hdf5_reader/

btree_v2.rs

//! HDF5 B-tree Version 2.
//!
//! V2 B-trees are used by newer-style groups and datasets for indexed link
//! storage, attribute storage, and chunked dataset indexing. The header
//! (`BTHD`) describes the tree parameters. Internal nodes (`BTIN`) and leaf
//! nodes (`BTLF`) contain the actual records.
//!
//! This module provides the header parse, record types, and a traversal
//! function that collects all records from a tree.

use crate::checksum::jenkins_lookup3;
use crate::error::{Error, Result};
use crate::io::Cursor;

// ---------------------------------------------------------------------------
// Signatures
// ---------------------------------------------------------------------------

const BTHD_SIGNATURE: [u8; 4] = *b"BTHD";
const BTIN_SIGNATURE: [u8; 4] = *b"BTIN";
const BTLF_SIGNATURE: [u8; 4] = *b"BTLF";

// ---------------------------------------------------------------------------
// Header
// ---------------------------------------------------------------------------

/// Parsed B-tree v2 header.
#[derive(Debug, Clone)]
pub struct BTreeV2Header {
    /// B-tree type (determines the record format).
    pub btree_type: u8,
    /// Size in bytes of each B-tree node (both internal and leaf).
    pub node_size: u32,
    /// Size in bytes of each record.
    pub record_size: u16,
    /// Depth of the tree (0 = root is a leaf).
    pub depth: u16,
    /// Percent full at which to split a node.
    pub split_percent: u8,
    /// Percent full at which to merge a node.
    pub merge_percent: u8,
    /// Address of the root node.
    pub root_node_address: u64,
    /// Number of records in the root node.
    pub num_records_in_root: u16,
    /// Total number of records in the entire tree.
    pub total_records: u64,
}

impl BTreeV2Header {
    /// Parse a B-tree v2 header at the current cursor position.
    ///
    /// Format:
    /// - Signature: `BTHD` (4 bytes)
    /// - Version: 0 (1 byte)
    /// - B-tree type (u8)
    /// - Node size (u32 LE)
    /// - Record size (u16 LE)
    /// - Depth (u16 LE)
    /// - Split percent (u8)
    /// - Merge percent (u8)
    /// - Root node address (`offset_size` bytes)
    /// - Number of records in root node (u16 LE)
    /// - Total number of records in tree (`length_size` bytes)
    /// - Checksum (u32 LE)
    pub fn parse(cursor: &mut Cursor, offset_size: u8, length_size: u8) -> Result<Self> {
        let start = cursor.position();

        let sig = cursor.read_bytes(4)?;
        if sig != BTHD_SIGNATURE {
            return Err(Error::InvalidBTreeV2Signature { context: "header" });
        }

        let version = cursor.read_u8()?;
        if version != 0 {
            return Err(Error::UnsupportedBTreeVersion(version));
        }

        let btree_type = cursor.read_u8()?;
        let node_size = cursor.read_u32_le()?;
        let record_size = cursor.read_u16_le()?;
        let depth = cursor.read_u16_le()?;
        let split_percent = cursor.read_u8()?;
        let merge_percent = cursor.read_u8()?;
        let root_node_address = cursor.read_offset(offset_size)?;
        let num_records_in_root = cursor.read_u16_le()?;
        let total_records = cursor.read_length(length_size)?;

        // Checksum covers everything from signature through total_records.
        let checksum_end = cursor.position();
        let stored_checksum = cursor.read_u32_le()?;

        let computed = jenkins_lookup3(&cursor.data()[start as usize..checksum_end as usize]);
        if computed != stored_checksum {
            return Err(Error::ChecksumMismatch {
                expected: stored_checksum,
                actual: computed,
            });
        }

        Ok(BTreeV2Header {
            btree_type,
            node_size,
            record_size,
            depth,
            split_percent,
            merge_percent,
            root_node_address,
            num_records_in_root,
            total_records,
        })
    }
}

// ---------------------------------------------------------------------------
// Records
// ---------------------------------------------------------------------------

