Streaming JSON

Parse sequences, arrays and borrowed records incrementally.

use rydantic::{stream, Model};
use std::io::Cursor;

#[derive(Debug, Model)]
struct Row { id: u32 }

for row in stream::ndjson::<_, Row>(Cursor::new("{\"id\":1}\n{\"id\":2}\n")) {
    println!("{}", row?.id);
}

stream::visit_array::<_, Row, _>(Cursor::new("[{\"id\":1},{\"id\":2}]"), |row| {
    println!("{}", row?.id);
    Ok(())
})?;

Entry point	Input and error handling
Model::parse_reader	Read one JSON document from Read
stream::json_stream	Read whitespace-separated documents; continue after validation errors and stop after JSON syntax errors
stream::ndjson	Read lines from BufRead; skip blank lines, continue after syntax/validation errors, and attach stream_line
stream::visit_array	Visit each element; validation errors include the array index, and a callback error stops reading
stream::borrow_stream/visit_borrowed_array	Borrow fields from &str; returned values remain usable while the input buffer lives
stream::documents	Yield Box<RawValue> documents for calls to parse_json_async inside the loop

These entry points use synchronous I/O. Sequence and array visitors materialize only the current record, so memory use scales with that record’s size. The caller controls the reader’s buffering strategy. Asynchronous applications can integrate at the appropriate I/O layer and await validation for each model. Synchronous typed streams return async_validation_required for models with asynchronous rules.

Run the examples:

cargo run -p rydantic --example borrowed
cargo run -p rydantic --example streaming
cargo run -p rydantic --example asynchronous