Home » U++ Library support » U++ MT-multithreading and servers » [SOLVED] TcpSocket Connect error
| [SOLVED] TcpSocket Connect error [message #42396] |
Tue, 11 March 2014 12:35  |
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Hi,
Newest uppsrc revision 7033.
Here on my Ubuntu 12.04 workstation I see a problem with TcpSocket.Connect, it always returns true, even if no server is listening at the other end:
TcpSocket client_socket;
client_socket.Timeout(5000);
if (client_socket.Connect("127.0.0.1", 12345)) // Connect to non existing server
{
LOG("ERROR, Connect returned true");
}
else
{
LOG("Correct, The connection could not be established");
}
The doc mentions the operation is blocking, but it is not. It does not say anything about the return value, I just assume it would be true on success.
It works if I comment the O_NONBLOCK from Socket.cpp->TcpSocket::SetupSocket(), like this:
if(fcntl(socket, F_SETFL, (fcntl(socket, F_GETFL, 0)/* | O_NONBLOCK*/))) {
I discovered this while trying to connect to a slow server and the not so reader friendly TcpSocket::RawConnect function passed on the SOCKERR(EINPROGRESS) check. No matter if a connection was established or not.
I don't have the in depth knowledge on the upp code base, to say if removing the O_NONBLOCK will cause undesired problems in other places.
[Updated on: Wed, 02 April 2014 07:03] Report message to a moderator |
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| Re: TcpSocket Connect error [message #42415 is a reply to message #42396] |
Wed, 12 March 2014 10:52  |
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mirek
Messages: 14255
Registered: November 2005
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Ultimate Member |
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| steffen wrote on Tue, 11 March 2014 07:35 |
Hi,
Newest uppsrc revision 7033.
Here on my Ubuntu 12.04 workstation I see a problem with TcpSocket.Connect, it always returns true, even if no server is listening at the other end:
TcpSocket client_socket;
client_socket.Timeout(5000);
if (client_socket.Connect("127.0.0.1", 12345)) // Connect to non existing server
{
LOG("ERROR, Connect returned true");
}
else
{
LOG("Correct, The connection could not be established");
}
The doc mentions the operation is blocking, but it is not. It does not say anything about the return value, I just assume it would be true on success.
It works if I comment the O_NONBLOCK from Socket.cpp->TcpSocket::SetupSocket(), like this:
if(fcntl(socket, F_SETFL, (fcntl(socket, F_GETFL, 0)/* | O_NONBLOCK*/))) {
I discovered this while trying to connect to a slow server and the not so reader friendly TcpSocket::RawConnect function passed on the SOCKERR(EINPROGRESS) check. No matter if a connection was established or not.
I don't have the in depth knowledge on the upp code base, to say if removing the O_NONBLOCK will cause undesired problems in other places.
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The documentation is misleading. It is only blocking w.r.t. DNS resolve.
[Updated on: Wed, 12 March 2014 10:55] Report message to a moderator |
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| Re: TcpSocket Connect error [message #42416 is a reply to message #42396] |
Wed, 12 March 2014 17:24 |
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Thanks Mirek,
But what about the return value? I would expect TcpSocket.Connect to return true, when it has established a connection.
This is definitely not how it works, if the server is not responding.
I looked at the Linux man page on connect and for non blocking connections it says the following:
| Quote: |
EINPROGRESS
The socket is nonblocking and the connection cannot be completed immediately.
It is possible to select(2) or poll(2) for completion by selecting the socket for writing.
After select(2) indicates writability, use getsockopt(2) to read the SO_ERROR option at level
SOL_SOCKET to determine whether connect() completed successfully (SO_ERROR is zero) or unsuccessfully
(SO_ERROR is one of the usual error codes listed here, explaining the reason for the failure).
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I have attached a small example showing the error and the solution mentioned in the man page:
When connecting to a non existing server, TcpSocket.Connect returns true, but fails on a subsequent write.
I have tested the example on both Windows and Linux, and both systems has the error.
So a solution could be one of these two:
1. Change TcpSocket::SetupSocket() to make a blocking socket:
Change Socket.cpp line 302 to
if(fcntl(socket, F_SETFL, (fcntl(socket, F_GETFL, 0)))) {
or
2. Implement the getsockopt call to check the connection before returning from RawConnect.
I can make a patch to RawConnect if you would prefer that solution.
[Updated on: Wed, 12 March 2014 17:25] Report message to a moderator |
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| Re: TcpSocket Connect error [message #42424 is a reply to message #42396] |
Thu, 13 March 2014 08:28 |
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I used the WaitWrite in the Connect2 function in my example, but checking errno just after the WaitWrite returns, it still shows 115 (EINPROGRESS).
It only works if I call getsockopt afterwards, then optval is set to 111 (Connection refused).
