Target-is

Create a RecordPredicate that returns true only when a record target exactly matches the expected string. Use it when one specific logical source should pass through a filter.

Interface

pub fn target_is(target : String) -> RecordPredicate {}

input

• target : String - Exact target value expected from the record.

output

• RecordPredicate - Predicate that matches records whose rec.target equals target.

Explanation

Detailed rules explaining key parameters and behaviors

• Matching uses direct string equality.
• This helper does not perform prefix or fuzzy matching.
• It is useful for isolating one subsystem when targets are intentionally stable.
• Combine it with level predicates when a single target needs stricter routing rules.

How to Use

Here are some specific examples provided.

When Keep One Exact Target

When only one service target should pass:

let logger = Logger::new(console_sink())
  .with_filter(target_is("gateway.http"))

In this example, records from sibling targets such as gateway.ws are excluded.

When Route A Single Target To A Sink

When a split path needs an exact match:

let predicate = all_of([
  target_is("audit"),
  level_at_least(Level::Info),
])

In this example, the filter remains predictable because it does not rely on naming prefixes.

Error Case

e.g.:

• If target is empty, only records whose target is also an empty string will match.

• If record targets are generated dynamically, exact matching may be too strict and lead to no matches.

Notes

1. Prefer target_has_prefix(...) when targets are hierarchical and you want subtree matching.

2. Exact target filters are easiest to maintain when target naming is stable across the project.