// Copyright (C) 2009-2023 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#include <config.h>

#include <stdint.h>

#include <algorithm>
#include <cassert>
#include <string>
#include <sstream>
#include <vector>

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

#include <exceptions/exceptions.h>

#include <util/buffer.h>

#include <dns/edns.h>
#include <dns/exceptions.h>
#include <dns/message.h>
#include <dns/messagerenderer.h>
#include <dns/name.h>
#include <dns/opcode.h>
#include <dns/rcode.h>
#include <dns/question.h>
#include <dns/rdataclass.h>
#include <dns/rrclass.h>
#include <dns/rrtype.h>
#include <dns/rrttl.h>
#include <dns/rrset.h>
#include <dns/tsig.h>

using namespace std;
using boost::lexical_cast;
using namespace isc::dns::rdata;
using namespace isc::util;

namespace isc {
namespace dns {

namespace {
// protocol constants
const size_t HEADERLEN = 12;

const unsigned int OPCODE_MASK = 0x7800;
const unsigned int OPCODE_SHIFT = 11;
const unsigned int RCODE_MASK = 0x000f;

// This diagram shows the wire-format representation of the 2nd 16 bits of
// the DNS header section, which contain all defined flag bits.
//
//    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//    |QR|   Opcode  |AA|TC|RD|RA|  |AD|CD|   RCODE   |
//    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//      1  0  0  0| 0  1  1  1| 1  0  1  1| 0  0  0  0|
//         0x8         0x7         0xb         0x0
//
// This mask covers all the flag bits, and those bits only.
// Note: we reject a "flag" the is not covered by this mask in some of the
// public methods.  This means our current definition is not fully extendable;
// applications cannot introduce a new flag bit temporarily without modifying
// the source code.
const unsigned int HEADERFLAG_MASK = 0x87b0;

// This is a set of flag bits that should be preserved when building a reply
// from a request.
// Note: we assume the specific definition of HEADERFLAG_xx.  We may change
// the definition in future, in which case we need to adjust this definition,
// too (see also the description about the Message::HeaderFlag type).
const uint16_t MESSAGE_REPLYPRESERVE = (Message::HEADERFLAG_RD |
                                        Message::HEADERFLAG_CD);

const char* const sectiontext[] = {
    "QUESTION",
    "ANSWER",
    "AUTHORITY",
    "ADDITIONAL"
};
}

class MessageImpl {
public:
    MessageImpl(Message::Mode mode);
    // Open issues: should we rather have a header in wire-format
    // for efficiency?
    Message::Mode mode_;
    qid_t qid_;

    // We want to use NULL for [op,r]code_ to mean the code being not
    // correctly parsed or set.  We store the real code object in
    // xxcode_placeholder_ and have xxcode_ refer to it when the object
    // is valid.
    const Rcode* rcode_;
    Rcode rcode_placeholder_;
    const Opcode* opcode_;
    Opcode opcode_placeholder_;

    uint16_t flags_;            // wire-format representation of header flags.

    bool header_parsed_;
    static const unsigned int NUM_SECTIONS = 4; // TODO: revisit this design
    int counts_[NUM_SECTIONS];   // TODO: revisit this definition
    vector<QuestionPtr> questions_;
    vector<RRsetPtr> rrsets_[NUM_SECTIONS];
    ConstEDNSPtr edns_;
    ConstTSIGRecordPtr tsig_rr_;

    // RRsetsSorter* sorter_; : TODO

    void init();
    void setOpcode(const Opcode& opcode);
    void setRcode(const Rcode& rcode);
    int parseQuestion(InputBuffer& buffer);
    int parseSection(const Message::Section section, InputBuffer& buffer,
                     Message::ParseOptions options);
    void addRR(Message::Section section, const Name& name,
               const RRClass& rrclass, const RRType& rrtype,
               const RRTTL& ttl, ConstRdataPtr rdata,
               Message::ParseOptions options);
    // There are also times where an RR needs to be added that
    // represents an empty RRset. There is no Rdata in that case
    void addRR(Message::Section section, const Name& name,
               const RRClass& rrclass, const RRType& rrtype,
               const RRTTL& ttl, Message::ParseOptions options);
    void addEDNS(Message::Section section, const Name& name,
                 const RRClass& rrclass, const RRType& rrtype,
                 const RRTTL& ttl, const Rdata& rdata);
    void addTSIG(Message::Section section, unsigned int count,
                 const InputBuffer& buffer, size_t start_position,
                 const Name& name, const RRClass& rrclass,
                 const RRTTL& ttl, const Rdata& rdata);
    void toWire(AbstractMessageRenderer& renderer, TSIGContext* tsig_ctx);
};

/// @brief Pointer to the @ref MessageImpl object.
typedef boost::shared_ptr<MessageImpl> MessageImplPtr;

