an initial cut of the EDNS class (code + tests), mainly for backup.

git-svn-id: svn://bind10.isc.org/svn/bind10/branches/trac311@2794 e5f2f494-b856-4b98-b285-d166d9295462

configure.ac

@@ -452,6 +452,7 @@ AC_CONFIG_FILES([Makefile
                  src/lib/config/testdata/Makefile
                  src/lib/dns/Makefile
                  src/lib/dns/tests/Makefile
+                 src/lib/dns/tests/testdata/Makefile
                  src/lib/dns/python/Makefile
                  src/lib/dns/python/tests/Makefile
                  src/lib/exceptions/Makefile

src/bin/auth/auth_srv.cc

@@ -24,6 +24,7 @@
 #include <exceptions/exceptions.h>
 
 #include <dns/buffer.h>
+#include <dns/edns.h>
 #include <dns/exceptions.h>
 #include <dns/messagerenderer.h>
 #include <dns/name.h>
@@ -164,7 +165,6 @@ makeErrorMessage(Message& message, MessageRenderer& renderer,
     message.setQid(qid);
     message.setOpcode(opcode);
     message.setHeaderFlag(MessageFlag::QR());
-    message.setUDPSize(AuthSrvImpl::DEFAULT_LOCAL_UDPSIZE);
     if (rd) {
         message.setHeaderFlag(MessageFlag::RD());
     }
@@ -292,14 +292,21 @@ bool
 AuthSrvImpl::processNormalQuery(const IOMessage& io_message, Message& message,
                                 MessageRenderer& response_renderer)
 {
-    const bool dnssec_ok = message.isDNSSECSupported();
-    const uint16_t remote_bufsize = message.getUDPSize();
+    ConstEDNSPtr remote_edns = message.getEDNS();
+    const bool dnssec_ok = remote_edns && remote_edns->isDNSSECSupported();
+    const uint16_t remote_bufsize = remote_edns ? remote_edns->getUDPSize() :
+        Message::DEFAULT_MAX_UDPSIZE; 
 
     message.makeResponse();
     message.setHeaderFlag(MessageFlag::AA());
     message.setRcode(Rcode::NOERROR());
-    message.setDNSSECSupported(dnssec_ok);
-    message.setUDPSize(AuthSrvImpl::DEFAULT_LOCAL_UDPSIZE);
+
+    if (remote_edns) {
+        EDNSPtr local_edns = EDNSPtr(new EDNS());
+        local_edns->setDNSSECSupported(dnssec_ok);
+        local_edns->setUDPSize(AuthSrvImpl::DEFAULT_LOCAL_UDPSIZE);
+        message.setEDNS(local_edns);
+    }
 
     try {
         Query query(message, cache_, dnssec_ok);

src/bin/auth/tests/auth_srv_unittest.cc

@@ -444,13 +444,20 @@ TEST_F(AuthSrvTest, ednsBadVers) {
     EXPECT_EQ(true, server.processMessage(*io_message, parse_message,
                                           response_renderer));
 
-    // The response must have an EDNS OPT RR in the additional section.
+    // The response must have an EDNS OPT RR in the additional section, but
+    // it will be added automatically at the render time.
     // Note that the DNSSEC DO bit is cleared even if this bit in the query
     // is set.  This is a limitation of the current implementation.
     headerCheck(parse_message, default_qid, Rcode::BADVERS(), opcode.getCode(),
                 QR_FLAG, 1, 0, 0, 1);
-    EXPECT_EQ(4096, parse_message.getUDPSize());
-    EXPECT_FALSE(parse_message.isDNSSECSupported());
+    EXPECT_FALSE(parse_message.getEDNS()); // EDNS isn't added at this point
+
+    parse_message.clear(Message::PARSE);
+    InputBuffer ib(response_renderer.getData(), response_renderer.getLength());
+    parse_message.fromWire(ib);
+    EXPECT_EQ(Rcode::BADVERS(), parse_message.getRcode());
+    EXPECT_TRUE(parse_message.getEDNS());
+    EXPECT_FALSE(parse_message.getEDNS()->isDNSSECSupported());
 }
 
