I am currently working on a network program. We know that when the remote host disconnects from you, it might be a normal disconnection or a reset. If it is a reset, the RST flag in the TCP packet is set. I want to know how to judge whether a disconnection is a normal one or a reset (using QTcpSocket when disconnected() is emitted). Additionally, if I want to send a packet with RST flag set, what should I do? Emit abort()?

@ yvbbrjdr As I said, I'm pretty sure Qt doesn't expose these low-level details, but posting your question on the the mail group , as @ koahnig suggested, certainly can't hurt.

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How to detect RST flag with QTcpSocket

Solved General and Desktop

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yvbbrjdr

wrote on last edited by

#1

I am currently working on a network program. We know that when the remote host disconnects from you, it might be a normal disconnection or a reset. If it is a reset, the RST flag in the TCP packet is set. I want to know how to judge whether a disconnection is a normal one or a reset (using QTcpSocket when disconnected() is emitted). Additionally, if I want to send a packet with RST flag set, what should I do? Emit abort()?
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Y yvbbrjdr

I am currently working on a network program. We know that when the remote host disconnects from you, it might be a normal disconnection or a reset. If it is a reset, the RST flag in the TCP packet is set. I want to know how to judge whether a disconnection is a normal one or a reset (using QTcpSocket when disconnected() is emitted). Additionally, if I want to send a packet with RST flag set, what should I do? Emit abort()?
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kshegunov
Moderators
wrote on last edited by

#2

@yvbbrjdr
Hello,

I want to know how to judge whether a disconnection is a normal one or a reset (using QTcpSocket when disconnected() is emitted)

I don't think that's possible with QTcpSocket.

Additionally, if I want to send a packet with RST flag set, what should I do?

Why should you want to do that in the first place?

Emit abort()?

abort() is not a signal and you don't emit signals from outside of the objects themselves, but yes, you call the abort() method. It should do what you want.

Kind regards.
Read and abide by the Qt Code of Conduct
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Y yvbbrjdr

I am currently working on a network program. We know that when the remote host disconnects from you, it might be a normal disconnection or a reset. If it is a reset, the RST flag in the TCP packet is set. I want to know how to judge whether a disconnection is a normal one or a reset (using QTcpSocket when disconnected() is emitted). Additionally, if I want to send a packet with RST flag set, what should I do? Emit abort()?
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koahnig

wrote on last edited by koahnig

#3

@yvbbrjdr

to add to @kshegunov
You can check using state and error() giving you SocketState and SocketError
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K koahnig

@yvbbrjdr

to add to @kshegunov
You can check using state and error() giving you SocketState and SocketError
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yvbbrjdr

wrote on last edited by

#4

@koahnig Thanks. So which exactly of the element in QAbstractSocket::SocketError represents reset?

There are
ConnectionRefusedError
RemoteHostClosedError
HostNotFoundError
SocketAccessError
SocketResourceError
SocketTimeoutError
DatagramTooLargeError
NetworkError
AddressInUseError
SocketAddressNotAvailableError
UnsupportedSocketOperationError
ProxyAuthenticationRequiredError
SslHandshakeFailedError
UnfinishedSocketOperationError
ProxyConnectionRefusedError
ProxyConnectionClosedError
ProxyConnectionTimeoutError
ProxyNotFoundError
ProxyProtocolError
OperationError
SslInternalError
SslInvalidUserDataError
TemporaryError
UnknownSocketError
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Y yvbbrjdr

@koahnig Thanks. So which exactly of the element in QAbstractSocket::SocketError represents reset?

There are
ConnectionRefusedError
RemoteHostClosedError
HostNotFoundError
SocketAccessError
SocketResourceError
SocketTimeoutError
DatagramTooLargeError
NetworkError
AddressInUseError
SocketAddressNotAvailableError
UnsupportedSocketOperationError
ProxyAuthenticationRequiredError
SslHandshakeFailedError
UnfinishedSocketOperationError
ProxyConnectionRefusedError
ProxyConnectionClosedError
ProxyConnectionTimeoutError
ProxyNotFoundError
ProxyProtocolError
OperationError
SslInternalError
SslInvalidUserDataError
TemporaryError
UnknownSocketError
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koahnig

wrote on last edited by

#5

@yvbbrjdr

@koahnig said:

to add to @kshegunov
You can check using state and error() giving you SocketState and SocketError

You need to follow the links already in the post before. There you find explanations much better than I can briefly summarize. The reset flag is part of a lower layer in TCP/IP. As already lined out by @kshegunov what for do you require to that there has been exactly this flag sent?
I fear when you are using Qt wrappings for TCP comms, this might be completely out of your control, because issued by the lower level routines not part of Qt.
Vote the answer(s) that helped you to solve your issue(s)
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K koahnig

@yvbbrjdr

@koahnig said:

to add to @kshegunov
You can check using state and error() giving you SocketState and SocketError

You need to follow the links already in the post before. There you find explanations much better than I can briefly summarize. The reset flag is part of a lower layer in TCP/IP. As already lined out by @kshegunov what for do you require to that there has been exactly this flag sent?
I fear when you are using Qt wrappings for TCP comms, this might be completely out of your control, because issued by the lower level routines not part of Qt.
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yvbbrjdr

wrote on last edited by

#6

@koahnig Actually I am working on a TCP relay server. When server resets the connection, I have to reset the connection to the client, too.
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Y yvbbrjdr

@koahnig Actually I am working on a TCP relay server. When server resets the connection, I have to reset the connection to the client, too.
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koahnig

wrote on last edited by

#7

@yvbbrjdr
OK, that is explaining your need. ;)
Sometimes "simple" users got stuck with some thoughts of their needs, but actually do not need those details.

I am not sure, if you will receive response from here. This is typically more user oriented.
The developer's email list might be better for such details.
Vote the answer(s) that helped you to solve your issue(s)
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Y yvbbrjdr

@koahnig Actually I am working on a TCP relay server. When server resets the connection, I have to reset the connection to the client, too.
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kshegunov
Moderators
wrote on last edited by

#8

@yvbbrjdr
As I said, I'm pretty sure Qt doesn't expose these low-level details, but posting your question on the the mail group, as @koahnig suggested, certainly can't hurt.
Read and abide by the Qt Code of Conduct
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