I am attempting to write a price listener.
the data arrives as a 'push' response, ie: chunked transfer-encoding.
i have decided to use the http server api, as both async wininet and winHTTP read data apis both close the connection if there is no data for a short while.
first of all, am i correct to use the http server api?
second, if i try to, as per the msdn example:
retCode = HttpInitialize(
HttpApiVersion,
HTTP_INITIALIZE_SERVER,
NULL
); // return is NO_ERROR
retCode = HttpCreateHttpHandle(
&hReqQueue,
0
); // return is NO_ERROR
std::wstring url = _T( "http://apidintegra.tkfweb.com:80/" );
retCode = HttpAddUrl(
hReqQueue,
url.c_str(),
NULL
); // always fails with ERROR_SHARING_VIOLATION
i always get a sharing violation. do i need to use netsh to configure the connection somehow? if so how? ive seen mention of configuring http.sys, and ive even tried executing the above code as an administrator.
I would be extremely grateful for some help, as there seems very little code out there for this!
Many thanks,
Jon
This error happens if the port is already in use by another process. That means another application uses the port (for example IIS or another web server).
Related
When working with Binance REST API using WinHTTP, I noticed that requests sometimes are failed with the error
12030 the connection with the server was terminated abnormally
Each request is made like this: (the complete example is here)
WinHttpOpen(...)
WinHttpConnect(...)
{... making request itself; }
if (hRequest) WinHttpCloseHandle(hRequest);
if (hConnect) WinHttpCloseHandle(hConnect);
if (hSession) WinHttpCloseHandle(hSession);
However, despite I close handles, the connection is reused (which I see in the HttpAnalyzer).
I suppose that this is the issue: the server starts dropping connection after N requests or seconds, accoring to server's keep-alive settings; At the same moment my client starts new request which failed with 12030.
Moreover. inspesting successful requests headers, I noticed that
Connection: Close
is passed from the server from time to time; I'd like to reconnect in such cases.
The question is: how do I prevent WInHTTP from trying to reuse connection which is about to be dropped by server?
Changing the registry "TcpTimedWaitDelay" parameter would not be efficient because request count per time may vary.
The same quesstion is actual for Delphi TNetHTTPClient (which uses WinHTTP) and Indy TIdHTTP.
As for Indy, releasing of the TIdHTTP object does not close the connection; however in this case we have source codes. The following patch in the IdSSLOpenSSL.pas solves it:
If SSL_shutdown(fSSL) = 0
then SSL_shutdown(fSSL);
// SSL_shutdown(fSSL); <= was in original Indy10 IdSSLOpenSSL
I'm currently running a FileZilla FTP server on a network. My issue is that on seemingly random machines, when the user navigates to a directory (which they are able to do) and attempts to ls (i.e. data transfer) their end hangs waiting for a response, while the server reports this 425: Can't open data connection for transfer mentioned above. This result varies depending on the client machine used, where some (either local or remote) are able to proceed and others stuck here. I understand that this is because simple FTP commands like CWDing operate on the 20/21 ports, whereas FTP data transfer operate on some other port number, which in turn may be blocked by a firewall somewhere along the chain. My question is, how do I account for these varying ports (if this truly is the issue), as as best I know they could be anything above 1024?
My end goal with this project is to implement a very simple FTP solution, ideally using WinINet, however, so far I've run into the same problem:
BOOL CWebFileFinder::FindFile(const CString& URL)
{
CString ServerName;
CString strObject;
INTERNET_PORT nPort;
DWORD dwServiceType = AFX_INET_SERVICE_FTP;
if (AfxParseURL(URL, dwServiceType, ServerName, strObject, nPort))
{
m_Connection = m_Session.GetFtpConnection(ServerName, m_Username, m_Password, nPort/*, true*/); // results in findfile still failing
if (m_Connection)
{
m_Connection->SetCurrentDirectory("sms"); // CDs into this dir
m_Finder = new CFtpFileFind(m_Connection);
if (m_Finder)
{
More = m_Finder->FindFile(_T("*.*")); // hangs here
}
}
}
catch (CException* pEx)
{
CString str;
LPTSTR error = str.GetBuffer(255);
pEx->GetErrorMessage(error, 255);
pEx->Delete();
str.ReleaseBuffer();
}
return More;
}
As far as I can see, either I need to call to open this data port prior to the LIST, or find the firewalls blocking these ports and create a rule to prevent that (What ports does Wininet listen on for Active FTP data connection?). Of course I could also be just completely off-base – Any insights at all would be greatly appreciated!