 TEST_F(AuthSrvTest, AXFROverUDP) {

src/lib/dns/Makefile.am

@@ -63,6 +63,7 @@ libdns___la_SOURCES += util/binary_from_base32hex.h
 libdns___la_SOURCES += util/base16_from_binary.h util/binary_from_base16.h
 libdns___la_SOURCES += buffer.h
 libdns___la_SOURCES += dnssectime.h dnssectime.cc
+libdns___la_SOURCES += edns.h edns.cc
 libdns___la_SOURCES += exceptions.h exceptions.cc
 libdns___la_SOURCES += util/hex.h
 libdns___la_SOURCES += message.h message.cc

src/lib/dns/edns.cc

+// Copyright (C) 2010  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.
+
+// $Id$
+
+#include <config.h>
+
+#include <stdint.h>
+
+#include <cassert>
+
+#include <boost/lexical_cast.hpp>
+
+#include <exceptions/exceptions.h>
+
+#include <dns/edns.h>
+#include <dns/exceptions.h>
+#include <dns/message.h>
+#include <dns/messagerenderer.h>
+#include <dns/name.h>
+#include <dns/rdata.h>
+#include <dns/rdataclass.h>
+#include <dns/rrclass.h>
+#include <dns/rrttl.h>
+#include <dns/rrtype.h>
+
+using namespace std;
+using namespace boost;
+using namespace isc::dns::rdata;
+
+namespace isc {
+namespace dns {
+
+namespace {
+//           0             7               15                              31
+//          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//          | EXTENDED-RCODE|    VERSION     |D|               Z             |
+//          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//                                          <= VERSION_SHIFT (16 bits)
+//EXTFLAG_DO:0 0 0 ....................... 0 1 0 0 0 0.....................0
+const uint32_t VERSION_MASK = 0x00ff0000;
+const unsigned int VERSION_SHIFT = 16;
+const uint32_t EXTFLAG_DO = 0x00008000;
+
+//     0             7       11                                      31
+//    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//    | EXTENDED-RCODE| RCODE  |                                       |
+//    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//                    <= EXTRCODE_SHIFT
+const uint32_t EXTRCODE_MASK = 0xff000000;
+const unsigned int EXTRCODE_SHIFT = 24;
+}
+
+EDNS::EDNS(const uint8_t version) :
+    version_(version),
+    udp_size_(Message::DEFAULT_MAX_UDPSIZE),
+    dnssec_ok_(false)
+{
+    if (version_ > SUPPORTED_VERSION) {
+        isc_throw(isc::InvalidParameter,
+                  "failed to construct EDNS: unsupported version: " <<
+                  static_cast<unsigned int>(version_));
+    }
+}
+
+EDNS::EDNS(const Name& name, const RRClass& rrclass, const RRType& rrtype,
+           const RRTTL& ttl, const Rdata& rdata UNUSED_PARAM) :
+    version_((ttl.getValue() & VERSION_MASK) >> VERSION_SHIFT)
+{
+    if (rrtype != RRType::OPT()) {
+        isc_throw(isc::InvalidParameter,
+                  "EDNS is being created with incompatible RR type: "
+                  << rrtype);
+    }
