A fast non-allocating and streaming reader for chess games in PGN notation, as a Rust library.

Reader parses games and calls methods of a user provided Visitor. Implementing custom visitors allows for maximum flexibility:

• The reader itself does not allocate (besides a single fixed-size buffer). The visitor can decide if and how to represent games in memory.
• The reader does not validate move legality. This allows implementing support for custom chess variants, or delaying move validation.
• The visitor can signal to the reader that it does not care about a game or variation.

A visitor that counts the number of syntactically valid moves in the mainline of each game.

use std::io;
use pgn_reader::{Visitor, Skip, BufferedReader, SanPlus};

struct MoveCounter {
    moves: usize,
}

impl MoveCounter {
    fn new() -> MoveCounter {
        MoveCounter { moves: 0 }
    }
}

impl Visitor for MoveCounter {
    type Result = usize;

    fn begin_game(&mut self) {
        self.moves = 0;
    }

    fn san(&mut self, _san_plus: SanPlus) {
        self.moves += 1;
    }

    fn begin_variation(&mut self) -> Skip {
        Skip(true) // stay in the mainline
    }

    fn end_game(&mut self) -> Self::Result {
        self.moves
    }
}

fn main() -> io::Result<()> {
    let pgn = b"1. e4 e5 2. Nf3 (2. f4)
                { game paused due to bad weather }
                2... Nf6 *";

    let mut reader = BufferedReader::new_cursor(&pgn[..]);

    let mut counter = MoveCounter::new();
    let moves = reader.read_game(&mut counter)?;

    assert_eq!(moves, Some(4));
    Ok(())
}

Read the documentation

The API could be cleaner and performance may have regressed slightly compared to the mmap based approach from old versions (#12). This needs some attention. Until I get around to it, I am doing only minimal maintenance, following shakmaty as required.

Nonetheless, it is probably still one of the fastest PGN parsers around.

Run with lichess_db_standard_rated_2018-10.pgn (24,784,600 games, 52,750 MB uncompressed) on an SSD (Samsung 850), Intel i7-6850K CPU @ 3.60 GHz:

examples/stats.rs with compressed files:

pgn-reader is licensed under the GPL-3.0 (or any later version at your option). See the COPYING file for the full license text.