tcp_server.cc 8.67 KB
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// Copyright (C) 2011  Internet Systems Consortium, Inc. ("ISC")
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//
// 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>

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#include <netinet/in.h>
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#include <sys/socket.h>
#include <unistd.h>             // for some IPC/network system calls
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#include <errno.h>
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#include <boost/shared_array.hpp>
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#include <log/dummylog.h>
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#include <asio.hpp>
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#include <asiolink/dummy_io_cb.h>
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#include <asiolink/tcp_endpoint.h>
#include <asiolink/tcp_socket.h>
#include <asiolink/tcp_server.h>
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using namespace asio;
using asio::ip::udp;
using asio::ip::tcp;

using namespace std;
using namespace isc::dns;

namespace asiolink {
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/// The following functions implement the \c TCPServer class.
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///
/// The constructor
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TCPServer::TCPServer(io_service& io_service,
                     const ip::address& addr, const uint16_t port, 
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                     const SimpleCallback* checkin,
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                     const DNSLookup* lookup,
                     const DNSAnswer* answer) :
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    io_(io_service), done_(false),
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    checkin_callback_(checkin), lookup_callback_(lookup),
    answer_callback_(answer)
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{
    tcp::endpoint endpoint(addr, port);
    acceptor_.reset(new tcp::acceptor(io_service));
    acceptor_->open(endpoint.protocol());
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    // Set v6-only (we use a separate instantiation for v4,
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    // 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) {
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    /// Because the coroutine reentry block is implemented as
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    /// a switch statement, inline variable declarations are not
    /// permitted.  Certain variables used below can be declared here.
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    boost::array<const_buffer,2> bufs;
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    OutputBuffer lenbuf(TCP_MESSAGE_LENGTHSIZE);
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    CORO_REENTER (this) {
        do {
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            /// Create a socket to listen for connections
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            socket_.reset(new tcp::socket(acceptor_->get_io_service()));
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            /// Wait for new connections. In the event of non-fatal error,
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            /// try again
            do {
                CORO_YIELD acceptor_->async_accept(*socket_, *this);
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                // Abort on fatal errors
                // TODO: Log error?
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                if (ec) {
                    using namespace asio::error;
                    if (ec.value() != would_block && ec.value() != try_again &&
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                        ec.value() != connection_aborted &&
                        ec.value() != interrupted) {
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                        return;
                    }
                }
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            } while (ec);
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            /// 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.
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            CORO_FORK io_.post(TCPServer(*this));
        } while (is_parent());
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        /// Instantiate the data buffer that will be used by the
        /// asynchronous read call.
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        data_.reset(new char[MAX_LENGTH]);
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        /// Read the message, in two parts.  First, the message length:
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        CORO_YIELD async_read(*socket_, asio::buffer(data_.get(),
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                              TCP_MESSAGE_LENGTHSIZE), *this);
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        if (ec) {
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            socket_->close();
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            CORO_YIELD return;
        }
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        /// Now read the message itself. (This is done in a different scope
        /// to allow inline variable declarations.)
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        CORO_YIELD {
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            InputBuffer dnsbuffer(data_.get(), length);
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            uint16_t msglen = dnsbuffer.readUint16();
            async_read(*socket_, asio::buffer(data_.get(), msglen), *this);
        }

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

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        // Create an \c IOMessage object to store the query.
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        //
        // (XXX: It would be good to write a factory function
        // that would quickly generate an IOMessage object without
        // all these calls to "new".)
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        peer_.reset(new TCPEndpoint(socket_->remote_endpoint()));
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        // 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
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        // the underlying Boost TCP socket - DummyIOCallback is used.  This
        // provides the appropriate operator() but is otherwise functionless.
        iosock_.reset(new TCPSocket<DummyIOCallback>(*socket_));
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        io_message_.reset(new IOMessage(data_.get(), length, *iosock_, *peer_));
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        bytes_ = length;
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        // 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_);
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        }

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

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        // Reset or instantiate objects that will be needed by the
        // DNS lookup and the write call.
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        respbuf_.reset(new OutputBuffer(0));
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        query_message_.reset(new Message(Message::PARSE));
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        answer_message_.reset(new Message(Message::RENDER));
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        // 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));
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        // The 'done_' flag indicates whether we have an answer
        // to send back.  If not, exit the coroutine permanently.
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        if (!done_) {
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            // TODO: should we keep the connection open for a short time
            // to see if new requests come in?
            socket_->close();
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            CORO_YIELD return;
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        }
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        if (ec) {
            CORO_YIELD return;
        }
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        // Call the DNS answer provider to render the answer into
        // wire format
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        (*answer_callback_)(*io_message_, query_message_,
                            answer_message_, respbuf_);
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        // Set up the response, beginning with two length bytes.
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        lenbuf.writeUint16(respbuf_->getLength());
        bufs[0] = buffer(lenbuf.getData(), lenbuf.getLength());
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        bufs[1] = buffer(respbuf_->getData(), respbuf_->getLength());
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        // 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).
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        CORO_YIELD async_write(*socket_, bufs, *this);
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        // TODO: should we keep the connection open for a short time
        // to see if new requests come in?
        socket_->close();
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    }
}

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

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void TCPServer::stop() {
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    /// we use close instead of cancel, with the same reason
    /// with udp server stop, refer to the udp server code
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    acceptor_->close();
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    // User may stop the server even when it hasn't started to
    // run, in that that socket_ is empty
    if (socket_) {
        socket_->close();
    }
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}
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/// 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.
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void
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TCPServer::resume(const bool done) {
    done_ = done;
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    io_.post(*this);
}

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} // namespace asiolink