Add WebSocket path for CDN mode

add new option to README

Change field name and default value of CDNWsUrlPath

README.md

@@ -155,8 +155,13 @@ Example:
 `CDNOriginHost` is the domain name of the _origin_ server (i.e. the server running Cloak) under `CDN` mode. This only
 has effect when `Transport` is set to `CDN`. If unset, it will default to the remote hostname supplied via the
 commandline argument (in standalone mode), or by Shadowsocks (in plugin mode). After a TLS session is established with
-the CDN server, this domain name will be used in the HTTP request to ask the CDN server to establish a WebSocket
-connection with this host.
+the CDN server, this domain name will be used in the `Host` header of the HTTP request to ask the CDN server to
+establish a WebSocket connection with this host.
+
+`CDNWsUrlPath` is the url path used to build websocket request sent under `CDN` mode, and also only has effect
+when `Transport` is set to `CDN`. If unset, it will default to "/". This option is used to build the first line of the
+HTTP request after a TLS session is extablished. It's mainly for a Cloak server behind a reverse proxy, while only
+requests under specific url path are forwarded.
 
 `NumConn` is the amount of underlying TCP connections you want to use. The default of 4 should be appropriate for most
 people. Setting it too high will hinder the performance. Setting it to 0 will disable connection multiplexing and each

internal/client/state.go

@@ -37,6 +37,7 @@ type RawConfig struct {
 	BrowserSig    string // nullable
 	Transport     string // nullable
 	CDNOriginHost string // nullable
+	CDNWsUrlPath  string // nullable
 	StreamTimeout int    // nullable
 	KeepAlive     int    // nullable
 }
@@ -225,10 +226,13 @@ func (raw *RawConfig) ProcessRawConfig(worldState common.WorldState) (local Loca
 		} else {
 			cdnDomainPort = net.JoinHostPort(raw.CDNOriginHost, raw.RemotePort)
 		}
+		if raw.CDNWsUrlPath == "" {
+			raw.CDNWsUrlPath = "/"
+		}
 
 		remote.TransportMaker = func() Transport {
 			return &WSOverTLS{
-				cdnDomainPort: cdnDomainPort,
+				wsUrl: "ws://" + cdnDomainPort + raw.CDNWsUrlPath,
 			}
 		}
 	case "direct":

internal/client/websocket.go

@@ -15,7 +15,7 @@ import (
 
 type WSOverTLS struct {
 	*common.WebSocketConn
-	cdnDomainPort string
+	wsUrl string
 }
 
 func (ws *WSOverTLS) Handshake(rawConn net.Conn, authInfo AuthInfo) (sessionKey [32]byte, err error) {
@@ -41,7 +41,7 @@ func (ws *WSOverTLS) Handshake(rawConn net.Conn, authInfo AuthInfo) (sessionKey
 		return
 	}
 
-	u, err := url.Parse("ws://" + ws.cdnDomainPort)
+	u, err := url.Parse(ws.wsUrl)
 	if err != nil {
 		return sessionKey, fmt.Errorf("failed to parse ws url: %v", err)
 	}