// Copyright (C) 2009  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 <netinet/in.h>

#include <algorithm>
#include <vector>
#include <cassert>

#include <asiolink/asiolink.h>

#include <boost/foreach.hpp>
#include <boost/lexical_cast.hpp>

#include <config/ccsession.h>

#include <exceptions/exceptions.h>

#include <dns/opcode.h>
#include <dns/rcode.h>
#include <dns/buffer.h>
#include <dns/exceptions.h>
#include <dns/name.h>
#include <dns/question.h>
#include <dns/rrset.h>
#include <dns/rrttl.h>
#include <dns/message.h>
#include <dns/messagerenderer.h>

#include <log/dummylog.h>

#include <resolver/resolver.h>

using namespace std;

using namespace isc;
using namespace isc::dns;
using namespace isc::data;
using namespace isc::config;
using isc::log::dlog;
using namespace asiolink;

typedef pair<string, uint16_t> addr_t;

class ResolverImpl {
private:
    // prohibit copy
    ResolverImpl(const ResolverImpl& source);
    ResolverImpl& operator=(const ResolverImpl& source);
public:
    ResolverImpl() :
        config_session_(NULL),
        query_timeout_(2000),
        client_timeout_(4000),
        lookup_timeout_(30000),
        retries_(3),
        rec_query_(NULL)
    {}

    ~ResolverImpl() {
        queryShutdown();
    }

    void querySetup(DNSService& dnss) {
        assert(!rec_query_); // queryShutdown must be called first
        dlog("Query setup");
        rec_query_ = new RecursiveQuery(dnss, upstream_,
                                        upstream_root_,
                                        query_timeout_,
                                        client_timeout_,
                                        lookup_timeout_,
                                        retries_);
    }

    void queryShutdown() {
        // only shut down if we have actually called querySetup before
        // (this is not a safety check, just to prevent logging of
        // actions that are not performed
        if (rec_query_) {
            dlog("Query shutdown");
            delete rec_query_;
            rec_query_ = NULL;
        }
    }

    void setForwardAddresses(const vector<addr_t>& upstream,
        DNSService *dnss)
    {
        upstream_ = upstream;
        if (dnss) {
            if (!upstream_.empty()) {
                dlog("Setting forward addresses:");
                BOOST_FOREACH(const addr_t& address, upstream) {
                    dlog(" " + address.first + ":" +
                        boost::lexical_cast<string>(address.second));
                }
            } else {
                dlog("No forward addresses, running in recursive mode");
            }
        }
    }

    void setRootAddresses(const vector<addr_t>& upstream_root,
                          DNSService *dnss)
    {
        upstream_root_ = upstream_root;
        if (dnss) {
            if (!upstream_root_.empty()) {
                dlog("Setting root addresses:");
                BOOST_FOREACH(const addr_t& address, upstream_root) {
                    dlog(" " + address.first + ":" +
                        boost::lexical_cast<string>(address.second));
                }
            } else {
                dlog("No root addresses");
            }
        }
    }

    void resolve(const isc::dns::QuestionPtr& question,
        const isc::resolve::ResolverInterface::CallbackPtr& callback);

    void processNormalQuery(const Question& question,
                            MessagePtr answer_message,
                            OutputBufferPtr buffer,
                            DNSServer* server);

    /// Currently non-configurable, but will be.
    static const uint16_t DEFAULT_LOCAL_UDPSIZE = 4096;

    /// These members are public because Resolver accesses them directly.
    ModuleCCSession* config_session_;
    /// Addresses of the root nameserver(s)
    vector<addr_t> upstream_root_;
    /// Addresses of the forward nameserver
    vector<addr_t> upstream_;
    /// Addresses we listen on
    vector<addr_t> listen_;

    /// Timeout for outgoing queries in milliseconds
    int query_timeout_;
    /// Timeout for incoming client queries in milliseconds
    int client_timeout_;
    /// Timeout for lookup processing in milliseconds
    int lookup_timeout_;
    
    /// Number of retries after timeout
    unsigned retries_;

private:

    /// Object to handle upstream queries
    RecursiveQuery* rec_query_;
};

