log levels: Trace, Debug, Info, Warn, Error
日志级别：Trace、Debug、Info、Warn、Error
structured key-value fields
结构化字段：field("key", "value")
sink abstraction
sink 抽象与组合边界
default global console logger
默认全局 logger 辅助函数
context fields via with_context_fields(...)
通过 with_context_fields(...) 添加上下文字段
child target composition via child(...)
通过 child(...) 组合层级 target
optional timestamps via with_timestamp()
通过 with_timestamp() 启用时间戳
JSON console output via json_console_sink()
json_console_sink() 提供 JSON 控制台输出
sink composition via fanout_sink(...)
fanout_sink(...) 支持多 sink 组合
sink routing via split_sink(...) and split_by_level(...)
split_sink(...)、split_by_level(...) 支持按谓词或 level 将日志路由到不同 sink
custom callback sink via callback_sink(...)
callback_sink(...) 支持自定义外部集成
buffered sink via buffered_sink(...)
buffered_sink(...) 支持内存缓冲与 flush
filter sink via filter_sink(...)
filter_sink(...) 支持按 Record 条件筛选输出
reusable filter helpers such as target_has_prefix(...), message_contains(...), and field_equals(...)
提供 target_has_prefix(...)、message_contains(...)、field_equals(...) 等可复用过滤辅助函数
record patching via with_patch(...) and patch_sink(...)
支持 with_patch(...)、patch_sink(...) 以及常见 record patch helper
context binding via bind(...) and fields(...)
支持 bind(...)、fields(...)，更顺手地封装上下文字段
explicit queued delivery via queued_sink(...) and with_queue(...)
支持 queued_sink(...)、with_queue(...)、有界积压与溢出策略
configurable text formatting via text_formatter(...), format_text(...), text_console_sink(...), and template-driven template output
支持 text_formatter(...)、format_text(...)、text_console_sink(...) 以及模板化 template 文本输出
JSON config parsing via parse_logger_config_text(...) and stringify_logger_config(...)
支持 parse_logger_config_text(...)、stringify_logger_config(...) 进行最小 JSON 配置读写
config-driven logger assembly via build_logger(...)
支持 build_logger(...) 将配置组装为可直接使用的 logger
native-only file output via file_sink(...), with basic size rotation, backup retention, explicit reopen(), and failure counters
支持 file_sink(...)、基础 size rotation / backup retention、显式 reopen() 与失败计数，但当前仅保证 native/llvm backend 可用

Example / 示例

test {
  let logger = Logger::new(console_sink(), min_level=Level::Debug, target="demo")
    .with_timestamp()
  logger.info("starting", fields=[field("port", "8080")])
}

test {
  let logger = Logger::new(console_sink(), target="app").child("worker")
  logger.info("ready")
}

test {
  let logger = Logger::new(
    fanout_sink(console_sink(), json_console_sink()),
    min_level=Level::Info,
    target="demo",
  )
  logger.info("ready", fields=[field("mode", "fanout")])
}

test {
  let logger = Logger::new(
    callback_sink(fn(rec) {
      println("callback saw [\{rec.target}] \{rec.message}")
    }),
    target="hook",
  )
  logger.info("hello")
}

test {
  let sink = buffered_sink(console_sink(), flush_limit=2)
  let logger = Logger::new(sink, target="buffered")
  logger.info("one")
  logger.info("two")
  sink.flush()
}

test {
  let sink = filter_sink(console_sink(), fn(rec) {
    rec.target == "kept"
  })
  let kept = Logger::new(sink, target="kept")
  let dropped = Logger::new(sink, target="dropped")
  kept.info("visible")
  dropped.info("hidden")
}

test {
  let logger = Logger::new(console_sink(), target="service")
    .with_filter(all_of([
      target_has_prefix("service"),
      message_contains("visible"),
    ]))
  logger.info("hidden")
  logger.child("api").info("visible")
}

test {
  let logger = Logger::new(console_sink(), target="auth")
    .with_patch(compose_patches([
      prefix_message("[safe] "),
      redact_fields(["token"]),
      append_fields([field("service", "bitlogger")]),
    ]))
  logger.info("login", fields=[field("user", "alice"), field("token", "secret")])
}

