kea/src/lib/asiodns/tcp_server.cc

// Copyright (C) 2011  Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.

#include <config.h>

#include <unistd.h>             // for some IPC/network system calls
#include <netinet/in.h>
#include <sys/socket.h>
#include <errno.h>

#include <boost/shared_array.hpp>

#include <log/dummylog.h>

#include <util/buffer.h>

#include <asio.hpp>
#include <asiolink/dummy_io_cb.h>
#include <asiolink/tcp_endpoint.h>
#include <asiolink/tcp_socket.h>
#include <asiodns/tcp_server.h>
#include <asiodns/logger.h>

using namespace asio;
using asio::ip::udp;
using asio::ip::tcp;

using namespace std;
using namespace isc::dns;
using namespace isc::util;
using namespace isc::asiolink;

namespace isc {
namespace asiodns {

/// The following functions implement the \c TCPServer class.
///
/// The constructor
TCPServer::TCPServer(io_service& io_service, int fd, int af,
                     const SimpleCallback* checkin,
                     const DNSLookup* lookup,
                     const DNSAnswer* answer) :
    io_(io_service), done_(false),
    checkin_callback_(checkin), lookup_callback_(lookup),
    answer_callback_(answer)
{
    if (af != AF_INET && af != AF_INET6) {
        isc_throw(InvalidParameter, "Address family must be either AF_INET "
                  "or AF_INET6, not " << af);
    }
    LOG_DEBUG(logger, DBGLVL_TRACE_BASIC, ASIODNS_FD_ADD_TCP).arg(fd);

    try {
        acceptor_.reset(new tcp::acceptor(io_service));
        acceptor_->assign(af == AF_INET6 ? tcp::v6() : tcp::v4(), fd);
        acceptor_->listen();
    } catch (const std::exception& exception) {
        // Whatever the thing throws, it is something from ASIO and we convert
        // it
        isc_throw(IOError, exception.what());
    }
    // Set it to some value. It should be set to the right one
    // immediately, but set it to something non-zero just in case.
    tcp_recv_timeout_.reset(new size_t(5000));
}

namespace {
    // Called by the timeout_ deadline timer if the client takes too long.
    // If not aborted, cancels the given socket
    // (in which case TCPServer::operator() will be called to continue,
    // with an 'aborted' error code
    void do_timeout(asio::ip::tcp::socket& socket,
                    const asio::error_code& error)
    {
        if (error != asio::error::operation_aborted) {
            socket.cancel();
        }
    }
}

void
TCPServer::operator()(asio::error_code ec, size_t length) {
    /// Because the coroutine reentry block is implemented as
    /// a switch statement, inline variable declarations are not
    /// permitted.  Certain variables used below can be declared here.

    boost::array<const_buffer,2> bufs;
    OutputBuffer lenbuf(TCP_MESSAGE_LENGTHSIZE);

    CORO_REENTER (this) {
        do {
            /// Create a socket to listen for connections
            socket_.reset(new tcp::socket(acceptor_->get_io_service()));

            /// Wait for new connections. In the event of non-fatal error,
            /// try again
            do {
                CORO_YIELD acceptor_->async_accept(*socket_, *this);

                // Abort on fatal errors
                // TODO: Log error?
                if (ec) {
                    using namespace asio::error;
                    if (ec.value() != would_block && ec.value() != try_again &&
                        ec.value() != connection_aborted &&
                        ec.value() != interrupted) {
                        return;
                    }
                }
            } while (ec);

            /// Fork the coroutine by creating a copy of this one and
            /// scheduling it on the ASIO service queue.  The parent
            /// will continue listening for DNS connections while the
            /// handles the one that has just arrived.
            CORO_FORK io_.post(TCPServer(*this));
        } while (is_parent());

        /// Instantiate the data buffer that will be used by the
        /// asynchronous read call.
        data_.reset(new char[MAX_LENGTH]);

        /// Start a timer to drop the connection if it is idle
        if (*tcp_recv_timeout_ > 0) {
            timeout_.reset(new asio::deadline_timer(io_));
            timeout_->expires_from_now(
                boost::posix_time::milliseconds(*tcp_recv_timeout_));
            timeout_->async_wait(boost::bind(&do_timeout, boost::ref(*socket_),
                                 asio::placeholders::error));
        }

        /// Read the message, in two parts.  First, the message length:
        CORO_YIELD async_read(*socket_, asio::buffer(data_.get(),
                              TCP_MESSAGE_LENGTHSIZE), *this);
        if (ec) {
            socket_->close();
            CORO_YIELD return;
        }

