I'm using the non-Boost version of Asio and have made a TCP server based on the code at http://think-async.com/Asio/asio-1.11.0/doc/asio/tutorial/tutdaytime3.html
I can establish a connection to the server just fine, but only the first time. If I disconnect my client and then attempt to connect again, Asio passes an "Already Open" error to my accept handler. As you can see from the code, before a connection is accepted, a new instance of the tcp_connection class is created. I'm not sure why I'm getting this error, even though it's a completely separate instance whose socket shouldn't already be open. Any help would be greatly appreciated.
Thanks in advance.
EDIT:
Here's the server class:
http://pastebin.com/yvZmFQvA
And the client class (equivalent to the tcp_connection class in the example):
http://pastebin.com/LDhr2nZz
This might be because you are not correctly closing the socket upon disconnection. As a disconnection might happen due to an exception that can't be handled (such as signal 9), you need a solution to work even if the process didn't die gracefully...
I bealive this can solve it:
Socket options SO_REUSEADDR and SO_REUSEPORT, how do they differ? Do they mean the same across all major operating systems?
You have:
void server::do_accept() {
//client::pointer con = client::create(acceptor_.get_executor().context());
client::pointer con = client::create(acceptor_.get_io_service());
acceptor_.async_accept(con->socket(),
std::bind(&server::on_accepted, this, con,
std::placeholders::_1));
}
Client classes don't belong in the server. This doesn't make sense.
Your source material has:
void start_accept()
{
tcp_connection::pointer new_connection =
tcp_connection::create(acceptor_.get_executor().context());
acceptor_.async_accept(new_connection->socket(),
boost::bind(&tcp_server::handle_accept, this, new_connection,
asio::placeholders::error));
}
Related
I have written a threaded server much like this one: https://www.boost.org/doc/libs/1_36_0/doc/html/boost_asio/example/echo/async_tcp_echo_server.cpp
And a client: https://www.boost.org/doc/libs/1_53_0/doc/html/boost_asio/example/timeouts/blocking_tcp_client.cpp
They seem to work fine together when the client is talking directly with the server session. But now I would like to create another thread that would use the servers ioservice to send small messages. How would this be possible? I have read that shared_ptr would be one option, but have not got it working...
Inside the session class I define:
typedef boost::shared_ptr<session> session1;
static session1 create(boost::asio::io_service& io_service)
{
return session1(new session(io_service));
}
Then I define a global session_ptr as
session::session1 new_session1 = nullptr;
Then in the acceptor I start the session as:
new_session1 = session::create(tcp_io_serviceServer);
acceptor_.listen();
acceptor_.async_accept(new_session1->socket(), boost::bind(&server::handle_accept, this, boost::asio::placeholders::error));
and in the handle_accept:
new_session1->start();
Now what I would like to achieve, is that when the async_read of the server session gets a message from client to start a new thread:
if (dataReceived[0] == _dataStartCameraThread)
{
pthread = boost::thread(boost::bind(StartProcess, server));
}
then in that thread I want to send messages to the client as: new_session1->write1(error) as
void write1(const boost::system::error_code& error)
{
boost::asio::async_write(tcpsocket, boost::asio::buffer(sbuf, 1), boost::bind(&session::handle_dummy, this, boost::asio::placeholders::error));
}
But without the shared_ptr approach I cannot make this work. It claims that the file handle is not valid.
And using the shared_ptr approach I cannot seem to write anything from the server side, I can only read:
write failed. The file handle supplied is not valid
I checked that the socket is closed even though it just received the message.
Any suggestions where I should go here?
Thank you!
I'm creating multithreading application, that will work as "router" but on application layer.
The software will run on multiple hosts with multiple network interfaces.
In my application in one thread runs server, that accepts every connection on every interface and pass it to another worker-thread, which decide if the message will be forwarded and which interface schould be used.
I decided to use boost-asio.
So summarizing: incoming messages only in server (only here the read function), outgoing depending on typ through different gateway (only send function). The gateway should always connect to one interface, therefore I try to use the bind method.