Your FTP server seems to require an encrypted connection (TLS/SSL).
WinInet does not support encrypted FTP.
See C++/Win32 The basics of FTP security and using SSL.
I'm working on Boost Asio and Boost Beast for simple RESTful server. For normal HTTP and TCP socket, it works perfectly. I put it under load test with JMeter, everything works fine.
I tried to add the SSL socket. I set the 'ssl::context' and also called the 'async_handshake()' - additional steps for SSL compared to normal socket. It works for the first time only. Client can connected with me (server) and I also able to receive the data via 'boost::beast::http::async_read()'.
Because this is RESTful, so the connection will drop after the request & respond. I call 'SSL_Socket.shutdown()' and follow by 'SSL_Socket.lowest_layer().close()' to close the SSL socket.
When the next incoming request, the client able to connect with me (server). I called 'SSL_Socket.async_handshake()' and then follow by 'boost::beast::http::async_read()'. But this time I not able to receive any data. But the connection is successfully established.
Anyone has any clue what i missed?
Thank you very much!
If you want to reuse the stream instance, you need to manipulate SSL_Socket.native_handle() with openssl lib function. After ssl shutdown, use SSL_clear() before start a new ssl handshake.
please read(pay attention to warnings) link for detail
SSL_clear() resets the SSL object to allow for another connection. The reset operation however keeps several settings of the last sessions (some of these settings were made automatically during the last handshake)
.........
WARNINGS
SSL_clear() resets the SSL object to allow for another connection. The reset operation however keeps several settings of the last sessions (some of these settings were made automatically during the last handshake). It only makes sense for a new connection with the exact same peer that shares these settings, and may fail if that peer changes its settings between connections. Use the sequence SSL_get_session(3); SSL_new(3); SSL_set_session(3); SSL_free(3) instead to avoid such failures (or simply SSL_free(3); SSL_new(3) if session reuse is not desired).
In regard to ssl shutdown issue, link explain how boost asio ssl shutdown work.
In Boost.Asio, the shutdown() operation is considered complete upon error or if the party has sent and received a close_notify message.
If you look at boost.asio (1.68) source code boost\asio\ssl\detail\impl\engine.ipp, it shows how boost.asio do ssl shutdown and stream_truncated happens when there is data to be read or ssl shutdown expected from peer not received.
int engine::do_shutdown(void*, std::size_t)
{
int result = ::SSL_shutdown(ssl_);
if (result == 0)
result = ::SSL_shutdown(ssl_);
return result;
}
const boost::system::error_code& engine::map_error_code(
boost::system::error_code& ec) const
......
// If there's data yet to be read, it's an error.
if (BIO_wpending(ext_bio_))
{
ec = boost::asio::ssl::error::stream_truncated;
return ec;
}
......
// Otherwise, the peer should have negotiated a proper shutdown.
if ((::SSL_get_shutdown(ssl_) & SSL_RECEIVED_SHUTDOWN) == 0)
{
ec = boost::asio::ssl::error::stream_truncated;
}
}
Also you can see boost.asio ssl shutdown routine may call openssl SSL_shutdown() twice if first return 0, openssl document allows it but advice call SSL_read() to do a bidirectional shutdown if first SSL_shutdown() returns 0.
Read link for details.
I had a similar issue, the 2nd time onward my asynchonous accept always failed with session id uninitialized.
