Client cannot open large PGN files (>100 MB) for viewing

[jozef2svrcek]

Summary

Opening a large PGN file in the client for viewing (not importing) fails with:

File too large (11503 MB, max 100 MB)

Reproduced with a megabase.pgn of ~11.5 GB.

Root cause

read_pgn_file reads the entire file into memory as a single String and rejects anything over a hardcoded 100 MB cap:

chess-client/src-tauri/src/local.rs:82-96

const MAX_FILE_SIZE: u64 = 100 * 1024 * 1024; // 100 MB

#[tauri::command]
pub async fn read_pgn_file(path: String) -> Result<String, String> {
    let p = PathBuf::from(&path);
    let meta = std::fs::metadata(&p).map_err(|e| format!("{path}: {e}"))?;
    if meta.len() > MAX_FILE_SIZE {
        return Err(format!(
            "File too large ({:.0} MB, max 100 MB)",
            meta.len() as f64 / 1_048_576.0
        ));
    }
    let bytes = std::fs::read(&p).map_err(|e| format!("{path}: {e}"))?;
    Ok(String::from_utf8_lossy(&bytes).into_owned())
}

The 100 MB limit is a guardrail against the current read-everything-into-RAM approach — loading a multi-GB file this way would exhaust memory. So the cap itself isn't the bug; the whole-file-in-memory design is the constraint.

Notes / possible directions (for later)

• This is the view/open path, distinct from import (which already streams).
• A real fix likely means not materializing the whole file: e.g. stream/index game offsets and read games lazily as the user navigates, or page through the file, rather than returning one giant String to the webview.
• Until then, the error message is at least accurate; could optionally point users to import for large files.

Logged from manual testing; no code changed.