Re: boost::asio::read() gets stuck when there's no internet

From: Richard Hodges (hodges.r_at_[hidden])
Date: 2021-02-19 17:19:43

The TCP/IP protocol was designed to work over unreliable networks,
including sections that hop over radio links and dial-up telephone lines.

In a nutshell, the way the internet works is that packets are transmitted
and it is assumed that they may or may not arrive at some time in the
future. There are timeouts built in, but they are longer than you would
probably want, on account of all the unreliable dial-ups between you and
the other peer.

Therefore, to involve a timeout you need to run a timer in parallel with
the send/receive operation and cancel the operation if the timeout occurs
before the operation has completed.

This is easier with asio's async interface, but you can still do it with
the synchronous interface by using SIGALM (or equivalent).

The relevant voodoo is documented here for linux:
https://man7.org/linux/man-pages/man7/signal.7.html

On Fri, 19 Feb 2021 at 17:52, Child OfGod via Boost-users <
boost-users_at_[hidden]> wrote:

> In TgBot library i use under MSVC++,
> in tgbot/net/BoostHttpOnlySslClient.cpp,
> a call to boost::asio::read() does not return when internet is
> disconnected for a few minutes.
>
> I would appreciate any help to get this resolved, i.e. for the read
> function to return if it fails after some timeout has passed
>
> the code block in the tgbot/net/BoostHttpOnlySslClient.cpp file:
>
> [code]
> string BoostHttpOnlySslClient::makeRequest(const Url& url, const
> vector<HttpReqArg>& args) const {
>     tcp::resolver resolver(_ioService);
>     tcp::resolver::query query(url.host, "443");
>
>     ssl::context context(ssl::context::tlsv12_client);
>     context.set_default_verify_paths();
>     ssl::stream<tcp::socket> socket(_ioService, context);
>     connect(socket.lowest_layer(), resolver.resolve(query));
>
>     #ifdef TGBOT_DISABLE_NAGLES_ALGORITHM
>     socket.lowest_layer().set_option(tcp::no_delay(true));
>     #endif //TGBOT_DISABLE_NAGLES_ALGORITHM
>     #ifdef TGBOT_CHANGE_SOCKET_BUFFER_SIZE
>     #if _arm64 || _WIN64 || __amd64__ || __x86_64__ || __MINGW64__ ||
> __aarch64__ || __powerpc64__
>     socket.lowest_layer().set_option(socket_base::send_buffer_size(65536));
>
> socket.lowest_layer().set_option(socket_base::receive_buffer_size(65536));
>     #else //for 32-bit
>     socket.lowest_layer().set_option(socket_base::send_buffer_size(32768));
>
> socket.lowest_layer().set_option(socket_base::receive_buffer_size(32768));
>     #endif //Processor architecture
>     #endif //TGBOT_CHANGE_SOCKET_BUFFER_SIZE
>     socket.set_verify_mode(ssl::verify_none);
>     socket.set_verify_callback(ssl::rfc2818_verification(url.host));
>
>     socket.handshake(ssl::stream<tcp::socket>::client);
>
>     string requestText = _httpParser.generateRequest(url, args, false);
>     write(socket, buffer(requestText.c_str(), requestText.length()));
>
>     string response;
>
>     #ifdef TGBOT_CHANGE_READ_BUFFER_SIZE
>     #if _M_ARM64 || _WIN64 || __amd64__ || __x86_64__ || __MINGW64__ ||
> __aarch64__ || __powerpc64__
>     char buff[65536];
>     #else //for 32-bit
>     char buff[32768];
>     #endif //Processor architecture
>     #else
>     char buff[1024];
>     #endif //TGBOT_CHANGE_READ_BUFFER_SIZE
>
>     boost::system::error_code error;
>     while (!error) {
>         std::size_t bytes = read(socket, buffer(buff), error);
>         response += string(buff, bytes);
>     }
>
>     return _httpParser.extractBody(response);
> }
> [/code]
>
> Thankyou in advance😀🙏
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> https://lists.boost.org/mailman/listinfo.cgi/boost-users
>

-- 
Richard Hodges
hodges.r_at_[hidden]
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