I solved this problem calling SSL_CTX_set_session_id_context on context or
setting context cache mode with SSL_SESS_CACHE_OFF and SSL_OP_NO_TICKET on context options.
This is my cents to someone else's problem.
I managed to resolve the problem by switching 'ssl::stream' socket to 'boost::optional' and then added 'SSL_Socket.emplace(io_context, oSSLContext)' each time the socket is shutdown and closed.
Big credit to sehe at 'Can't implement boost::asio::ssl::stream<boost::asio::ip::tcp::socket> reconnect to server'. His statement "the purest solution would be to not reuse the stream/socket objects" rocks! Save my time.
Thanks.
When you use the simple ZeroMQ REQ/REP pattern you depend on a fixed send()->recv() / recv()->send() sequence.
As this article describes you get into trouble when a participant disconnects in the middle of a request because then you can't just start over with receiving the next request from another connection but the state machine would force you to send a request to the disconnected one.
Has there emerged a more elegant way to solve this since the mentioned article has been written?
Is reconnecting the only way to solve this (apart from not using REQ/REP but use another pattern)
As the accepted answer seem so terribly sad to me, I did some research and have found that everything we need was actually in the documentation.
The .setsockopt() with the correct parameter can help you resetting your socket state-machine without brutally destroy it and rebuild another on top of the previous one dead body.
(yeah I like the image).
ZMQ_REQ_CORRELATE: match replies with requests
The default behaviour of REQ sockets is to rely on the ordering of messages to match requests and responses and that is usually sufficient. When this option is set to 1, the REQ socket will prefix outgoing messages with an extra frame containing a request id. That means the full message is (request id, 0, user frames…). The REQ socket will discard all incoming messages that don't begin with these two frames.
Option value type int
Option value unit 0, 1
Default value 0
Applicable socket types ZMQ_REQ
ZMQ_REQ_RELAXED: relax strict alternation between request and reply
By default, a REQ socket does not allow initiating a new request with zmq_send(3) until the reply to the previous one has been received. When set to 1, sending another message is allowed and has the effect of disconnecting the underlying connection to the peer from which the reply was expected, triggering a reconnection attempt on transports that support it. The request-reply state machine is reset and a new request is sent to the next available peer.
If set to 1, also enable ZMQ_REQ_CORRELATE to ensure correct matching of requests and replies. Otherwise a late reply to an aborted request can be reported as the reply to the superseding request.
Option value type int
Option value unit 0, 1
Default value 0
Applicable socket types ZMQ_REQ
A complete documentation is here
The good news is that, as of ZMQ 3.0 and later (the modern era), you can set a timeout on a socket. As others have noted elsewhere, you must do this after you have created the socket, but before you connect it:
zmq_req_socket.setsockopt( zmq.RCVTIMEO, 500 ) # milliseconds
Then, when you actually try to receive the reply (after you have sent a message to the REP socket), you can catch the error that will be asserted if the timeout is exceeded:
try:
send( message, 0 )
send_failed = False
except zmq.Again:
logging.warning( "Image send failed." )
send_failed = True
However! When this happens, as observed elsewhere, your socket will be in a funny state, because it will still be expecting the response. At this point, I cannot find anything that works reliably other than just restarting the socket. Note that if you disconnect() the socket and then re connect() it, it will still be in this bad state. Thus you need to
def reset_my_socket:
zmq_req_socket.close()
zmq_req_socket = zmq_context.socket( zmq.REQ )
zmq_req_socket.setsockopt( zmq.RCVTIMEO, 500 ) # milliseconds
zmq_req_socket.connect( zmq_endpoint )
You will also notice that because I close()d the socket, the receive timeout option was "lost", so it is important set that on the new socket.
I hope this helps. And I hope that this does not turn out to be the best answer to this question. :)
There is one solution to this and that is adding timeouts to all calls. Since ZeroMQ by itself does not really provide simple timeout functionality I recommend using a subclass of the ZeroMQ socket that adds a timeout parameter to all important calls.
