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Nanaloveyuki
80 lines
2.1 KiB
Markdown
80 lines
2.1 KiB
Markdown
---
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name: format-json
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group: api
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category: formatter
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update-time: 20260613
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description: Render a Record into compact JSON text for machine-readable logging output.
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key-word:
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- format
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- json
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- record
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- public
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---
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## Format-json
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Render a `Record` into compact JSON text. This helper is the direct structured-output path used by JSON-oriented logging workflows when you want machine-readable serialization without building a sink.
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### Interface
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```moonbit
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pub fn format_json(rec : Record) -> String {
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```
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#### input
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- `rec : Record` - Log record to serialize.
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#### output
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- `String` - Compact JSON text built from the record contents.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- The output always includes `level`, `message`, and `fields`.
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- `timestamp_ms` is only included when `rec.timestamp_ms != 0`.
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- `target` is only included when `rec.target` is not empty.
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- The result is compact JSON text rather than pretty-printed output.
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- Field values are serialized through the record's structured field array instead of reparsing formatted text.
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### How to Use
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Here are some specific examples provided.
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#### When Need Machine-readable Output In Tests Or Adapters
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When record data should be passed along as structured JSON text:
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```moonbit
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let rec = Record::new(Level::Info, "ready", fields=[field("service", "api")])
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println(format_json(rec))
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```
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In this example, the returned string can be consumed by JSON-aware tooling.
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#### When Need Structured Output Without A Json Sink Instance
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When a callback or bridge already has a `Record` and only needs serialization:
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```moonbit
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let callback = fn(rec : Record) {
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let payload = format_json(rec)
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println(payload)
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}
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```
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In this example, the code reuses the built-in JSON record shape directly.
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### Error Case
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e.g.:
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- There is no separate failure path for valid `Record` values.
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- If a caller needs readable aligned text rather than JSON, `format_text(...)` is the better API.
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### Notes
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1. This helper returns compact JSON and does not expose a pretty-print option.
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2. It is a natural companion to `json_console_sink()` for structured logging flows.
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