But I get an exception: "bind: Bad file descriptor"
Here is the code snippet:
try
{
MY_LOG(trace) << "Connecting on IFace" << routingConf->connections[interface].ipSource;
boost::asio::io_service *svc = new boost::asio::io_service();
this->socket = new boost::asio::ip::tcp::socket(*svc);
boost::asio::ip::tcp::endpoint localEndpoint =
ip::tcp::endpoint(boost::asio::ip::address::from_string("127.0.0.1"), 0);
boost::asio::ip::tcp::endpoint remoteEndpoint = ip::tcp::endpoint(
boost::asio::ip::address::from_string("127.0.0.1"), port);
this->socket->bind(localEndpoint);
MY_LOG(trace) << "socket success";
this->socket->connect(remoteEndpoint);
} catch (std::exception &e)
{
MY_LOG(fatal) << e.what();
}
I tried different settings for local and remote endpoint. The server is already running in another thread, and if I not perform the binding operation, it is getting the sent message from send function (not included here).
socket::bind throws bad file descrption when socket was created but it is not open. You used constructor
basic_stream_socket(
boost::asio::io_service & io_service);
which constructs socket without opening it.
You should call open method before calling bind or use one of overloaded version of socket constructor which creates and also opens socket.
I want to create simple boost.beast websocket server which accept connection saves pointer to it and and when someone is connecting send message to every connected socket.
I've taken code from boost.beast async_server example: https://github.com/vinniefalco/Beast/blob/master/example/websocket-server-async/websocket_server_async.cpp
And added:
static std::vector<std::shared_ptr<connection>> server::players_connections;
and
void server::connection::send_message(std::string msg){
boost::beast::ostream(buffer_) << msg;
ws_.binary(ws_.got_binary());
ws_.async_write(buffer_.data(),
strand_.wrap(std::bind(
&connection::on_write,
shared_from_this(),
std::placeholders::_1)));
}
At the end of void server::connection::on_read(error_code ec) method i've added
for(auto player : server::players_connections){
player->send_message("already accepted");
}
and at the end of server::connection::on_accept:
players_connections.push_back(std::make_shared<connection>(*this, ep_, std::move(sock_)));
players_connections.back()->run();
When second socket connects i have this error:
websocket-server-async: /usr/local/boost_1_64_0/boost/beast/websocket/detail/pausation.hpp:210: void boost::beast::websocket::detail::pausation::emplace(F&&) [with F = boost::beast::websocket::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >::write_some_op<boost::beast::buffer_prefix_view<boost::beast::consuming_buffers<boost::beast::basic_multi_buffer<std::allocator<char> >::const_buffers_type> >, boost::beast::websocket::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >::write_op<boost::beast::basic_multi_buffer<std::allocator<char> >::const_buffers_type, boost::asio::detail::wrapped_handler<boost::asio::io_service::strand, std::_Bind<std::_Mem_fn<void (server::connection::*)(boost::system::error_code)>(std::shared_ptr<server::connection>, std::_Placeholder<1>)>, boost::asio::detail::is_continuation_if_running> > >]: Assertion `! base_' failed.
Aborted
Full modified code of server: http://morse.swirski.name/pastes/vrv552rf2yc7fyyflxhejukjdpr4vxe
What am I missing?
It looks like the bug was because i was calling
ws_.async_write(buffer_.data(),
strand_.wrap(std::bind(
&connection::on_write,
shared_from_this(),
std::placeholders::_1)));
two times in a row an this was causing the problem. I am not sure why. I suspect that method do_read called one after another was causing the problem. I would appriciate any suggestions.
There's a non-blocking Boost::Beast based WebSocket library that simplifies WebSockets integration.
It's called WebSockets-Callback.CPP available on GitHub.
