📝 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-policy-to-json
+group: api
+category: runtime
+update-time: 20260512
+description: Convert FileSinkPolicy into a JSON value for runtime diagnostics, policy snapshots, or transport.
+key-word:
+    - file
+    - policy
+    - json
+    - public
+---
+
+## File-sink-policy-to-json
+
+Convert `FileSinkPolicy` into a `JsonValue`. This helper exports append mode, auto-flush, and optional rotation as a structured runtime policy snapshot.
+
+### Interface
+
+```moonbit
+pub fn file_sink_policy_to_json(policy : FileSinkPolicy) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `policy : FileSinkPolicy` - File sink runtime policy to export.
+
+#### output
+
+- `JsonValue` - Structured JSON representation of the file policy.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The output includes `append`, `auto_flush`, and `rotation`.
+- `rotation` is exported as `null` when rotation is disabled.
+- This helper exports runtime file policy, not current file health counters or availability.
+- The JSON value is useful for policy snapshots, comparisons, and diagnostics payloads.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Structured Policy Snapshots
+
+When file sink policy should be embedded into a larger JSON payload:
+```moonbit
+let value = file_sink_policy_to_json(sink.policy())
+```
+
+In this example, the runtime file policy becomes a reusable structured value.
+
+#### When Need Policy Comparison Data
+
+When current and default policy should be exported separately:
+```moonbit
+let current = file_sink_policy_to_json(sink.policy())
+```
+
+In this example, callers can compare policy snapshots without formatting text first.
+
+### Error Case
+
+e.g.:
+- If rotation is disabled, the exported `rotation` field is `null` rather than omitted.
+
+- If callers need direct text output, `stringify_file_sink_policy(...)` is the better API.
+
+### Notes
+
+1. Use this helper when downstream code expects `JsonValue` rather than text.
+
+2. It pairs naturally with `policy()` and `default_policy()` runtime accessors.