asyncjsonstream

Async JSON stream reader for selective parsing of large payloads. This is the standalone home of Extract's AsyncJsonStreamReader implementation.

Why asyncjsonstream

• Stream through large JSON without deserializing the full payload.
• Selectively read keys, values, and arrays using a tokenized reader.
• Handles chunk boundaries and escaped strings correctly.
• Built on Tokio AsyncRead.
• No unsafe code.

Install

cargo add asyncjsonstream

Quick start

use asyncjsonstream::AsyncJsonStreamReader;
use std::io::Cursor;

#[tokio::main]
async fn main() -> Result<(), asyncjsonstream::AsyncJsonStreamReaderError> {
    let data = r#"{"status":"success","results":[{"id":1},{"id":2}]}"#;
    let mut reader = AsyncJsonStreamReader::new(Cursor::new(data.as_bytes().to_vec()));

    while let Some(key) = reader.next_object_entry().await? {
        match key.as_str() {
            "status" => {
                let status = reader.read_string().await?;
                println!("status={status}");
            }
            "results" => {
                while reader.start_array_item().await? {
                    let obj = reader.deserialize_object().await?;
                    println!("id={}", obj["id"]);
                }
            }
            _ => {}
        }
    }

    Ok(())
}

Common patterns

• Read object entries with next_object_entry.
• Skip values by calling next_object_entry again without consuming the value.
• Stream arrays with start_array_item.
• Parse string/number/bool with read_string, read_number, read_boolean.
• Deserialize a sub-object with deserialize_object.

Error handling

All fallible operations return AsyncJsonStreamReaderError:

• Io for reader failures
• JsonError for malformed JSON
• UnexpectedToken when the stream doesn't match the expected structure

MSRV

Minimum supported Rust version is 1.74.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.