MessageImpl::MessageImpl(Message::Mode mode) :
    mode_(mode),
    rcode_placeholder_(Rcode(0)), // for placeholders the value doesn't matter
    opcode_placeholder_(Opcode(0)) {
    init();
}

void
MessageImpl::init() {
    flags_ = 0;
    qid_ = 0;
    rcode_ = NULL;
    opcode_ = NULL;
    edns_ = EDNSPtr();
    tsig_rr_ = ConstTSIGRecordPtr();

    for (int i = 0; i < NUM_SECTIONS; ++i) {
        counts_[i] = 0;
    }

    header_parsed_ = false;
    questions_.clear();
    rrsets_[Message::SECTION_ANSWER].clear();
    rrsets_[Message::SECTION_AUTHORITY].clear();
    rrsets_[Message::SECTION_ADDITIONAL].clear();
}

void
MessageImpl::setOpcode(const Opcode& opcode) {
    opcode_placeholder_ = opcode;
    opcode_ = &opcode_placeholder_;
}

void
MessageImpl::setRcode(const Rcode& rcode) {
    rcode_placeholder_ = rcode;
    rcode_ = &rcode_placeholder_;
}

namespace {
// This helper class is used by MessageImpl::toWire() to render a set of
// RRsets of a specific section of message to a given MessageRenderer.
//
// A RenderSection object is expected to be used with a QuestionIterator or
// SectionIterator.  Its operator() is called for each RRset as the iterator
// iterates over the corresponding section, and it renders the RRset to
// the given MessageRenderer, while counting the number of RRs (note: not
// RRsets) successfully rendered.  If the MessageRenderer reports the need
// for truncation (via its isTruncated() method), the RenderSection object
// stops rendering further RRsets.  In addition, unless partial_ok (given on
// construction) is true, it removes any RRs that are partially rendered
// from the MessageRenderer.
//
// On the completion of rendering the entire section, the owner of the
// RenderSection object can get the number of rendered RRs via the
// getTotalCount() method.
template <typename T>
struct RenderSection {
    RenderSection(AbstractMessageRenderer& renderer, const bool partial_ok) :
        counter_(0), renderer_(renderer), partial_ok_(partial_ok),
        truncated_(false) {
    }

    void operator()(const T& entry) {
        // If it's already truncated, ignore the rest of the section.
        if (truncated_) {
            return;
        }
        const size_t pos0 = renderer_.getLength();
        counter_ += entry->toWire(renderer_);
        if (renderer_.isTruncated()) {
            truncated_ = true;
            if (!partial_ok_) {
                // roll back to the end of the previous RRset.
                renderer_.trim(renderer_.getLength() - pos0);
            }
        }
    }

    unsigned int getTotalCount() {
        return (counter_);
    }

    unsigned int counter_;

    AbstractMessageRenderer& renderer_;

    const bool partial_ok_;

    bool truncated_;
};
}

void
MessageImpl::toWire(AbstractMessageRenderer& renderer, TSIGContext* tsig_ctx) {
    if (mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "Message rendering attempted in non render mode");
    }
    if (rcode_ == NULL) {
        isc_throw(InvalidMessageOperation,
                  "Message rendering attempted without Rcode set");
    }
    if (opcode_ == NULL) {
        isc_throw(InvalidMessageOperation,
                  "Message rendering attempted without Opcode set");
    }

    // Reserve the space for TSIG (if needed) so that we can handle truncation
    // case correctly later when that happens.  orig_xxx variables remember
    // some configured parameters of renderer in case they are needed in
    // truncation processing below.
    const size_t tsig_len = (tsig_ctx != NULL) ? tsig_ctx->getTSIGLength() : 0;
    const size_t orig_msg_len_limit = renderer.getLengthLimit();
    const AbstractMessageRenderer::CompressMode orig_compress_mode =
        renderer.getCompressMode();

    // We are going to skip soon, so we need to clear the renderer
    // But we'll leave the length limit  and the compress mode intact
    // (or shortened in case of TSIG)
    renderer.clear();
    renderer.setCompressMode(orig_compress_mode);

    if (tsig_len > 0) {
        if (tsig_len > orig_msg_len_limit) {
            isc_throw(InvalidParameter, "Failed to render DNS message: "
                      "too small limit for a TSIG (" <<
                      orig_msg_len_limit << ")");
        }
        renderer.setLengthLimit(orig_msg_len_limit - tsig_len);
    } else {
        renderer.setLengthLimit(orig_msg_len_limit);
    }

    // reserve room for the header
    if (renderer.getLengthLimit() < HEADERLEN) {
        isc_throw(InvalidParameter, "Failed to render DNS message: "
                  "too small limit for a Header");
    }
    renderer.skip(HEADERLEN);

    uint16_t qdcount =
        for_each(questions_.begin(), questions_.end(),
                 RenderSection<QuestionPtr>(renderer, false)).getTotalCount();

