http3: introduce a Settingser to query the client's SETTINGS (#4389)

The http.Request.Body can be type-asserted to a http3.Settingser. The
Settings method on this interface blocks until the client's SETTINGS
frame has been received.

http3/body.go

@@ -37,27 +37,28 @@ type Hijacker interface {
 	StreamCreator() StreamCreator
 }
 
-// The body of a http.Request or http.Response.
+// Settingser allows the server to retrieve the client's SETTINGS.
+// The http.Request.Body implements this interface.
+type Settingser interface {
+	// Settings returns the client's HTTP settings.
+	// It blocks until the SETTINGS frame has been received.
+	// Note that it is not guaranteed that this happens during the lifetime of the request.
+	Settings(context.Context) (*Settings, error)
+}
+
+// The body is used in the requestBody (for a http.Request) and the responseBody (for a http.Response).
 type body struct {
 	str quic.Stream
 
 	wasHijacked bool // set when HTTPStream is called
 }
 
-var (
-	_ io.ReadCloser = &body{}
-	_ HTTPStreamer  = &body{}
-)
-
-func newRequestBody(str Stream) *body {
-	return &body{str: str}
-}
-
 func (r *body) HTTPStream() Stream {
 	r.wasHijacked = true
 	return r.str
 }
 
+func (r *body) StreamID() quic.StreamID { return r.str.StreamID() }
 func (r *body) wasStreamHijacked() bool {
 	return r.wasHijacked
 }
@@ -72,6 +73,39 @@ func (r *body) Close() error {
 	return nil
 }
 
+type requestBody struct {
+	body
+	connCtx      context.Context
+	rcvdSettings <-chan struct{}
+	getSettings  func() *Settings
+}
+
+var (
+	_ io.ReadCloser = &requestBody{}
+	_ HTTPStreamer  = &requestBody{}
+	_ Settingser    = &requestBody{}
+)
+
+func newRequestBody(str Stream, connCtx context.Context, rcvdSettings <-chan struct{}, getSettings func() *Settings) *requestBody {
+	return &requestBody{
+		body:         body{str: str},
+		connCtx:      connCtx,
+		rcvdSettings: rcvdSettings,
+		getSettings:  getSettings,
+	}
+}
+
+func (r *requestBody) Settings(ctx context.Context) (*Settings, error) {
+	select {
+	case <-ctx.Done():
+		return nil, context.Cause(ctx)
+	case <-r.connCtx.Done():
+		return nil, context.Cause(r.connCtx)
+	case <-r.rcvdSettings:
+		return r.getSettings(), nil
+	}
+}
+
 type hijackableBody struct {
 	body
 	conn quic.Connection // only needed to implement Hijacker
@@ -84,24 +118,19 @@ type hijackableBody struct {
 }
 
 var (
-	_ Hijacker     = &hijackableBody{}
-	_ HTTPStreamer = &hijackableBody{}
+	_ io.ReadCloser = &hijackableBody{}
+	_ Hijacker      = &hijackableBody{}
+	_ HTTPStreamer  = &hijackableBody{}
 )
 
 func newResponseBody(str Stream, conn quic.Connection, done chan<- struct{}) *hijackableBody {
 	return &hijackableBody{
-		body: body{
-			str: str,
-		},
+		body:    body{str: str},
 		reqDone: done,
 		conn:    conn,
 	}
 }
 
-func (r *hijackableBody) StreamCreator() StreamCreator {
-	return r.conn
-}
-
 func (r *hijackableBody) Read(b []byte) (int, error) {
 	n, err := r.str.Read(b)
 	if err != nil {
@@ -120,10 +149,6 @@ func (r *hijackableBody) requestDone() {
 	r.reqDoneClosed = true
 }
 
-func (r *body) StreamID() quic.StreamID {
-	return r.str.StreamID()
-}
-
 func (r *hijackableBody) Close() error {
 	r.requestDone()
 	// If the EOF was read, CancelRead() is a no-op.
@@ -131,6 +156,5 @@ func (r *hijackableBody) Close() error {
 	return nil
 }
 
-func (r *hijackableBody) HTTPStream() Stream {
-	return r.str
-}
+func (r *hijackableBody) HTTPStream() Stream           { return r.str }
+func (r *hijackableBody) StreamCreator() StreamCreator { return r.conn }