- added detaild documentation

- some more tests
- overall cleanup


git-svn-id: svn://bind10.isc.org/svn/bind10/branches/jinmei-dnsrrset@917 e5f2f494-b856-4b98-b285-d166d9295462

doc/Doxyfile

@@ -568,7 +568,7 @@ WARN_LOGFILE           =
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = ../src/lib/cc/cpp
+INPUT                  = ../src/lib/cc/cpp ../src/lib/dns/cpp
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is

src/lib/dns/cpp/rdata.h

@@ -65,6 +65,7 @@ public:
 
 class Rdata;
 typedef boost::shared_ptr<Rdata> RdataPtr;
+typedef boost::shared_ptr<const Rdata> ConstRdataPtr;
 
 /// Abstract RDATA class
 class Rdata {

src/lib/dns/cpp/rrset.cc

@@ -46,16 +46,20 @@ AbstractRRset::toText() const
     string s;
     RdataIteratorPtr it = getRdataIterator();
 
-    for (it->first(); !it->isLast(); it->next()) {
-        s += getName().toText() + " " +
-            getTTL().toText() + " " +
-            getClass().toText() + " " +
-            getType().toText() + " " +
-            it->getCurrent().toText() + "\n";
+    it->first();
+    if (it->isLast()) {
+        dns_throw(EmptyRRset, "ToText() is attempted for an empty RRset");
     }
 
+    do {
+        s += getName().toText() + " " + getTTL().toText() + " " +
+            getClass().toText() + " " + getType().toText() + " " +
+            it->getCurrent().toText() + "\n";
+        it->next();
+    } while (!it->isLast());
+
     return (s);
-}
+}   
 
 namespace {
 template <typename T>
@@ -65,9 +69,14 @@ rrsetToWire(const AbstractRRset& rrset, T& output)
     unsigned int n = 0;
     RdataIteratorPtr it = rrset.getRdataIterator();
 
+    it->first();
+    if (it->isLast()) {
+        dns_throw(EmptyRRset, "ToWire() is attempted for an empty RRset");
+    }
+
     // sort the set of Rdata based on rrset-order and sortlist, and possible
     // other options.  Details to be considered.
-    for (it->first(); !it->isLast(); it->next(), ++n) {
+    do {
         rrset.getName().toWire(output);
         rrset.getType().toWire(output);
         rrset.getClass().toWire(output);
@@ -77,7 +86,10 @@ rrsetToWire(const AbstractRRset& rrset, T& output)
         output.skip(sizeof(uint16_t)); // leave the space for RDLENGTH
         it->getCurrent().toWire(output);
         output.writeUint16At(output.getLength() - pos - sizeof(uint16_t), pos);
-    }
+
+        it->next();
+        ++n;
+    } while (!it->isLast());
 
     return (n);
 }
@@ -102,7 +114,10 @@ operator<<(ostream& os, const AbstractRRset& rrset)
     return (os);
 }
 
-struct BasicRRsetImpl {
+/// \brief This encapsulates the actual implementation of the \c BasicRRset
+/// class.  It's hidden from applications.
+class BasicRRsetImpl {
+public:
     BasicRRsetImpl(const Name& name, const RRClass& rrclass,
                    const RRType& rrtype, const RRTTL& ttl) :
         name_(name), rrclass_(rrclass), rrtype_(rrtype), ttl_(ttl) {}
@@ -110,7 +125,10 @@ struct BasicRRsetImpl {
     RRClass rrclass_;
     RRType rrtype_;
     RRTTL ttl_;
-    vector<RdataPtr> rdatalist_;
+    // XXX: "list" is not a good name: It in fact isn't a list; more conceptual
+    // name than a data structure name is generally better.  But since this
+    // is only used in the internal implementation we'll live with it.
+    vector<ConstRdataPtr> rdatalist_;
 };
 
 BasicRRset::BasicRRset(const Name& name, const RRClass& rrclass,
@@ -125,11 +143,17 @@ BasicRRset::~BasicRRset()
 }
 
 void
-BasicRRset::addRdata(const RdataPtr rdata)
+BasicRRset::addRdata(ConstRdataPtr rdata)
 {
     impl_->rdatalist_.push_back(rdata);
 }
 
+void
+BasicRRset::addRdata(const Rdata& rdata)
+{
+    AbstractRRset::addRdata(rdata);
+}
+
 unsigned int
 BasicRRset::getRdataCount() const
 {
@@ -160,18 +184,42 @@ BasicRRset::getTTL() const
     return (impl_->ttl_);
 }
 
+void
+BasicRRset::setName(const Name& name)
+{
+    impl_->name_ = name;
+}
+
 void
 BasicRRset::setTTL(const RRTTL& ttl)
 {
     impl_->ttl_ = ttl;
 }
 
