tursodatabase/turso · error · anyhow::Error

buffer too short for u64 at offset

Error message

buffer too short for u64 at offset {offset}

What it means

read_u64_le is the bounds-checked little-endian u64 reader; it errors when fewer than 8 bytes remain at the requested offset. Within read_mvcc_frame_boundary the callers only invoke it after verifying header_size + trailer fit, so a live occurrence means a truncated/garbage buffer reached the reader or a new call site skipped its length guard.

Solutions

  1. Go through read_mvcc_frame_boundary / scan_mvcc_log so header+trailer length checks run first
  2. Require buf.len() >= offset + 8 before any read_u64_le call
  3. Add a regression test with a buffer cut exactly at each read boundary
Defensive patterns

Strategy: validation

Validate before calling

fn has_u64_at(buf: &[u8], offset: usize) -> bool {
    buf.len() >= offset.saturating_add(8)
}

Type guard

fn can_read_u64(buf: &[u8], offset: usize) -> bool {
    offset.checked_add(8).is_some_and(|end| end <= buf.len())
}

Try / catch

let size = read_u64_le(&log, offset + 4)
    .map_err(|err| err.context(format!("short frame buffer: len={} offset={}", log.len(), offset)))?;

Prevention

When it happens

Trigger: read_u64_le at offset+4 (payload size) or offset+24 (extension size) on a buffer shorter than offset + 8 - e.g. an extension frame claimed to fit but the slice was clipped.

Common situations: Reusing the readers on test fixtures or captured partial logs; refactors that bypass the frame-boundary length pre-checks; embedded scanner misuse.

Related errors

AI-assisted analysis of tursodatabase/turso@492c4a71cd (2026-08-20). Data as JSON: /api/errors/c0456a3b17cf5d3d. Report an issue: GitHub.

Appendix: source

Thrown at cli/sync_server.rs:1228

    if end_magic != MVCC_TX_END_MAGIC {
        return Err(anyhow!(
            "invalid MVCC logical log frame end magic at offset {offset}"
        ));
    }
    Ok(Some((frame_end, stored_crc)))
}

fn read_u32_le(buf: &[u8], offset: usize) -> Result<u32> {
    let bytes = buf
        .get(offset..offset + 4)
        .ok_or_else(|| anyhow!("buffer too short for u32 at offset {offset}"))?;
    Ok(u32::from_le_bytes(bytes.try_into().unwrap()))
}

fn read_u64_le(buf: &[u8], offset: usize) -> Result<u64> {
    let bytes = buf
        .get(offset..offset + 8)
        .ok_or_else(|| anyhow!("buffer too short for u64 at offset {offset}"))?;
    Ok(u64::from_le_bytes(bytes.try_into().unwrap()))
}

fn current_db_size_pages(conn: &Connection, max_frame: u64) -> Result<u64> {
    if max_frame > 0 {
        let frame_size = WAL_FRAME_HEADER_SIZE + PAGE_SIZE;
        let mut last_frame = vec![0u8; frame_size];
        let last_info = conn.wal_get_frame(max_frame, &mut last_frame)?;
        Ok(last_info.db_size as u64)
    } else {
        Ok(0)
    }
}

fn current_snapshot_db_size_pages(conn: &Connection, max_frame: u64) -> Result<u64> {
    if max_frame > 0 {
        return current_db_size_pages(conn, max_frame);
    }

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