Combining filters in boost log

Question

I use boost log and want to define a composed filter. I use boost::log::init_from_streamto read the configuration from a stream. Filtering on single conditions works fine. I can do

Filter = "%Channel% = A"

to get only log entries from channel A. I can do

Filter = "%Severity% >= warn"

to get only log entries that have a severity which is warning or above.

Here comes the question: I want to do someting like

Filter = "   (%Channel% = A AND %Severity% >= warn)
          OR (%Channel% = B AND %Severity% >= info)"

I was not able to find any documentation regarding such a combination of filters. Is there a way to do this when using boost::log::init_from_stream?

Answer 1

I've found this documentation page which documents the grammar:

• Filter and formatter parsers

  filter:
      condition { op condition }
  
  op:
      &
      and
      |
      or
  
  condition:
      !condition
      not condition
      (filter)
      %attribute_name%
      %attribute_name% relation operand
  
  relation:
      >
      <
      =
      !=
      >=
      <=
      begins_with
      ends_with
      contains
      matches
  

Using this, the example given in the question can be expressed as follows:

Filter = "(%Channel% = A & %Severity% >= warn) | (%Channel% = B & %Severity% >= info)"