+string
+BasicRRset::toText() const
+{
+    return (AbstractRRset::toText());
+}
+
+unsigned int
+BasicRRset::toWire(OutputBuffer& buffer) const
+{
+    return (AbstractRRset::toWire(buffer));
+}
+
+unsigned int
+BasicRRset::toWire(MessageRenderer& renderer) const
+{
+    return (AbstractRRset::toWire(renderer));
+}
+
 namespace {
 class BasicRdataIterator : public RdataIterator {
 private:
     BasicRdataIterator() {}
 public:
-    BasicRdataIterator(const std::vector<rdata::RdataPtr>& datavector) :
+    BasicRdataIterator(const std::vector<rdata::ConstRdataPtr>& datavector) :
         datavector_(&datavector) {}
     ~BasicRdataIterator() {}
     virtual void first() { it_ = datavector_->begin(); }
@@ -179,8 +227,8 @@ public:
     virtual const rdata::Rdata& getCurrent() const { return (**it_); }
     virtual bool isLast() const { return (it_ == datavector_->end()); }
 private:
-    const std::vector<rdata::RdataPtr>* datavector_;
-    std::vector<rdata::RdataPtr>::const_iterator it_;
+    const std::vector<rdata::ConstRdataPtr>* datavector_;
+    std::vector<rdata::ConstRdataPtr>::const_iterator it_;
 };
 }
 

src/lib/dns/cpp/rrset.h

@@ -22,148 +22,657 @@
 
 #include <boost/shared_ptr.hpp>
 
+#include <exceptions/exceptions.h>
+
 #include "rdata.h"
 
 namespace isc {
 namespace dns {
 
+///
+/// \brief A standard DNS module exception that is thrown if an RRset object
+/// does not contain any RDATA where required.
+///
+class EmptyRRset : public Exception {
+public:
+    EmptyRRset(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) {}
+};
+
+// forward declarations
 class Name;
 class RRType;
 class RRClass;
 class RRTTL;
 class OututBuffer;
 class MessageRenderer;
-
 class AbstractRRset;
-typedef boost::shared_ptr<AbstractRRset> RRsetPtr;
 class BasicRRset;
-typedef BasicRRset RRset;
+class RdataIterator;
 class BasicRRsetImpl;
 
-class RdataIterator;
+/// \brief A pointer-like type pointing to an \c AbstractRRset object.
+///
+/// This type is commonly used as an argument of various functions defined
+/// in this library in order to handle RRsets in a polymorphic manner.
+typedef boost::shared_ptr<AbstractRRset> RRsetPtr;
+
+/// \brief A pointer-like type pointing to an (immutable) \c AbstractRRset
+/// object.
+///
+/// This type is commonly used as an argument of various functions defined
+/// in this library in order to handle RRsets in a polymorphic manner.
+typedef boost::shared_ptr<const AbstractRRset> ConstRRsetPtr;
+
+/// \brief A convenient abbreviation for the most generic derived RRset class.
+typedef BasicRRset RRset;
+
+/// \brief A pointer-like type point to an \c RdataIterator object.
 typedef boost::shared_ptr<RdataIterator> RdataIteratorPtr;
 