/// A record from a B-tree v2.
///
/// The record format depends on the B-tree type field in the header.
#[derive(Debug, Clone)]
pub enum BTreeV2Record {
    /// Type 5: Link name for indexed group (hashed).
    LinkNameHash { hash: u32, heap_id: Vec<u8> },
    /// Type 6: Creation order for indexed group.
    CreationOrder { order: u64, heap_id: Vec<u8> },
    /// Type 8: Attribute name for indexed group (hashed).
    AttributeNameHash {
        hash: u32,
        flags: u8,
        creation_order: u32,
        heap_id: Vec<u8>,
    },
    /// Type 9: Attribute creation order.
    AttributeCreationOrder { order: u32, heap_id: Vec<u8> },
    /// Type 10: Non-filtered chunked dataset record (v2 chunk index).
    ChunkedNonFiltered { address: u64, offsets: Vec<u64> },
    /// Type 11: Filtered chunked dataset record (v2 chunk index).
    ChunkedFiltered {
        address: u64,
        chunk_size: u64,
        filter_mask: u32,
        offsets: Vec<u64>,
    },
    /// Unknown/unsupported record type — raw bytes preserved.
    Unknown { record_type: u8, data: Vec<u8> },
}

// ---------------------------------------------------------------------------
// Record parsing
// ---------------------------------------------------------------------------

/// Parse a single record of the given B-tree type.
fn parse_record(
    cursor: &mut Cursor,
    btree_type: u8,
    record_size: u16,
    offset_size: u8,
    length_size: u8,
    _ndims: Option<u32>,
    heap_id_len: usize,
) -> Result<BTreeV2Record> {
    let record_start = cursor.position();

    let record = match btree_type {
        // Type 5: link name hash
        5 => {
            let hash = cursor.read_u32_le()?;
            let heap_id = cursor.read_bytes(heap_id_len)?.to_vec();
            BTreeV2Record::LinkNameHash { hash, heap_id }
        }

        // Type 6: creation order
        6 => {
            let order = cursor.read_u64_le()?;
            let heap_id = cursor.read_bytes(heap_id_len)?.to_vec();
            BTreeV2Record::CreationOrder { order, heap_id }
        }

        // Type 8: attribute name hash
        8 => {
            let hash = cursor.read_u32_le()?;
            let flags = cursor.read_u8()?;
            let creation_order = cursor.read_u32_le()?;
            let heap_id = cursor.read_bytes(heap_id_len)?.to_vec();
            BTreeV2Record::AttributeNameHash {
                hash,
                flags,
                creation_order,
                heap_id,
            }
        }

        // Type 9: attribute creation order
        9 => {
            let order = cursor.read_u32_le()?;
            let heap_id = cursor.read_bytes(heap_id_len)?.to_vec();
            BTreeV2Record::AttributeCreationOrder { order, heap_id }
        }

        // Type 10: non-filtered chunk
        10 => {
            let address = cursor.read_offset(offset_size)?;
            // Chunk offsets are encoded as scaled 64-bit values.
            // The number of offset dimensions is calculated from the record size.
            // Each offset is 8 bytes in a type-10 record.
            let offset_bytes_available = record_size as usize - offset_size as usize;
            let num_offsets = offset_bytes_available / 8;
            let mut offsets = Vec::with_capacity(num_offsets);
            for _ in 0..num_offsets {
                offsets.push(cursor.read_u64_le()?);
            }
            BTreeV2Record::ChunkedNonFiltered { address, offsets }
        }

        // Type 11: filtered chunk
        11 => {
            let address = cursor.read_offset(offset_size)?;
            // nbytes (chunk size on disk) is encoded using length_size bytes.
            let nbytes_size = length_size as usize;
            let chunk_size = cursor.read_length(length_size)?;
            let filter_mask = cursor.read_u32_le()?;
            let remaining = record_size as usize - offset_size as usize - nbytes_size - 4; // filter_mask
            let num_offsets = remaining / 8;
            let mut offsets = Vec::with_capacity(num_offsets);
            for _ in 0..num_offsets {
                offsets.push(cursor.read_u64_le()?);
            }
            BTreeV2Record::ChunkedFiltered {
                address,
                chunk_size,
                filter_mask,
                offsets,
            }
        }

