[trac569] forgot to add udp_server.cc

src/lib/asiolink/udp_server.cc

@@ -0,0 +1,281 @@
+// 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/udp_endpoint.h>
+#include <asiolink/udp_socket.h>
+
+#include <asiolink/udp_server.h>
+
+using namespace asio;
+using asio::ip::udp;
+using asio::ip::tcp;
+using isc::log::dlog;
+
+using namespace std;
+using namespace isc::dns;
+
+namespace asiolink {
+
+/*
+ * Some of the member variables here are shared_ptrs and some are
+ * auto_ptrs. There will be one instance of Data for the lifetime
+ * of packet. The variables that are state only for a single packet
+ * use auto_ptr, as it is more lightweight. In the case of shared
+ * configuration (eg. the callbacks, socket), we use shared_ptrs.
+ */
+struct UDPServer::Data {
+    /*
+     * Constructor from parameters passed to UDPServer constructor.
+     * This instance will not be used to retrieve and answer the actual
+     * query, it will only hold parameters until we wait for the
+     * first packet. But we do initialize the socket in here.
+     */
+    Data(io_service& io_service, const ip::address& addr, const uint16_t port,
+        SimpleCallback* checkin, DNSLookup* lookup, DNSAnswer* answer) :
+        io_(io_service), done_(false), checkin_callback_(checkin),
+        lookup_callback_(lookup), answer_callback_(answer)
+    {
+        // We must use different instantiations for v4 and v6;
+        // otherwise ASIO will bind to both
+        udp proto = addr.is_v4() ? udp::v4() : udp::v6();
+        socket_.reset(new udp::socket(io_service, proto));
+        socket_->set_option(socket_base::reuse_address(true));
+        if (addr.is_v6()) {
+            socket_->set_option(asio::ip::v6_only(true));
+        }
+        socket_->bind(udp::endpoint(addr, port));
+    }
+
+    /*
+     * Copy constructor. Default one would probably do, but it is unnecessary
+     * to copy many of the member variables every time we fork to handle
+     * another packet.
+     *
+     * We also allocate data for receiving the packet here.
+     */
+    Data(const Data& other) :
+        io_(other.io_), socket_(other.socket_), done_(false),
+        checkin_callback_(other.checkin_callback_),
+        lookup_callback_(other.lookup_callback_),
+        answer_callback_(other.answer_callback_)
+    {
+        // Instantiate the data buffer and endpoint that will
+        // be used by the asynchronous receive call.
+        data_.reset(new char[MAX_LENGTH]);
+        sender_.reset(new udp::endpoint());
+    }
+
+    // The ASIO service object
+    asio::io_service& io_;
+
+    // Class member variables which are dynamic, and changes to which
+    // need to accessible from both sides of a coroutine fork or from
+    // outside of the coroutine (i.e., from an asynchronous I/O call),
+    // should be declared here as pointers and allocated in the
+    // constructor or in the coroutine.  This allows state information
+    // to persist when an individual copy of the coroutine falls out
+    // scope while waiting for an event, *so long as* there is another
+    // object that is referencing the same data.  As a side-benefit, using
+    // pointers also reduces copy overhead for coroutine objects.
+    //
+    // Note: Currently these objects are allocated by "new" in the
+    // constructor, or in the function operator while processing a query.
+    // Repeated allocations from the heap for every incoming query is
+    // clearly a performance issue; this must be optimized in the future.
+    // The plan is to have a structure pre-allocate several "Data"
+    // objects which can be pulled off a free list and placed on an in-use
+    // list whenever a query comes in.  This will serve the dual purpose
+    // of improving performance and guaranteeing that state information
+    // will *not* be destroyed when any one instance of the coroutine
+    // falls out of scope while waiting for an event.
+    //
+    // Socket used to for listen for queries.  Created in the
+    // constructor and stored in a shared_ptr because socket objects
+    // are not copyable.
+    boost::shared_ptr<asio::ip::udp::socket> socket_;
+
+    // The ASIO-internal endpoint object representing the client
+    std::auto_ptr<asio::ip::udp::endpoint> sender_;
+
+    // \c IOMessage and \c Message objects to be passed to the
+    // DNS lookup and answer providers
+    std::auto_ptr<asiolink::IOMessage> io_message_;
+
+    // The original query as sent by the client
+    isc::dns::MessagePtr query_message_;
+
+    // The response message we are building
+    isc::dns::MessagePtr answer_message_;
+
+    // The buffer into which the response is written
+    isc::dns::OutputBufferPtr respbuf_;
+
+    // The buffer into which the query packet is written
+    boost::shared_array<char> data_;
+
+    // State information that is entirely internal to a given instance
+    // of the coroutine can be declared here.