-/// \brief TBD
+/// \brief The \c AbstractRRset class is an abstract base class that
+/// models a DNS RRset.
 ///
-/// An \c RRset object models an RRset as described in the DNS standard:
-/// a set of DNS resource records (RRs) of the same type and class.
+/// An object of (a specific derived class of) \c AbstractRRset
+/// models an RRset as described in the DNS standard:
+/// A set of DNS resource records (RRs) of the same type and class.
 /// The standard requires the TTL of all RRs in an RRset be the same;
 /// this class follows that requirement.
-/// Note about duplication: we probably don't enforce the RDATA is unique
-/// as a class responsibility - but may revisit the decision.
+
+/// Note about duplicate RDATA: RFC2181 states that it's meaningless that an
+/// RRset contains two identical RRs and that name servers should suppress
+/// such duplicates.
+/// This class is not responsible for ensuring this requirement: For example,
+/// \c addRdata() method doesn't check if there's already RDATA identical
+/// to the one being added.
+/// This is because such checks can be expensive, and it's often easy to
+/// ensure the uniqueness requirement at the %data preparation phase
+/// (e.g. when loading a zone).
+/// When parsing an incoming DNS message, the uniqueness may not be guaranteed,
+/// so the application needs to detect and ignore any duplicate RDATA
+/// (the \c Message class of this library should provide this responsibility).
 ///
-// This is a primary class internally used in our major software such as name
-// servers.
-//
-// Note about terminology: there has been a discussion at the IETF namedroppers
-// ML about RRset vs RRSet (case of "s").  While RFC2181 uses the latter,
-// many other RFCs use the former, and most of the list members who showed
-// their opinion seem to prefer RRset.  We follow that preference in this
-// implementation.
-//
-// Open Issues:
-//   - add more set-like operations, e.g, merge?
-//   - add a "sort" method?  "search(find)" method?
-//   - BIND9 libdns has some special DNSSEC-related methods
-//     such as addnoqname(), addclosest().  do we need these?
-//   - need to check duplicate rdata in addrdata()?
-//   - need a comparison method?  if so, should it compare
-//     rdata's as a set or as a list (compare each rdata one
-//     by one)?  ldns has ldns_rr_list_compare(), which takes
-//     the latter approach (assuming the caller sorts the lists
-//     beforehand?).
-//   - do we need to allow the user to remove specific Rdata?
-///    Looking at the BIND9 code, don't see the strong need for this at the
-///    moment.
+/// Another point to note is that \c AbstractRRset and its derived classes
+/// allow an object to have an empty set of RDATA.
+/// Even though there's no corresponding notion in the protocol specification,
+/// it would be more intuitive for a container-like %data structure
+/// to allow an empty set.
 ///
+/// Since \c AbstractRRset is an abstract class, it is generally used
+/// via a pointer (or pointer like object) or a reference.
+/// In particular, \c RRsetPtr, a pointer like type for \c AbstractRRset,
+/// is used for polymorphic RRset operations throughout this library.
+///
+/// The \c AbstractRRset class is also intended to be a major customization
+/// point.  For example, a high performance server implementation may want
+/// to define an optimized "pre-compiled" RRset and provide an optimized
+/// implementation of the \c toWire() method.
+///
+/// Note about design choice: In BIND9, a set of RDATA with a common tuple
+/// of RR class, RR type, and TTL was represented in a structure named
+/// \c rdataset.  Unlike the RRset classes, an \c rdataset did not contain
+/// the information of the owner name.
+/// This might be advantageous if we want to handle "RRsets", that is,
+/// a set of different types of RRset for the same owner name, because
+/// a single "name" structure can be used for multiple RRsets, minimizing
+/// %data copy and memory footprint.
+/// On the other hand, it's inconvenient for API users since in many cases
+/// a pair of name and an \c rdataset must be maintained.  It's also counter
+/// intuitive in implementing protocol operations as an RRset is often used
+/// as an atomic entity in DNS protocols while an \c rdataset is a component
+/// of an RRset.
+///
+/// We have therefore defined the notion of RRset explicitly in our initial
+/// API design.  We believe memory footprint is not a big concern because
+/// RRsets are generally expected to be used as temporary objects, e.g.
+/// while parsing or constructing a DNS message, or searching a DNS %data
+/// source; for longer term purposes such as in-memory %data source entries,
+/// the corresponding %data would be represented in a different, memory
+/// optimized format.  As for the concern about %data copy, we believe
+/// it can be mitigated by using copy-efficient implementation for the
+/// \c Name class implementation, such as reference counted objects.
+/// Later, We plan to perform benchmark tests later to see if this assumption
+/// is valid and to revisit the design if necessary.
+///
+/// Note about terminology: there has been a discussion at the IETF
+/// namedroppers ML about RRset vs RRSet (case of "s")
+/// [http://ops.ietf.org/lists/namedroppers/namedroppers.2009/msg02737.html].
+/// While RFC2181 uses the latter, many other RFCs use the former,
+/// and most of the list members who showed their opinion seem to prefer
+/// "RRset".  We follow that preference in this implementation.
+///
+/// The current design of \c AbstractRRset is still in flux.
+/// There are many open questions in design details:
+///   - support more set-like operations, e.g, merge two RRsets of the same
+///     type?
+///   - more convenient methods or non member utility functions, e.g.
+///      "sort" and "search(find)" method?
+///   - what about comparing two RRsets of the same type?  If we need this,
+///     should it compare rdata's as a set or as a list (i.e. compare
+///     each %rdata one by one or as a whole)?  c.f. NLnet Labs'
+///     <a href="http://www.nlnetlabs.nl/projects/ldns/doc/index.html">ldns</a>
+///     has \c ldns_rr_list_compare(), which takes the latter approach
+///     (seemingly assuming the caller sorts the lists beforehand).
+///   - BIND9 libdns has some special DNSSEC-related methods
+///     such as \c addnoqname() or \c addclosest().  Do we need these?
+///     (Probably not.  We wouldn't want to make the class design too
+///     monolithic.)
+///   - Do we need to allow the user to remove specific Rdata?
+///     Probably not, according to the current usage of the BIND9 code.
 class AbstractRRset {
+    ///
+    /// \name Constructors and Destructor
+    ///
+    /// Note: The copy constructor and the assignment operator are intentionally
+    /// defined as private to make it explicit that this is a pure base class.
+    //@{
+private:
+    AbstractRRset(const AbstractRRset& source);
+    AbstractRRset& operator=(const AbstractRRset& source);
+protected:
+    /// \brief The default constructor.
+    ///
+    /// This is intentionally defined as \c protected as this base class should
+    /// never be instantiated (except as part of a derived class).
+    AbstractRRset() {}
 public:
+    /// The destructor.
     virtual ~AbstractRRset() {}
-    virtual std::string toText() const;
-    /// Note: perhaps we may want to add more arguments to convey optional
-    /// information such as an "rrset-order" policy.
-    /// no name compression, no truncation
-    virtual unsigned int toWire(OutputBuffer& buffer) const;
-    /// name compression when necessary, taking into account truncation
-    virtual unsigned int toWire(MessageRenderer& renderer) const;
+    //@}
+
+    ///
+    /// \name Getter and Setter Methods
+    ///
+    /// These methods are generally expected to be exception free, but it's
+    /// not guaranteed at the interface level;
+    /// for example, some performance optimized derived class may manage
+    /// the information corresponding to the class "attributes" to get or set,
+    /// and may require dynamic memory allocation to execute the method.
+    /// Consult the derived class description to see if a specific derived
+    /// \c RRset class may throw an exception from these methods.
+    ///
+    /// Note that setter methods are not provided for \c RRClass and
+    /// \c RRType.  This is intentional.  Since the format and semantics of
+    /// \c Rdata are dependent on the RR type (and RR class for some RR types),
+    /// allowing dynamically modify these attributes can easily lead to a
+    /// bug where the RDATA and type and/or class become inconsistent.
+    /// We want to avoid that situation by restricting the access.
+    //@{
+    /// \brief Returns the number of \c Rdata objects contained in the \c RRset.
+    ///
