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 <boost/shared_array.hpp>

#include <asio.hpp>

#include <log/dummylog.h>

#include <asiolink/io_completion_cb.h>
#include <asiolink/tcp_endpoint.h>
#include <asiolink/tcp_socket.h>
#include <asiolink/tcp_server.h>


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

using namespace std;
using namespace isc::dns;

namespace asiolink {

/// The following functions implement the \c TCPServer class.
///
/// The constructor
TCPServer::TCPServer(io_service& io_service,
                     const ip::address& addr, const uint16_t port, 
                     const SimpleCallback* checkin,
                     const DNSLookup* lookup,
                     const DNSAnswer* answer) :
    io_(io_service), done_(false),
    checkin_callback_(checkin), lookup_callback_(lookup),
    answer_callback_(answer)
{
    tcp::endpoint endpoint(addr, port);
    acceptor_.reset(new tcp::acceptor(io_service));
    acceptor_->open(endpoint.protocol());
    // Set v6-only (we use a separate instantiation for v4,
    // otherwise asio will bind to both v4 and v6
    if (addr.is_v6()) {
        acceptor_->set_option(ip::v6_only(true));
    }
    acceptor_->set_option(tcp::acceptor::reuse_address(true));
    acceptor_->bind(endpoint);
    acceptor_->listen();
}

void
TCPServer::operator()(error_code ec, size_t length) {
    /// Because the coroutine reeentry 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 error,
            /// try again
            do {
                CORO_YIELD acceptor_->async_accept(*socket_, *this);
            } 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]);

        /// 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) {
            CORO_YIELD return;
        }

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

        if (ec) {
            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 - use "IOCompletionCallback" -
        // a basic callback class: it is not used but provides the appropriate
        // signature.
        iosock_.reset(new TCPSocket<IOCompletionCallback>(*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) {
            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_) {
            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);
    }
}

/// 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);
}

/// 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 asiolink