Why QWebSocketServer sends TCP [FIN] message on client connection attempt

Question

I use a QWebSocketServer with Qt5.8. Most of the WebSocket clients have no troubles connecting to it, but one of them provokes a singular behaviour. Below is the WireShark capture I get with this client (client 10.8.0.1, server 10.8.0.8). 10.8.0.1 10.8.0.8 TCP 44 51331 → 8888 [SYN] Seq=0 Win=2920 Len=0 MSS=1355 10.8.0.8 10.8.0.1 TCP 44 8888 → 51331 [SYN, ACK] Seq=0 Ack=1 Win=29200 Len=0 MSS=1460 10.8.0.1 10.8.0.8 TCP 40 51331 → 8888 [ACK] Seq=1 Ack=1 Win=2920 Len=0 10.8.0.1 10.8.0.8 TCP 64 51331 → 8888 [PSH, ACK] Seq=1 Ack=1 Win=2920 Len=24 [TCP segment of a reassembled PDU] 10.8.0.8 10.8.0.1 TCP 40 8888 → 51331 [ACK] Seq=1 Ack=25 Win=29200 Len=0 10.8.0.8 10.8.0.1 TCP 40 8888 → 51331 [FIN, ACK] Seq=1 Ack=25 Win=29200 Len=0 10.8.0.1 10.8.0.8 HTTP 209 GET /example HTTP/1.1 10.8.0.8 10.8.0.1 TCP 40 8888 → 51331 [RST] Seq=1 Win=0 Len=0 10.8.0.1 10.8.0.8 TCP 40 51331 → 8888 [ACK] Seq=194 Ack=2 Win=2919 Len=0 10.8.0.8 10.8.0.1 TCP 40 8888 → 51331 [RST] Seq=2 Win=0 Len=0 10.8.0.1 10.8.0.8 TCP 40 51331 → 8888 [FIN, ACK] Seq=194 Ack=2 Win=2919 Len=0 10.8.0.8 10.8.0.1 TCP 40 8888 → 51331 [RST] Seq=2 Win=0 Len=0 Below is the WireShark capture I get from a working client connecting to the same server (client 192.168.1.48, server 192.168.1.111). 192.168.1.48 192.168.1.111 TCP 74 37556 → 8888 [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=7880001 TSecr=0 WS=16 192.168.1.111 192.168.1.48 TCP 74 8888 → 37556 [SYN, ACK] Seq=0 Ack=1 Win=28960 Len=0 MSS=1460 SACK_PERM=1 TSval=3996923817 TSecr=7880001 WS=128 192.168.1.48 192.168.1.111 TCP 66 37556 → 8888 [ACK] Seq=1 Ack=1 Win=29200 Len=0 TSval=7880013 TSecr=3996923817 192.168.1.48 192.168.1.111 HTTP 264 GET /example HTTP/1.1 192.168.1.111 192.168.1.48 TCP 66 8888 → 37556 [ACK] Seq=1 Ack=199 Win=30080 Len=0 TSval=3996923820 TSecr=7880013 192.168.1.111 192.168.1.48 HTTP 540 HTTP/1.1 101 Switching Protocols Continuation 192.168.1.48 192.168.1.111 TCP 66 37556 → 8888 [ACK] Seq=199 Ack=475 Win=30272 Len=0 TSval=7880034 TSecr=3996924025 192.168.1.48 192.168.1.111 WebSocket 136 WebSocket Text [FIN] [MASKED] As far as I understand, in the first case, my QWebSocketServer implementation sends a [FIN] message for a reason I don't understand, before the client can send its HTTP Upgrade Get Request. Could that be caused by the fact the first client sends [PSH,ACK] TCP message whereas the second does not ? Who is not compliant with the WebSocket protocol here ? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

I just found this Qt bug report that explains my situation. As stated by Timur Pocheptsov, this appears to be a known bug that would require a major QWebSockets refactoring to fix. Unfortunately, it's by design so: QWebSocketHandshakeRequest tries to parse a client's handshake and sees nothing except this line, it considers such a request invalid and then QWebsocketServerPrivate::handshakeReceived closes the connection. A major re-write/re-design in qtwebsockets is needed to handle this correctly.