        // Unknown type — read raw bytes.
        _ => {
            let data = cursor.read_bytes(record_size as usize)?.to_vec();
            return Ok(BTreeV2Record::Unknown {
                record_type: btree_type,
                data,
            });
        }
    };

    // Ensure we consumed exactly record_size bytes (skip any remaining).
    let consumed = (cursor.position() - record_start) as usize;
    if consumed < record_size as usize {
        cursor.skip(record_size as usize - consumed)?;
    }

    Ok(record)
}

fn record_matches_chunk_bounds(
    record: &BTreeV2Record,
    chunk_dims: &[u32],
    chunk_bounds: Option<(&[u64], &[u64])>,
) -> bool {
    let Some((first_chunk, last_chunk)) = chunk_bounds else {
        return true;
    };

    let offsets = match record {
        BTreeV2Record::ChunkedNonFiltered { offsets, .. }
        | BTreeV2Record::ChunkedFiltered { offsets, .. } => offsets,
        _ => return true,
    };

    offsets.iter().enumerate().all(|(dim, offset)| {
        let chunk_index = *offset / u64::from(chunk_dims[dim]);
        chunk_index >= first_chunk[dim] && chunk_index <= last_chunk[dim]
    })
}

// ---------------------------------------------------------------------------
// Node parsing
// ---------------------------------------------------------------------------

/// Compute the number of bytes needed to represent `max_records` as an
/// unsigned integer (used for child-node record counts in internal nodes).
fn num_records_size(max_records: u64) -> usize {
    if max_records <= 0xFF {
        1
    } else if max_records <= 0xFFFF {
        2
    } else if max_records <= 0xFFFF_FFFF {
        4
    } else {
        8
    }
}

/// Compute the maximum number of records that fit in a leaf node.
fn max_leaf_records(node_size: u32, record_size: u16) -> u64 {
    // Leaf node overhead: signature(4) + version(1) + type(1) + checksum(4) = 10
    let overhead = 10u32;
    if node_size <= overhead || record_size == 0 {
        return 0;
    }
    ((node_size - overhead) / record_size as u32) as u64
}

/// Compute the maximum number of records that fit in an internal node.
/// This depends on the pointer size (offset_size) and the number-of-records
/// encoding for child nodes, which makes it recursive in principle. We use
/// an iterative approach.
fn max_internal_records(
    node_size: u32,
    record_size: u16,
    offset_size: u8,
    max_child_records: u64,
) -> u64 {
    // Internal node overhead: signature(4) + version(1) + type(1) + checksum(4) = 10
    let overhead = 10u32;
    if node_size <= overhead || record_size == 0 {
        return 0;
    }
    let available = (node_size - overhead) as u64;
    // Each entry in an internal node is: record(record_size) + child_pointer(offset_size) + num_records(var)
    let nrec_size = num_records_size(max_child_records) as u64;
    let entry_size = record_size as u64 + offset_size as u64 + nrec_size;
    // There is one more child pointer + num_records than records.
    // So: n * record_size + (n+1) * (offset_size + nrec_size) <= available
    // => n * (record_size + offset_size + nrec_size) + offset_size + nrec_size <= available
    let extra = offset_size as u64 + nrec_size;
    if available <= extra {
        return 0;
    }
    (available - extra) / entry_size
}

/// Parse a leaf node and collect its records.
#[allow(clippy::too_many_arguments)]
fn parse_leaf_node(
    cursor: &mut Cursor,
    header: &BTreeV2Header,
    offset_size: u8,
    length_size: u8,
    ndims: Option<u32>,
    chunk_dims: &[u32],
    chunk_bounds: Option<(&[u64], &[u64])>,
    num_records: u16,
    heap_id_len: usize,
    records: &mut Vec<BTreeV2Record>,
) -> Result<()> {
    let start = cursor.position();

    let sig = cursor.read_bytes(4)?;
    if sig != BTLF_SIGNATURE {
        return Err(Error::InvalidBTreeV2Signature {
            context: "leaf node",
        });
    }

