BIND 10 #2369: InputSource helper class for MasterLexer

[BIND 10 Development]

#2369: InputSource helper class for MasterLexer
-------------------------------------+-------------------------------------
                   Reporter:         |                 Owner:  muks
  jinmei                             |                Status:  reviewing
                       Type:  task   |             Milestone:
                   Priority:         |  Sprint-20121106
  medium                             |            Resolution:
                  Component:         |             Sensitive:  0
  libdns++                           |           Sub-Project:  DNS
                   Keywords:         |  Estimated Difficulty:  4
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
  loadzone-ng                        |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
-------------------------------------+-------------------------------------

Comment (by muks):

 Hi Jinmei

 Replying to [comment:16 jinmei]:
 > In my attempt of integrating this branch into #2371, I noticed a few
 > more things:
 >
 > - I suggest including what's wrong when throwing OpenError:
 > {{{#!cpp
 >         isc_throw(OpenError,
 >                   "Error opening the input source file: " << filename);
 > }}}
 >   "no such file", "permission denied", etc.
 > - if not super hard, I'd test a different failure case for `OpenError`
 >   like it's not readable (due to permission or possible some other
 >   reason)

 I'd like to do these two, and return the appropriate error, but I could
 not find a way of getting such messages from fstream. It's possible to
 make fstream throw an exception by setting the exception bits, but the
 description (`ex.what()`) contains a weird message "basic_ios::clear". We
 can alternatively check `stat()` output, but it's better to get a proper
 error from fstream if it's possible.

 > - In `InputSource::getChar` variables `c` should become const.  Also
 >   check other possible cases where you can make them const.

 Done. :)

-- 
Ticket URL: <http://bind10.isc.org/ticket/2369#comment:19>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development