        /// Now read the message itself. (This is done in a different scope
        /// to allow inline variable declarations.)
        CORO_YIELD {
            InputBuffer dnsbuffer(data_.get(), length);
            uint16_t msglen = dnsbuffer.readUint16();
            async_read(*socket_, asio::buffer(data_.get(), msglen), *this);
        }

        if (ec) {
            socket_->close();
            CORO_YIELD return;
        }

        // Due to possible timeouts and other bad behaviour, after the
        // timely reads are done, there is a chance the socket has
        // been closed already. So before we move on to the actual
        // processing, check that, and stop if so.
        if (!socket_->is_open()) {
            CORO_YIELD return;
        }

        // Create an \c IOMessage object to store the query.
        //
        // (XXX: It would be good to write a factory function
        // that would quickly generate an IOMessage object without
        // all these calls to "new".)
        peer_.reset(new TCPEndpoint(socket_->remote_endpoint()));

        // The TCP socket class has been extended with asynchronous functions
        // and takes as a template parameter a completion callback class.  As
        // TCPServer does not use these extended functions (only those defined
        // in the IOSocket base class) - but needs a TCPSocket to get hold of
        // the underlying Boost TCP socket - DummyIOCallback is used.  This
        // provides the appropriate operator() but is otherwise functionless.
        iosock_.reset(new TCPSocket<DummyIOCallback>(*socket_));
        io_message_.reset(new IOMessage(data_.get(), length, *iosock_, *peer_));
        bytes_ = length;

        // Perform any necessary operations prior to processing the incoming
        // packet (e.g., checking for queued configuration messages).
        //
        // (XXX: it may be a performance issue to have this called for
        // every single incoming packet; we may wish to throttle it somehow
        // in the future.)
        if (checkin_callback_ != NULL) {
            (*checkin_callback_)(*io_message_);
        }

        // If we don't have a DNS Lookup provider, there's no point in
        // continuing; we exit the coroutine permanently.
        if (lookup_callback_ == NULL) {
            socket_->close();
            CORO_YIELD return;
        }

        // Reset or instantiate objects that will be needed by the
        // DNS lookup and the write call.
        respbuf_.reset(new OutputBuffer(0));
        query_message_.reset(new Message(Message::PARSE));
        answer_message_.reset(new Message(Message::RENDER));

        // Schedule a DNS lookup, and yield.  When the lookup is
        // finished, the coroutine will resume immediately after
        // this point.
        CORO_YIELD io_.post(AsyncLookup<TCPServer>(*this));

        // The 'done_' flag indicates whether we have an answer
        // to send back.  If not, exit the coroutine permanently.
        if (!done_) {
            // TODO: should we keep the connection open for a short time
            // to see if new requests come in?
            socket_->close();
            CORO_YIELD return;
        }

        if (ec) {
            CORO_YIELD return;
        }
        // Call the DNS answer provider to render the answer into
        // wire format
        (*answer_callback_)(*io_message_, query_message_,
                            answer_message_, respbuf_);

        // Set up the response, beginning with two length bytes.
        lenbuf.writeUint16(respbuf_->getLength());
        bufs[0] = buffer(lenbuf.getData(), lenbuf.getLength());
        bufs[1] = buffer(respbuf_->getData(), respbuf_->getLength());

        // Begin an asynchronous send, and then yield.  When the
        // send completes, we will resume immediately after this point
        // (though we have nothing further to do, so the coroutine
        // will simply exit at that time).
        CORO_YIELD async_write(*socket_, bufs, *this);

        // All done, cancel the timeout timer
        timeout_->cancel();

        // TODO: should we keep the connection open for a short time
        // to see if new requests come in?
        socket_->close();
    }
}

/// Call the DNS lookup provider.  (Expected to be called by the
/// AsyncLookup<TCPServer> handler.)
void
TCPServer::asyncLookup() {
    (*lookup_callback_)(*io_message_, query_message_,
                        answer_message_, respbuf_, this);
}

void TCPServer::stop() {
    /// we use close instead of cancel, with the same reason
    /// with udp server stop, refer to the udp server code

    acceptor_->close();
    // User may stop the server even when it hasn't started to
    // run, in that that socket_ is empty
    if (socket_) {
        socket_->close();
    }
}
/// Post this coroutine on the ASIO service queue so that it will
/// resume processing where it left off.  The 'done' parameter indicates
/// whether there is an answer to return to the client.
void
TCPServer::resume(const bool done) {
    done_ = done;
    io_.post(*this);
}

} // namespace asiodns
} // namespace isc