I currently have a very simple boost::asio server that sends a status update upon connecting (using google proto buffers):
try
{
boost::asio::io_service io_service;
tcp::acceptor acceptor(io_service,tcp::endpoint(tcp::v4(), 13));
for (;;)
{
tcp::socket socket(io_service);
acceptor.accept(socket);
...
std::stringstream message;
protoMsg.SerializeToOstream(&message);
boost::system::error_code ignored_error;
boost::asio::write(socket, boost::asio::buffer(message.str()), ignored_error);
}
}
catch (std::exception& e) { }
I would like to extend it to first read after accepting a new connection, check what request was received, and send different messages back depending on this message. I'd also like to keep the TCP connection open so the client doesn't have to re-connect, and would like to handle multiple clients (not many, maybe 2 or 3).
I had a look at a few examples on boost asio, namely the async time tcp server and the chat server, but both are a bit over my head tbh. I don't even understand whether I need an async server. I guess I could just do a read after acceptor.accept(socket), but I guess then I wouldn't keep on listening for further requests. And if I go into a loop I guess that would mean I could only handle one client. So I guess that means I have to go async? Is there a simpler example maybe that isn't 250 lines of code? Or do I just have to bite my way through those examples? Thanks
The examples you mention from the Boost.Asio documentation are actually pretty good to see how things work. You're right that at first it might look a bit difficult to understand, especially if you're new to these concepts. However, I would recommend that you start with the chat server example and get that built on your machine. This will allow you to closer look into things and start changing things in order to learn how it works. Let me guide you through a few things I find important to get started.
From your description what you want to do, it seems that the chat server gives you a good starting point as it already has similar pieces you need. Having the server asynchronous is what you want as you then quite easily can handle multiple clients with a single thread. Nothing too complicated from the start.
Simplified, asynchronous in this case means that your server works off a queue, taking a handler (task) and executes it. If there is nothing on the queue, it just waits for something to be put on the queue. In your case that means it could be a connect from a client, a new read of a message from a client or something like this. In order for this to work, each handler (the function handling the reaction to a particular event) needs to be set up.
Let me explain a bit using code from the chat server example.
In the server source file, you see the chat_server class which calls start_accept in the constructor. Here the accept handler gets set up.
void start_accept()
{
chat_session_ptr new_session(new chat_session(io_service_, room_)); // 1
acceptor_.async_accept(new_session->socket(), // 2
boost::bind(&chat_server::handle_accept, this, new_session, // 3
boost::asio::placeholders::error)); // 4
}
Line 1: A chat_session object is created which represents a session between one client and the server. A session is created for the accept (no client has connected yet).
Line 2: An asynchronous accept for the socket...
Line 3: ...bound to call chat_server::handle_accept when it happens. The session is passed along to be used by the first client which connects.
Now, if we look at the handle_accept we see that upon client connect, start is called for the session (this just starts stuff between the server and this client). Lastly a new accept is put outstanding in case other clients want to connect as well.
void handle_accept(chat_session_ptr session,
const boost::system::error_code& error)
{
if (!error)
{
session->start();
}
start_accept();
}
This is what you want to have as well. An outstanding accept for incoming connections. And if multiple clients can connect, there should always be one of these outstanding so the server can handle the accept.
How the server and the client(s) interact is all in the session and you could follow the same design and modify this to do what you want. You mention that the server needs to look at what is sent and do different things. Take a look at chat_session and the start function which was called by the server in handle_accept.
void start()
{
room_.join(shared_from_this());
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.data(), chat_message::header_length),
boost::bind(
&chat_session::handle_read_header, shared_from_this(),
boost::asio::placeholders::error));
}
What is important here is the call to boost::asio::async_read. This is what you want too. This puts an outstanding read on the socket, so the server can read what the client sends. There is a handler (function) which is bound to this event chat_session::handle_read_header. This will be called whenever the server reads something on the socket. In this handler function you could start putting your specific code to determine what to do if a specific message is sent and so on.
What is important to know is that whenever calling these asynchronous boost::asio functions things will not happen within that call (i.e. the socket is not read if you call the function read). This is the asynchronous aspect. You just kind of register a handler for something and your code is called back when this happens. Hence, when this read is called it will immediately return and you're back in the handle_accept for the server (if you follow how things get called). And if you remember there we also call start_accept to set up another asynchronous accept. At this point you have two outstanding handlers waiting for either another client to connect or the first client to send something. Depending on what happens first, that specific handler will be called.