+    /// Note that an \c RRset with an empty set of \c Rdata can exist, so
+    /// this method may return 0.
+    ///
+    /// \return The number of \c Rdata objects contained.
     virtual unsigned int getRdataCount() const = 0;
+
+    /// \brief Returns the owner name of the \c RRset.
+    ///
+    /// \return A reference to a \c Name class object corresponding to the
+    /// \c RRset owner name.
     virtual const Name& getName() const = 0;
+
+    /// \brief Returns the RR Class of the \c RRset.
+    ///
+    /// \return A reference to a \c RRClass class object corresponding to the
+    /// RR class of the \c RRset.
     virtual const RRClass& getClass() const = 0;
+
+    /// \brief Returns the RR Type of the \c RRset.
+    ///
+    /// \return A reference to a \c RRType class object corresponding to the
+    /// RR type of the \c RRset.
     virtual const RRType& getType() const = 0;
+
+    /// \brief Returns the TTL of the RRset.
+    ///
+    /// \return A reference to a \c RRTTL class object corresponding to the
+    /// TTL of the \c RRset.
     virtual const RRTTL& getTTL() const = 0;
+
+    /// \brief Updates the owner name of the \c RRset.
     ///
-    /// once constructed, only TTL and the set of Rdata can be modified,
-    /// so \c setTTL() is the only explicit setter method.
+    /// \param name A reference to a \c RRTTL class object to be copied as the
+    /// new TTL.
+    virtual void setName(const Name& name) = 0;
+
+    /// \brief Updates the TTL of the \c RRset.
     ///
+    /// \param ttl A reference to a \c RRTTL class object to be copied as the
+    /// new TTL.
     virtual void setTTL(const RRTTL& ttl) = 0;
+    //@}
+
+    ///
+    /// \name Converter Methods
+    ///
+    /// These methods have the default implementation that can be reused by
+    /// derived classes.
+    /// Since they are defined as pure virtual, derived classes
+    /// that want to reuse the default implementation must explicitly
+    /// invoke their base class version (see the description for
+    /// <code>addRdata(const rdata::Rdata&)</code>).
+    ///
+    /// Design Note: the default implementations are defined only using
+    /// other public methods of the \c AbstractRRset class, and could be
+    /// implemented as non member functions (as some C++ textbooks suggest).
+    /// However, since derived classes may want to provide customized versions
+    /// (especially of the \c toWire() method for performance reasons)
+    /// we chose to define them as virtual functions, and, as a result,
+    /// member functions.
+    //@{
+    /// \brief Convert the RRset to a string.
+    ///
+    /// Unlike other similar methods of this library, this method terminates
+    /// the resulting string with a trailing newline character.
+    /// (following the BIND9 convention)
+    ///
+    /// The RRset must contain some RDATA; otherwise, an exception of class
+    /// \c EmptyRRset will be thrown.
+    /// If resource allocation fails, a corresponding standard exception
+    /// will be thrown.
+    /// The default implementation may throw other exceptions if the
+    /// \c toText() method of the RDATA objects throws.
+    /// If a derived class of \c AbstractRRset overrides the default
+    /// implementation, the derived version may throw its own exceptions.
+    ///
+    /// Open issue: We may want to support multiple output formats as
+    /// BIND9 does.  For example, we might want to allow omitting the owner
+    /// name when possible in the context of zone dump.  This is a future
+    /// TODO item.
+    ///
+    /// \param rrset A reference to a (derived class of) \c AbstractRRset object
+    /// whose content is to be converted.
+    /// \return A string representation of the RRset.
+    virtual std::string toText() const = 0;
+
+    /// \brief Render the RRset in the wire format with name compression and
+    /// truncation handling.
+    ///
+    /// This method compresses the owner name of the RRset and domain names
+    /// used in RDATA that should be compressed.
+    /// In addition, this method detects the case where rendering the entire
+    /// RRset would cause truncation, and handles the case appropriately
+    /// (this is a TODO item, and not implemented in this version).
+    ///
+    /// Note: perhaps we may want to add more arguments to convey optional
+    /// information such as an "rrset-order" policy or how to handle truncation
+    /// case.  This is a TODO item.
+    ///
+    /// If resource allocation fails, a corresponding standard exception
+    /// will be thrown.
+    /// The RRset must contain some RDATA; otherwise, an exception of class
+    /// \c EmptyRRset will be thrown.
+    /// The default implementation may throw other exceptions if the
+    /// \c toWire() method of the RDATA objects throws.
+    /// If a derived class of \c AbstractRRset overrides the default
+    /// implementation, the derived version may throw its own exceptions.
+    ///
+    /// \param renderer DNS message rendering context that encapsulates the
+    /// output buffer and name compression information.
+    /// \return The number of RRs rendered.  If the truncation is necessary
+    /// this value may be different from the number of RDATA objects contained
+    /// in the RRset.
+    virtual unsigned int toWire(MessageRenderer& renderer) const = 0;
+
+    /// \brief Render the RRset in the wire format without any compression.
+    ///
+    /// See the other toWire() description about possible exceptions.
+    ///
+    /// \param buffer An output buffer to store the wire data.
+    /// \return The number of RRs rendered.
+    virtual unsigned int toWire(OutputBuffer& buffer) const = 0;
+    //@}
+
+    ///
+    /// \name RDATA Manipulation Methods
+    ///
+    //@{
+    /// \brief Add an RDATA to the RRset (pointer version).
+    ///
+    /// This method adds the given RDATA (as a pointer-like type to a
+    /// derived class object of \c rdata::Rdata) to the \c RRset.
+    ///
+    /// \param rdata A pointer (like) type of \c rdata::RdataPtr to be added
+    /// to the \c RRset.
+    virtual void addRdata(rdata::ConstRdataPtr rdata) = 0;
+
+    /// \brief Add an RDATA to the RRset (reference version).
+    ///
+    /// This method adds the given RDATA (as a reference to a
+    /// derived class object of \c rdata::Rdata) to the \c RRset.
+    ///
+    /// This method has the default implementation that can be reused by
+    /// derived classes.
+    /// Since this method is defined as pure virtual, derived classes
+    /// that want to reuse the default implementation must explicitly
+    /// invoke this base class version.
+    /// For example, if the class \c CustomizedRRset, a derived class of
+    /// \c AbstractRRset, wants to reuse the default implementation of
+    /// \c %addRdata() (reference version), it would be defined as follows:
+    /// \code void
+    /// CustomizedRRset::addRdata(const rdata::Rdata& rdata)
+    /// {
+    ///     AbstractRRset::addRdata(rdata);
+    /// }
+    /// \endcode
+    ///
+    /// This method is more strictly typed than the pointer version:
+    /// If \c %rdata does not refer to the appropriate derived
+    /// \c Rdata class
+    /// for the \c RRType for this \c RRset, it throws an exception of class
+    /// \c std::bad_cast.
+    /// If resource allocation fails, a corresponding standard exception
+    /// will be thrown.
+    /// The RRset must contain some RDATA; otherwise, an exception of class
+    /// \c EmptyRRset will be thrown.
+    /// The default implementation may throw other exceptions if the
+    /// \c toWire() method of the RDATA objects throws.
+    /// If a derived class of \c AbstractRRset overrides the default
+    /// implementation, the derived version may throw its own exceptions.
+    ///
+    /// The default implementation simply constructs an \c rdata::RdataPtr
+    /// object from a newly allocated RDATA object copying from parameter
+    /// \c rdata, and calls the other version of
+    /// \c addRdata(const rdata::RdataPtr).
+    /// So it is inherently less efficient than the other version.
+    /// Still, this version would offer a more intuitive interface and is
+    /// provided as such.
+    ///
+    /// \param rdata A reference to a \c rdata::RdataPtr (derived) class
+    /// object, a copy of which is to be added to the \c RRset.
+    virtual void addRdata(const rdata::Rdata& rdata) = 0;
+
+    /// \brief Return an iterator to go through all RDATA stored in the
+    /// \c RRset.
+    ///
+    /// Using the design pattern terminology, \c getRdataIterator()
+    /// is an example of a <em>factory method</em>.
+    ///
+    /// Whether this method throws an exception depends on the actual
+    /// implementation of the derived \c AbstractRRset class, but in general
+    /// it will involve resource allocation and can throw a standard exception
