Websockify does not pass information further, connection is dropped prematurely

Question

I need to use websockify as a proxy. The final setup will be:

a websocket on a webpage connects to websockify server on the same machine
websockify server initiates connection with a TCP socket program listening somewhere else (in this case, the same machine)
TCP socket receives information, performs computation, answers websockify
websockify gets the answer and sends the information to the socket on webpage
answer is presented in a user's browser

However, for some reason websockify refuses to pass the information further and receives FIN message sooner than expected. Websockify says "Unsupported: Unknown opcode 0x01".

To investigate this case, I have created a MWE and intercepted traffic with tcpdump.

The setup is as follows:

Firstly, I run netcat -v -v -l -p 40000 - that's the application we want to receive the information
Then, I run websockify --verbose 50000 localhost:40000 - that's the proxying command
Finally, I run wscat -c localhost:50000 - that's an app making a websocket connection to websockify proxy

As soon as I send something with wscat, wscat's connection is dropped with code 1003. Quoting RFC 6455:

1003 indicates that an endpoint is terminating the connection because it has received a type of data it cannot accept (e.g., an endpoint that understands only text data MAY send this if it receives a binary message).

Here is the visual representation of that setup (the erorr message 'disconnected because closed 1003' is written that way because I have manally altered the source to extract more information about disconnection):

Here is Wireshark's representation of the data:

and here are the packets number 11,12,13 and 14 that caught my attention:

Frame 11: 81 bytes on wire (648 bits), 81 bytes captured (648 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Sep 19, 2017 20:35:46.491762000 CEST
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1505846146.491762000 seconds
    [Time delta from previous captured frame: 3.788711000 seconds]
    [Time delta from previous displayed frame: 3.788711000 seconds]
    [Time since reference or first frame: 3.887638000 seconds]
    Frame Number: 11
    Frame Length: 81 bytes (648 bits)
    Capture Length: 81 bytes (648 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ip:tcp:http:websocket:data-text-lines]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Destination: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Source: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IPv4 (0x0800)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        0000 00.. = Differentiated Services Codepoint: Default (0)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 67
    Identification: 0x1581 (5505)
    Flags: 0x02 (Don't Fragment)
        0... .... = Reserved bit: Not set
        .1.. .... = Don't fragment: Set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (6)
    Header checksum: 0x2732 [validation disabled]
    [Header checksum status: Unverified]
    Source: 127.0.0.1
    Destination: 127.0.0.1
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
TCP Src Port: 53832, Dst Port: 50000, Seq: 225, Ack: 130, Len: 15
    Src Port: 53832
    Dest Port: 50000
    [Stream index: 0]
    [TCP Segment Len: 15]
    Sequence number: 225    (relative sequence number)
    [Next sequence number: 240    (relative sequence number)]
    Acknowledgment number: 130    (relative ack number)
    1000 .... = Header Length: 32 bytes (8)
    Flags: 0x018 (PSH, ACK)
        000. .... .... = Reserved: Not set
        ...0 .... .... = Nonce: Not set
        .... 0... .... = Congestion Window Reduced (CWR): Not set
        .... .0.. .... = ECN-Echo: Not set
        .... ..0. .... = Urgent: Not set
        .... ...1 .... = Acknowledgment: Set
        .... .... 1... = Push: Set
        .... .... .0.. = Reset: Not set
        .... .... ..0. = Syn: Not set
        .... .... ...0 = Fin: Not set
        [TCP Flags: ·······AP···]
    Window size value: 350
    [Calculated window size: 44800]
    [Window size scaling factor: 128]
    Checksum: 0xfe37 [unverified]
    [Checksum Status: Unverified]
    Urgent pointer: 0
    Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - Timestamps: TSval 1764320477, TSecr 1764319312
            Kind: Time Stamp Option (8)
            Length: 10
            Timestamp value: 1764320477
            Timestamp echo reply: 1764319312
    [SEQ/ACK analysis]
        [iRTT: 0.000021000 seconds]
        [Bytes in flight: 15]
        [Bytes sent since last PSH flag: 15]
    TCP payload (15 bytes)
    [PDU Size: 15]
WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0001 = Opcode: Text (1)
    1... .... = Mask: True
    .000 1001 = Payload length: 9
    Masking-Key: 2f0bda1c
    Masked payload
    Payload
Line-based text data
    alamakota
Frame 12: 102 bytes on wire (816 bits), 102 bytes captured (816 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Sep 19, 2017 20:35:46.492378000 CEST
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1505846146.492378000 seconds
    [Time delta from previous captured frame: 0.000616000 seconds]
    [Time delta from previous displayed frame: 0.000616000 seconds]
    [Time since reference or first frame: 3.888254000 seconds]
    Frame Number: 12
    Frame Length: 102 bytes (816 bits)
    Capture Length: 102 bytes (816 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ip:tcp:http:websocket]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Destination: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Source: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IPv4 (0x0800)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        0000 00.. = Differentiated Services Codepoint: Default (0)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 88
    Identification: 0xd42e (54318)
    Flags: 0x02 (Don't Fragment)
        0... .... = Reserved bit: Not set
        .1.. .... = Don't fragment: Set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (6)
    Header checksum: 0x686f [validation disabled]
    [Header checksum status: Unverified]
    Source: 127.0.0.1
    Destination: 127.0.0.1
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
TCP Src Port: 50000, Dst Port: 53832, Seq: 130, Ack: 240, Len: 36
    Src Port: 50000
    Dest Port: 53832
    [Stream index: 0]
    [TCP Segment Len: 36]
    Sequence number: 130    (relative sequence number)
    [Next sequence number: 166    (relative sequence number)]
    Acknowledgment number: 240    (relative ack number)
    1000 .... = Header Length: 32 bytes (8)
    Flags: 0x018 (PSH, ACK)
        000. .... .... = Reserved: Not set
        ...0 .... .... = Nonce: Not set
        .... 0... .... = Congestion Window Reduced (CWR): Not set
        .... .0.. .... = ECN-Echo: Not set
        .... ..0. .... = Urgent: Not set
        .... ...1 .... = Acknowledgment: Set
        .... .... 1... = Push: Set
        .... .... .0.. = Reset: Not set
        .... .... ..0. = Syn: Not set
        .... .... ...0 = Fin: Not set
        [TCP Flags: ·······AP···]
    Window size value: 350
    [Calculated window size: 44800]
    [Window size scaling factor: 128]
    Checksum: 0xfe4c [unverified]
    [Checksum Status: Unverified]
    Urgent pointer: 0
    Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - Timestamps: TSval 1764320478, TSecr 1764320477
            Kind: Time Stamp Option (8)
            Length: 10
            Timestamp value: 1764320478
            Timestamp echo reply: 1764320477
    [SEQ/ACK analysis]
        [This is an ACK to the segment in frame: 11]
        [The RTT to ACK the segment was: 0.000616000 seconds]
        [iRTT: 0.000021000 seconds]
        [Bytes in flight: 36]
        [Bytes sent since last PSH flag: 36]
    TCP payload (36 bytes)
    [PDU Size: 36]
WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 1000 = Opcode: Connection Close (8)
    0... .... = Mask: False
    .010 0010 = Payload length: 34
    Payload
        Close
            Status code: Unsupported Data (1003)
            Reason: Unsupported: Unknown opcode 0x01
Frame 13: 66 bytes on wire (528 bits), 66 bytes captured (528 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Sep 19, 2017 20:35:46.492394000 CEST
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1505846146.492394000 seconds