So, instead of calling s.recv() you would call s.recv(timeout=5.0) and if a response does not come back within that 5 second window it will return None and stop blocking. I had made a futile attempt at this when I run into this problem.
I'm actually looking into this at the moment, because I am retro fitting a legacy system.
I am coming across code constantly that "needs" to know about the state of the connection. However the thing is I want to move to the message passing paradigm that the library promotes.
I found the following function : zmq_socket_monitor
What it does is monitor the socket passed to it and generate events that are then passed to an "inproc" endpoint - at that point you can add handling code to actually do something.
There is also an example (actually test code) here : github
I have not got any specific code to give at the moment (maybe at the end of the week) but my intention is to respond to the connect and disconnects such that I can actually perform any resetting of logic required.
Hope this helps, and despite quoting 4.2 docs, I am using 4.0.4 which seems to have the functionality
as well.
Note I notice you talk about python above, but the question is tagged C++ so that's where my answer is coming from...
Update: I'm updating this answer with this excellent resource here: https://blog.cloudflare.com/when-tcp-sockets-refuse-to-die/ Socket programming is complicated so do checkout the references in this post.
None of the answers here seem accurate or useful. The OP is not looking for information on BSD socket programming. He is trying to figure out how to robustly handle accept()ed client-socket failures in ZMQ on the REP socket to prevent the server from hanging or crashing.
As already noted -- this problem is complicated by the fact that ZMQ tries to pretend that the servers listen()ing socket is the same as an accept()ed socket (and there is no where in the documentation that describes how to set basic timeouts on such sockets.)
My answer:
After doing a lot of digging through the code, the only relevant socket options passed along to accept()ed socks seem to be keep alive options from the parent listen()er. So the solution is to set the following options on the listen socket before calling send or recv:
void zmq_setup(zmq::context_t** context, zmq::socket_t** socket, const char* endpoint)
{
// Free old references.
if(*socket != NULL)
{
(**socket).close();
(**socket).~socket_t();
}
if(*context != NULL)
{
// Shutdown all previous server client-sockets.
zmq_ctx_destroy((*context));
(**context).~context_t();
}
*context = new zmq::context_t(1);
*socket = new zmq::socket_t(**context, ZMQ_REP);
// Enable TCP keep alive.
int is_tcp_keep_alive = 1;
(**socket).setsockopt(ZMQ_TCP_KEEPALIVE, &is_tcp_keep_alive, sizeof(is_tcp_keep_alive));
// Only send 2 probes to check if client is still alive.
int tcp_probe_no = 2;
(**socket).setsockopt(ZMQ_TCP_KEEPALIVE_CNT, &tcp_probe_no, sizeof(tcp_probe_no));
// How long does a con need to be "idle" for in seconds.
int tcp_idle_timeout = 1;
(**socket).setsockopt(ZMQ_TCP_KEEPALIVE_IDLE, &tcp_idle_timeout, sizeof(tcp_idle_timeout));
// Time in seconds between individual keep alive probes.
int tcp_probe_interval = 1;
(**socket).setsockopt(ZMQ_TCP_KEEPALIVE_INTVL, &tcp_probe_interval, sizeof(tcp_probe_interval));
// Discard pending messages in buf on close.
int is_linger = 0;
(**socket).setsockopt(ZMQ_LINGER, &is_linger, sizeof(is_linger));
// TCP user timeout on unacknowledged send buffer
int is_user_timeout = 2;
(**socket).setsockopt(ZMQ_TCP_MAXRT, &is_user_timeout, sizeof(is_user_timeout));
// Start internal enclave event server.
printf("Host: Starting enclave event server\n");
(**socket).bind(endpoint);
}
What this does is tell the operating system to aggressively check the client socket for timeouts and reap them for cleanup when a client doesn't return a heart beat in time. The result is that the OS will send a SIGPIPE back to your program and socket errors will bubble up to send / recv - fixing a hung server. You then need to do two more things:
1. Handle SIGPIPE errors so the program doesn't crash
#include <signal.h>
#include <zmq.hpp>
// zmq_setup def here [...]
int main(int argc, char** argv)
{
// Ignore SIGPIPE signals.
signal(SIGPIPE, SIG_IGN);
// ... rest of your code after
// (Could potentially also restart the server
// sock on N SIGPIPEs if you're paranoid.)