Also what is important to understand is that whenever something is run, it will run uninterrupted until everything it needs to do has been done. Other handlers have to wait even if there is are outstanding events which trigger them.
Finally, in order to run the server you'll need the io_service which is a central concept in Asio.
io_service.run();
This is one line you see in the main function. This just says that the thread (only one in the example) should run the io_service, which is the queue where handlers get enqueued when there is work to be done. When nothing, the io_service just waits (blocking the main thread there of course).
I hope this helps you get started with what you want to do. There is a lot of stuff you can do and things to learn. I find it a great piece of software! Good luck!
In case anyone else wants to do this, here is the minimum to get above going: (similar to the tutorials, but a bit shorter and a bit different)
class Session : public boost::enable_shared_from_this<Session>
{
tcp::socket socket;
char buf[1000];
public:
Session(boost::asio::io_service& io_service)
: socket(io_service) { }
tcp::socket& SocketRef() { return socket; }
void Read() {
boost::asio::async_read( socket,boost::asio::buffer(buf),boost::asio::transfer_at_least(1),boost::bind(&Session::Handle_Read,shared_from_this(),boost::asio::placeholders::error));
}
void Handle_Read(const boost::system::error_code& error) {
if (!error)
{
//read from buffer and handle requests
//if you want to write sth, you can do it sync. here: e.g. boost::asio::write(socket, ..., ignored_error);
Read();
}
}
};
typedef boost::shared_ptr<Session> SessionPtr;
class Server
{
boost::asio::io_service io_service;
tcp::acceptor acceptor;
public:
Server() : acceptor(io_service,tcp::endpoint(tcp::v4(), 13)) { }
~Server() { }
void operator()() { StartAccept(); io_service.run(); }
void StartAccept() {
SessionPtr session_ptr(new Session(io_service));
acceptor.async_accept(session_ptr->SocketRef(),boost::bind(&Server::HandleAccept,this,session_ptr,boost::asio::placeholders::error));
}
void HandleAccept(SessionPtr session,const boost::system::error_code& error) {
if (!error)
session->Read();
StartAccept();
}
};
From what I gathered through trial and error and reading: I kick it off in the operator()() so you can have it run in the background in an additional thread. You run one Server instance. To handle multiple clients, you need an extra class, I called this a session class. For asio to clean up dead sessions, you need a shared pointer as pointed out above. Otherwise the code should get you started.
I'm using Boost.Asio for network operations, they have to (and actually, can, there's no complex data structures or anything) remain pretty low level since I can't afford the luxury of serialization overhead (and the libs I found that did offer well enough performance seemed to be badly suited for my case).
The problem is with an async write I'm doing from the client (in QT, but that should probably be irrelevant here). The callback specified in the async_write doesn't get called, ever, and I'm at a complete loss as to why. The code is:
void SpikingMatrixClient::addMatrix() {
std::cout << "entered add matrix" << std::endl;
int action = protocol::Actions::AddMatrix;
int matrixSize = this->ui->editNetworkSize->text().toInt();
std::ostream out(&buf);
out.write(reinterpret_cast<const char*>(&action), sizeof(action));
out.write(reinterpret_cast<const char*>(&matrixSize), sizeof(matrixSize));
boost::asio::async_write(*connection.socket(), buf.data(),
boost::bind(&SpikingMatrixClient::onAddMatrix, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
}
which calls the first write. The callback is
void SpikingMatrixClient::onAddMatrix(const boost::system::error_code& error, size_t bytes_transferred) {
std::cout << "entered onAddMatrix" << std::endl;
if (!error) {
buf.consume(bytes_transferred);
requestMatrixList();
} else {
QString message = QString::fromStdString(error.message());
this->ui->statusBar->showMessage(message, 15000);
}
}
The callback never gets called, even though the server receives all the data. Can anyone think of any reason why it might be doing that?
