Struct KeyFilter 

pub struct KeyFilter<T> { /* private fields */ }

KeyFilter is wrapper from Filter, with one additional key into log format.

The name of the key can be customized.

Example for an http service, api handling log will have a field req_id. When you received error from one of the request, you can grep all the relevant log with that req_id.

use captains_log::{*, filter::{LogFilter, KeyFilter}};
use std::sync::Arc;
fn debug_format_req_id_f(r: FormatRecord) -> String {
    let time = r.time();
    let level = r.level();
    let file = r.file();
    let line = r.line();
    let msg = r.msg();
    let req_id = r.key("req_id");
    format!("[{time}][{level}][{file}:{line}] {msg}{req_id}\n").to_string()
}
let builder = recipe::raw_file_logger_custom(
                "/tmp/log_filter.log", log::Level::Debug,
                recipe::DEFAULT_TIME, debug_format_req_id_f)
    .build().expect("setup log");

// Wrapping and Arc
let filter = Arc::new(LogFilter::new());
let logger = KeyFilter::with(filter.clone(), "req_id", format!("{:016x}", 123).to_string());
info!("API service started");
logger_debug!(logger, "Req / received");
logger_debug!(logger, "header xxx");
logger_info!(logger, "Req / 200 complete");

The log will be:

[2025-06-11 14:33:08.089090][DEBUG][request.rs:67] API service started
[2025-06-11 14:33:10.099092][DEBUG][request.rs:67] Req / received (000000000000007b)
[2025-06-11 14:33:10.099232][WARN][request.rs:68] header xxx (000000000000007b)
[2025-06-11 14:33:11.009092][DEBUG][request.rs:67] Req / 200 complete (000000000000007b)

Using reference:

use captains_log::{*, filter::{LogFilter, KeyFilter}};
let filter = LogFilter::new();
let logger = KeyFilter::with(&filter, "req_id", format!("{:016x}", 123).to_string());
logger_debug!(logger, "Req / received");

Implementations

impl<T> KeyFilter<T>

pub fn with(inner: T, key: &'static str, value: String) -> Self

impl KeyFilter<DummyFilter>

pub fn new(key: &'static str, value: String) -> Self

Trait Implementations

impl<T: Clone> Clone for KeyFilter<T>

fn clone(&self) -> KeyFilter<T>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Filter> Filter for KeyFilter<T>

fn is_enabled(&self, level: Level) -> bool

whether a log level is enable

impl<T> Source for KeyFilter<T>

fn visit<'kvs>(&'kvs self, visitor: &mut dyn Visitor<'kvs>) -> Result<(), Error>

Visit key-values.

fn get<'a>(&'a self, key: Key<'_>) -> Option<Value<'a>>

Get the value for a given key.

fn count(&self) -> usize

Count the number of key-values that can be visited.