I'm converting an application from using Juce asynchronous i/o to asio. The first part is to rewrite the code that receives traffic from another application on the same machine (it's a Lightroom Lua plugin that sends \n delimited messages on port 58764). Whenever I successfully connect to that port with my C++ program, I get a series of error codes, all the same:
An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.
Can someone point out my error? I can see that the socket is successfully opened. I've reduced this from my full program to a minimal example. I also tried it with connect instead of async_connect and had the same problem.
#include <iostream>
#include "asio.hpp"
asio::io_context io_context_;
asio::ip::tcp::socket socket_{io_context_};
void loop_me()
{
asio::streambuf streambuf{};
while (true) {
if (!socket_.is_open()) {
return;
}
else {
asio::async_read_until(socket_, streambuf, '\n',
[&streambuf](const asio::error_code& error_code, std::size_t bytes_transferred) {
if (error_code) {
std::cerr << "Socket error " << error_code.message() << std::endl;
return;
}
// Extract up to the first delimiter.
std::string command{buffers_begin(streambuf.data()),
buffers_begin(streambuf.data()) + bytes_transferred};
std::cout << command << std::endl;
streambuf.consume(bytes_transferred);
});
}
}
}
int main()
{
auto work_{asio::make_work_guard(io_context_)};
std::thread io_thread_;
std::thread run_thread_;
io_thread_ = std::thread([] { io_context_.run(); });
socket_.async_connect(asio::ip::tcp::endpoint(asio::ip::address_v4::loopback(), 58764),
[&run_thread_](const asio::error_code& error) {
if (!error) {
std::cout << "Socket connected in LR_IPC_In\n";
run_thread_ = std::thread(loop_me);
}
else {
std::cerr << "LR_IPC_In socket connect failed " << error.message() << std::endl;
}
});
std::this_thread::sleep_for(std::chrono::seconds(1));
socket_.close();
io_context_.stop();
if (io_thread_.joinable())
io_thread_.join();
if (run_thread_.joinable())
run_thread_.join();
}
You are trying to start an infinite number of asynchronous read operations at the same time. You shouldn't start a new asynchronous read until the previous one finished.
async_read_until returns immediately, even though the data hasn't been received yet. That's the point of "async".
Related
I have this requirement where my app have to connect to another app via sockets and will have to maintain persistent connection for quiet long time. My app will be a TCP client and the other is a TCP server. My app will send commands and the server will respond accordingly.
The problem am facing right now is how to read the whole data from server a string and return for app which will issue the next command. Reading synchronously (with asio::read) looked like a good option up until I observed socket hanging up until I terminate the server. Looking at the documentation I found that the library is correctly working.
his function is used to read a certain number of bytes of data from a stream. The call will block until one of the following conditions is true:
1. The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes.
2. An error occurred.
The problem is I don't know correct buffer size as the response from the server varies. So If I put a too small buffer it returns fine but missing some data. If I put too big it will hang forever until server quits.
So I thought I would do the async reading. It works only once and I don't know how to make it fetch data until whole data it read.
here is the relevant async code
#define ASIO_STANDALONE 1
#include <iostream>
#include <asio.hpp>
int main()
{
asio::io_context context;
size_t reply_length;
size_t length = 1024;
std::vector<char> buffer;
//create socket
asio::ip::tcp::socket socket(context);
socket.connect(asio::ip::tcp::endpoint(asio::ip::address::from_string("127.0.0.1"), 8088));
std::string dataOut = "list --files"; //some command to write
std::error_code error;
asio::write(socket, asio::buffer(dataOut), error);
if (!error)
{
std::cout << "Receiving...!" << std::endl;
buffer.resize(length);
asio::async_read(socket, asio::buffer(buffer), [&buffer, &context](const asio::error_code &ec, std::size_t bytes_transferred) {
std::copy(buffer.begin(), buffer.end(), std::ostream_iterator<char>(std::cout, ""));
std::cout << "\nRead total of:" << bytes_transferred << "\n";
context.run();
});
}
else
{
std::cout << "send failed: " << error.message() << std::endl;
}
context.run();
}
Searching didn't help much solving my issue.
So my question is, how can I read all the data in a persistent socket with asio? Am not using boost.
You need to loop async_read calls. If you don't want your client to hang on read operation you can define the smallest possible buffer i.e. 1 byte.