I have improved the logging in my example, so now the output is like this:
| Quote: |
Test1 Connecting
After Connect: 115 Operation now in progress
Connected
Sending: My Test String
ERROR: 111 Connection refused
Test2 Connecting
After WaitWrite: 115 Operation now in progress
optval: 111 Connection refused
SUCCESS: No Connection to non existing server.
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Test1 is getting the error after the first write attempt, but it should have failed on connect.
Test2 calls getsockopt and detects the missing connection correctly.
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| Re: TcpSocket Connect error [message #42425 is a reply to message #42396] |
Thu, 13 March 2014 08:43 |
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Here is a patched version of RawConnect, I have NOT tried it with IPv6:
bool TcpSocket::RawConnect(addrinfo *arp)
{
if(!arp) {
SetSockError("connect", -1, "not found");
return false;
}
String err;
for(int pass = 0; pass < 2; pass++) {
addrinfo *rp = arp;
while(rp)
{
if(rp->ai_family == AF_INET == !pass) // Try to connect IPv4 in the first pass
{
if (Open(rp->ai_family, rp->ai_socktype, rp->ai_protocol))
{
int r = connect(socket, rp->ai_addr, (int)rp->ai_addrlen);
if(r != 0)
{
if (WaitWrite())
{
int optval = 0;
socklen_t optlen = sizeof(optval);
if (getsockopt(GetSOCKET(), SOL_SOCKET, SO_ERROR, (char*)&optval, &optlen) == 0)
{
if (optval == 0)
r = 0;
else
{
if(err.GetCount())
err << '\n';
err << TcpSocketErrorDesc(optval);
}
}
}
}
if (r == 0)
{
mode = CONNECT;
return true;
}
if(err.GetCount())
err << '\n';
err << TcpSocketErrorDesc(GetErrorCode());
Close();
}
}
rp = rp->ai_next;
}
}
SetSockError("connect", -1, Nvl(err, "failed"));
return false;
}
And the output from my connect test is:
| Quote: |
Test1 Connecting
SUCCESS: No Connection to non existing server.
Test2 Connecting
SUCCESS: No Connection to non existing server.
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Regards,
Steffen
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| Re: TcpSocket Connect error [message #42549 is a reply to message #42396] |
Mon, 24 March 2014 08:22 |
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Hi Mirek,
Thank you for the answer. I thought it might be complicated and I understand you concerns.
I have another suggestion then, that wont break anything:
Could you add a function that can be called prior to Connect, where one can determine if the socket should be blocking or not?
Storing a member variable containing either O_BLOCK or O_NONBLOCK and then use this variable in the SetupSocket function.
bool TcpSocket::SetupSocket()
{
#ifdef PLATFORM_WIN32
connection_start = msecs();
u_long arg = 1;
if(ioctlsocket(socket, FIONBIO, &arg)) {
SetSockError("ioctlsocket(FIO[N]BIO)");
return false;
}
#else
#ifdef PLATFORM_BSD
connection_start = msecs();
#endif
if(fcntl(socket, F_SETFL, (fcntl(socket, F_GETFL, 0) | O_NONBLOCK))) {
SetSockError("fcntl(O_[NON]BLOCK)");
return false;
}
#endif
return true;
}
Would be something like this:
bool TcpSocket::SetupSocket()
{
#ifdef PLATFORM_WIN32
connection_start = msecs();
u_long arg = 1;
if(ioctlsocket(socket, mBlockingMode, &arg)) {
SetSockError("ioctlsocket(FIO[N]BIO)");
return false;
}
#else
#ifdef PLATFORM_BSD
connection_start = msecs();
#endif
if(fcntl(socket, F_SETFL, (fcntl(socket, F_GETFL, 0) | mBlockingMode))) {
SetSockError("fcntl(O_[NON]BLOCK)");
return false;
}
#endif
return true;
}
As I wrote earlier, commenting out the O_NONBLOCK part also gives correct result.
Regards,
Steffen
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| Re: TcpSocket Connect error [message #42552 is a reply to message #42396] |
Mon, 24 March 2014 12:02 |
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Yes it would be correct according to documentation, but wouldn't it break the web crawler example?
It seems like I always end up struggling with the same parts when doing communication code. There is excellent helper functions for detecting read and write readiness. But I often have problems with the connection part, either because of slow lines or servers being offline.
It could be a great help if there was an IsConnected() function and/or a WaitConnect() function, like the WaitRead and WaitWrite functions.
Regards,
Steffen
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| Re: TcpSocket Connect error [message #42763 is a reply to message #42396] |
Wed, 02 April 2014 07:02 |
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Thank you very much Mirek, it works fine now. 
Just leave it out of Connect. It's easy enough to do:
if (socket.Connect(...) && socket.WaitConnect())
{
// Connected
}
else
{
LOG(socket.GetErrorDesc());
}
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