Boost asio http deadline error? - c++

Question

The code bellow is mainly the HTTP client example with very few changes to support a download deadline.
It works as expected, but in rare cases e.g. if the internet is unstable, it doesn't work and the deadline can be more than what I set (20 or more seconds when I set 10). This happens very rarely and I am unable to reproduce this, it happens when I don't expect it.
To avoid posting a ton of lines (because few will read them) here is the place where I believe the error lies:
deadline_.expires_from_now(boost::posix_time::milliseconds(deadline));
tcp::resolver::query query(server, "http");
resolver_.async_resolve(query,
boost::bind(&client::handle_resolve, this,
boost::asio::placeholders::error,
boost::asio::placeholders::iterator));
deadline_.async_wait(boost::bind(&client::check_deadline, this));
Is the order of those lines correct?
And here is the check deadline function:
void check_deadline()
{
if(deadline_cancelled)
return;
else if (deadline_.expires_at() <= deadline_timer::traits_type::now())
socket_.close();
else
deadline_.async_wait(boost::bind(&client::check_deadline, this));
}

Answer 1

You should async_wait() on the deadline timer too. If you don't, you won't get notified, you just check (after the fact) whether the time had expired.
Then if it completes (with an ec other than operation_aborted) then you should
cancel() the async operations on the socket
optionally close the socket
PS. Mmm. It /seems/ that you are doing something similar, although it's unclear where
deadline_cancelled comes from
why you don't accept the error_code in the completion handler for deadline_.async_await and
why you are juggling with time comparisons manually, instead of trusting that the completion handler means what it says
Update Here's a full example doing a HTTP request. In fact, it downloads a million digits of PI from http://www.angio.net/pi/digits.html. This takes a while.
At the start of receiving the response I set a deadline timer for 800ms (and so the transfer should be - correctly - aborted).
This works as advertised. Pay special attention to the canceling of the socket and timer. Note that you could call expires_from_now() again after receiving each chunk of data. This is likely what you want. It will implicitly cancel() the timer each time it hadn't yet expired, so be prepared to handle the operatorion_aborted messages.
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/asio/deadline_timer.hpp>
class client
{
public:
client(boost::asio::io_service& io_service,
boost::asio::ip::tcp::resolver::iterator endpoint_iterator)
: deadline_(io_service),
socket_(io_service)
{
boost::asio::async_connect(socket_.lowest_layer(), endpoint_iterator,
boost::bind(&client::handle_connect, this,
boost::asio::placeholders::error));
}
void handle_connect(const boost::system::error_code& error)
{
if (!error)
{
std::cout << "Enter message: ";
static char const raw[] = "GET /pi/digits/pi1000000.txt HTTP/1.1\r\nHost: www.angio.net\r\nConnection: close\r\n\r\n";
static_assert(sizeof(raw)<=sizeof(request_), "too large");
size_t request_length = strlen(raw);
std::copy(raw, raw+request_length, request_);
boost::asio::async_write(socket_,
boost::asio::buffer(request_, request_length),
boost::bind(&client::handle_write, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
std::cout << "Handshake failed: " << error.message() << "\n";
}
}
void deadline_expiration(const boost::system::error_code& error)
{
if (error == boost::asio::error::operation_aborted)
return;
std::cout << "\nDEADLINE REACHED\n";
socket_.cancel();
}
void handle_write(const boost::system::error_code& error,
size_t /*bytes_transferred*/)
{
if (!error)
{
std::cout << "starting read loop\n";
deadline_.expires_from_now(boost::posix_time::millisec(800));
//deadline_.expires_from_now(boost::posix_time::seconds(800));
deadline_.async_wait(boost::bind(&client::deadline_expiration, this, boost::asio::placeholders::error));
boost::asio::async_read_until(socket_,
//boost::asio::buffer(reply_, sizeof(reply_)),
reply_, '\n',
boost::bind(&client::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
std::cout << "Write failed: " << error.message() << "\n";
}
}
void handle_read(const boost::system::error_code& error, size_t /*bytes_transferred*/)
{
if (!error)
{
std::cout << "Reply: " << &reply_ << "\n";
boost::asio::async_read_until(socket_,
//boost::asio::buffer(reply_, sizeof(reply_)),
reply_, '\n',
boost::bind(&client::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
std::cout << "Read failed: " << error.message() << "\n";
deadline_.cancel(); // no need for after transfer completed
}
}
private:
boost::asio::deadline_timer deadline_;
boost::asio::ip::tcp::socket socket_;
char request_[1024];
boost::asio::streambuf reply_;
};
int main()
{
try
{
boost::asio::io_service io_service;
boost::asio::ip::tcp::resolver resolver(io_service);
boost::asio::ip::tcp::resolver::query query("www.angio.net", "80");
boost::asio::ip::tcp::resolver::iterator iterator = resolver.resolve(query);
client c(io_service, iterator);
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
}
Coliru link (Coliru doesn't support internet connectivity)