Define function which takes socket, buffer and two additional parameters according to async_read's handler signature, and this function calls itself with async_read to make the loop of async_read calls - it reads until some error occures:
void onRead (
asio::ip::tcp::socket& socket,
std::array<char,1>& buf,
const system::error_code& ec,
std::size_t bytes)
{
if (ec)
{
if (ec == asio::error::eof && bytes == 1)
std::cout << buf[0];
return;
}
std::cout << buf[0];
asio::async_read(socket,asio::buffer(buf),
std::bind(onRead, std::ref(socket), std::ref(buf),
std::placeholders::_1, // error code
std::placeholders::_2)); // transferred bytes
}
and the changes in main:
std::array<char,1> buf;
asio::write(socket, asio::buffer(dataOut), error);
if (!error)
{
std::cout << "Receiving...!" << std::endl;
asio::async_read(socket, asio::buffer(buf),
std::bind(onRead, std::ref(socket), std::ref(buf),
std::placeholders::_1,
std::placeholders::_2));
context.run();
}
else
{
std::cout << "send failed: " << error.message() << std::endl;
}
(I am using Boost, so you should replace system::error_code on asio::error_code).
I am learning about boost and was messing around with its server and client communication to make a simple chat server, where anything that a client sends, is just displayed on the server. The server itself doesn't send anything and starts the receiving part. It is pretty straight-forward.
Server code:
#include <boost\asio\placeholders.hpp>
#include <boost\bind.hpp>
#include <boost\asio\ip\tcp.hpp>
#include <boost\asio\io_context.hpp>
#include <iostream>
class Server
{
private :
boost::asio::ip::tcp::socket server_socket;
boost::asio::ip::tcp::endpoint server_endpoint;
boost::asio::ip::tcp::acceptor acceptor;
std::string msg;
public :
Server(boost::asio::io_context &io) :
server_socket(io),
server_endpoint(boost::asio::ip::make_address("127.0.0.1"), 27015),
acceptor(io, server_endpoint)
{
acceptor.async_accept(server_socket,
boost::bind(&Server::async_acceptor_handler, this,
boost::asio::placeholders::error));
}
void async_acceptor_handler(const boost::system::error_code &ec)
{
if (!ec)
{
std::cout << "One client connected...\n";
server_socket.async_read_some(boost::asio::buffer(msg),
boost::bind(&Server::async_read_some_handler, this,
boost::asio::placeholders::error));
}
else
{
std::cout << "async_acceptor failed with error code : " << ec.value() << std::endl;
std::cout << "Error description : " << ec.message() << std::endl;
}
}
void async_read_some_handler(const boost::system::error_code &ec)
{
if (!ec)
{
std::cout << msg << std::endl;
server_socket.async_read_some(boost::asio::buffer(msg),
boost::bind(&Server::async_read_some_handler, this,
boost::asio::placeholders::error));
}
else
{
std::cout << "async_acceptor failed with error code : " << ec.value() << std::endl;
std::cout << "Error description : " << ec.message() << std::endl;
}
}
};
int main()
{
boost::asio::io_context io;
Server s(io);
io.run();
return 0;
}
In the client part, it is again a pretty straight-forward code, simply connects to the server and starts taking input from user and sends to server.
Client code:
#include <boost\asio\placeholders.hpp>
#include <boost\bind.hpp>
#include <boost\asio\ip\tcp.hpp>
#include <boost\asio\io_context.hpp>
#include <iostream>
class Client
{
private :
boost::asio::ip::tcp::socket client_socket;
boost::asio::ip::tcp::endpoint server_endpoint;
std::string msg;
public :
Client(boost::asio::io_context &iocontext) :
client_socket(iocontext),
server_endpoint(boost::asio::ip::make_address("127.0.0.1"), 27015)
{
//connect to server endpoint
client_socket.async_connect(server_endpoint,
boost::bind(&Client::async_connect_handler, this,
boost::asio::placeholders::error));
}
void async_connect_handler(const boost::system::error_code &ec)
{
if (!ec)
{
std::cout << "Connected to chat server...\n";
//wait for user input
std::cin >> msg;
std::cout << "\rC : " << msg << std::endl;
client_socket.async_write_some(boost::asio::buffer(msg),
boost::bind(&Client::async_write_some_handler, this,
boost::asio::placeholders::error));
}
else
{
std::cout << "async_connect failed with error code : " << ec.value() << std::endl;
std::cout << "Error description : " << ec.message() << std::endl;
}
}
void async_write_some_handler(const boost::system::error_code &ec)
{
//wait for user input
std::cin >> msg;
std::cout << "\rC : " << msg << std::endl;
client_socket.async_write_some(boost::asio::buffer(msg),
boost::bind(&Client::async_write_some_handler, this,
boost::asio::placeholders::error));
}
};
int main()
{
boost::asio::io_context io;
Client c(io);
io.run();
return 0;
}
Now the problem:
It works fine, and connects to the server too. I get the proper "Connected to chat server..." in client and "One client connected..." in server. The problem arises after that :
In the server console, after the "One client" message, it just starts printing nothing and goes on and on.
