/readrequest_test.go

@@ -450,9 +450,12 @@ Content-Length: 3
 Content-Length: 4
 
 abc`)},
-	{"smuggle_content_len_head", reqBytes(`HEAD / HTTP/1.1
+	{"smuggle_two_content_len_head", reqBytes(`HEAD / HTTP/1.1
 Host: foo
-Content-Length: 5`)},
+Content-Length: 4
+Content-Length: 5
+
+1234`)},
 
 	// golang.org/issue/22464
 	{"leading_space_in_header", reqBytes(`GET / HTTP/1.1

src/net/http/request_test.go

@@ -485,10 +485,6 @@ var readRequestErrorTests = []struct {
 	1: {"GET / HTTP/1.1\r\nheader:foo\r\n", io.ErrUnexpectedEOF.Error(), nil},
 	2: {"", io.EOF.Error(), nil},
 	3: {
-		in:  "HEAD / HTTP/1.1\r\nContent-Length:4\r\n\r\n",
-		err: "http: method cannot contain a Content-Length",
-	},
-	4: {
 		in:     "HEAD / HTTP/1.1\r\n\r\n",
 		header: Header{},
 	},
@@ -496,32 +492,32 @@ var readRequestErrorTests = []struct {
 	// Multiple Content-Length values should either be
 	// deduplicated if same or reject otherwise
 	// See Issue 16490.
-	5: {
+	4: {
 		in:  "POST / HTTP/1.1\r\nContent-Length: 10\r\nContent-Length: 0\r\n\r\nGopher hey\r\n",
 		err: "cannot contain multiple Content-Length headers",
 	},
-	6: {
+	5: {
 		in:  "POST / HTTP/1.1\r\nContent-Length: 10\r\nContent-Length: 6\r\n\r\nGopher\r\n",
 		err: "cannot contain multiple Content-Length headers",
 	},
-	7: {
+	6: {
 		in:     "PUT / HTTP/1.1\r\nContent-Length: 6 \r\nContent-Length: 6\r\nContent-Length:6\r\n\r\nGopher\r\n",
 		err:    "",
 		header: Header{"Content-Length": {"6"}},
 	},
-	8: {
+	7: {
 		in:  "PUT / HTTP/1.1\r\nContent-Length: 1\r\nContent-Length: 6 \r\n\r\n",
 		err: "cannot contain multiple Content-Length headers",
 	},
-	9: {
+	8: {
 		in:  "POST / HTTP/1.1\r\nContent-Length:\r\nContent-Length: 3\r\n\r\n",
 		err: "cannot contain multiple Content-Length headers",
 	},
-	10: {
+	9: {
 		in:     "HEAD / HTTP/1.1\r\nContent-Length:0\r\nContent-Length: 0\r\n\r\n",
 		header: Header{"Content-Length": {"0"}},
 	},
-	11: {
+	10: {
 		in:  "HEAD / HTTP/1.1\r\nHost: foo\r\nHost: bar\r\n\r\n\r\n\r\n",
 		err: "too many Host headers",
 	},

src/net/http/serve_test.go

@@ -6907,3 +6907,73 @@ func testParseFormCleanup(t *testing.T, h2 bool) {
 		t.Errorf("file %q exists after HTTP handler returned", string(fname))
 	}
 }
+
+func TestHeadBody(t *testing.T) {
+	const identityMode = false
+	const chunkedMode = true
+	t.Run("h1", func(t *testing.T) {
+		t.Run("identity", func(t *testing.T) { testHeadBody(t, h1Mode, identityMode, "HEAD") })
+		t.Run("chunked", func(t *testing.T) { testHeadBody(t, h1Mode, chunkedMode, "HEAD") })
+	})
+	t.Run("h2", func(t *testing.T) {
+		t.Run("identity", func(t *testing.T) { testHeadBody(t, h2Mode, identityMode, "HEAD") })
+		t.Run("chunked", func(t *testing.T) { testHeadBody(t, h2Mode, chunkedMode, "HEAD") })
+	})
+}
+
+func TestGetBody(t *testing.T) {
+	const identityMode = false
+	const chunkedMode = true
+	t.Run("h1", func(t *testing.T) {
+		t.Run("identity", func(t *testing.T) { testHeadBody(t, h1Mode, identityMode, "GET") })
+		t.Run("chunked", func(t *testing.T) { testHeadBody(t, h1Mode, chunkedMode, "GET") })
+	})
+	t.Run("h2", func(t *testing.T) {
+		t.Run("identity", func(t *testing.T) { testHeadBody(t, h2Mode, identityMode, "GET") })
+		t.Run("chunked", func(t *testing.T) { testHeadBody(t, h2Mode, chunkedMode, "GET") })
+	})
+}
+
+func testHeadBody(t *testing.T, h2, chunked bool, method string) {
+	setParallel(t)
+	defer afterTest(t)
+	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
+		b, err := io.ReadAll(r.Body)
+		if err != nil {
+			t.Errorf("server reading body: %v", err)
+			return
+		}
+		w.Header().Set("X-Request-Body", string(b))
+		w.Header().Set("Content-Length", "0")
+	}))
+	defer cst.close()
+	for _, reqBody := range []string{
+		"",
+		"",
+		"request_body",
+		"",
+	} {
+		var bodyReader io.Reader
+		if reqBody != "" {
+			bodyReader = strings.NewReader(reqBody)
+			if chunked {
+				bodyReader = bufio.NewReader(bodyReader)
+			}
+		}
+		req, err := NewRequest(method, cst.ts.URL, bodyReader)
+		if err != nil {
+			t.Fatal(err)
+		}
+		res, err := cst.c.Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		res.Body.Close()
+		if got, want := res.StatusCode, 200; got != want {
+			t.Errorf("%v request with %d-byte body: StatusCode = %v, want %v", method, len(reqBody), got, want)
+		}
+		if got, want := res.Header.Get("X-Request-Body"), reqBody; got != want {
+			t.Errorf("%v request with %d-byte body: handler read body %q, want %q", method, len(reqBody), got, want)
+		}
+	}
+}

src/net/http/transfer.go

@@ -557,7 +557,7 @@ func readTransfer(msg any, r *bufio.Reader) (err error) {
 	// or close connection when finished, since multipart is not supported yet
 	switch {
 	case t.Chunked:
-		if noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode) {
+		if isResponse && (noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode)) {
 			t.Body = NoBody
 		} else {
 			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
@@ -691,14 +691,7 @@ func fixLength(isResponse bool, status int, requestMethod string, header Header,
 	}
 
 	// Logic based on response type or status
-	if noResponseBodyExpected(requestMethod) {
-		// For HTTP requests, as part of hardening against request
-		// smuggling (RFC 7230), don't allow a Content-Length header for
-		// methods which don't permit bodies. As an exception, allow
-		// exactly one Content-Length header if its value is "0".
-		if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
-			return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
-		}
+	if isResponse && noResponseBodyExpected(requestMethod) {
 		return 0, nil
 	}
 	if status/100 == 1 {