    // TODO: sort RRsets in each section based on configuration policy.
    uint16_t ancount = 0;
    if (!renderer.isTruncated()) {
        ancount =
            for_each(rrsets_[Message::SECTION_ANSWER].begin(),
                     rrsets_[Message::SECTION_ANSWER].end(),
                     RenderSection<RRsetPtr>(renderer, true)).getTotalCount();
    }
    uint16_t nscount = 0;
    if (!renderer.isTruncated()) {
        nscount =
            for_each(rrsets_[Message::SECTION_AUTHORITY].begin(),
                     rrsets_[Message::SECTION_AUTHORITY].end(),
                     RenderSection<RRsetPtr>(renderer, true)).getTotalCount();
    }
    uint16_t arcount = 0;
    if (renderer.isTruncated()) {
        flags_ |= Message::HEADERFLAG_TC;
    } else {
        arcount =
            for_each(rrsets_[Message::SECTION_ADDITIONAL].begin(),
                     rrsets_[Message::SECTION_ADDITIONAL].end(),
                     RenderSection<RRsetPtr>(renderer, false)).getTotalCount();
    }

    // Add EDNS OPT RR if necessary.  Basically, we add it only when EDNS
    // has been explicitly set.  However, if the RCODE would require it and
    // no EDNS has been set we generate a temporary local EDNS and use it.
    if (!renderer.isTruncated()) {
        ConstEDNSPtr local_edns = edns_;
        if (!local_edns && rcode_->getExtendedCode() != 0) {
            local_edns = ConstEDNSPtr(new EDNS());
        }
        if (local_edns) {
            arcount += local_edns->toWire(renderer, rcode_->getExtendedCode());
        }
    }

    // If we're adding a TSIG to a truncated message, clear all RRsets
    // from the message except for the question before adding the TSIG.
    // If even (some of) the question doesn't fit, don't include it.
    if (tsig_ctx != NULL && renderer.isTruncated()) {
        renderer.clear();
        renderer.setLengthLimit(orig_msg_len_limit - tsig_len);
        renderer.setCompressMode(orig_compress_mode);
        renderer.skip(HEADERLEN);
        qdcount = for_each(questions_.begin(), questions_.end(),
                           RenderSection<QuestionPtr>(renderer,
                                                      false)).getTotalCount();
        ancount = 0;
        nscount = 0;
        arcount = 0;
    }

    // Adjust the counter buffer.
    // XXX: these may not be equal to the number of corresponding entries
    // in rrsets_[] or questions_ if truncation occurred or an EDNS OPT RR
    // was inserted.  This is not good, and we should revisit the entire
    // design.
    counts_[Message::SECTION_QUESTION] = qdcount;
    counts_[Message::SECTION_ANSWER] = ancount;
    counts_[Message::SECTION_AUTHORITY] = nscount;
    counts_[Message::SECTION_ADDITIONAL] = arcount;

    // fill in the header
    size_t header_pos = 0;
    renderer.writeUint16At(qid_, header_pos);
    header_pos += sizeof(uint16_t);

    uint16_t codes_and_flags =
        (opcode_->getCode() << OPCODE_SHIFT) & OPCODE_MASK;
    codes_and_flags |= (rcode_->getCode() & RCODE_MASK);
    codes_and_flags |= (flags_ & HEADERFLAG_MASK);
    renderer.writeUint16At(codes_and_flags, header_pos);
    header_pos += sizeof(uint16_t);
    // TODO: should avoid repeated pattern
    renderer.writeUint16At(qdcount, header_pos);
    header_pos += sizeof(uint16_t);
    renderer.writeUint16At(ancount, header_pos);
    header_pos += sizeof(uint16_t);
    renderer.writeUint16At(nscount, header_pos);
    header_pos += sizeof(uint16_t);
    renderer.writeUint16At(arcount, header_pos);

    // Add TSIG, if necessary, at the end of the message.
    if (tsig_ctx != NULL) {
        // Release the reserved space in the renderer.
        renderer.setLengthLimit(orig_msg_len_limit);

        const int tsig_count =
            tsig_ctx->sign(qid_, renderer.getData(),
                           renderer.getLength())->toWire(renderer);
        if (tsig_count != 1) {
            isc_throw(Unexpected, "Failed to render a TSIG RR");
        }

        // update the ARCOUNT for the TSIG RR.  Note that for a sane DNS
        // message arcount should never overflow to 0.
        renderer.writeUint16At(++arcount, header_pos);
    }
}