// Start server socket.
const char* endpoint = "tcp://127.0.0.1:47357";
zmq::context_t* context;
zmq::socket_t* socket;
zmq_setup(&context, &socket, endpoint);
// Message buffers.
zmq::message_t request;
zmq::message_t reply;
// ... rest of your socket code here
}
2. Check for -1 returned by send or recv and catch ZMQ errors.
// E.g. skip broken accepted sockets (pseudo-code.)
while (1):
{
try
{
if ((*socket).recv(&request)) == -1)
throw -1;
}
catch (...)
{
// Prevent any endless error loops killing CPU.
sleep(1)
// Reset ZMQ state machine.
try
{
zmq::message_t blank_reply = zmq::message_t();
(*socket).send (blank_reply);
}
catch (...)
{
1;
}
continue;
}
Notice the weird code that tries to send a reply on a socket failure? In ZMQ, a REP server "socket" is an endpoint to another program making a REQ socket to that server. The result is if you go do a recv on a REP socket with a hung client, the server sock becomes stuck in a broken receive loop where it will wait forever to receive a valid reply.
To force an update on the state machine, you try send a reply. ZMQ detects that the socket is broken, and removes it from its queue. The server socket becomes "unstuck", and the next recv call returns a new client from the queue.
To enable timeouts on an async client (in Python 3), the code would look something like this:
import asyncio
import zmq
import zmq.asyncio
#asyncio.coroutine
def req(endpoint):
ms = 2000 # In milliseconds.
sock = ctx.socket(zmq.REQ)
sock.setsockopt(zmq.SNDTIMEO, ms)
sock.setsockopt(zmq.RCVTIMEO, ms)
sock.setsockopt(zmq.LINGER, ms) # Discard pending buffered socket messages on close().
sock.setsockopt(zmq.CONNECT_TIMEOUT, ms)
# Connect the socket.
# Connections don't strictly happen here.
# ZMQ waits until the socket is used (which is confusing, I know.)
sock.connect(endpoint)
# Send some bytes.
yield from sock.send(b"some bytes")
# Recv bytes and convert to unicode.
msg = yield from sock.recv()
msg = msg.decode(u"utf-8")
Now you have some failure scenarios when something goes wrong.
By the way -- if anyone's curious -- the default value for TCP idle timeout in Linux seems to be 7200 seconds or 2 hours. So you would be waiting a long time for a hung server to do anything!
Sources:
https://github.com/zeromq/libzmq/blob/84dc40dd90fdc59b91cb011a14c1abb79b01b726/src/tcp_listener.cpp#L82 TCP keep alive options preserved for client sock
http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/ How does keep alive work
https://github.com/zeromq/libzmq/blob/master/builds/zos/README.md Handling sig pipe errors
https://github.com/zeromq/libzmq/issues/2586 for information on closing sockets
https://blog.cloudflare.com/when-tcp-sockets-refuse-to-die/
https://github.com/zeromq/libzmq/issues/976
Disclaimer:
I've tested this code and it seems to be working, but ZMQ does complicate testing this a fair bit because the client re-connects on failure? If anyone wants to use this solution in production, I recommend writing some basic unit tests, first.
The server code could also be improved a lot with threading or polling to be able to handle multiple clients at once. As it stands, a malicious client can temporarily take up resources from the server (3 second timeout) which isn't ideal.
I am writing an XMLRPC client in c++ that is intended to talk to a python XMLRPC server.