+    
+    if (version_ > EDNS::SUPPORTED_VERSION) {
+        isc_throw(DNSMessageBADVERS, "unsupported EDNS version: " <<
+                  static_cast<unsigned int>(version_));
+    }
+
+    if (name != Name::ROOT_NAME()) {
+        isc_throw(DNSMessageFORMERR, "invalid owner name for EDNS OPT RR: " <<
+                  name);
+    }
+
+    dnssec_ok_ = ((ttl.getValue() & EXTFLAG_DO) != 0);
+    udp_size_ = rrclass.getCode();
+}
+
+string
+EDNS::toText() const {
+    string ret = "; EDNS: version: ";
+
+    ret += lexical_cast<string>(static_cast<int>(getVersion()));
+    ret += ", flags:";
+    if (isDNSSECSupported()) {
+        ret += " do";
+    }
+    ret += "; udp: " + lexical_cast<string>(getUDPSize());
+    
+    return (ret);
+}
+
+template <typename Output>
+int
+EDNS::toWire(Output& output, const uint8_t extended_rcode) const {
+    // Render EDNS OPT RR
+    uint32_t extrcode_flags = extended_rcode << EXTRCODE_SHIFT;
+    extrcode_flags |= (version_ << VERSION_SHIFT) & VERSION_MASK;
+    if (dnssec_ok_) {
+        extrcode_flags |= EXTFLAG_DO;
+    }
+
+    // Construct an RRset corresponding to the EDNS.
+    // We don't support any options for now, so the OPT RR can be empty.
+    RRsetPtr edns_rrset = RRsetPtr(new RRset(Name::ROOT_NAME(),
+                                             RRClass(udp_size_), RRType::OPT(),
+                                             RRTTL(extrcode_flags)));
+    edns_rrset->addRdata(ConstRdataPtr(new generic::OPT()));
+
+    edns_rrset->toWire(output);
+
+    return (1);
+}
+
+unsigned int
+EDNS::toWire(MessageRenderer& renderer, const uint8_t extended_rcode) const {
+    // If adding the OPT RR would exceed the size limit, don't do it.
+    // 11 = len(".") + type(2byte) + class(2byte) + TTL(4byte) + RDLEN(2byte)
+    // (RDATA is empty in this simple implementation)
+    if (renderer.getLength() + 11 > renderer.getLengthLimit()) {
+        return (0);
+    }
+
+    return (toWire<MessageRenderer>(renderer, extended_rcode));
+}
+
+unsigned int
+EDNS::toWire(OutputBuffer& buffer, const uint8_t extended_rcode) const {
+    return (toWire<OutputBuffer>(buffer, extended_rcode));
+}
+
+EDNS*
+createEDNSFromRR(const Name& name, const RRClass& rrclass,
+                 const RRType& rrtype, const RRTTL& ttl,
+                 const Rdata& rdata UNUSED_PARAM,
+                 uint8_t& extended_rcode)
+{
+    // Create a new EDNS object first for exception guarantee.
+    EDNS* edns = new EDNS(name, rrclass, rrtype, ttl, rdata);
+
+    // At this point we can update extended_rcode safely.
+    extended_rcode = ttl.getValue() >> EXTRCODE_SHIFT;
+
+    return (edns);
+}
+
+ostream&
+operator<<(std::ostream& os, const EDNS& edns) {
+    os << edns.toText();
+    return (os);
+}
+
+} // end of namespace dns
+} // end of namespace isc

