Allow for filtered logging using onRecord()

[DartBot]

This issue was originally filed by @stevenroose

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The Logger class from the logging package has an onRecord getter that gives the stream of logrecords. However, often users want only logs from a certain level and up. Currently that is possible by doing the filtering yourself like this:

  myLogger.onRecord.where((LogRecord logRecord) => logRecord.level >= filterLevel).listen(loggerHandler);

Java's java.util.logging has filtered handlers built in to make this easy, but Dart does not.

I suggest to change the onRecord getter to a method that allows you to specify a level on which to filter records]. It works like this:

  myLogger.onRecord(filterLevel).listen(loggerHandler);

In attachment is a patch with this change and the required changes to the unit tests.

I know this is a breaking change, so it requires a new version. An alternative might be to introduce an additional method for this change, but I think using onRecord for this purpose is more suitable.

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Attachment:
logging-filtering.diff (4.97 KB)

[DartBot]

This comment was originally written by @stevenroose

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An alternative solution would be to let onRecord return a FilterableLogRecordStream that extends Stream but also has a getter for each loglevel, so that it would look like this:

  myLogger.onRecord.filter(Level.WARNING).listen(loggerHandler);

or

  myLogger.onRecord.warning.listen(loggerHandler);

I added implementation for this change as a patch.

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Attachment:
logging-filteredstream.diff (4.86 KB)

[iposva-google]

Added Pkg-Logging, Area-Pkg, Triaged labels.

[DartBot]

This issue has been moved to dart-lang/logging#21.