Unfortunately, at this time, the python XMLRPC server is only capable of fielding one request on a connection, then it shuts down, I discovered this thanks to mhawke's response to my previous query about a related subject
Because of this, I have to create a new socket connection to my python server every time I want to make an XMLRPC request. This means the creation and deletion of a lot of sockets. Everything works fine, until I approach ~4000 requests. At this point I get socket error 10048, Socket in use.
I've tried sleeping the thread to let winsock fix its file descriptors, a trick that worked when a python client of mine had an identical issue, to no avail.
I've tried the following
int err = setsockopt(s_,SOL_SOCKET,SO_REUSEADDR,(char*)TRUE,sizeof(BOOL));
with no success.
I'm using winsock 2.0, so WSADATA::iMaxSockets shouldn't come into play, and either way, I checked and its set to 0 (I assume that means infinity)
4000 requests doesn't seem like an outlandish number of requests to make during the run of an application. Is there some way to use SO_KEEPALIVE on the client side while the server continually closes and reopens?
Am I totally missing something?
The problem is being caused by sockets hanging around in the TIME_WAIT state which is entered once you close the client's socket. By default the socket will remain in this state for 4 minutes before it is available for reuse. Your client (possibly helped by other processes) is consuming them all within a 4 minute period. See this answer for a good explanation and a possible non-code solution.
Windows dynamically allocates port numbers in the range 1024-5000 (3977 ports) when you do not explicitly bind the socket address. This Python code demonstrates the problem:
import socket
sockets = []
while True:
s = socket.socket()
s.connect(('some_host', 80))
sockets.append(s.getsockname())
s.close()
print len(sockets)
sockets.sort()
print "Lowest port: ", sockets[0][1], " Highest port: ", sockets[-1][1]
# on Windows you should see something like this...
3960
Lowest port: 1025 Highest port: 5000
If you try to run this immeditaely again, it should fail very quickly since all dynamic ports are in the TIME_WAIT state.
There are a few ways around this:
Manage your own port assignments and
use bind() to explicitly bind your
client socket to a specific port
that you increment each time your
create a socket. You'll still have
to handle the case where a port is
already in use, but you will not be
limited to dynamic ports. e.g.
port = 5000
while True:
s = socket.socket()
s.bind(('your_host', port))
s.connect(('some_host', 80))
s.close()
port += 1
Fiddle with the SO_LINGER socket
option. I have found that this
sometimes works in Windows (although
not exactly sure why):
s.setsockopt(socket.SOL_SOCKET,
socket.SO_LINGER, 1)
I don't know if this will help in
your particular application,
however, it is possible to send
multiple XMLRPC requests over the
same connection using the
multicall method. Basically
this allows you to accumulate
several requests and then send them
all at once. You will not get any
responses until you actually send
the accumulated requests, so you can
essentially think of this as batch
processing - does this fit in with
your application design?
Update:
I tossed this into the code and it seems to be working now.
if(::connect(s_, (sockaddr *) &addr, sizeof(sockaddr)))
{
int err = WSAGetLastError();
if(err == 10048) //if socket in user error, force kill and reopen socket
{
closesocket(s_);
WSACleanup();
WSADATA info;
WSAStartup(MAKEWORD(2,0), &info);
s_ = socket(AF_INET,SOCK_STREAM,0);
setsockopt(s_,SOL_SOCKET,SO_REUSEADDR,(char*)&x,sizeof(BOOL));
}
}
Basically, if you encounter the 10048 error (socket in use), you can simply close the socket, call cleanup, and restart WSA, the reset the socket and its sockopt
(the last sockopt may not be necessary)
i must have been missing the WSACleanup/WSAStartup calls before, because closesocket() and socket() were definitely being called
this error only occurs once every 4000ish calls.
I am curious as to why this may be, even though this seems to fix it.
If anyone has any input on the subject i would be very curious to hear it
Do you close the sockets after using it?