    let version = cursor.read_u8()?;
    if version != 0 {
        return Err(Error::UnsupportedBTreeVersion(version));
    }

    let node_type = cursor.read_u8()?;
    if node_type != header.btree_type {
        return Err(Error::InvalidData(format!(
            "B-tree v2 leaf node type mismatch: header says {}, node says {}",
            header.btree_type, node_type
        )));
    }

    for _ in 0..num_records {
        let record = parse_record(
            cursor,
            header.btree_type,
            header.record_size,
            offset_size,
            length_size,
            ndims,
            heap_id_len,
        )?;
        if record_matches_chunk_bounds(&record, chunk_dims, chunk_bounds) {
            records.push(record);
        }
    }

    // Verify checksum: covers signature through the end of records.
    let checksum_data_end = cursor.position();
    let stored_checksum = cursor.read_u32_le()?;
    let computed = jenkins_lookup3(&cursor.data()[start as usize..checksum_data_end as usize]);
    if computed != stored_checksum {
        return Err(Error::ChecksumMismatch {
            expected: stored_checksum,
            actual: computed,
        });
    }

    Ok(())
}

/// Parse an internal node, collecting child addresses and recursing.
#[allow(clippy::too_many_arguments)]
fn parse_internal_node(
    data: &[u8],
    address: u64,
    header: &BTreeV2Header,
    offset_size: u8,
    length_size: u8,
    ndims: Option<u32>,
    chunk_dims: &[u32],
    chunk_bounds: Option<(&[u64], &[u64])>,
    num_records: u16,
    depth: u16,
    heap_id_len: usize,
    records: &mut Vec<BTreeV2Record>,
) -> Result<()> {
    let mut cursor = Cursor::new(data);
    cursor.set_position(address);

    let start = cursor.position();

    let sig = cursor.read_bytes(4)?;
    if sig != BTIN_SIGNATURE {
        return Err(Error::InvalidBTreeV2Signature {
            context: "internal node",
        });
    }

    let version = cursor.read_u8()?;
    if version != 0 {
        return Err(Error::UnsupportedBTreeVersion(version));
    }

    let node_type = cursor.read_u8()?;
    if node_type != header.btree_type {
        return Err(Error::InvalidData(format!(
            "B-tree v2 internal node type mismatch: header says {}, node says {}",
            header.btree_type, node_type
        )));
    }

    // Compute max records for children to know the encoding size for
    // child record counts.
    let max_child_records = if depth == 1 {
        max_leaf_records(header.node_size, header.record_size)
    } else {
        // For deeper trees, compute iteratively.
        let leaf_max = max_leaf_records(header.node_size, header.record_size);
        let mut prev_max = leaf_max;
        for _ in 1..depth {
            prev_max =
                max_internal_records(header.node_size, header.record_size, offset_size, prev_max);
        }
        prev_max
    };
    let nrec_bytes = num_records_size(max_child_records);

    // Read records and child pointers interleaved:
    // child[0], record[0], child[1], record[1], ..., record[n-1], child[n]
    // Plus total_records counts for each child.
    //
    // Actually per the HDF5 spec the layout is:
    // record[0], record[1], ..., record[n-1],
    // child_ptr[0], nrec[0], total[0], child_ptr[1], nrec[1], total[1], ..., child_ptr[n], nrec[n], total[n]
    //
    // Records first, then child pointers with their metadata.

    // Read all records.
    let mut node_records = Vec::with_capacity(num_records as usize);
    for _ in 0..num_records {
        let record = parse_record(
            &mut cursor,
            header.btree_type,
            header.record_size,
            offset_size,
            length_size,
            ndims,
            heap_id_len,
        )?;
        if record_matches_chunk_bounds(&record, chunk_dims, chunk_bounds) {
            node_records.push(record);
        }
    }

    // Read child node pointers (num_records + 1 of them).
    let num_children = num_records as usize + 1;