src/lib/dns/edns.h

+// Copyright (C) 2010  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.
+
+// $Id$
+
+#ifndef __EDNS_H
+#define __EDNS_H 1
+
+#include <stdint.h>
+
+#include <boost/shared_ptr.hpp>
+
+#include <ostream>
+
+#include <dns/rdata.h>
+
+namespace isc {
+namespace dns {
+
+class EDNS;
+class Name;
+class MessageRenderer;
+class RRClass;
+class RRTTL;
+class RRType;
+class Rcode;
+
+/// \brief A pointer-like type pointing to an \c EDNS object.
+typedef boost::shared_ptr<EDNS> EDNSPtr;
+typedef boost::shared_ptr<const EDNS> ConstEDNSPtr;
+
+/// Document why this is separated from \c Message.
+///
+/// Stores normalized information: unknown flags will be ignored on
+/// construction.
+///
+/// Decision: separate the knowledge about the relationship with rcode and
+/// the wire format.  EDNS is only responsible for the 8-bit part of the
+/// 12-bit extended RCODE.
+///
+/// note: extended Rcode is handled in the Message class.  We may want to
+/// generalize this by passing the whole Message and letting the \c EDNS
+/// object modify or refer to it based on the EDNS protocol.  But it would
+/// couple the \c Message and \c EDNS more tightly.  Right now, our decision
+/// is to consider \c Rcode is a special case; if a future version of the EDNS
+/// protocol introduces further relationship between the message and the EDNS,
+/// we might reconsider the interface, probably with higher abstraction.
+///
+/// MEMO: performance consideration: toWire() can be optimized by caching
+/// the rendered image and reuse EDNS
+///
+///TBD: how to manage options is an open issue.
+class EDNS {
+public:
+    explicit EDNS(const uint8_t version = SUPPORTED_VERSION);
+
+    EDNS(const Name& name, const RRClass& rrclass, const RRType& rrtype,
+         const RRTTL& ttl, const rdata::Rdata& rdata);
+
+    /// \brief Returns the version of EDNS.
+    uint8_t getVersion() const { return (version_); }
+
+    /// \brief Return the maximum buffer size of UDP messages for the sender
+    /// of the message.
+    uint16_t getUDPSize() const { return (udp_size_); }
+
+    /// \brief Specify the maximum buffer size of UDP messages that use
+    /// this EDNS.
+    ///
+    /// Unless explicitly specified, \c DEFAULT_MAX_UDPSIZE will be assumed
+    /// for the maximum buffer size, regardless of whether EDNS OPT RR is
+    /// included or not.  This means if an application wants to send a message
+    /// with an EDNS OPT RR for specifying a larger UDP size, it must
+    /// explicitly specify the value using this method.
+    void setUDPSize(const uint16_t udp_size) { udp_size_ = udp_size; }
+
+    /// \brief Return whether the message sender indicates DNSSEC is supported.
+    ///
+    /// \return TBD
+    bool isDNSSECSupported() const { return (dnssec_ok_); }
+
+    /// \brief Specify whether DNSSEC is supported in the message.
+    void setDNSSECSupported(const bool on) { dnssec_ok_ = on; }
+
+    // In the current implementation the return value is either 0 or 1, but
+    // the return type is <code>unsigned int</code> to be consistent with
+    // RRset::toWire().  In any case the caller shouldn't assume these are
+    // only possible return values from this method.
+    unsigned int toWire(MessageRenderer& renderer,
+                        const uint8_t extended_rcode) const;
+    unsigned int toWire(OutputBuffer& buffer,
+                        const uint8_t extended_rcode) const;
+
+    /// TBD
+    std::string toText() const;
+
+    // TBD: currently not implemented.
+    void addOption();
+
+private:
+    /// Helper method to define unified implementation for the public versions
+    /// of toWire().
+    template <typename Output>
+    int toWire(Output& output, const uint8_t extended_rcode) const;
+
+public:
+    /// \brief The highest EDNS version this implementation supports.
+    static const uint8_t SUPPORTED_VERSION = 0;
+private:
+    // We may want to use pimpl, especially when we support EDNS options.
+    const uint8_t version_;
+    uint16_t udp_size_;
+    bool dnssec_ok_;
+};
+
+/// \brief Create a new EDNS object from a set of RR parameters, also providing
+/// the extended RCODE value.
+///
+/// Document why this function isn't a constructor.
+/// Document why this function does two things: create an EDNS and adjust
+/// Rcode.
+///
+/// This function provides the strong exception guarantee: Unless an
+/// exception is thrown \c extended_code won't be modified.
+EDNS* createEDNSFromRR(const Name& name, const RRClass& rrclass,
+                       const RRType& rrtype, const RRTTL& ttl,
+                       const rdata::Rdata& rdata,
+                       uint8_t& extended_rcode);
+
+/// Should we define this?
+std::ostream& operator<<(std::ostream& os, const EDNS& edns);
+}
+}
+#endif  // __EDNS_H
+
+// Local Variables: 
+// mode: c++
+// End: 

