BIND 10 #1071: introduce "null" output for logs

[BIND 10 Development]

#1071: introduce "null" output for logs
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                   Reporter:         |                 Owner:  vorner
  jinmei                             |                Status:  reviewing
                       Type:  task   |             Milestone:
                   Priority:  major  |  Sprint-20110712
                  Component:         |            Resolution:
  logging                            |             Sensitive:  0
                   Keywords:         |           Sub-Project:  DNS
            Defect Severity:  N/A    |  Estimated Difficulty:  0.0
Feature Depending on Ticket:         |           Total Hours:  0
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Changes (by stephen):

 * owner:  stephen => vorner


Comment:

 > I don't know if I look correctly, but this seems to be more setting-up
 of logging options through environment variables. There seems to be no
 code regarding any null output. Do I look at a wrong branch or is it
 related in some way I don't see?
 It adds B10_LOGGER_DESTINATION.  Setting that to /dev/null will route the
 output to the null device.  I've added some text to
 [wiki:LoggingCppApiDesign] to describe this and will post a message to
 bind10-dev prior to committing #1024 to explain it.

 > This doesn't seem to be completely true (the part about "as is", the %1,
 etc are replaced): The rest of the line - from the first non-space
 character to the last non-space character - is taken exactly as-is for the
 text of the message.
 I've combined this paragraph and the succeeding one (that talks about the
 replacement tokens); does this remove the ambiguity?

 > "The main program unit should include a call to isc.log.init()" ‒
 wouldn't "must" be better?
 Yes - changed.

 > Is this a typo or word I don't know? "Checks that the logger will limit
 the output of messages less _severy_ than"?
 Typo - changed. (And updated test descriptions.)

 > In the tests, when the output is routed to stdout or stderr, wouldn't it
 be better to use a single pipeline instead of (slower and more error
 prone) store-to-file and load again? Like this?:
 > B10_LOGGER_SEVERITY=WARN ./init_logger_test 2>&1 | cut -d' ' -f3- | diff
 $tempfile -
 Where appropriate the tests have been changed to use this construct.

 > Also, this looks really strange. Why is the "1" there?
 > ./init_logger_test 1> $destfile
 For symmetry: the following test a few lines down routes output to stderr
 (and so contains a "2>").  The "1>" is meant to emphasise the difference.

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Ticket URL: <https://bind10.isc.org/ticket/1071#comment:8>
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