+    /// if it fails.
+    ///
+    /// \return A pointer-like object pointing to the derived \c RdataIterator
+    /// object.
+    virtual RdataIteratorPtr getRdataIterator() const = 0;
+    //@}
+};
+
+/// \brief The \c RdataIterator class is an abstract base class that
+/// provides an interface for accessing RDATA objects stored in an RRset.
+///
+/// While different derived classes of \c AbstractRRset may maintain the RDATA
+/// objects in different ways, the \c RdataIterator class provides a
+/// unified interface to iterate over the RDATA objects in a polymorphic
+/// manner.
+///
+/// Each derived class of \c AbstractRRset is expected to provide a concrete
+/// derived class of \c RdataIterator, and each derived \c RdataIterator
+/// class implements the unified interface in a way specific to the
+/// implementation of the corresponding derived \c AbstractRRset class.
+/// Using the design pattern terminology, this is a typical example of
+/// the \e Iterator pattern.
+///
+/// The RDATA objects stored in the \c RRset are considered to form
+/// a unidirectional list from the \c RdataIterator point of view (while
+/// the actual implementation in the derived \c RRset may not use a list).
+/// We call this unidirectional list the <em>%rdata list</em>.
+///
+/// An \c RdataIterator object internally (and conceptually) holds a
+/// <em>%rdata cursor</em>, which points to a specific item of the %rdata list.
+///
+/// Note about design choice: as is clear from the interface, \c RdataIterator
+/// is not compatible with the standard iterator classes.
+/// Although it would be useful (for example, we could then use STL algorithms)
+/// and is not necessarily impossible, it would make the iterator implementation
+/// much more complicated.
+/// For instance, any standard iterator must be assignable and
+/// copy-constructible.
+/// So we'd need to implement \c RdataIterator::operator=() in a polymorphic
+/// way.  This will require non-trivial implementation tricks.
+/// We believe the simplified iterator interface as provided by the
+/// \c RdataIterator class is sufficient in practice:
+/// Most applications will simply go through the RDATA objects contained in
+/// an RRset, examining (and possibly using) each object, as one path
+/// operation.
+class RdataIterator {
+    ///
+    /// \name Constructors and Destructor
+    ///
+    /// Note: The copy constructor and the assignment operator are intentionally
+    /// defined as private to make it explicit that this is a pure base class.
+    //@{
+protected:
+    /// \brief The default constructor.
+    ///
+    /// This is intentionally defined as \c protected as this base class should
+    /// never be instantiated (except as part of a derived class).
+    RdataIterator() {}
+public:
+    /// \brief Destructor
+    virtual ~RdataIterator() {}
+private:
+    RdataIterator(const RdataIterator& source);
+    RdataIterator& operator=(const RdataIterator& source);
+    //@}
+
+public:
+    /// \brief Move the %rdata cursor to the first RDATA in the %rdata list
+    /// (if any).
+    ///
+    /// This method can safely be called multiple times, even after moving
+    /// the %rdata cursor forward by the \c next() method.
+    ///
+    /// This method should never throw an exception.
+    virtual void first() = 0;
+
+    /// \brief Move the %rdata cursor to the next RDATA in the %rdata list
+    /// (if any).
+    ///
+    /// This method should never throw an exception.
+    virtual void next() = 0;
+
+    /// \brief Return the current \c Rdata corresponding to the %rdata cursor.
+    ///
+    /// \return A reference to an \c rdata::::Rdata object corresponding
+    /// to the %rdata cursor.
+    virtual const rdata::Rdata& getCurrent() const = 0;
+
+    /// \brief Return true iff the %rdata cursor has reached the end of the
+    /// %rdata list.
+    ///
+    /// Once this method returns \c true, the behavior of any subsequent
+    /// call to \c next() or \c getCurrent() is undefined.
+    /// Likewise, the result of \c isLast() call followed by such undefined
+    /// operations is also undefined.
+    ///
+    /// This method should never throw an exception.
+    ///
+    /// \return \c true if the %rdata cursor has reached the end of the
+    /// %rdata list; otherwise \c false.
+    virtual bool isLast() const = 0;
+};
+
+/// \brief The \c BasicRRset class is a concrete derived class of
+/// \c AbstractRRset that defines a straightforward RRset implementation.
+///
+/// designed to be as portable as possible.  performance is a secondary
+/// concern for this class.
+///
+/// We'd use the default implementations for the toWire()
+/// variants as defined in the base class.  These are not fully optimized
+/// for performance, but, again, it's a secondary goal for this generic
+/// class.
+class BasicRRset : public AbstractRRset {
+    ///
+    /// \name Constructors and Destructor
+    ///
+    /// Note: The copy constructor and the assignment operator are intentionally
+    /// defined as private.  The intended use case wouldn't require copies of
+    /// a \c BasicRRset object; once created, it would normally be used
+    /// as a \c const object (via references).
+    //@{
+private:
+    BasicRRset(const BasicRRset& source);
+    BasicRRset& operator=(const BasicRRset& source);
+public:
+    /// \brief Constructor from (mostly) fixed parameters of the RRset.
+    ///
+    /// This constructor is normally expected to be exception free, but
+    /// copying the name may involve resource allocation, and if it fails
+    /// the corresponding standard exception will be thrown.
+    ///
+    /// \param name The owner name of the RRset.
+    /// \param rrclass The RR class of the RRset.
+    /// \param rrtype The RR type of the RRset.
+    /// \param ttl The TTL of the RRset.
+    explicit BasicRRset(const Name& name, const RRClass& rrclass,
+                        const RRType& rrtype, const RRTTL& ttl);
+    /// \brief The destructor.
+    virtual ~BasicRRset();
+    //@}
+
+    ///
+    /// \name Getter and Setter Methods
+    ///
+    //@{
+    /// \brief Returns the number of \c Rdata objects contained in the \c RRset.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return The number of \c Rdata objects contained.
+    virtual unsigned int getRdataCount() const;
+
+    /// \brief Returns the owner name of the \c RRset.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return A reference to a \c Name class object corresponding to the
+    /// \c RRset owner name.
+    virtual const Name& getName() const;
+
+    /// \brief Returns the RR Class of the \c RRset.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return A reference to a \c RRClass class object corresponding to the
+    /// RR class of the \c RRset.
+    virtual const RRClass& getClass() const;
+
+    /// \brief Returns the RR Type of the \c RRset.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return A reference to a \c RRType class object corresponding to the
+    /// RR type of the \c RRset.
+    virtual const RRType& getType() const;
+
+    /// \brief Returns the TTL of the \c RRset.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return A reference to a \c RRTTL class object corresponding to the
+    /// TTL of the \c RRset.
+    virtual const RRTTL& getTTL() const;
+
+    /// \brief Updates the owner name of the \c RRset.
+    ///
+    /// This method normally does not throw an exception, but could throw
+    /// some standard exception on resource allocation failure if the
+    /// internal copy of the \c name involves resource allocation and it
+    /// fails.
+    ///
+    /// \param name A reference to a \c RRTTL class object to be copied as the
+    /// new TTL.
+    virtual void setName(const Name& name);
+
+    /// \brief Updates the TTL of the \c RRset.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \param ttl A reference to a \c RRTTL class object to be copied as the
+    /// new TTL.
+    virtual void setTTL(const RRTTL& ttl);
+    //@}
+
+    ///
+    /// \name Converter Methods
+    ///
+    //@{
+    /// \brief Convert the RRset to a string.
+    ///
+    /// This method simply uses the default implementation.
+    /// See \c AbstractRRset::toText().
+    virtual std::string toText() const;
+
+    /// \brief Render the RRset in the wire format with name compression and
+    /// truncation handling.
+    ///
+    /// This method simply uses the default implementation.
+    /// See \c AbstractRRset::toWire(MessageRenderer&)const.
+    virtual unsigned int toWire(MessageRenderer& renderer) const;
+
+    /// \brief Render the RRset in the wire format without any compression.
+    ///
+    /// This method simply uses the default implementation.
+    /// See \c AbstractRRset::toWire(OutputBuffer&)const.
+    virtual unsigned int toWire(OutputBuffer& buffer) const;
+    //@}
 
