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JSON Lines (a.k.a. newline-delimited JSON) is a simple format for storing sequences of JSON values in which each value is serialized on a single line and terminated by a newline sequence. The serde-jsonlines crate provides functionality for reading & writing these documents (whether all at once or line by line) using serde's serialization & deserialization features.

Basic usage involves simply importing the BufReadExt or WriteExt extension trait and then using the json_lines() or write_json_lines() method on a BufRead or Write value to read or write a sequence of JSON Lines values. Convenience functions are also provided for the common case of reading or writing a JSON Lines file given as a filepath.

At a lower level, values can be read or written one at a time (which is useful if, say, different lines are different types) by wrapping a BufRead or Write value in a JsonLinesReader or JsonLinesWriter and then calling the wrapped structure's read() or write() method, respectively.

When the async feature is enabled, analogous types for working with JSON Lines asynchronously under tokio become available.

Installation

serde-jsonlines requires version 1.56 of Rust or higher. To use the serde-jsonlines library in your Cargo project, add the following to your Cargo.toml:

[dependencies]
serde-jsonlines = "0.4.0"

Example

use serde::{Deserialize, Serialize};
use serde_jsonlines::{json_lines, write_json_lines};
use std::io::Result;

#[derive(Debug, Deserialize, Eq, PartialEq, Serialize)]
pub struct Structure {
    pub name: String,
    pub size: i32,
    pub on: bool,
}

fn main() -> Result<()> {
    let values = vec![
        Structure {
            name: "Foo Bar".into(),
            size: 42,
            on: true,
        },
        Structure {
            name: "Quux".into(),
            size: 23,
            on: false,
        },
        Structure {
            name: "Gnusto Cleesh".into(),
            size: 17,
            on: true,
        },
    ];
    write_json_lines("example.jsonl", &values)?;
    let values2 = json_lines("example.jsonl")?.collect::<Result<Vec<Structure>>>()?;
    assert_eq!(values, values2);
    Ok(())
}