/*
 * std::for_each has a broken interface. It makes no sense in a language
 * without lambda functions/closures. These two classes emulate the lambda
 * functions so for_each can be used.
 */
class QuestionInserter {
public:
    QuestionInserter(MessagePtr message) : message_(message) {}
    void operator()(const QuestionPtr question) {
        dlog(string("Adding question ") + question->getName().toText() +
            " to message");
        message_->addQuestion(question);
    }
    MessagePtr message_;
};

void
makeErrorMessage(MessagePtr message, OutputBufferPtr buffer,
                 const Rcode& rcode)
{
    // extract the parameters that should be kept.
    // XXX: with the current implementation, it's not easy to set EDNS0
    // depending on whether the query had it.  So we'll simply omit it.
    const qid_t qid = message->getQid();
    const bool rd = message->getHeaderFlag(Message::HEADERFLAG_RD);
    const bool cd = message->getHeaderFlag(Message::HEADERFLAG_CD);
    const Opcode& opcode = message->getOpcode();
    vector<QuestionPtr> questions;

    // If this is an error to a query or notify, we should also copy the
    // question section.
    if (opcode == Opcode::QUERY() || opcode == Opcode::NOTIFY()) {
        questions.assign(message->beginQuestion(), message->endQuestion());
    }

    message->clear(Message::RENDER);
    message->setQid(qid);
    message->setOpcode(opcode);
    message->setHeaderFlag(Message::HEADERFLAG_QR);
    if (rd) {
        message->setHeaderFlag(Message::HEADERFLAG_RD);
    }
    if (cd) {
        message->setHeaderFlag(Message::HEADERFLAG_CD);
    }
    for_each(questions.begin(), questions.end(), QuestionInserter(message));
    message->setRcode(rcode);
    MessageRenderer renderer(*buffer);
    message->toWire(renderer);

    dlog(string("Sending an error response (") +
        boost::lexical_cast<string>(renderer.getLength()) + " bytes):\n" +
        message->toText());
}

// This is a derived class of \c DNSLookup, to serve as a
// callback in the asiolink module.  It calls
// Resolver::processMessage() on a single DNS message.
class MessageLookup : public DNSLookup {
public:
    MessageLookup(Resolver* srv) : server_(srv) {}

    // \brief Handle the DNS Lookup
    virtual void operator()(const IOMessage& io_message,
                            MessagePtr query_message,
                            MessagePtr answer_message,
                            OutputBufferPtr buffer,
                            DNSServer* server) const
    {
        server_->processMessage(io_message, query_message,
                                answer_message, buffer, server);
    }
private:
    Resolver* server_;
};

// This is a derived class of \c DNSAnswer, to serve as a
// callback in the asiolink module.  It takes a completed
// set of answer data from the DNS lookup and assembles it
// into a wire-format response.
class MessageAnswer : public DNSAnswer {
public:
    virtual void operator()(const IOMessage& io_message,
                            MessagePtr query_message,
                            MessagePtr answer_message,
                            OutputBufferPtr buffer) const
    {
        const qid_t qid = query_message->getQid();
        const bool rd = query_message->getHeaderFlag(Message::HEADERFLAG_RD);
        const bool cd = query_message->getHeaderFlag(Message::HEADERFLAG_CD);
        const Opcode& opcode = query_message->getOpcode();

        // Fill in the final details of the answer message
        answer_message->setQid(qid);
        answer_message->setOpcode(opcode);

        answer_message->setHeaderFlag(Message::HEADERFLAG_QR);
        answer_message->setHeaderFlag(Message::HEADERFLAG_RA);
        if (rd) {
            answer_message->setHeaderFlag(Message::HEADERFLAG_RD);
        }
        if (cd) {
            answer_message->setHeaderFlag(Message::HEADERFLAG_CD);
        }

        vector<QuestionPtr> questions;
        questions.assign(query_message->beginQuestion(), query_message->endQuestion());
        for_each(questions.begin(), questions.end(), QuestionInserter(answer_message));
        
        // Now we can clear the buffer and render the new message into it
        buffer->clear();
        MessageRenderer renderer(*buffer);

        ConstEDNSPtr edns(query_message->getEDNS());
        const bool dnssec_ok = edns && edns->getDNSSECAwareness();
        if (edns) {
            EDNSPtr edns_response(new EDNS());
            edns_response->setDNSSECAwareness(dnssec_ok);