     ///
     /// \name RDATA manipulation methods
     ///
     //@{
-    virtual void addRdata(const rdata::RdataPtr rdata) = 0;
-    /// This method has the default implementation.
-    /// Note: since concrete classes would define the pure virtual version
-    /// of \c addRdata(), they'll need to declare the use of this method
-    /// to avoid name hiding (unless they redefine this method):
-    /// \code class CustomizedRRset : public AbstractRRset {
-    /// public:
-    ///     using AbstractRRset::addRdata;
-    ///     ...
-    /// }; \endcode
+    /// \brief Add an RDATA to the RRset (pointer version).
+    ///
+    /// This method is normally expected to be exception free, but it may
+    /// involve resource allocation, and if it fails the corresponding
+    /// standard exception will be thrown.
+    ///
+    /// \param rdata A pointer (like) type of \c rdata::RdataPtr to be added
+    /// to the \c BasicRRset.
+    virtual void addRdata(rdata::ConstRdataPtr rdata);
+
+    /// \brief Add an RDATA to the RRset (reference version).
+    ///
+    /// This method simply uses the default implementation.
+    /// See \c AbstractRRset::addRdata(const rdata::Rdata&).
     virtual void addRdata(const rdata::Rdata& rdata);
-    virtual RdataIteratorPtr getRdataIterator() const = 0;
-    //@}
-};
 
