📝 Add file state export API docs

2026-05-30 23:52:27 +00:00 · 2026-05-12 15:05:58 +08:00
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+---
+name: file-sink-state-to-json
+group: api
+category: runtime
+update-time: 20260512
+description: Convert FileSinkState into a JSON value for file sink diagnostics and state transport.
+key-word:
+    - file
+    - state
+    - json
+    - public
+---
+
+## File-sink-state-to-json
+
+Convert `FileSinkState` into a `JsonValue`. This helper exports file path, availability, policy flags, rotation config, and failure counters in a structured form.
+
+### Interface
+
+```moonbit
+pub fn file_sink_state_to_json(state : FileSinkState) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `state : FileSinkState` - File sink state snapshot to export.
+
+#### output
+
+- `JsonValue` - Structured JSON representation of the file sink state.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The output includes `path`, `available`, `append`, `auto_flush`, failure counters, and `rotation`.
+- `rotation` is exported as `null` when rotation is disabled.
+- This helper exports state snapshots, not mutable runtime control handles.
+- It is useful when file sink state should be embedded into larger diagnostics payloads.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Structured File Diagnostics
+
+When file sink status should be composed into a larger JSON object:
+```moonbit
+let value = file_sink_state_to_json(sink.state())
+```
+
+In this example, callers receive a structured file-state snapshot instead of plain text.
+
+#### When Need Runtime State Snapshots For Tooling
+
+When support tooling should ingest file sink state programmatically:
+```moonbit
+let snapshot = file_sink_state_to_json(state)
+```
+
+In this example, the helper exposes all major file-state fields in machine-readable form.
+
+### Error Case
+
+e.g.:
+- If the file is unavailable, the exported snapshot still serializes normally with `available=false`.
+
+- If callers need direct text output, `stringify_file_sink_state(...)` is the better API.
+
+### Notes
+
+1. Use this helper when diagnostics consumers expect `JsonValue`.
+
+2. It pairs naturally with `FileSink::state()` and `ConfiguredLogger::file_state()`.