new filter template function, and fix if inside map

[furiel]

Feature

A new filter template function is introduced in syslog-ng. Given a list, it executes a filter expression on each element, keeping only those that satisfy the filter expression. You can use macros, logical expressions, template functions inside the expression.

The current value is referred by $_, similarly to the map template function.

Syntax:

$(filter filter-expression list)

Example

Filtering even numbers:

log {
  source { example-msg-generator(num(1) values(INPUT => "0,1,2,3")); };
  destination {
     file("/dev/stdout"
           template("$(filter ('$(% $_ 2)' eq '0') $INPUT)\n)")
     );
  };
};

results in 0,2.

Bugfix

As context_id-s weren't passed when evaluating FilterExprNodes, if template function could not use $_: it received NULL ("") instead.

For example, these configurations will work after this PR:

log {
  source { example-msg-generator(num(1) values(INPUT => "0,1,2,3")); };
  destination {
     file("/dev/stdout"
           template("$(map $(if ('$(% $_ 2)' eq '0') 'even' 'odd') $INPUT)'\n)")
     );
  };
};

with result: even,odd,even,odd.

Referring: #2926

CC: @jszigetvari

[kira-syslogng]

Build SUCCESS

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build SUCCESS

[kira-syslogng]

Build SUCCESS

[kira-syslogng]

Build SUCCESS