P.S. There was a wrapper for that connection, and yes there will probably be one again. Ditched it a day or two ago because I couldn't find the problem with this callback.
As suggested, posting a solution I found to be the most suitable (at least for now).
The client application is [being] written in QT, and I need the IO to be async. For the most part, the client receives calculation data from the server application and has to render various graphical representations of them.
Now, there's some key aspects to consider:
The GUI has to be responsive, it should not be blocked by the IO.
The client can be connected / disconnected.
The traffic is pretty intense, data gets sent / refreshed to the client every few secs and it has to remain responsive (as per item 1.).
As per the Boost.Asio documentation,
Multiple threads may call io_service::run() to set up a pool of
threads from which completion handlers may be invoked.
Note that all threads that have joined an io_service's pool are considered equivalent, and the io_service may distribute work across them in an arbitrary fashion.
Note that io_service.run() blocks until the io_service runs out of work.
With this in mind, the clear solution is to run io_service.run() from another thread. The relevant code snippets are
void SpikingMatrixClient::connect() {
Ui::ConnectDialog ui;
QDialog *dialog = new QDialog;
ui.setupUi(dialog);
if (dialog->exec()) {
QString host = ui.lineEditHost->text();
QString port = ui.lineEditPort->text();
connection = TcpConnection::create(io);
boost::system::error_code error = connection->connect(host, port);
if (!error) {
io = boost::shared_ptr<boost::asio::io_service>(new boost::asio::io_service);
work = boost::shared_ptr<boost::asio::io_service::work>(new boost::asio::io_service::work(*io));
io_threads.create_thread(boost::bind(&SpikingMatrixClient::runIo, this, io));
}
QString message = QString::fromStdString(error.message());
this->ui->statusBar->showMessage(message, 15000);
}
}
for connecting & starting IO, where:
work is a private boost::shared_ptr to the boost::asio::io_service::work object it was passed,
io is a private boost::shared_ptr to a boost::asio::io_service,
connection is a boost::shared_ptr to my connection wrapper class, and the connect() call uses a resolver etc. to connect the socket, there's plenty examples of that around
and io_threads is a private boost::thread_group.
Surely it could be shortened with some typedefs if needed.
TcpConnection is my own connection wrapper implementation, which sortof lacks functionality for now, and I suppose I could move the whole thread thing into it when it gets reinstated. This snippet should be enough to get the idea anyway...
The disconnecting part goes like this:
void SpikingMatrixClient::disconnect() {
work.reset();
io_threads.join_all();
boost::system::error_code error = connection->disconnect();
if (!error) {
connection.reset();
}
QString message = QString::fromStdString(error.message());
this->ui->statusBar->showMessage(message, 15000);
}
the work object is destroyed, so that the io_service can run out of work eventually,
the threads are joined, meaning that all work gets finished before disconnecting, thus data shouldn't get corrupted,
the disconnect() calls shutdown() and close() on the socket behind the scenes, and if there's no error, destroys the connection pointer.
Note, that there's no error handling in case of an error while disconnecting in this snippet, but it could very well be done, either by checking the error code (which seems more C-like), or throwing from the disconnect() if the error code within it represents an error after trying to disconnect.
I encountered a similar problem (callbacks not fired) but the circumstances are different from this question (io_service had jobs but still would not fire the handlers ). I will post this anyway and maybe it will help someone.
In my program, I set up an async_connect() then followed by io_service.run(), which blocks as expected.
async_connect() goes to on_connect_handler() as expected, which in turn fires async_write().
on_write_complete_handler() does not fire, even though the other end of the connection has received all the data and has even sent back a response.
I discovered that it is caused by me placing program logic in on_connect_handler(). Specifically, after the connection was established and after I called async_write(), I entered an infinite loop to perform arbitrary logic, not allowing on_connect_handler() to exit. I assume this causes the io_service to not be able to execute other handlers, even if their conditions are met because it is stuck here. ( I had many misconceptions, and thought that io_service would automagically spawn threads for each async_x() call )
Hope that helps.