src/lib/dns/message.cc

@@ -28,6 +28,7 @@
 #include <exceptions/exceptions.h>
 
 #include <dns/buffer.h>
+#include <dns/edns.h>
 #include <dns/exceptions.h>
 #include <dns/message.h>
 #include <dns/messagerenderer.h>
@@ -64,10 +65,7 @@ const flags_t FLAG_CD = 0x0010;
 //
 // EDNS related constants
 //
-const flags_t EXTFLAG_MASK = 0xffff;
-const flags_t EXTFLAG_DO = 0x8000;
 const uint32_t EXTRCODE_MASK = 0xff000000; 
-const uint32_t EDNSVERSION_MASK = 0x00ff0000;
 
 const unsigned int OPCODE_MASK = 0x7800;
 const unsigned int OPCODE_SHIFT = 11;
@@ -167,12 +165,36 @@ Opcode::toText() const {
     return (opcodetext[code_]);
 }
 
-Rcode::Rcode(uint16_t code) : code_(code) {
+namespace {
+//     0     3               11      15
+//    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//    |UNUSED | EXTENDED-RCODE | RCODE |
+//    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//                            <= EXTRCODE_SHIFT
+const unsigned int EXTRCODE_SHIFT = 4;
+}
+
+Rcode::Rcode(const uint16_t code) : code_(code) {
     if (code_ > MAX_RCODE) {
-        isc_throw(OutOfRange, "Rcode is too large to construct");
+        isc_throw(OutOfRange, "Rcode is too large to construct: " << code_);
     }
 }
 
+Rcode::Rcode(const uint8_t code, const uint8_t extended_code) :
+    code_((extended_code << EXTRCODE_SHIFT) | (code & RCODE_MASK))
+{
+    if (code > RCODE_MASK) {
+        isc_throw(OutOfRange,
+                  "Base Rcode is too large to construct: "
+                  << static_cast<unsigned int>(code));
+    }
+}
+
+uint8_t
+Rcode::getExtendedCode() const {
+    return (code_ >> EXTRCODE_SHIFT);
+}
+
 string
 Rcode::toText() const {
     if (code_ < sizeof(rcodetext) / sizeof (const char *)) {
@@ -203,17 +225,13 @@ public:
     Rcode rcode_;
     const Opcode* opcode_;
     flags_t flags_;
-    bool dnssec_ok_;
 
     bool header_parsed_;
     static const unsigned int SECTION_MAX = 4; // TODO: revisit this design
     int counts_[SECTION_MAX];   // TODO: revisit this definition
     vector<QuestionPtr> questions_;
     vector<RRsetPtr> rrsets_[SECTION_MAX];
-    RRsetPtr remote_edns_;
-    uint16_t remote_udpsize_;
-    RRsetPtr local_edns_;
-    uint16_t udpsize_;
+    ConstEDNSPtr edns_;
 
 #ifdef notyet
     // tsig/sig0: TODO
@@ -237,11 +255,7 @@ MessageImpl::init() {
     qid_ = 0;
     rcode_ = Rcode::NOERROR();  // XXX
     opcode_ = NULL;
-    dnssec_ok_ = false;
-    remote_edns_ = RRsetPtr();
-    remote_udpsize_ = Message::DEFAULT_MAX_UDPSIZE;
-    local_edns_ = RRsetPtr();
-    udpsize_ = Message::DEFAULT_MAX_UDPSIZE;
+    edns_ = EDNSPtr();
 
     for (int i = 0; i < SECTION_MAX; ++i) {
         counts_[i] = 0;
@@ -285,38 +299,6 @@ Message::clearHeaderFlag(const MessageFlag& flag) {
     impl_->flags_ &= ~flag.getBit();
 }
 