-class RdataIterator {
-public:
-    virtual ~RdataIterator() {}
-    virtual void first() = 0;
-    virtual void next() = 0;
-    virtual const rdata::Rdata& getCurrent() const = 0;
-    virtual bool isLast() const = 0;
-};
-
-/// Straightforward RRset implementation.
-/// designed to be as portable as possible.  performance is a secondary
-/// concern for this class.
-class BasicRRset : public AbstractRRset {
-private:
-    BasicRRset(const BasicRRset& source);
-    void operator=(const BasicRRset& source);
-public:
-    explicit BasicRRset(const Name& name, const RRClass& rrclass,
-                        const RRType& rrtype, const RRTTL& ttl);
-    virtual ~BasicRRset();
+    /// \brief Return an iterator to go through all RDATA stored in the
+    /// \c BasicRRset.
     ///
-    /// See the note for the base class version.
+    /// This is a concrete derived implementation of
+    /// \c AbstractRRset::getRdataIterator().
     ///
-    using AbstractRRset::addRdata;
-    virtual void addRdata(const rdata::RdataPtr rdata);
-    ///
-    /// We'd use the default implementations for toText() and toWire()
-    /// variants as defined in the base class.  These are not fully optimized
-    /// for performance, but, again, it's a secondary goal for this generic
-    /// class.
-
-    ///
-    /// \name Getter and setter methods
-    ///
-    //@{
-    virtual unsigned int getRdataCount() const;
-    virtual const Name& getName() const;
-    virtual const RRClass& getClass() const;
-    virtual const RRType& getType() const;
-    virtual const RRTTL& getTTL() const;
-    virtual void setTTL(const RRTTL& ttl);
-    //@}
+    /// This method dynamically allocates resources.  If it fails it will
+    /// throw the corresponding standard exception.
+    /// The iterator methods for the \c BasicRRset class are exception free.
     ///
+    /// \return A pointer-like object pointing to the derived \c RdataIterator
+    /// object for the \c BasicRRset class.
     virtual RdataIteratorPtr getRdataIterator() const;
+    //@}
 private:
     BasicRRsetImpl* impl_;
 };
 
