http2: split cookie pair into separate hpack header fields

As per 8.1.2.5, To allow for better compression efficiency, the Cookie header
field MAY be split into separate header fields, each with one or more
cookie-pairs.

Fixes golang/go#29386

Change-Id: Ia73aea00b76350c822544f180b5da19d50e51f68
Reviewed-on: https://go-review.googlesource.com/c/net/+/155657
Reviewed-by: Katie Hockman <katie@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

http2/transport.go

@@ -1478,7 +1478,29 @@ func (cc *ClientConn) encodeHeaders(req *http.Request, addGzipHeader bool, trail
 				if vv[0] == "" {
 					continue
 				}
-
+			} else if strings.EqualFold(k, "cookie") {
+				// Per 8.1.2.5 To allow for better compression efficiency, the
+				// Cookie header field MAY be split into separate header fields,
+				// each with one or more cookie-pairs.
+				for _, v := range vv {
+					for {
+						p := strings.IndexByte(v, ';')
+						if p < 0 {
+							break
+						}
+						f("cookie", v[:p])
+						p++
+						// strip space after semicolon if any.
+						for p+1 <= len(v) && v[p] == ' ' {
+							p++
+						}
+						v = v[p:]
+					}
+					if len(v) > 0 {
+						f("cookie", v)
+					}
+				}
+				continue
 			}
 
 			for _, v := range vv {

http2/transport_test.go

@@ -1795,6 +1795,57 @@ func TestTransportChecksResponseHeaderListSize(t *testing.T) {
 	ct.run()
 }
 
+func TestTransportCookieHeaderSplit(t *testing.T) {
+	ct := newClientTester(t)
+	ct.client = func() error {
+		req, _ := http.NewRequest("GET", "https://dummy.tld/", nil)
+		req.Header.Add("Cookie", "a=b;c=d;  e=f;")
+		req.Header.Add("Cookie", "e=f;g=h; ")
+		req.Header.Add("Cookie", "i=j")
+		_, err := ct.tr.RoundTrip(req)
+		return err
+	}
+	ct.server = func() error {
+		ct.greet()
+		for {
+			f, err := ct.fr.ReadFrame()
+			if err != nil {
+				return err
+			}
+			switch f := f.(type) {
+			case *HeadersFrame:
+				dec := hpack.NewDecoder(initialHeaderTableSize, nil)
+				hfs, err := dec.DecodeFull(f.HeaderBlockFragment())
+				if err != nil {
+					return err
+				}
+				got := []string{}
+				want := []string{"a=b", "c=d", "e=f", "e=f", "g=h", "i=j"}
+				for _, hf := range hfs {
+					if hf.Name == "cookie" {
+						got = append(got, hf.Value)
+					}
+				}
+				if !reflect.DeepEqual(got, want) {
+					t.Errorf("Cookies = %#v, want %#v", got, want)
+				}
+
+				var buf bytes.Buffer
+				enc := hpack.NewEncoder(&buf)
+				enc.WriteField(hpack.HeaderField{Name: ":status", Value: "200"})
+				ct.fr.WriteHeaders(HeadersFrameParam{
+					StreamID:      f.StreamID,
+					EndHeaders:    true,
+					EndStream:     true,
+					BlockFragment: buf.Bytes(),
+				})
+				return nil
+			}
+		}
+	}
+	ct.run()
+}
+
 // Test that the Transport returns a typed error from Response.Body.Read calls
 // when the server sends an error. (here we use a panic, since that should generate
 // a stream error, but others like cancel should be similar)