Message::Message(Mode mode) :
    impl_(new MessageImpl(mode)) {
}

bool
Message::getHeaderFlag(const HeaderFlag flag) const {
    if (flag == 0 || (flag & ~HEADERFLAG_MASK) != 0) {
        isc_throw(InvalidParameter,
                  "Message::getHeaderFlag:: Invalid flag is specified: " <<
                  "0x" << std::hex << flag);
    }
    return ((impl_->flags_ & flag) != 0);
}

void
Message::setHeaderFlag(const HeaderFlag flag, const bool on) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "setHeaderFlag performed in non-render mode");
    }
    if (flag == 0 || (flag & ~HEADERFLAG_MASK) != 0) {
        isc_throw(InvalidParameter,
                  "Message::getHeaderFlag:: Invalid flag is specified: " <<
                  "0x" << std::hex << static_cast<int>(flag));
    }
    if (on) {
        impl_->flags_ |= flag;
    } else {
        impl_->flags_ &= ~flag;
    }
}

qid_t
Message::getQid() const {
    return (impl_->qid_);
}

void
Message::setQid(qid_t qid) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "setQid performed in non-render mode");
    }
    impl_->qid_ = qid;
}

const Rcode&
Message::getRcode() const {
    if (impl_->rcode_ == NULL) {
        isc_throw(InvalidMessageOperation, "getRcode attempted before set");
    }
    return (*impl_->rcode_);
}

void
Message::setRcode(const Rcode& rcode) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "setRcode performed in non-render mode");
    }
    impl_->setRcode(rcode);
}

const Opcode&
Message::getOpcode() const {
    if (impl_->opcode_ == NULL) {
        isc_throw(InvalidMessageOperation, "getOpcode attempted before set");
    }
    return (*impl_->opcode_);
}

void
Message::setOpcode(const Opcode& opcode) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "setOpcode performed in non-render mode");
    }
    impl_->setOpcode(opcode);
}

ConstEDNSPtr
Message::getEDNS() const {
    return (impl_->edns_);
}

void
Message::setEDNS(ConstEDNSPtr edns) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "setEDNS performed in non-render mode");
    }
    impl_->edns_ = edns;
}

const TSIGRecord*
Message::getTSIGRecord() const {
    if (impl_->mode_ != Message::PARSE) {
        isc_throw(InvalidMessageOperation,
                  "getTSIGRecord performed in non-parse mode");
    }

    return (impl_->tsig_rr_.get());
}

unsigned int
Message::getRRCount(const Section section) const {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }
    return (impl_->counts_[section]);
}

void
Message::addRRset(const Section section, RRsetPtr rrset) {
    if (!rrset) {
        isc_throw(InvalidParameter,
                  "NULL RRset is given to Message::addRRset");
    }
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "addRRset performed in non-render mode");
    }
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }

    impl_->rrsets_[section].push_back(rrset);
    impl_->counts_[section] += rrset->getRdataCount();
    impl_->counts_[section] += rrset->getRRsigDataCount();
}

bool
Message::hasRRset(const Section section, const Name& name,
                  const RRClass& rrclass, const RRType& rrtype) const {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }

    BOOST_FOREACH(ConstRRsetPtr r, impl_->rrsets_[section]) {
        if (r->getClass() == rrclass &&
            r->getType() == rrtype &&
            r->getName() == name) {
            return (true);
        }
    }

    return (false);
}

bool
Message::hasRRset(const Section section, const RRsetPtr& rrset) const {
    return (hasRRset(section, rrset->getName(),
                     rrset->getClass(), rrset->getType()));
}

bool
Message::removeRRset(const Section section, RRsetIterator& iterator) {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }

    bool removed = false;
    for (vector<RRsetPtr>::iterator i = impl_->rrsets_[section].begin();
            i != impl_->rrsets_[section].end(); ++i) {
        if (((*i)->getName() == (*iterator)->getName()) &&
            ((*i)->getClass() == (*iterator)->getClass()) &&
            ((*i)->getType() == (*iterator)->getType())) {

            // Found the matching RRset so remove it & ignore rest
            impl_->counts_[section] -= (*iterator)->getRdataCount();
            impl_->counts_[section] -= (*iterator)->getRRsigDataCount();
            impl_->rrsets_[section].erase(i);
            removed = true;
            break;
        }
    }

    return (removed);
}

void
Message::clearSection(const Section section) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "clearSection performed in non-render mode");
    }
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }
    if (section == Message::SECTION_QUESTION) {
        impl_->questions_.clear();
    } else {
        impl_->rrsets_[section].clear();
    }
    impl_->counts_[section] = 0;
}

void
Message::addQuestion(const QuestionPtr question) {
    if (impl_->mode_ != Message::RENDER) {
        isc_throw(InvalidMessageOperation,
                  "addQuestion performed in non-render mode");
    }

    impl_->questions_.push_back(question);
    ++impl_->counts_[SECTION_QUESTION];
}

void
Message::addQuestion(const Question& question) {
    addQuestion(QuestionPtr(new Question(question)));
}

void
Message::toWire(AbstractMessageRenderer& renderer, TSIGContext* tsig_ctx) {
    impl_->toWire(renderer, tsig_ctx);
}