+/// \brief Insert the \c RRset as a string into stream.
+///
+/// This method convert the \c rrset into a string and inserts it into the
+/// output stream \c os.
+///
+/// This function overloads the global \c operator<< to behave as described in
+/// \c %ostream::%operator<< but applied to RRset objects.
+///
+/// \param os A \c std::ostream object on which the insertion operation is
+/// performed.
+/// \param rrset A reference to a (derived class of) \c AbstractRRset object
+/// output by the operation.
+/// \return A reference to the same \c std::ostream object referenced by
+/// parameter \c os after the insertion operation.
 std::ostream& operator<<(std::ostream& os, const AbstractRRset& rrset);
 } // end of namespace dns
 } // end of namespace isc

src/lib/dns/cpp/rrset_unittest.cc

@@ -168,6 +168,17 @@ TEST_F(RRsetTest, iterator)
     rrset_a_empty.addRdata(in::A("192.0.2.1"));
     rrset_a_empty.addRdata(in::A("192.0.2.2"));
     addRdataTestCommon(rrset_a_empty);
+
+    // Rewind test: should be repeat the iteration by calling first().
+    for (int i = 0; i < 2; ++i) {
+        it = rrset_a_empty.getRdataIterator();
+        it->first();
+        EXPECT_FALSE(it->isLast());
+        it->next();
+        EXPECT_FALSE(it->isLast());
+        it->next();
+        EXPECT_TRUE(it->isLast());
+    }
 }
 
 TEST_F(RRsetTest, toText)
@@ -175,6 +186,9 @@ TEST_F(RRsetTest, toText)
     EXPECT_EQ("test.example.com. 3600 IN A 192.0.2.1\n"
               "test.example.com. 3600 IN A 192.0.2.2\n",
               rrset_a.toText());
+
+    // toText() cannot be performed for an empty RRset.
+    EXPECT_THROW(rrset_a_empty.toText(), EmptyRRset);
 }
 
 TEST_F(RRsetTest, toWireBuffer)
@@ -184,6 +198,10 @@ TEST_F(RRsetTest, toWireBuffer)
     UnitTestUtil::readWireData("testdata/rrset_toWire1", wiredata);
     EXPECT_PRED_FORMAT4(UnitTestUtil::matchWireData, buffer.getData(),
                         buffer.getLength(), &wiredata[0], wiredata.size());
+
+    // toWire() cannot be performed for an empty RRset.
+    buffer.clear();
+    EXPECT_THROW(rrset_a_empty.toWire(buffer), EmptyRRset);
 }
 
 TEST_F(RRsetTest, toWireRenderer)
@@ -196,6 +214,10 @@ TEST_F(RRsetTest, toWireRenderer)
     UnitTestUtil::readWireData("testdata/rrset_toWire2", wiredata);
     EXPECT_PRED_FORMAT4(UnitTestUtil::matchWireData, buffer.getData(),
                         buffer.getLength(), &wiredata[0], wiredata.size());
+
+    // toWire() cannot be performed for an empty RRset.
+    renderer.clear();
+    EXPECT_THROW(rrset_a_empty.toWire(renderer), EmptyRRset);
 }
 
 // test operator<<.  We simply confirm it appends the result of toText().