            // TODO: We should make our own edns bufsize length configurable
            edns_response->setUDPSize(Message::DEFAULT_MAX_EDNS0_UDPSIZE);
            answer_message->setEDNS(edns_response);
        }
        
        if (io_message.getSocket().getProtocol() == IPPROTO_UDP) {
            if (edns) {
                renderer.setLengthLimit(edns->getUDPSize());
            } else {
                renderer.setLengthLimit(Message::DEFAULT_MAX_UDPSIZE);
            }
        } else {
            renderer.setLengthLimit(65535);
        }

        answer_message->toWire(renderer);

        dlog(string("sending a response (") +
            boost::lexical_cast<string>(renderer.getLength()) + "bytes): \n" +
            answer_message->toText());
    }
};

// This is a derived class of \c SimpleCallback, to serve
// as a callback in the asiolink module.  It checks for queued
// configuration messages, and executes them if found.
class ConfigCheck : public SimpleCallback {
public:
    ConfigCheck(Resolver* srv) : server_(srv) {}
    virtual void operator()(const IOMessage&) const {
        if (server_->getConfigSession()->hasQueuedMsgs()) {
            server_->getConfigSession()->checkCommand();
        }
    }
private:
    Resolver* server_;
};

Resolver::Resolver() :
    impl_(new ResolverImpl()),
    checkin_(new ConfigCheck(this)),
    dns_lookup_(new MessageLookup(this)),
    dns_answer_(new MessageAnswer)
{}

Resolver::~Resolver() {
    delete impl_;
    delete checkin_;
    delete dns_lookup_;
    delete dns_answer_;
}

void
Resolver::setDNSService(asiolink::DNSService& dnss) {
    dnss_ = &dnss;
}

void
Resolver::setConfigSession(ModuleCCSession* config_session) {
    impl_->config_session_ = config_session;
}

ModuleCCSession*
Resolver::getConfigSession() const {
    return (impl_->config_session_);
}

void
Resolver::resolve(const isc::dns::QuestionPtr& question,
    const isc::resolve::ResolverInterface::CallbackPtr& callback)
{
    impl_->resolve(question, callback);
}


void
Resolver::processMessage(const IOMessage& io_message,
                         MessagePtr query_message,
                         MessagePtr answer_message,
                         OutputBufferPtr buffer,
                         DNSServer* server)
{
    dlog("Got a DNS message");
    InputBuffer request_buffer(io_message.getData(), io_message.getDataSize());
    // First, check the header part.  If we fail even for the base header,
    // just drop the message.
    try {
        query_message->parseHeader(request_buffer);

        // Ignore all responses.
        if (query_message->getHeaderFlag(Message::HEADERFLAG_QR)) {
            dlog("Received unexpected response, ignoring");
            server->resume(false);
            return;
        }
    } catch (const Exception& ex) {
        dlog(string("DNS packet exception: ") + ex.what(),true);
        server->resume(false);
        return;
    }

    // Parse the message.  On failure, return an appropriate error.
    try {
        query_message->fromWire(request_buffer);
    } catch (const DNSProtocolError& error) {
        dlog(string("returning ") + error.getRcode().toText() + ": " + 
            error.what());
        makeErrorMessage(query_message, buffer, error.getRcode());
        server->resume(true);
        return;
    } catch (const Exception& ex) {
        dlog(string("returning SERVFAIL: ") + ex.what());
        makeErrorMessage(query_message, buffer, Rcode::SERVFAIL());
        server->resume(true);
        return;
    } // other exceptions will be handled at a higher layer.

    dlog("received a message:\n" + query_message->toText());