void
Message::parseHeader(InputBuffer& buffer) {
    if (impl_->mode_ != Message::PARSE) {
        isc_throw(InvalidMessageOperation,
                  "Message parse attempted in non parse mode");
    }

    if (impl_->header_parsed_) {
        return;
    }

    if ((buffer.getLength() - buffer.getPosition()) < HEADERLEN) {
        isc_throw(MessageTooShort, "Malformed DNS message (short length): "
                  << buffer.getLength() - buffer.getPosition());
    }

    impl_->qid_ = buffer.readUint16();
    const uint16_t codes_and_flags = buffer.readUint16();
    impl_->setOpcode(Opcode((codes_and_flags & OPCODE_MASK) >> OPCODE_SHIFT));
    impl_->setRcode(Rcode(codes_and_flags & RCODE_MASK));
    impl_->flags_ = (codes_and_flags & HEADERFLAG_MASK);
    impl_->counts_[SECTION_QUESTION] = buffer.readUint16();
    impl_->counts_[SECTION_ANSWER] = buffer.readUint16();
    impl_->counts_[SECTION_AUTHORITY] = buffer.readUint16();
    impl_->counts_[SECTION_ADDITIONAL] = buffer.readUint16();

    impl_->header_parsed_ = true;
}

void
Message::fromWire(InputBuffer& buffer, ParseOptions options) {
    if (impl_->mode_ != Message::PARSE) {
        isc_throw(InvalidMessageOperation,
                  "Message parse attempted in non parse mode");
    }

    // Clear any old parsed data
    clear(Message::PARSE);

    buffer.setPosition(0);
    parseHeader(buffer);

    impl_->counts_[SECTION_QUESTION] = impl_->parseQuestion(buffer);
    impl_->counts_[SECTION_ANSWER] =
        impl_->parseSection(SECTION_ANSWER, buffer, options);
    impl_->counts_[SECTION_AUTHORITY] =
        impl_->parseSection(SECTION_AUTHORITY, buffer, options);
    impl_->counts_[SECTION_ADDITIONAL] =
        impl_->parseSection(SECTION_ADDITIONAL, buffer, options);
}

int
MessageImpl::parseQuestion(InputBuffer& buffer) {
    unsigned int added = 0;

    for (unsigned int count = 0;
         count < counts_[Message::SECTION_QUESTION];
         ++count) {
        const Name name(buffer);

        if ((buffer.getLength() - buffer.getPosition()) <
            2 * sizeof(uint16_t)) {
            isc_throw(DNSMessageFORMERR, "Question section too short: " <<
                      (buffer.getLength() - buffer.getPosition()) << " bytes");
        }
        const RRType rrtype(buffer.readUint16());
        const RRClass rrclass(buffer.readUint16());

        // XXX: need a duplicate check.  We might also want to have an
        // optimized algorithm that requires the question section contain
        // exactly one RR.

        questions_.push_back(QuestionPtr(new Question(name, rrclass, rrtype)));
        ++added;
    }

    return (added);
}

namespace {
struct MatchRR {
    MatchRR(const Name& name, const RRType& rrtype, const RRClass& rrclass) :
        name_(name), rrtype_(rrtype), rrclass_(rrclass) {
    }

    bool operator()(const RRsetPtr& rrset) const {
        return (rrset->getType() == rrtype_ &&
                rrset->getClass() == rrclass_ &&
                rrset->getName() == name_);
    }

    const Name& name_;

    const RRType& rrtype_;

    const RRClass& rrclass_;
};
}

// Note about design decision:
// we need some type specific processing here, including EDNS and TSIG.
// how much we should generalize/hardcode the special logic is subject
// to discussion.  In terms of modularity it would be ideal to introduce
// an abstract class (say "MessageAttribute") and let other such
// concrete notions as EDNS or TSIG inherit from it.  Then we would
// just do:
// message->addAttribute(rrtype, rrclass, buffer);
// to create and attach type-specific concrete object to the message.
//
// A major downside of this approach is, as usual, complexity due to
// indirection and performance penalty.  Also, it may not be so easy
// to separate the processing logic because in many cases we'll need
// parse context for which the message class is responsible (e.g.
// to check the EDNS OPT RR only appears in the additional section,
// and appears only once).
//
// Another point to consider is that we may not need so many special
// types other than EDNS and TSIG (and when and if we implement it,
// SIG(0)); newer optional attributes of the message would more likely
// be standardized as new flags or options of EDNS.  If that's the case,
// introducing an abstract class with all the overhead and complexity
// may not make much sense.
//
// Conclusion: don't over-generalize type-specific logic for now.
// introduce separate concrete classes, and move context-independent
// logic to that class; processing logic dependent on parse context
// is hardcoded here.
int
MessageImpl::parseSection(const Message::Section section,
                          InputBuffer& buffer, Message::ParseOptions options) {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }

    unsigned int added = 0;

    for (unsigned int count = 0; count < counts_[section]; ++count) {
        // We need to remember the start position for TSIG processing
        const size_t start_position = buffer.getPosition();

        const Name name(buffer);