    // Whether to include a "total records" field for each child.
    // This is present when depth > 1.
    let has_total_records = depth > 1;
    // total_records encoding size for deeper nodes
    let total_nrec_bytes = if has_total_records {
        // Total records in a sub-tree — need enough bytes to hold the
        // maximum total records. We use length_size as an upper bound.
        length_size as usize
    } else {
        0
    };

    let mut child_addresses = Vec::with_capacity(num_children);
    let mut child_nrecords = Vec::with_capacity(num_children);

    for _ in 0..num_children {
        let child_addr = cursor.read_offset(offset_size)?;
        child_addresses.push(child_addr);
        let nrec = cursor.read_uvar(nrec_bytes)?;
        child_nrecords.push(nrec as u16);
        if has_total_records {
            // Skip total records count
            cursor.read_uvar(total_nrec_bytes)?;
        }
    }

    // Verify checksum.
    let checksum_data_end = cursor.position();
    let stored_checksum = cursor.read_u32_le()?;
    let computed = jenkins_lookup3(&cursor.data()[start as usize..checksum_data_end as usize]);
    if computed != stored_checksum {
        return Err(Error::ChecksumMismatch {
            expected: stored_checksum,
            actual: computed,
        });
    }

    // The records from this internal node are NOT included in the leaf
    // collection — they are separators. We do NOT add them to results.
    // Only leaf records are collected.
    // (Actually, in HDF5 v2 B-trees, records in internal nodes are real
    // records too, not just separators. We should collect them.)
    records.extend(node_records);

    // Recurse into children.
    let child_depth = depth - 1;
    for (i, &child_addr) in child_addresses.iter().enumerate() {
        if Cursor::is_undefined_offset(child_addr, offset_size) {
            continue;
        }
        let child_nrec = child_nrecords[i];
        if child_depth == 0 {
            // Child is a leaf.
            let mut child_cursor = Cursor::new(data);
            child_cursor.set_position(child_addr);
            parse_leaf_node(
                &mut child_cursor,
                header,
                offset_size,
                length_size,
                ndims,
                chunk_dims,
                chunk_bounds,
                child_nrec,
                heap_id_len,
                records,
            )?;
        } else {
            // Child is another internal node.
            parse_internal_node(
                data,
                child_addr,
                header,
                offset_size,
                length_size,
                ndims,
                chunk_dims,
                chunk_bounds,
                child_nrec,
                child_depth,
                heap_id_len,
                records,
            )?;
        }
    }

    Ok(())
}

// ---------------------------------------------------------------------------
// Public traversal
// ---------------------------------------------------------------------------

/// Collect all records from a B-tree v2 by traversing from the root.
///
/// `header` must be a previously parsed `BTreeV2Header`. `data` is the full
/// file buffer. `ndims` is needed for chunk index record types (10 and 11).
pub fn collect_btree_v2_records(
    data: &[u8],
    header: &BTreeV2Header,
    offset_size: u8,
    length_size: u8,
    ndims: Option<u32>,
    chunk_dims: &[u32],
    chunk_bounds: Option<(&[u64], &[u64])>,
) -> Result<Vec<BTreeV2Record>> {
    if Cursor::is_undefined_offset(header.root_node_address, offset_size) {
        return Ok(Vec::new());
    }

    if header.total_records == 0 || header.num_records_in_root == 0 {
        return Ok(Vec::new());
    }

    // Determine heap_id_len from the record_size and btree_type.
    let heap_id_len = compute_heap_id_len(header);

    let mut records = Vec::new();

    if header.depth == 0 {
        // Root is a leaf node.
        let mut cursor = Cursor::new(data);
        cursor.set_position(header.root_node_address);
        parse_leaf_node(
            &mut cursor,
            header,
            offset_size,
            length_size,
            ndims,
            chunk_dims,
            chunk_bounds,
            header.num_records_in_root,
            heap_id_len,
            &mut records,
        )?;
    } else {
        // Root is an internal node.
        parse_internal_node(
            data,
            header.root_node_address,
            header,
            offset_size,
            length_size,
            ndims,
            chunk_dims,
            chunk_bounds,
            header.num_records_in_root,
            header.depth,
            heap_id_len,
            &mut records,
        )?;
    }

