strip default ports from Host header in http proxy

Previously the Host header used the destination address verbatim, including
the port even for default ports (80 for HTTPS, 443 for HTTPS). This violates
HTTP specifications which require omitting default ports in Host headers.

This ensures compliant Host headers like "example.com" instead of "example.com:80"

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>

http.go

@@ -139,9 +139,7 @@ func doHttpProxy(srv *RttyServer, c net.Conn) {
 		return
 	}
 
-	hostHeaderRewrite := ses.destaddr
-
-	destAddr := genDestAddr(hostHeaderRewrite, ses.https)
+	destAddr, hostHeaderRewrite := genDestAddrAndHost(ses.destaddr, ses.https)
 
 	hpw := &HttpProxyWriter{
 		destAddr:          destAddr,
@@ -318,10 +316,10 @@ func sendHttpReq(dev *Device, https bool, srcAddr []byte, destAddr []byte, data
 	dev.WriteMsg(proto.MsgTypeHttp, bb)
 }
 
-func genDestAddr(addr string, https bool) []byte {
+func genDestAddrAndHost(addr string, https bool) ([]byte, string) {
 	destIP, destPort, err := httpProxyVaildAddr(addr, https)
 	if err != nil {
-		return nil
+		return nil, ""
 	}
 
 	b := make([]byte, 6)
@@ -329,7 +327,14 @@ func genDestAddr(addr string, https bool) []byte {
 
 	binary.BigEndian.PutUint16(b[4:], destPort)
 
-	return b
+	host := addr
+
+	ips, ports, _ := net.SplitHostPort(addr)
+	if ports == "80" || ports == "443" {
+		host = ips
+	}
+
+	return b, host
 }
 
 func tcpAddr2Bytes(addr *net.TCPAddr, b []byte) {