BIND 10 #2369: InputSource helper class for MasterLexer

[BIND 10 Development]

#2369: InputSource helper class for MasterLexer
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |  UnAssigned
            Priority:  medium        |                       Status:  new
           Component:  libdns++      |                    Milestone:  New
           Sensitive:  0             |  Tasks
         Sub-Project:  DNS           |                     Keywords:
Estimated Difficulty:  0             |              Defect Severity:  N/A
         Total Hours:  0             |  Feature Depending on Ticket:
                                     |  loadzone-ng
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 Subtask of #2368, no dependency.

 This is a helper internal class for `MasterLexer`, and represents
 state of a single source of the entire zone data to be parsed.
 Normally this means the master zone file, but `MasterLexer` can
 have multiple `InputSource`s if $INCLUDE is used.  The source can
 also be generic input stream (std::istream).

 This is a port of BIND 9's lib/isc/lex.c:inputsource{}, but is defined
 as a separate class to improve data integrity and testability.
 It's essentially private to `MasterLexer`, but we'll define it in
 a semi-public header file (not installed) so tests can directly refer
 to the definition.  To clarify it's not really public, define it some
 specific sub-namespace, like master_lexer_internal.

 A tentative class definition is:

 {{{#!cpp
 namespace master_lexer_internal {
 class InputSource {
 public:
     InputSource(std::istream& input, const std::string& name);

     // if buffer_ is empty, read 1 byte from input_, push_back it to
 buffer_.
     // extract c = buffer_[buffer_pos_], ++buffer_pos_, return c.
     // EOF case is a bit tricky.  See BIND 9's lex.c.
     int getNextChar();

     // "forget" the most recent character, c (decrease buffer_pos_ by 1).
     // doesn't touch buffer_.  if c == EOF, just reset at_eof_ to false.
     // if c == '\n' decrease line_ by 1.
     void ungetChar(int c);

     // "forget" everything in the buffer_.  set buffer_pos_ to 0.
     // doesn't touch buffer_. set at_eof to false. line_ = saved_line_.
     void ungetAll();

     bool isAtEOF() const { return (at_eof_); }

     size_t getCurrentLine() const { return (line_); }

     void saveLine() { saved_line_ = line_; }

     const std::string name_;          // filename or "stream-%p"

 private:
     size_t line_;               // current line number in this source
 (file)
     size_t saved_line_; // lexer save line_ when it starts using the
 source
     bool at_eof_; // set to true if lexer reaches the "end of file" of
 this src
     std::istream& input_;       // given via the constructor

     // temporary copy of data read from input_
     vector<char> buffer_;

     // normally == buffer_.size(), but can be smaller if ungetChar() or
     // ungetAll() is called.
     size_t buffer_pos_;
 };
 }
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/2369>
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