    [Time delta from previous captured frame: 0.000016000 seconds]
    [Time delta from previous displayed frame: 0.000016000 seconds]
    [Time since reference or first frame: 3.888270000 seconds]
    Frame Number: 13
    Frame Length: 66 bytes (528 bits)
    Capture Length: 66 bytes (528 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ip:tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Destination: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Source: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IPv4 (0x0800)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        0000 00.. = Differentiated Services Codepoint: Default (0)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 52
    Identification: 0x1582 (5506)
    Flags: 0x02 (Don't Fragment)
        0... .... = Reserved bit: Not set
        .1.. .... = Don't fragment: Set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (6)
    Header checksum: 0x2740 [validation disabled]
    [Header checksum status: Unverified]
    Source: 127.0.0.1
    Destination: 127.0.0.1
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
TCP Src Port: 53832, Dst Port: 50000, Seq: 240, Ack: 166, Len: 0
    Src Port: 53832
    Dest Port: 50000
    [Stream index: 0]
    [TCP Segment Len: 0]
    Sequence number: 240    (relative sequence number)
    Acknowledgment number: 166    (relative ack number)
    1000 .... = Header Length: 32 bytes (8)
    Flags: 0x010 (ACK)
        000. .... .... = Reserved: Not set
        ...0 .... .... = Nonce: Not set
        .... 0... .... = Congestion Window Reduced (CWR): Not set
        .... .0.. .... = ECN-Echo: Not set
        .... ..0. .... = Urgent: Not set
        .... ...1 .... = Acknowledgment: Set
        .... .... 0... = Push: Not set
        .... .... .0.. = Reset: Not set
        .... .... ..0. = Syn: Not set
        .... .... ...0 = Fin: Not set
        [TCP Flags: ·······A····]
    Window size value: 350
    [Calculated window size: 44800]
    [Window size scaling factor: 128]
    Checksum: 0xfe28 [unverified]
    [Checksum Status: Unverified]
    Urgent pointer: 0
    Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - Timestamps: TSval 1764320478, TSecr 1764320478
            Kind: Time Stamp Option (8)
            Length: 10
            Timestamp value: 1764320478
            Timestamp echo reply: 1764320478
    [SEQ/ACK analysis]
        [This is an ACK to the segment in frame: 12]
        [The RTT to ACK the segment was: 0.000016000 seconds]
        [iRTT: 0.000021000 seconds]
Frame 14: 106 bytes on wire (848 bits), 106 bytes captured (848 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Sep 19, 2017 20:35:46.494661000 CEST
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1505846146.494661000 seconds
    [Time delta from previous captured frame: 0.002267000 seconds]
    [Time delta from previous displayed frame: 0.002267000 seconds]
    [Time since reference or first frame: 3.890537000 seconds]
    Frame Number: 14
    Frame Length: 106 bytes (848 bits)
    Capture Length: 106 bytes (848 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ip:tcp:http:websocket]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Destination: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Source: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Address: 00:00:00_00:00:00 (00:00:00:00:00:00)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IPv4 (0x0800)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        0000 00.. = Differentiated Services Codepoint: Default (0)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 92
    Identification: 0x1583 (5507)
    Flags: 0x02 (Don't Fragment)
        0... .... = Reserved bit: Not set
        .1.. .... = Don't fragment: Set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (6)
    Header checksum: 0x2717 [validation disabled]
    [Header checksum status: Unverified]
    Source: 127.0.0.1
    Destination: 127.0.0.1
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
TCP Src Port: 53832, Dst Port: 50000, Seq: 240, Ack: 166, Len: 40
    Src Port: 53832
    Dest Port: 50000
    [Stream index: 0]
    [TCP Segment Len: 40]
    Sequence number: 240    (relative sequence number)
    [Next sequence number: 280    (relative sequence number)]
    Acknowledgment number: 166    (relative ack number)
    1000 .... = Header Length: 32 bytes (8)
    Flags: 0x018 (PSH, ACK)
        000. .... .... = Reserved: Not set
        ...0 .... .... = Nonce: Not set
        .... 0... .... = Congestion Window Reduced (CWR): Not set
        .... .0.. .... = ECN-Echo: Not set
        .... ..0. .... = Urgent: Not set
        .... ...1 .... = Acknowledgment: Set
        .... .... 1... = Push: Set
        .... .... .0.. = Reset: Not set
        .... .... ..0. = Syn: Not set
        .... .... ...0 = Fin: Not set
        [TCP Flags: ·······AP···]
    Window size value: 350
    [Calculated window size: 44800]
    [Window size scaling factor: 128]
    Checksum: 0xfe50 [unverified]
    [Checksum Status: Unverified]
    Urgent pointer: 0
    Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - No-Operation (NOP)
            Kind: No-Operation (1)
        TCP Option - Timestamps: TSval 1764320478, TSecr 1764320478
            Kind: Time Stamp Option (8)
            Length: 10
            Timestamp value: 1764320478
            Timestamp echo reply: 1764320478
    [SEQ/ACK analysis]
        [iRTT: 0.000021000 seconds]
        [Bytes in flight: 40]
        [Bytes sent since last PSH flag: 40]
    TCP payload (40 bytes)
    [PDU Size: 40]
WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 1000 = Opcode: Connection Close (8)
    1... .... = Mask: True
    .010 0010 = Payload length: 34
    Masking-Key: 3daec4d6
    Masked payload
    Payload
        Close
            Status code: Unsupported Data (1003)
            Reason: Unsupported: Unknown opcode 0x01

It seems like wscat sends an opcode (0x1) which websockify understands as 0x01 and fails to recognize, but I don't know why.

How do I make this setup work? I have tried connecting to websockify with different programs (browser websocket implementation, wscat alternatives), but they all fail.

score 3 · Answer 1 · answered Nov 06 '17 at 15:07

3

I hit the same issue:

socket.send("hi"); // websockify chokes

... which got fixed by this:

b = new Blob(["hi", "\n"], {type: 'text/plain'});
socket.send(b); // works as expected

answered Nov 06 '17 at 15:07

Elmo Todurov

77

Websockify does not pass information further, connection is dropped prematurely

1 Answers1