        // buffer must store at least RR TYPE, RR CLASS, TTL, and RDLEN.
        if ((buffer.getLength() - buffer.getPosition()) <
            3 * sizeof(uint16_t) + sizeof(uint32_t)) {
            isc_throw(DNSMessageFORMERR, sectiontext[section] <<
                      " section too short: " <<
                      (buffer.getLength() - buffer.getPosition()) << " bytes");
        }

        const RRType rrtype(buffer.readUint16());
        const RRClass rrclass(buffer.readUint16());
        const RRTTL ttl(buffer.readUint32());
        const size_t rdlen = buffer.readUint16();

        // If class is ANY or NONE, rdlength may be zero, to signal
        // an empty RRset.
        // (the class check must be done to differentiate from RRTypes
        // that can have zero length rdata
        if ((rrclass == RRClass::ANY() || rrclass == RRClass::NONE()) &&
            rdlen == 0) {
            addRR(section, name, rrclass, rrtype, ttl, options);
            ++added;
            continue;
        }
        ConstRdataPtr rdata = createRdata(rrtype, rrclass, buffer, rdlen);

        if (rrtype == RRType::OPT()) {
            addEDNS(section, name, rrclass, rrtype, ttl, *rdata);
        } else if (rrtype == RRType::TSIG()) {
            addTSIG(section, count, buffer, start_position, name, rrclass, ttl,
                    *rdata);
        } else {
            addRR(section, name, rrclass, rrtype, ttl, rdata, options);
            ++added;
        }
    }

    return (added);
}

void
MessageImpl::addRR(Message::Section section, const Name& name,
                   const RRClass& rrclass, const RRType& rrtype,
                   const RRTTL& ttl, ConstRdataPtr rdata,
                   Message::ParseOptions options) {
    if ((options & Message::PRESERVE_ORDER) == 0) {
        vector<RRsetPtr>::iterator it =
            find_if(rrsets_[section].begin(), rrsets_[section].end(),
                    MatchRR(name, rrtype, rrclass));
        if (it != rrsets_[section].end()) {
            (*it)->setTTL(min((*it)->getTTL(), ttl));
            (*it)->addRdata(rdata);
            return;
        }
    }
    RRsetPtr rrset(new RRset(name, rrclass, rrtype, ttl));
    rrset->addRdata(rdata);
    rrsets_[section].push_back(rrset);
}

void
MessageImpl::addRR(Message::Section section, const Name& name,
                   const RRClass& rrclass, const RRType& rrtype,
                   const RRTTL& ttl, Message::ParseOptions options) {
    if ((options & Message::PRESERVE_ORDER) == 0) {
        vector<RRsetPtr>::iterator it =
            find_if(rrsets_[section].begin(), rrsets_[section].end(),
                    MatchRR(name, rrtype, rrclass));
        if (it != rrsets_[section].end()) {
            (*it)->setTTL(min((*it)->getTTL(), ttl));
            return;
        }
    }
    RRsetPtr rrset(new RRset(name, rrclass, rrtype, ttl));
    rrsets_[section].push_back(rrset);
}

void
MessageImpl::addEDNS(Message::Section section,  const Name& name,
                     const RRClass& rrclass, const RRType& rrtype,
                     const RRTTL& ttl, const Rdata& rdata) {
    if (section != Message::SECTION_ADDITIONAL) {
        isc_throw(DNSMessageFORMERR,
                  "EDNS OPT RR found in an invalid section");
    }
    if (edns_) {
        isc_throw(DNSMessageFORMERR, "multiple EDNS OPT RR found");
    }

    uint8_t extended_rcode;
    edns_ = ConstEDNSPtr(createEDNSFromRR(name, rrclass, rrtype, ttl, rdata,
                                          extended_rcode));
    setRcode(Rcode(rcode_->getCode(), extended_rcode));
}

void
MessageImpl::addTSIG(Message::Section section, unsigned int count,
                     const InputBuffer& buffer, size_t start_position,
                     const Name& name, const RRClass& rrclass,
                     const RRTTL& ttl, const Rdata& rdata) {
    if (section != Message::SECTION_ADDITIONAL) {
        isc_throw(DNSMessageFORMERR,
                  "TSIG RR found in an invalid section");
    }
    if (count != counts_[section] - 1) {
        isc_throw(DNSMessageFORMERR, "TSIG RR is not the last record");
    }
    // This check will never fail as the multiple TSIG RR case is
    // caught before by the not the last record check...
    if (tsig_rr_) {
        isc_throw(DNSMessageFORMERR, "multiple TSIG RRs found");
    }
    tsig_rr_ = ConstTSIGRecordPtr(new TSIGRecord(name, rrclass,
                                                 ttl, rdata,
                                                 buffer.getPosition() -
                                                 start_position));
}