    Ok(records)
}

/// Compute the heap ID length from the record size and tree type.
///
/// For link/attribute B-trees (types 5, 6, 8, 9), the heap ID occupies
/// the remaining bytes after the fixed fields. For chunk types (10, 11)
/// or unknown types, return 0 (heap_id is not used).
fn compute_heap_id_len(header: &BTreeV2Header) -> usize {
    let rs = header.record_size as usize;
    match header.btree_type {
        5 => rs.saturating_sub(4),         // hash(4)
        6 => rs.saturating_sub(8),         // order(8)
        8 => rs.saturating_sub(4 + 1 + 4), // hash(4) + flags(1) + creation_order(4)
        9 => rs.saturating_sub(4),         // order(4)
        _ => 0,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Build a minimal BTHD with the given parameters.
    #[allow(clippy::too_many_arguments)]
    fn build_header(
        btree_type: u8,
        node_size: u32,
        record_size: u16,
        depth: u16,
        root_node_address: u64,
        num_records_in_root: u16,
        total_records: u64,
        offset_size: u8,
        length_size: u8,
    ) -> Vec<u8> {
        let mut buf = Vec::new();
        buf.extend_from_slice(b"BTHD");
        buf.push(0); // version
        buf.push(btree_type);
        buf.extend_from_slice(&node_size.to_le_bytes());
        buf.extend_from_slice(&record_size.to_le_bytes());
        buf.extend_from_slice(&depth.to_le_bytes());
        buf.push(75); // split percent
        buf.push(40); // merge percent
        match offset_size {
            4 => buf.extend_from_slice(&(root_node_address as u32).to_le_bytes()),
            8 => buf.extend_from_slice(&root_node_address.to_le_bytes()),
            _ => panic!("unsupported"),
        }
        buf.extend_from_slice(&num_records_in_root.to_le_bytes());
        match length_size {
            4 => buf.extend_from_slice(&(total_records as u32).to_le_bytes()),
            8 => buf.extend_from_slice(&total_records.to_le_bytes()),
            _ => panic!("unsupported"),
        }
        // Compute and append checksum.
        let checksum = jenkins_lookup3(&buf);
        buf.extend_from_slice(&checksum.to_le_bytes());
        buf
    }

    #[test]
    fn test_parse_header() {
        let data = build_header(5, 4096, 12, 0, 0x1000, 3, 3, 8, 8);
        let mut cursor = Cursor::new(&data);
        let hdr = BTreeV2Header::parse(&mut cursor, 8, 8).unwrap();

        assert_eq!(hdr.btree_type, 5);
        assert_eq!(hdr.node_size, 4096);
        assert_eq!(hdr.record_size, 12);
        assert_eq!(hdr.depth, 0);
        assert_eq!(hdr.split_percent, 75);
        assert_eq!(hdr.merge_percent, 40);
        assert_eq!(hdr.root_node_address, 0x1000);
        assert_eq!(hdr.num_records_in_root, 3);
        assert_eq!(hdr.total_records, 3);
    }

    #[test]
    fn test_bad_signature() {
        let mut data = build_header(5, 4096, 12, 0, 0x1000, 0, 0, 8, 8);
        data[0] = b'X';
        let mut cursor = Cursor::new(&data);
        assert!(matches!(
            BTreeV2Header::parse(&mut cursor, 8, 8),
            Err(Error::InvalidBTreeV2Signature { .. })
        ));
    }

    #[test]
    fn test_bad_checksum() {
        let mut data = build_header(5, 4096, 12, 0, 0x1000, 0, 0, 8, 8);
        // Corrupt a byte in the middle.
        data[6] = 0xFF;
        let mut cursor = Cursor::new(&data);
        assert!(matches!(
            BTreeV2Header::parse(&mut cursor, 8, 8),
            Err(Error::ChecksumMismatch { .. })
        ));
    }