    // Perform further protocol-level validation.
    bool sendAnswer = true;
    if (query_message->getOpcode() == Opcode::NOTIFY()) {
        makeErrorMessage(query_message, buffer, Rcode::NOTAUTH());
        dlog("Notify arrived, but we are not authoritative");
    } else if (query_message->getOpcode() != Opcode::QUERY()) {
        dlog("Unsupported opcode (got: " + query_message->getOpcode().toText() +
            ", expected: " + Opcode::QUERY().toText());
        makeErrorMessage(query_message, buffer, Rcode::NOTIMP());
    } else if (query_message->getRRCount(Message::SECTION_QUESTION) != 1) {
        dlog("The query contained " +
            boost::lexical_cast<string>(query_message->getRRCount(
            Message::SECTION_QUESTION) + " questions, exactly one expected"));
        makeErrorMessage(query_message, buffer, Rcode::FORMERR());
    } else {
        ConstQuestionPtr question = *query_message->beginQuestion();
        const RRType &qtype = question->getType();
        if (qtype == RRType::AXFR()) {
            if (io_message.getSocket().getProtocol() == IPPROTO_UDP) {
                makeErrorMessage(query_message, buffer, Rcode::FORMERR());
            } else {
                makeErrorMessage(query_message, buffer, Rcode::NOTIMP());
            }
        } else if (qtype == RRType::IXFR()) {
            makeErrorMessage(query_message, buffer, Rcode::NOTIMP());
        } else {
            // The RecursiveQuery object will post the "resume" event to the
            // DNSServer when an answer arrives, so we don't have to do it now.
            sendAnswer = false;
            impl_->processNormalQuery(*question, answer_message,
                                      buffer, server);
        }
    }

    if (sendAnswer) {
        server->resume(true);
    }
}

void
ResolverImpl::resolve(const QuestionPtr& question,
    const isc::resolve::ResolverInterface::CallbackPtr& callback)
{
    rec_query_->resolve(question, callback);
}

void
ResolverImpl::processNormalQuery(const Question& question,
                                 MessagePtr answer_message,
                                 OutputBufferPtr buffer,
                                 DNSServer* server)
{
    dlog("Processing normal query");
    rec_query_->resolve(question, answer_message, buffer, server);
}

namespace {

vector<addr_t>
parseAddresses(ConstElementPtr addresses) {
    vector<addr_t> result;
    if (addresses) {
        if (addresses->getType() == Element::list) {
            for (size_t i(0); i < addresses->size(); ++ i) {
                ConstElementPtr addrPair(addresses->get(i));
                ConstElementPtr addr(addrPair->get("address"));
                ConstElementPtr port(addrPair->get("port"));
                if (!addr || ! port) {
                    isc_throw(BadValue, "Address must contain both the IP"
                        "address and port");
                }
                try {
                    IOAddress(addr->stringValue());
                    if (port->intValue() < 0 ||
                        port->intValue() > 0xffff) {
                        isc_throw(BadValue, "Bad port value (" <<
                            port->intValue() << ")");
                    }
                    result.push_back(addr_t(addr->stringValue(),
                        port->intValue()));
                }
                catch (const TypeError &e) { // Better error message
                    isc_throw(TypeError,
                        "Address must be a string and port an integer");
                }
            }
        } else if (addresses->getType() != Element::null) {
            isc_throw(TypeError,
                "root_addresses, forward_addresses, and listen_on config element must be a list");
        }
    }
    return (result);
}

}

ConstElementPtr
Resolver::updateConfig(ConstElementPtr config) {
    dlog("New config comes: " + config->toWire());

    try {
        // Parse forward_addresses
        ConstElementPtr rootAddressesE(config->get("root_addresses"));
        vector<addr_t> rootAddresses(parseAddresses(rootAddressesE));
        ConstElementPtr forwardAddressesE(config->get("forward_addresses"));
        vector<addr_t> forwardAddresses(parseAddresses(forwardAddressesE));
        ConstElementPtr listenAddressesE(config->get("listen_on"));
        vector<addr_t> listenAddresses(parseAddresses(listenAddressesE));
        bool set_timeouts(false);
        int qtimeout = impl_->query_timeout_;
        int ctimeout = impl_->client_timeout_;
        int ltimeout = impl_->lookup_timeout_;
        unsigned retries = impl_->retries_;
        ConstElementPtr qtimeoutE(config->get("timeout_query")),
                        ctimeoutE(config->get("timeout_client")),
                        ltimeoutE(config->get("timeout_lookup")),
                        retriesE(config->get("retries"));
        if (qtimeoutE) {
            // It should be safe to just get it, the config manager should
            // check for us
            qtimeout = qtimeoutE->intValue();
            if (qtimeout < -1) {
                isc_throw(BadValue, "Query timeout too small");
            }
            set_timeouts = true;
        }
        if (ctimeoutE) {
            ctimeout = ctimeoutE->intValue();
            if (ctimeout < -1) {
                isc_throw(BadValue, "Client timeout too small");
            }
            set_timeouts = true;
        }
        if (ltimeoutE) {
            ltimeout = ltimeoutE->intValue();
            if (ltimeout < -1) {
                isc_throw(BadValue, "Lookup timeout too small");
            }
            set_timeouts = true;
        }
        if (retriesE) {
            if (retriesE->intValue() < 0) {
                isc_throw(BadValue, "Negative number of retries");
            }
            retries = retriesE->intValue();
            set_timeouts = true;
        }
        // Everything OK, so commit the changes
        // listenAddresses can fail to bind, so try them first
        bool need_query_restart = false;
        
