A JSON Lines formatter for Rust `serde_json` #jsonl #rust #serde

json_lines.rs

#[derive(Default)]
pub(crate) struct JsonLinesFormatter {
    depth: usize,
}

use serde_json::ser::{CompactFormatter, Formatter as JsonFormatter};

impl JsonFormatter for JsonLinesFormatter {
    fn begin_object<W>(&mut self, writer: &mut W) -> io::Result<()>
    where
        W: ?Sized + io::Write,
    {
        self.depth += 1;
        CompactFormatter.begin_object(writer)
    }

    fn end_object<W>(&mut self, writer: &mut W) -> io::Result<()>
    where
        W: ?Sized + io::Write,
    {
        self.depth -= 1;
        CompactFormatter.end_object(writer).and_then(|_| {
            if self.depth == 0 {
                writer.write(&[b'\n']).map(|_| ())
            } else {
                Ok(())
            }
        })
    }
}