The messages sent by the client are never showed in the server console.
Problem 1 can be a issue on my part as I am yet to check the wait functions and other calls which make the server wait. If you can guide me on that, it will be more than amazing. But the major problem is the part 2 of the problem, since, I have no idea why the server is always receiving nothing from client.
PS: This is an incomplete code and I plan to play a bit more with it, so, if there are some major flaws, please tell me so... :)
PPS: Before you say check other questions similar to this, I went through all the similar questions. For ex: this and this, but this are not relevant.
What is the size of string msg in the server side? It is 0. So the server reads always 0 bytes.
When you want to read to string and you call buffer::asio::buffer string must have some size, for example 10. It means you want to read 10 bytes into msg. You can call msg.resize(10) (before reading operation is initiated), then some data will be read into msg by async_read_some (it could be 1,2 bytes, whatever - it is how async_read_some works, but the maximum read characters is 10). But it is poor solution.
You are sending text, so you may consider using read data into streambuf instead of string, when you don't know how many bytes can come from the client side. Then you can call async_read_until with delimiter - it can be for example new line character.
Another solution is to use dynamic buffer. Where data is appened into string and you don't care about the initial size of string buffer. But dynamic buffer doesn't work with member functions of socket like async_read_some, it could be used with async_read as free function.
I am referring to Chat Client
My write Operation is:
void CSession::beginWrite(const Buffer & message)
{
//Check if the socket is open or not?
bool writeInProgress = !writeQueue_.empty();
writeQueue_.push_back(message);
if (!writeInProgress) //Exception Thrown here
{
asio::async_write(socket_, asio::buffer(writeQueue_.front().received_, writeQueue_.front().buffsize),
std::bind(&CSession::handle_write, this,
std::placeholders::_1, std::placeholders::_2));
}
}
void CSession::handle_write(const asio::error_code& error /*error*/, size_t bytes_transferred /*bytes_transferred*/)
{
//std::cout << "CSession::handle_write() Called" << "(" << __FILE__ << " : " << __LINE__ << ")" << std::endl;
if (!error)
{
//std::cout << bytes_transferred << " bytes written to the socket." << std::endl;
writeQueue_.pop_front();
if (!writeQueue_.empty())
{
asio::async_write(socket_, asio::buffer(writeQueue_.front().received_, writeQueue_.front().buffsize),
std::bind(&CSession::handle_write, this,
std::placeholders::_1, std::placeholders::_2));
}
}
else
{
std::cout << "Write Error Detected" << std::endl;
std::cout << error.message() << std::endl;
state_ = false;
doClose();
return;
}
}
It works fine. Then I tried load testing by making client write message Client 2 to the server continuously for 11 minutes as shown below:
bool flag = false;
void setFlag(const asio::error_code& /*e*/)
{
flag = true;
}
void Client(std::string IP, std::string port)
{
CSession Session(IP, port);
Session.initSession();
asio::thread t(boost::bind(&asio::io_service::run, &(*CIOService::fetchIOService().getIO())));
asio::deadline_timer timer(*CIOService::fetchIOService().getIO(), boost::posix_time::seconds(675));
timer.async_wait(&setFlag);
while (!flag)
{
Session.write("Client 2");
}
Session.close();
t.join();
}
void main()
{
Client("localhost", "8974");
system("Pause");
}
After 2-3 minutes of successful write operation, the code throws exception Unhandled exception at 0x75B7C42D in NetworkComponentsClient.exe: Microsoft C++ exception: std::bad_alloc at memory location 0x026DE87C. at line
if (!writeInProgress) //Exception Thrown here
{
asio::async_write(socket_, asio::buffer(writeQueue_.front().received_, writeQueue_.front().buffsize),
std::bind(&CSession::handle_write, this,
std::placeholders::_1, std::placeholders::_2));
}
Debug shows:
- writeQueue_ { size=16777215 } std::deque<channel::Buffer,std::allocator<channel::Buffer> >
+ [0] {received_=0x052a0ac8 "Client 2" } channel::Buffer
+ [1] {received_=0x052a0b28 "Client 2" } channel::Buffer
+ [2] {received_=0x052a0b88 "Client 2" } channel::Buffer
....
....
I can see size of writeQueue_ { size=16777215 } which is very large and hence std::bad_alloc.