namespace {
template <typename T>
struct SectionFormatter {
    SectionFormatter(const Message::Section section, string& output) :
        section_(section), output_(output) {
    }

    void operator()(const T& entry) {
        if (section_ == Message::SECTION_QUESTION) {
            output_ += ";";
            output_ += entry->toText();
            output_ += "\n";
        } else {
            output_ += entry->toText();
        }
    }

    const Message::Section section_;

    string& output_;
};
}

string
Message::toText() const {
    if (impl_->rcode_ == NULL) {
        isc_throw(InvalidMessageOperation,
                  "Message::toText() attempted without Rcode set");
    }
    if (impl_->opcode_ == NULL) {
        isc_throw(InvalidMessageOperation,
                  "Message::toText() attempted without Opcode set");
    }

    string s;

    s += ";; ->>HEADER<<- opcode: " + impl_->opcode_->toText();
    // for simplicity we don't consider extended rcode (unlike BIND9)
    s += ", status: " + impl_->rcode_->toText();
    s += ", id: " + boost::lexical_cast<string>(impl_->qid_);
    s += "\n;; flags:";
    if (getHeaderFlag(HEADERFLAG_QR)) {
        s += " qr";
    }
    if (getHeaderFlag(HEADERFLAG_AA)) {
        s += " aa";
    }
    if (getHeaderFlag(HEADERFLAG_TC)) {
        s += " tc";
    }
    if (getHeaderFlag(HEADERFLAG_RD)) {
        s += " rd";
    }
    if (getHeaderFlag(HEADERFLAG_RA)) {
        s += " ra";
    }
    if (getHeaderFlag(HEADERFLAG_AD)) {
        s += " ad";
    }
    if (getHeaderFlag(HEADERFLAG_CD)) {
        s += " cd";
    }

    // for simplicity, don't consider the update case for now
    s += "; QUERY: " + // note: not "QUESTION" to be compatible with BIND 9 dig
        lexical_cast<string>(impl_->counts_[SECTION_QUESTION]);
    s += ", ANSWER: " +
        lexical_cast<string>(impl_->counts_[SECTION_ANSWER]);
    s += ", AUTHORITY: " +
        lexical_cast<string>(impl_->counts_[SECTION_AUTHORITY]);

    unsigned int arcount = impl_->counts_[SECTION_ADDITIONAL];
    if (impl_->edns_ != NULL) {
        ++arcount;
    }
    if (impl_->tsig_rr_ != NULL) {
        ++arcount;
    }
    s += ", ADDITIONAL: " + lexical_cast<string>(arcount) + "\n";

    if (impl_->edns_ != NULL) {
        s += "\n;; OPT PSEUDOSECTION:\n";
        s += impl_->edns_->toText();
    }

    if (!impl_->questions_.empty()) {
        s += "\n;; " +
            string(sectiontext[SECTION_QUESTION]) + " SECTION:\n";
        for_each(impl_->questions_.begin(), impl_->questions_.end(),
                 SectionFormatter<QuestionPtr>(SECTION_QUESTION, s));
    }
    if (!impl_->rrsets_[SECTION_ANSWER].empty()) {
        s += "\n;; " +
            string(sectiontext[SECTION_ANSWER]) + " SECTION:\n";
        for_each(impl_->rrsets_[SECTION_ANSWER].begin(),
                 impl_->rrsets_[SECTION_ANSWER].end(),
                 SectionFormatter<RRsetPtr>(SECTION_ANSWER, s));
    }
    if (!impl_->rrsets_[SECTION_AUTHORITY].empty()) {
        s += "\n;; " +
            string(sectiontext[SECTION_AUTHORITY]) + " SECTION:\n";
        for_each(impl_->rrsets_[SECTION_AUTHORITY].begin(),
                 impl_->rrsets_[SECTION_AUTHORITY].end(),
                 SectionFormatter<RRsetPtr>(SECTION_AUTHORITY, s));
    }
    if (!impl_->rrsets_[SECTION_ADDITIONAL].empty()) {
        s += "\n;; " +
            string(sectiontext[SECTION_ADDITIONAL]) +
            " SECTION:\n";
        for_each(impl_->rrsets_[SECTION_ADDITIONAL].begin(),
                 impl_->rrsets_[SECTION_ADDITIONAL].end(),
                 SectionFormatter<RRsetPtr>(SECTION_ADDITIONAL, s));
    }

    if (impl_->tsig_rr_ != NULL) {
        s += "\n;; TSIG PSEUDOSECTION:\n";
        s += impl_->tsig_rr_->toText();
    }

    return (s);
}

void
Message::clear(Mode mode) {
    impl_->init();
    impl_->mode_ = mode;
}

void
Message::appendSection(const Section section, const Message& source) {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }

    if (section == SECTION_QUESTION) {
        for (QuestionIterator qi = source.beginQuestion();
             qi != source.endQuestion();
             ++qi) {
            addQuestion(*qi);
        }
    } else {
        for (RRsetIterator rrsi = source.beginSection(section);
             rrsi != source.endSection(section);
             ++rrsi) {
            addRRset(section, *rrsi);
        }
    }
}

void
Message::makeResponse() {
    if (impl_->mode_ != Message::PARSE) {
        isc_throw(InvalidMessageOperation,
                  "makeResponse() is performed in non-parse mode");
    }

    impl_->mode_ = Message::RENDER;

    impl_->edns_ = EDNSPtr();
    impl_->flags_ &= MESSAGE_REPLYPRESERVE;
    setHeaderFlag(HEADERFLAG_QR, true);

    impl_->rrsets_[SECTION_ANSWER].clear();
    impl_->counts_[SECTION_ANSWER] = 0;
    impl_->rrsets_[SECTION_AUTHORITY].clear();
    impl_->counts_[SECTION_AUTHORITY] = 0;
    impl_->rrsets_[SECTION_ADDITIONAL].clear();
    impl_->counts_[SECTION_ADDITIONAL] = 0;
}

///
/// Template version of Section Iterator
///
template <typename T>
struct SectionIteratorImpl {
    SectionIteratorImpl(const typename vector<T>::const_iterator& it) :
        it_(it) {
    }

    typename vector<T>::const_iterator it_;
};

template <typename T>
SectionIterator<T>::SectionIterator(const SectionIteratorImpl<T>& impl) {
    impl_ = new SectionIteratorImpl<T>(impl.it_);
}

template <typename T>
SectionIterator<T>::~SectionIterator() {
    delete impl_;
}

template <typename T>
SectionIterator<T>::SectionIterator(const SectionIterator<T>& source) :
    impl_(new SectionIteratorImpl<T>(source.impl_->it_)) {
}

template <typename T>
void
SectionIterator<T>::operator=(const SectionIterator<T>& source) {
    if (impl_ == source.impl_) {
        return;
    }
    SectionIteratorImpl<T>* newimpl =
        new SectionIteratorImpl<T>(source.impl_->it_);
    delete impl_;
    impl_ = newimpl;
}

template <typename T>
SectionIterator<T>&
SectionIterator<T>::operator++() {
    ++(impl_->it_);
    return (*this);
}

template <typename T>
SectionIterator<T>
SectionIterator<T>::operator++(int) {
    SectionIterator<T> tmp(*this);
    ++(*this);
    return (tmp);
}

template <typename T>
const T&
SectionIterator<T>::operator*() const {
    return (*(impl_->it_));
}

template <typename T>
const T*
SectionIterator<T>::operator->() const {
    return (&(operator*()));
}

template <typename T>
bool
SectionIterator<T>::operator==(const SectionIterator<T>& other) const {
    return (impl_->it_ == other.impl_->it_);
}

template <typename T>
bool
SectionIterator<T>::operator!=(const SectionIterator<T>& other) const {
    return (impl_->it_ != other.impl_->it_);
}

///
/// We need to explicitly instantiate these template classes because these
/// are public classes but defined in this implementation file.
///
template class SectionIterator<QuestionPtr>;
template class SectionIterator<RRsetPtr>;

namespace {
typedef SectionIteratorImpl<QuestionPtr> QuestionIteratorImpl;
typedef SectionIteratorImpl<RRsetPtr> RRsetIteratorImpl;
}

///
/// Question iterator
///
const QuestionIterator
Message::beginQuestion() const {
    return (QuestionIterator(QuestionIteratorImpl(impl_->questions_.begin())));
}

const QuestionIterator
Message::endQuestion() const {
    return (QuestionIterator(QuestionIteratorImpl(impl_->questions_.end())));
}

///
/// RRsets iterators
///
const SectionIterator<RRsetPtr>
Message::beginSection(const Section section) const {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }
    if (section == SECTION_QUESTION) {
        isc_throw(InvalidMessageSection,
                  "RRset iterator is requested for question");
    }

    return (RRsetIterator(RRsetIteratorImpl(impl_->rrsets_[section].begin())));
}

const SectionIterator<RRsetPtr>
Message::endSection(const Section section) const {
    if (static_cast<int>(section) >= MessageImpl::NUM_SECTIONS) {
        isc_throw(OutOfRange, "Invalid message section: " << static_cast<int>(section));
    }
    if (section == SECTION_QUESTION) {
        isc_throw(InvalidMessageSection,
                  "RRset iterator is requested for question");
    }

    return (RRsetIterator(RRsetIteratorImpl(impl_->rrsets_[section].end())));
}

ostream&
operator<<(ostream& os, const Message& message) {
    return (os << message.toText());
}
} // end of namespace dns
} // end of namespace isc