test {
  let logger = Logger::new(console_sink(), target="audit")
    .bind(fields([("service", "bitlogger"), ("scope", "login")]))
  logger.info("accepted", fields=[field("user", "alice")])
}

test {
  let logger = Logger::new(console_sink(), target="queue")
    .with_queue(max_pending=2, overflow=QueueOverflowPolicy::DropOldest)
  logger.info("one")
  logger.info("two")
  logger.info("three")
  ignore(logger.sink.flush())
}

test {
  let logger = Logger::new(
    split_by_level(
      callback_sink(fn(rec) {
        println("high priority: \{rec.level.label()} \{rec.message}")
      }),
      console_sink(),
      min_level=Level::Warn,
    ),
    min_level=Level::Trace,
    target="split",
  )
  logger.info("normal output")
  logger.warn("warning output")
}

test {
  let formatter = text_formatter(
    show_timestamp=false,
    field_separator=",",
    template="[{level}] {target} {message} :: {fields}",
  )
  let logger = Logger::new(text_console_sink(formatter), target="pretty")
  logger.info("hello", fields=[field("mode", "pretty")])
}

test {
  let config = parse_logger_config_text(
    "{\"min_level\":\"debug\",\"target\":\"config.demo\",\"timestamp\":true,\"sink\":{\"kind\":\"text_console\",\"text_formatter\":{\"show_timestamp\":false,\"field_separator\":\",\",\"template\":\"[{level}] {target} {message} :: {fields}\"}},\"queue\":{\"max_pending\":2,\"overflow\":\"DropOldest\"}}",
  )
  let logger = build_logger(config)
  logger.info("configured from json")
  ignore(logger.flush())
}

Formatter Template / 模板格式

supported tokens / 支持的 token: {timestamp}, {timestamp_ms}, {level}, {target}, {message}, {fields}
disabled or missing parts render as empty text / 被关闭或缺失的部分会渲染为空字符串
template is intentionally a simple token replacement layer, not a full DSL / template 当前刻意保持为轻量 token 替换层，而不是完整 DSL

test {
  if native_files_supported() {
    let logger = Logger::new(
      file_sink("bitlogger.log", rotation=Some(file_rotation(128, max_backups=2))),
      target="file",
    )
    logger.info("hello", fields=[field("kind", "file")])
    ignore(logger.sink.flush())
    ignore(logger.sink.close())
  }
}

File Rotation / 文件轮转

basic rotation is size-based / 当前基础轮转为按文件大小触发
file_rotation(max_bytes, max_backups=...) controls threshold and retained backups / file_rotation(max_bytes, max_backups=...) 控制触发阈值和保留备份数
JSON config uses sink.rotation.max_bytes and sink.rotation.max_backups / JSON 配置使用 sink.rotation.max_bytes 与 sink.rotation.max_backups
FileSink::reopen() can explicitly reopen the current file handle / FileSink::reopen() 可显式重开当前文件句柄
append_mode() exposes the current append policy, and reopen(append=...) updates that policy for later reopen calls / append_mode() 可读取当前 append 策略，reopen(append=...) 会更新后续 reopen 复用的 append 策略
path() and auto_flush_enabled() expose core file sink policy state / path() 与 auto_flush_enabled() 可读取 file sink 的基础策略状态
rotation_enabled() and rotation_config() expose whether rotation is active and which settings are currently applied / rotation_enabled() 与 rotation_config() 可读取 rotation 是否启用及当前配置参数
open_failures()、write_failures()、flush_failures()、rotation_failures() expose basic sink health counters / open_failures()、write_failures()、flush_failures()、rotation_failures() 可用于观察基础 sink 健康状态
ConfiguredLogger also forwards file reopen, flush, close, append-mode, path, auto-flush, rotation-config, and failure-counter helpers for config-built file sinks / ConfiguredLogger 也会为配置生成的 file sink 转发 reopen、flush、close、append-mode、path、auto-flush、rotation 配置与失败计数访问器
current scope is observability-first, not a full self-healing sink runtime / 当前定位仍以可观测性优先，不是完整自愈型 sink runtime