        if (listenAddressesE) {
            setListenAddresses(listenAddresses);
            need_query_restart = true;
        }
        if (forwardAddressesE) {
            setForwardAddresses(forwardAddresses);
            need_query_restart = true;
        }
        if (rootAddressesE) {
            setRootAddresses(rootAddresses);
            need_query_restart = true;
        }
        if (set_timeouts) {
            setTimeouts(qtimeout, ctimeout, ltimeout, retries);
            need_query_restart = true;
        }

        if (need_query_restart) {
            impl_->queryShutdown();
            impl_->querySetup(*dnss_);
        }
        return (isc::config::createAnswer());
    } catch (const isc::Exception& error) {
        dlog(string("error in config: ") + error.what(),true);
        return (isc::config::createAnswer(1, error.what()));
    }
}

void
Resolver::setForwardAddresses(const vector<addr_t>& addresses)
{
    impl_->setForwardAddresses(addresses, dnss_);
}

void
Resolver::setRootAddresses(const vector<addr_t>& addresses)
{
    impl_->setRootAddresses(addresses, dnss_);
}

bool
Resolver::isForwarding() const {
    return (!impl_->upstream_.empty());
}

vector<addr_t>
Resolver::getForwardAddresses() const {
    return (impl_->upstream_);
}

vector<addr_t>
Resolver::getRootAddresses() const {
    return (impl_->upstream_root_);
}

namespace {

void
setAddresses(DNSService *service, const vector<addr_t>& addresses) {
    service->clearServers();
    BOOST_FOREACH(const addr_t &address, addresses) {
        service->addServer(address.second, address.first);
    }
}

}

void
Resolver::setListenAddresses(const vector<addr_t>& addresses) {
    try {
        dlog("Setting listen addresses:");
        BOOST_FOREACH(const addr_t& addr, addresses) {
            dlog(" " + addr.first + ":" +
                        boost::lexical_cast<string>(addr.second));
        }
        setAddresses(dnss_, addresses);
        impl_->listen_ = addresses;
    }
    catch (const exception& e) {
        /*
         * We couldn't set it. So return it back. If that fails as well,
         * we have a problem.
         *
         * If that fails, bad luck, but we are useless anyway, so just die
         * and let boss start us again.
         */
        dlog(string("Unable to set new address: ") + e.what(),true);
        try {
            setAddresses(dnss_, impl_->listen_);
        }
        catch (const exception& e2) {
            dlog(string("Unable to recover from error;"),true);
            dlog(string("Rollback failed with: ") + e2.what(),true);
            abort();
        }
        throw e; // Let it fly a little bit further
    }
}

void
Resolver::setTimeouts(int query_timeout, int client_timeout,
                      int lookup_timeout, unsigned retries) {
    dlog("Setting query timeout to " + boost::lexical_cast<string>(query_timeout) +
         ", client timeout to " + boost::lexical_cast<string>(client_timeout) +
         ", lookup timeout to " + boost::lexical_cast<string>(lookup_timeout) +
         " and retry count to " + boost::lexical_cast<string>(retries));
    impl_->query_timeout_ = query_timeout;
    impl_->client_timeout_ = client_timeout;
    impl_->lookup_timeout_ = lookup_timeout;
    impl_->retries_ = retries;
}

int
Resolver::getQueryTimeout() const {
    return impl_->query_timeout_;
}

int
Resolver::getClientTimeout() const {
    return impl_->client_timeout_;
}

int
Resolver::getLookupTimeout() const {
    return impl_->lookup_timeout_;
}

int
Resolver::getRetries() const {
    return impl_->retries_;
}

vector<addr_t>
Resolver::getListenAddresses() const {
    return (impl_->listen_);
}