BitLogger/docs/api/file-sink.md

name, group, category, update-time, description, key-word

name	group	category	update-time	description	key-word
file-sink	api	sink	20260512	Create a native file sink with append, auto-flush, rotation, reopen, and runtime observability helpers.	file sink native public

File-sink

Create a native file sink for text-oriented or custom-formatted file logging. This API includes lifecycle controls, rotation configuration, reopen behavior, policy inspection, and failure counters.

Interface

pub fn file_sink(
  path : String,
  append~ : Bool = true,
  auto_flush~ : Bool = true,
  rotation~ : FileRotation? = None,
  formatter~ : RecordFormatter = fn(rec) { format_text(rec) },
) -> FileSink {}

input

• path : String - Destination file path.
• append : Bool - Whether opening/reopening should append rather than truncate.
• auto_flush : Bool - Whether flush is attempted after each write.
• rotation : FileRotation? - Optional size-based rotation policy.
• formatter : RecordFormatter - Formatter used to render each record before writing.

output

• FileSink - A native-only sink with write, flush, close, reopen, policy, and state helpers.

Explanation

Detailed rules explaining key parameters and behaviors

• This sink is only available on native/llvm; use native_files_supported() for capability detection.
• append is persistent policy state and also affects later reopen behavior.
• auto_flush trades durability for more flush work per record.
• Rotation is currently size-based and rename-retention-oriented, not time-based.

How to Use

Here are some specific examples provided.

When Need Persistent Local Logs

When logs should be written to a host filesystem:

if native_files_supported() {
  let sink = file_sink("app.log")
  let logger = Logger::new(sink, target="file")
  logger.info("started")
  ignore(sink.flush())
}

In this example, the sink writes normal text-formatted records to app.log.

And capability detection prevents non-native misuse.

When Need Rotation And Runtime Inspection

When you want bounded local log retention plus observability:

let sink = file_sink("app.log", rotation=Some(file_rotation(1024, max_backups=3)))
let state = sink.state()

In this example, rotation policy and sink health can both be read through runtime helpers.

Error Case

e.g.:

• If the backend is non-native, file availability is not provided and callers should not expect writes to succeed.

• If open, write, flush, or rotation fails, the sink records failure counters instead of exposing a large exception surface.

Notes

Notes are here.

1. Always pair this API with native_files_supported() in cross-target code.

2. Prefer state(), policy(), and failure counters when integrating diagnostics.

3. Use reopen_append() and reopen_truncate() for common recovery flows instead of raw reopen(...) where possible.

4. For config-driven file logging, the mirrored control surface is exposed through ConfiguredLogger and RuntimeSink.