SplitHTTP server: add ok padding (#3614)

infra/conf/transport_internet.go

@@ -229,10 +229,22 @@ type SplitHTTPConfig struct {
 	Host                 string            `json:"host"`
 	Path                 string            `json:"path"`
 	Headers              map[string]string `json:"headers"`
-	ScMaxConcurrentPosts Int32Range        `json:"scMaxConcurrentPosts"`
-	ScMaxEachPostBytes   Int32Range        `json:"scMaxEachPostBytes"`
-	ScMinPostsIntervalMs Int32Range        `json:"scMinPostsIntervalMs"`
+	ScMaxConcurrentPosts *Int32Range       `json:"scMaxConcurrentPosts"`
+	ScMaxEachPostBytes   *Int32Range       `json:"scMaxEachPostBytes"`
+	ScMinPostsIntervalMs *Int32Range       `json:"scMinPostsIntervalMs"`
 	NoSSEHeader          bool              `json:"noSSEHeader"`
+	ResponseOkPadding    *Int32Range       `json:"responseOkPadding"`
+}
+
+func splithttpNewRandRangeConfig(input *Int32Range) *splithttp.RandRangeConfig {
+	if input == nil {
+		return nil
+	}
+
+	return &splithttp.RandRangeConfig{
+		From: input.From,
+		To:   input.To,
+	}
 }
 
 // Build implements Buildable.
@@ -246,22 +258,14 @@ func (c *SplitHTTPConfig) Build() (proto.Message, error) {
 		c.Host = c.Headers["Host"]
 	}
 	config := &splithttp.Config{
-		Path:   c.Path,
-		Host:   c.Host,
-		Header: c.Headers,
-		ScMaxConcurrentPosts: &splithttp.RandRangeConfig{
-			From: c.ScMaxConcurrentPosts.From,
-			To:   c.ScMaxConcurrentPosts.To,
-		},
-		ScMaxEachPostBytes: &splithttp.RandRangeConfig{
-			From: c.ScMaxEachPostBytes.From,
-			To:   c.ScMaxEachPostBytes.To,
-		},
-		ScMinPostsIntervalMs: &splithttp.RandRangeConfig{
-			From: c.ScMinPostsIntervalMs.From,
-			To:   c.ScMinPostsIntervalMs.To,
-		},
-		NoSSEHeader: c.NoSSEHeader,
+		Path:                 c.Path,
+		Host:                 c.Host,
+		Header:               c.Headers,
+		ScMaxConcurrentPosts: splithttpNewRandRangeConfig(c.ScMaxConcurrentPosts),
+		ScMaxEachPostBytes:   splithttpNewRandRangeConfig(c.ScMaxEachPostBytes),
+		ScMinPostsIntervalMs: splithttpNewRandRangeConfig(c.ScMinPostsIntervalMs),
+		NoSSEHeader:          c.NoSSEHeader,
+		ResponseOkPadding:    splithttpNewRandRangeConfig(c.ResponseOkPadding),
 	}
 	return config, nil
 }

transport/internet/splithttp/config.go

@@ -69,6 +69,17 @@ func (c *Config) GetNormalizedScMinPostsIntervalMs() RandRangeConfig {
 	return *c.ScMinPostsIntervalMs
 }
 
+func (c *Config) GetNormalizedResponseOkPadding() RandRangeConfig {
+	if c.ResponseOkPadding == nil || c.ResponseOkPadding.To == 0 {
+		return RandRangeConfig{
+			From: 100,
+			To:   1000,
+		}
+	}
+
+	return *c.ResponseOkPadding
+}
+
 func init() {
 	common.Must(internet.RegisterProtocolConfigCreator(protocolName, func() interface{} {
 		return new(Config)

transport/internet/splithttp/config.proto

@@ -14,6 +14,7 @@ message Config {
   RandRangeConfig scMaxEachPostBytes = 5;
   RandRangeConfig scMinPostsIntervalMs = 6;
   bool noSSEHeader = 7;
+  RandRangeConfig responseOkPadding = 8;
 }
 
 message RandRangeConfig {

transport/internet/splithttp/hub.go

@@ -124,6 +124,7 @@ func (h *requestHandler) ServeHTTP(writer http.ResponseWriter, request *http.Req
 
 	currentSession := h.upsertSession(sessionId)
 	scMaxEachPostBytes := int(h.ln.config.GetNormalizedScMaxEachPostBytes().To)
+	responseOkPadding := h.ln.config.GetNormalizedResponseOkPadding()
 
 	if request.Method == "POST" {
 		seq := ""
@@ -192,6 +193,10 @@ func (h *requestHandler) ServeHTTP(writer http.ResponseWriter, request *http.Req
 		// send a chunk immediately to enable CDN streaming.
 		// many CDN buffer the response headers until the origin starts sending
 		// the body, with no way to turn it off.
+		padding := int(responseOkPadding.roll())
+		for i := 0; i < padding; i++ {
+			writer.Write([]byte("o"))
+		}
 		writer.Write([]byte("ok"))
 		responseFlusher.Flush()