[2383] Header of the Name constructor for parser

The master file parser will need a special Name constructor for
reasonable performance and for convenience/clarity of its code.
Introduce the header for the constructor, a new exception for it and
documentation.

src/lib/dns/name.h

@@ -105,6 +105,17 @@ public:
         NameParserException(file, line, what) {}
 };
 
+/// \brief Thrown when origin is NULL and is needed.
+///
+/// The exception is thrown when the Name constructor for master file
+/// is used, the provided data is relative and the origin parameter is
+/// set to NULL.
+class MissingNameOrigin : public NameParserException {
+public:
+    MissingNameOrigin(const char* file, size_t line, const char* what) :
+        NameParserException(file, line, what) {}
+};
+
 ///
 /// This is a supplemental class used only as a return value of
 /// Name::compare() and LabelSequence::compare().
@@ -261,6 +272,37 @@ public:
     /// \param namestr A string representation of the name to be constructed.
     /// \param downcase Whether to convert upper case alphabets to lower case.
     explicit Name(const std::string& namestr, bool downcase = false);
+
+    /// \brief Constructor for master file parser
+    ///
+    /// This acts similar to the above. But the data is passed as raw C-string
+    /// instead of wrapped-up C++ std::string.
+    ///
+    /// Also, when the origin is non-NULL and the name_data is not ending with
+    /// a dot, it is considered relative and the origin is appended to it.
+    ///
+    /// If the name_data is equal to "@", the content of origin is copied.
+    ///
+    /// \param name_data The raw data of the name.
+    /// \param data_len How many bytes in name_data is valid and considered
+    ///     part of the name.
+    /// \param origin If non-NULL, it is taken as the origin to complete
+    ///     relative names.
+    /// \param downcase Whether to convert upper case letters to lower case.
+    /// \throw NameParserException or any of its descendants in case the
+    ///     input data is invalid.
+    /// \throw isc::InvalidParameter In case name_data is NULL or data_len is
+    ///     0.
+    /// \throw std::bad_alloc In case allocation fails.
+    /// \note This constructor is specially designed for the use of master
+    ///     file parser. It mimics the behaviour of names in the master file
+    ///     and accepts raw data. It is not recommended to be used by anything
+    ///     else.
+    /// \todo Should we make it private and the parser a friend, to hide the
+    ///     constructor?
+    Name(const char* name_data, size_t data_len, const Name* origin,
+         bool downcase = false);
+
     /// Constructor from wire-format %data.
     ///
     /// The \c buffer parameter normally stores a complete DNS message