Why such behaviour? I can see the code popping messages from deque as below:
if (!error)
{
writeQueue_.pop_front();
if (!writeQueue_.empty())
{
asio::async_write(socket_, asio::buffer(writeQueue_.front().received_, writeQueue_.front().buffsize),
std::bind(&CSession::handle_write, this,
std::placeholders::_1, std::placeholders::_2));
}
}
So write deque should not have grown so large.
My client is supposed to run for days and should be involved large continuous data write. How do I ensure smooth long write operations?
Your consumer (CSession) is far slower than your producer (Client).
Your producer is doing a denial of service attack by producing messages as fast as it can. This is a good test.
Your consumer should (at least one, ideally all):
detect that the work is accumulating and set up a policy when such things happen, like "ignore new", "drop oldest"
Limit the consumption lag from happening by setting an active filter on incoming messages
Improve the performance of incoming messages handling.
My client is supposed to run for days and should be involved large
continuous data write. How do I ensure smooth long write operations?
Then you need a much better code than an example found online.
I'm trying to make a TCP/IP client using boost library. This is how I designed my program
->read thread to read from the server
->write thread to send commands
->a function that parses the read data from the server
int main()
{
TCP_IP_Connection router;
router.Create_Socket();
boost::thread_group t;
t.create_thread(boost::bind(&TCP_IP_Connection::get_status,&router,'i'));
t.create_thread(boost::bind(&TCP_IP_Connection::readTCP,&router));
std::string reply="\nend of main()";
std::cout<<reply;
t.join_all();
return 0;
}
void TCP_IP_Connection::Create_Socket()
{
tcp::resolver resolver(_io);//resolve into TCP endpoint
tcp::resolver::query query(routerip,rport);
tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
//list of endpoints
tcp::resolver::iterator end;
boost::asio::streambuf b;
_socket = new tcp::socket(_io); //create socket
boost::system::error_code error= boost::asio::error::host_not_found;
try
{
while (error && endpoint_iterator != end) //if error go to next endpoint
{
_socket->close();
_socket->connect(*endpoint_iterator++, error);
}
if(error)
throw boost::system::system_error(error);
//else the router is connected
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
void TCP_IP_Connection::get_status(char p)
{
try
{
if(p=='i')
_socket->send(boost::asio::buffer("llist\n\n"));
//sending command for input command
else
_socket->send(boost::asio::buffer(" sspo l1\n\n"));
//sending signal presence for output command
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
void TCP_IP_Connection::readTCP()
{
this->len=0;
boost::system::error_code error= boost::asio::error::host_not_found;
try
{ //loop reading all values from router
while(1)
{
//wait for reply??
_socket->async_read_some(boost::asio::buffer(this-
>reply,sizeof(this>reply)),boost::bind(&TCP_IP_Connection::dataProcess,this,
boost::asio::placeholders::error,boost::asio::placeholders::bytes_transferred));
_io.run();
if(error==boost::asio::error::eof) //connection closed by router
std::cout<<"connection closed by router";
}
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
void TCP_IP_Connection::dataProcess(const boost::system::error_code &er,size_t l)
{
if(!er)
{
if(l>0)
{
for(int i=0;i<l;i++)
{
this->data[i]=this->reply[i];
//if(data[i]="\n")
std::cout<<this->data[i];
}
}
}
}
When I run the code all I get is the response from the server that says the client is connected and not the response of the command I send. But when I try debugging I get full output as I need. Am I doing anything wrong in the threading, or in the TCP read buffer.
Your code is creating 2 threads. The first thread created has a thread function called get_status. In get_status, there is no looping so it only executes the code once. It appears to be sending the string "llist\n\n" to the server and this is done synchronously. After that, it does not send anything else. So, are you expecting the server to send other data after the first command is sent? The code in the first thread may or may not execute completely before the code in the second thread executes.
The second thread is created and this thread appears to be responsible for processing information coming off of the socket. There is an infinite loop of while(1), but no logic to exit the loop so it will run forever unless an exception is thrown. I believe that the async_read_some method will not cause any data to be transferred until the buffer is full. The size of the buffer is specified by the size of reply. This may be your problem since the dataProcess method won't get called until all of the data specified by the length of reply has been received. In many protocols, the first 4 bytes specifies the length of the message. So, if you are dealing with variable length messages, then your code will have to take this into account.
One other item worth mentioning is that the looping code in readTCP to call _io.Run is not really necessary. You can add a work object to your io_service object in order for it to run continuously. For example:
void SSLSocket::InitAsynchIO()
{
// This method is responsible for initiating asynch i/o.
boost::system::error_code Err;
string s;
stringstream ss;
//
try
{
ss << "SSLSocket::InitAsynchIO: Worker thread - " << Logger::NumberToString(boost::this_thread::get_id()) << " started.\n";
Log.LogString(ss.str(), LogInfo);
// Enable the handlers for asynch i/o. The thread will hang here until the stop method has been called or an error occurs.