    #[test]
    fn test_collect_empty_tree() {
        let header = BTreeV2Header {
            btree_type: 5,
            node_size: 4096,
            record_size: 12,
            depth: 0,
            split_percent: 75,
            merge_percent: 40,
            root_node_address: u64::MAX,
            num_records_in_root: 0,
            total_records: 0,
        };
        let data = vec![0u8; 100];
        let records = collect_btree_v2_records(&data, &header, 8, 8, None, &[], None).unwrap();
        assert!(records.is_empty());
    }

    #[test]
    fn test_compute_heap_id_len() {
        // Type 5: record_size - 4
        let h5 = BTreeV2Header {
            btree_type: 5,
            record_size: 12,
            node_size: 0,
            depth: 0,
            split_percent: 0,
            merge_percent: 0,
            root_node_address: 0,
            num_records_in_root: 0,
            total_records: 0,
        };
        assert_eq!(compute_heap_id_len(&h5), 8);

        // Type 8: record_size - 9
        let h8 = BTreeV2Header {
            btree_type: 8,
            record_size: 17,
            ..h5
        };
        assert_eq!(compute_heap_id_len(&h8), 8);
    }

    #[test]
    fn test_max_leaf_records() {
        // node_size=4096, record_size=12, overhead=10
        // => (4096 - 10) / 12 = 340
        assert_eq!(max_leaf_records(4096, 12), 340);
    }

    #[test]
    fn test_num_records_size() {
        assert_eq!(num_records_size(0), 1);
        assert_eq!(num_records_size(255), 1);
        assert_eq!(num_records_size(256), 2);
        assert_eq!(num_records_size(65535), 2);
        assert_eq!(num_records_size(65536), 4);
    }

    #[test]
    fn test_parse_leaf_with_type5_records() {
        // Build a leaf node with 2 type-5 records (link name hash).
        // record_size = 12 (hash=4 + heap_id=8)
        let record_size: u16 = 12;
        let node_size: u32 = 4096;

        let header = BTreeV2Header {
            btree_type: 5,
            node_size,
            record_size,
            depth: 0,
            split_percent: 75,
            merge_percent: 40,
            root_node_address: 0, // will point to our leaf
            num_records_in_root: 2,
            total_records: 2,
        };

        // Build the leaf node.
        let mut leaf = Vec::new();
        leaf.extend_from_slice(b"BTLF"); // signature
        leaf.push(0); // version
        leaf.push(5); // type

        // Record 1: hash=0xAABBCCDD, heap_id=[1,2,3,4,5,6,7,8]
        leaf.extend_from_slice(&0xAABBCCDDu32.to_le_bytes());
        leaf.extend_from_slice(&[1, 2, 3, 4, 5, 6, 7, 8]);

        // Record 2: hash=0x11223344, heap_id=[9,10,11,12,13,14,15,16]
        leaf.extend_from_slice(&0x11223344u32.to_le_bytes());
        leaf.extend_from_slice(&[9, 10, 11, 12, 13, 14, 15, 16]);

        // Checksum covers everything so far.
        let checksum = jenkins_lookup3(&leaf);
        leaf.extend_from_slice(&checksum.to_le_bytes());

        // Pad to node_size (not strictly needed for parsing, but realistic).
        leaf.resize(node_size as usize, 0);

        let mut records = Vec::new();
        let mut cursor = Cursor::new(&leaf);
        parse_leaf_node(
            &mut cursor,
            &header,
            8,
            8,
            None,
            &[],
            None,
            2,
            8, // heap_id_len
            &mut records,
        )
        .unwrap();

        assert_eq!(records.len(), 2);
        match &records[0] {
            BTreeV2Record::LinkNameHash { hash, heap_id } => {
                assert_eq!(*hash, 0xAABBCCDD);
                assert_eq!(heap_id, &[1, 2, 3, 4, 5, 6, 7, 8]);
            }
            _ => panic!("expected LinkNameHash"),
        }
        match &records[1] {
            BTreeV2Record::LinkNameHash { hash, heap_id } => {
                assert_eq!(*hash, 0x11223344);
                assert_eq!(heap_id, &[9, 10, 11, 12, 13, 14, 15, 16]);
            }
            _ => panic!("expected LinkNameHash"),
        }
    }
}