Simplify closing handshake

[lpinca]

Currently the close handshake works like this when initiated from the server:

        SERVER                                 CLIENT


+--------------------+
|ws.close()          |
|readyState = CLOSING|
+--------------------+
           |            +-----------+
           +----------->|close frame|-------------+
                        +-----------+             v
                                       +--------------------+
                                       |closeReceived = true|
                                       |ws.close()          |
                                       |readyState = CLOSING|
                                       +--------------------+
                        +-----------+             |
           +------------|close frame|<------------+
           v            +-----------+
+--------------------+
|closeReceived = true|
|ws.close()          |
|ws.terminate()      |
|socket.end()        |
+--------------------+
           |              +-------+
           +------------->|TCP FIN|---------------+
                          +-------+               v
                                        +-------------------+
                                        |readyState = CLOSED|
                                        |ws.emit('close')   |
                                        |socket.end()       |
                                        +-------------------+
                          +-------+               |
           +--------------|TCP FIN|<--------------+
           |              +-------+
           v
 +-------------------+
 |readyState = CLOSED|
 |ws.emit('close')   |
 +-------------------+

and like this when initiated from the client:

        CLIENT                                 SERVER


+--------------------+
|ws.close()          |
|readyState = CLOSING|
+--------------------+
           |            +-----------+
           +----------->|close frame|-------------+
                        +-----------+             v
                                       +--------------------+
                                       |closeReceived = true|
                                       |ws.close()          |
                                       |readyState = CLOSING|
                                       |ws.terminate()      |
                                       |socket.end()        |
                                       +--------------------+
                   +---------------------+        |
           +-------|close frame + TCP FIN|<-------+
           v       +---------------------+
+--------------------+
|closeReceived = true|
|ws.close()          |
|readyState = CLOSED |
|ws.emit('close')    |
|socket.end()        |
+--------------------+
           |              +-------+
           +------------->|TCP FIN|---------------+
                          +-------+               v
                                        +-------------------+
                                        |readyState = CLOSED|
                                        |ws.emit('close')   |
                                        +-------------------+

This patch uniforms the behavior making a close initiated by the server work in the same way of a close initiated by the client.

After reading https://tools.ietf.org/html/rfc6455#section-1.4 and https://tools.ietf.org/html/rfc6455#section-7, I think this is correct.

I have some doubts on this section which is why the close handshake is currently implemented in this way for the server but I also checked other implementations for Node.js and they use the same procedure for both client and server as proposed in this patch.

[lpinca]

cc: @nkzawa

[lpinca]

I guess the question to answer is:

Is there any advantage on calling socket.end() first on the server and then on the client when a close procedure is initiated by the server?

I don't know much about low level networking so if someone could shed some light on this, it would be great.

[lpinca]

@websockets/admin any thoughts on this?

[citrusjunoss]

When my client is Node and the server is Java(Netty), can it work?

[lpinca]

@citrusjunoss yes.

[citrusjunoss]

@citrusjunoss yes.

But the server does not receive any data when I call the close method

[lpinca]

It should receive a close frame. If you don't specify a close code, it will be something like this:

88 80 45 68 03 77

The last 4 bytes are random (the mask). You can check this with wireshark if you have no access to the TCP socket.