+    size_t bytes_;
+    bool done_;
+
+    // Callback functions provided by the caller
+    const SimpleCallback* checkin_callback_;
+    const DNSLookup* lookup_callback_;
+    const DNSAnswer* answer_callback_;
+
+    std::auto_ptr<IOEndpoint> peer_;
+    std::auto_ptr<IOSocket> iosock_;
+};
+
+/// The following functions implement the \c UDPServer class.
+///
+/// The constructor. It just creates new internal state object
+/// and lets it handle the initialization.
+UDPServer::UDPServer(io_service& io_service, const ip::address& addr,
+    const uint16_t port, SimpleCallback* checkin, DNSLookup* lookup,
+    DNSAnswer* answer) :
+    data_(new Data(io_service, addr, port, checkin, lookup, answer))
+{ }
+
+/// The function operator is implemented with the "stackless coroutine"
+/// pattern; see internal/coroutine.h for details.
+void
+UDPServer::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.
+
+    CORO_REENTER (this) {
+        do {
+            /*
+             * This is preparation for receiving a packet. We get a new
+             * state object for the lifetime of the next packet to come.
+             * It allocates the buffers to receive data into.
+             */
+            data_.reset(new Data(*data_));
+
+            do {
+                // Begin an asynchronous receive, then yield.
+                // When the receive event is posted, the coroutine
+                // will resume immediately after this point.
+                CORO_YIELD data_->socket_->async_receive_from(
+                    buffer(data_->data_.get(), MAX_LENGTH), *data_->sender_,
+                    *this);
+            } while (ec || length == 0);
+
+            data_->bytes_ = length;
+
+            /*
+             * We fork the coroutine now. One (the child) will keep
+             * the current state and handle the packet, then die and
+             * drop ownership of the state. The other (parent) will just
+             * go into the loop again and replace the current state with
+             * a new one for a new object.
+             *
+             * Actually, both of the coroutines will be a copy of this
+             * one, but that's just internal implementation detail.
+             */
+            CORO_FORK data_->io_.post(UDPServer(*this));
+        } while (is_parent());
+
+        // 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".)
+        data_->peer_.reset(new UDPEndpoint(*data_->sender_));
+        data_->iosock_.reset(new UDPSocket(*data_->socket_));
+        data_->io_message_.reset(new IOMessage(data_->data_.get(),
+            data_->bytes_, *data_->iosock_, *data_->peer_));
+
+        // Perform any necessary operations prior to processing an incoming
+        // query (e.g., checking for queued configuration messages).
+        //
+        // (XXX: it may be a performance issue to check in for every single
+        // incoming query; we may wish to throttle this in the future.)
+        if (data_->checkin_callback_ != NULL) {
+            (*data_->checkin_callback_)(*data_->io_message_);
+        }
+
+        // If we don't have a DNS Lookup provider, there's no point in
+        // continuing; we exit the coroutine permanently.
+        if (data_->lookup_callback_ == NULL) {
+            CORO_YIELD return;
+        }
+
+        // Instantiate objects that will be needed by the
+        // asynchronous DNS lookup and/or by the send call.
+        data_->respbuf_.reset(new OutputBuffer(0));
+        data_->query_message_.reset(new Message(Message::PARSE));
+        data_->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 data_->io_.post(AsyncLookup<UDPServer>(*this));
+
+        dlog("[XX] got an answer");
+
+        // The 'done_' flag indicates whether we have an answer
+        // to send back.  If not, exit the coroutine permanently.
+        if (!data_->done_) {
+            CORO_YIELD return;
+        }
+
+        // Call the DNS answer provider to render the answer into
+        // wire format
+        (*data_->answer_callback_)(*data_->io_message_, data_->query_message_,
+            data_->answer_message_, data_->respbuf_);
+
+        // 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 data_->socket_->async_send_to(
+            buffer(data_->respbuf_->getData(), data_->respbuf_->getLength()),
+            *data_->sender_, *this);
+    }
+}
+
+/// Call the DNS lookup provider.  (Expected to be called by the
+/// AsyncLookup<UDPServer> handler.)
+void
+UDPServer::asyncLookup() {
+    (*data_->lookup_callback_)(*data_->io_message_,
+        data_->query_message_, data_->answer_message_, data_->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
+UDPServer::resume(const bool done) {
+    data_->done_ = done;
+    data_->io_.post(*this);
+}
+
+bool
+UDPServer::hasAnswer() {
+    return (data_->done_);
+}
+
+} // namespace asiolink