-bool
-Message::isDNSSECSupported() const {
-    return (impl_->dnssec_ok_);
-}
-
-void
-Message::setDNSSECSupported(bool on) {
-    if (impl_->mode_ != Message::RENDER) {
-        isc_throw(InvalidMessageOperation,
-                  "setDNSSECSupported performed in non-render mode");
-    }
-    impl_->dnssec_ok_ = on;
-}
-
-uint16_t
-Message::getUDPSize() const {
-    return (impl_->udpsize_);
-}
-
-void
-Message::setUDPSize(uint16_t size) {
-    if (impl_->mode_ != Message::RENDER) {
-        isc_throw(InvalidMessageOperation,
-                  "setUDPSize performed in non-render mode");
-    }
-    if (size < DEFAULT_MAX_UDPSIZE) {
-        isc_throw(InvalidMessageUDPSize,
-                  "Specified UDP message size is too small");
-    }
-    impl_->udpsize_ = size;
-}
-
 qid_t
 Message::getQid() const {
     return (impl_->qid_);
@@ -359,6 +341,20 @@ Message::setOpcode(const Opcode& opcode) {
     impl_->opcode_ = &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;
+}
+
 unsigned int
 Message::getRRCount(const Section& section) const {
     return (impl_->counts_[section.getCode()]);
@@ -441,54 +437,6 @@ struct RenderSection {
 };
 }
 
-namespace {
-bool
-addEDNS(MessageImpl* mimpl, MessageRenderer& renderer) {
-    const bool is_query = ((mimpl->flags_ & MessageFlag::QR().getBit()) == 0); 
-
-    // If this is a reply, add EDNS either when the request had it, or
-    // if the Rcode is BADVERS, which is EDNS specific.
-    // XXX: this logic is tricky.  We should revisit this later.
-    if (!is_query) {
-        if (mimpl->remote_edns_ == NULL && mimpl->rcode_ != Rcode::BADVERS()) {
-            return (false);
-        }
-    } else {
-        // For queries, we add EDNS only when necessary:
-        // Local UDP size is not the default value, or
-        // DNSSEC DO bit is to be set, or
-        // Extended Rcode is to be specified.
-        if (mimpl->udpsize_ == Message::DEFAULT_MAX_UDPSIZE &&
-            !mimpl->dnssec_ok_ &&
-            mimpl->rcode_.getCode() < 0x10) {
-            return (false);
-        }
-    }
-
-    // If adding the OPT RR would exceed the size limit, don't do it.
-    // 11 = len(".") + type(2byte) + class(2byte) + TTL(4byte) + RDLEN(2byte)
-    // (RDATA is empty in this simple implementation)
-    if (renderer.getLength() + 11 > renderer.getLengthLimit()) {
-        return (false);
-    }
-
-    // Render EDNS OPT RR
-    uint32_t extrcode_flags = ((mimpl->rcode_.getCode() & 0xff0) << 24);
-    if (mimpl->dnssec_ok_) {
-        extrcode_flags |= 0x8000; // set DO bit
-    }
-    mimpl->local_edns_ = RRsetPtr(new RRset(Name::ROOT_NAME(),
-                                            RRClass(mimpl->udpsize_),
-                                            RRType::OPT(),
-                                            RRTTL(extrcode_flags)));
-    // We don't support any options in this simple implementation
-    mimpl->local_edns_->addRdata(ConstRdataPtr(new generic::OPT()));
-    mimpl->local_edns_->toWire(renderer);
-
-    return (true);
-}
-}
-
 void
 Message::toWire(MessageRenderer& renderer) {
     if (impl_->mode_ != Message::RENDER) {
@@ -528,12 +476,20 @@ Message::toWire(MessageRenderer& renderer) {
                      RenderSection<RRsetPtr>(renderer, false)).getTotalCount();
     }
 
-    // Added EDNS OPT RR if necessary (we want to avoid hardcoding specialized
-    // logic, see the parser case)
-    if (!renderer.isTruncated() && addEDNS(this->impl_, renderer)) {
-        ++arcount;
+    // 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 = this->impl_->edns_;