#moonbitlang/jsonl

A tiny async reader for JSON Lines (newline-delimited JSON, also called NDJSON). Each line is one independent JSON value; this package turns such a stream into MoonBit Json values using the built-in moonbitlang/core/json parser.

It is native-only because it reads from moonbitlang/async/io streams.

#API

parse(text : String) -> Array[Json] raise — pure helper that decodes already-buffered text. Blank lines are skipped; the first malformed line raises.
each(reader, visit) -> Unit raise (async) — stream values from any @io.Reader, invoking visit on each parsed value in order.
read_all(reader) -> Array[Json] raise (async) — collect every value from a reader into an array.
read_stdin() -> Array[Json] raise (async) — collect every value from standard input, so the caller need not import moonbitlang/async/stdio.

#Buffered Input

The pure parse helper needs no IO, so it is handy for testing and for input you already hold as a string:

///|
test "parse buffered JSON Lines" {
  let values = @jsonl.parse(
    (
      #|{"event": "agent_step", "step": 1}
      #|{"event": "agent_finished", "answer": "DONE"}
    ),
  )
  assert_eq(values.length(), 2)
  assert_true(values[1] == { "event": "agent_finished", "answer": "DONE" })
}

#Streaming From A Reader

each and read_all consume any moonbitlang/async/io reader — a pipe, a socket, @stdio.stdin, and so on — one line at a time:

///|
async test "stream JSON Lines from a pipe" {
  @async.with_task_group(group => {
    let (rd, wr) = @io.pipe()
    group.spawn_bg(() => {
      wr.write("{\"n\": 1}\n{\"n\": 2}\n")
      wr.close()
    })
    let values = @jsonl.read_all(rd)
    assert_eq(values.length(), 2)
  })
}

A common use is to consume a program's JSONL log over a pipe and assert on it with the typed Json values instead of an external tool such as jq.

#License

Apache-2.0.

each

source

async fn[R : @moonbitlang/async/io.Reader
Reader] each(reader : R, visit : (Json) -> Unit raise) -> Unit

Streams newline-delimited JSON values from reader, invoking visit on each parsed value in order. Blank lines are skipped. Raises on a malformed line or on a read error.

parse

source

fn parse(text : String) -> Array[Json] raise

Parses newline-delimited JSON text into an array of values, skipping blank lines and raising on the first malformed line.

This pure helper performs no IO, which makes it convenient for input that is already buffered and for tests.

read_all

source

async fn[R : @moonbitlang/async/io.Reader
Reader] read_all(reader : R) -> Array[Json]

Reads every newline-delimited JSON value from reader into an array.

read_stdin

source

async fn read_stdin() -> Array[Json]

Reads every newline-delimited JSON value from standard input into an array.

This is a convenience over [read_all] for the common case of consuming a program's JSONL output from a pipe, so the caller need not import moonbitlang/async/stdio itself.