// Add a work object so the thread will be dedicated to handling asynch i/o.
boost::asio::io_service::work work(*IOService);
IOService->run();
Log.LogString("SSLSocket::InitAsynchIO: receive worker thread done.\n", LogInfo);
}
catch (std::exception& e)
{
stringstream ss;
ss << "SSLSocket::InitAsynchIO: threw an error - " << e.what() << ".\n";
Log.LogString(ss.str(), LogError);
Stop();
}
}
It is ok to have your first thread do your first async read. Your read handler can be set up to call itself in order to handle the next message. For example:
void SSLSocket::HandleRead(const boost::system::error_code& error, size_t bytesTransferred)
{
// This method is called to process an incomming message.
//
std::stringstream ss;
int ByteCount;
try
{
ss << "SSLSocket::HandleRead: From worker thread " << boost::this_thread::get_id() << ".\n";
Log.LogString(ss.str(), LogInfo);
// Set to exit this thread if the user is done.
if (!ReqAlive)
{
// IOService->stop();
return;
}
if (!error)
{
// Get the number of bytes in the message.
if (bytesTransferred == 4)
{
ByteCount = BytesToInt(pDataBuf);
}
else
{
// Call the C# callback method that will handle the message.
ss << "SSLSocket::HandleRead: From worker thread " << boost::this_thread::get_id() << "; # bytes transferred = " << bytesTransferred << ".\n";
Log.LogString(ss.str(), LogDebug2);
Log.LogBuf(pDataBuf, (int)bytesTransferred, true, LogDebug3);
Log.LogString("SSLSocket::HandleRead: sending msg to the C# client.\n\n", LogDebug2);
CallbackFunction(this, bytesTransferred, (void*)pDataBuf);
// Prepare to read in the next message length.
ByteCount = MsgLenBytes;
}
pDataBuf = BufMang.GetPtr(ByteCount);
boost::system::error_code Err;
// boost::asio::async_read(pSocket, boost::asio::buffer(pDataBuf, ByteCount), boost::bind(&SSLSocket::HandleRead,
// this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
Locking CodeLock(SocketLock); // Single thread the code.
boost::asio::async_read(*pSocket, boost::asio::buffer(pDataBuf, ByteCount), boost::bind(&SSLSocket::HandleRead,
this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
// boost::asio::read(pSocket, boost::asio::buffer(reply_), boost::asio::transfer_exactly(ByteCount), Err);
}
else
{
Log.LogString("SSLSocket::HandleRead failed: " + error.message() + "\n", LogError);
Stop();
}
}
catch (std::exception& e)
{
stringstream ss;
ss << "SSLSocket::HandleRead: threw an error - " << e.what() << ".\n";
Log.LogString(ss.str(), LogError);
Stop();
}
}
If none of the above is helpful, then put in some debug code that logs all of the calls to a log file so that you can see what is going on. You might also want to consider downloading Wire Shark in order to see what data is going out and coming in.
I'm trying to create a TCP server where the Start() method blocks until a connection is accepted, and then begins a series of asynchronous reads. I have the following code, and when I connect using telnet I get this output:
Waiting for a new connection
Connection accepted
terminate called throwing an exceptionAbort trap: 6
Here is the code:
void SocketReadThread::Start()
{
bzero(m_headerBuffer, HEADER_LEN);
m_running = true;
asio::io_service ios;
asio::ip::tcp::acceptor acp (ios,
boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), GUI_PORT));
asio::ip::tcp::socket sock(ios);
std::cout << "Waiting for a new connection" << std::endl;
acp.accept(sock);
std::cout << "Connection accepted" << std::endl;
asio::async_read(sock, asio::buffer(m_headerBuffer, HEADER_LEN),
boost::bind(&SocketReadThread::handleReadHeader, shared_from_this(),
asio::placeholders::error));
ios.run();
}
void SocketReadThread::handleReadHeader(const system::error_code& error)
{
std::cout << "Read two bytes!" << std::endl;
}
You should wrap your main() function in try {...} catch (std::exception& e) { cout << e.what(); } block.
You're probably doing something scary (and awesome) to the stack by declaring your ReadHandler incorrectly. Even if you ignore some parameters, the signature must be:
void handler (
const boost::system::error_code& error, // Result of operation.
std::size_t bytes_transferred // Number of bytes copied into the
// buffers. If an error occurred,
// this will be the number of
// bytes successfully transferred
// prior to the error.
);