hdf5-reader 0.4.0

//! HDF5 External Data Files message (type 0x0007).
//!
//! Indicates that raw data for a dataset is stored in one or more external
//! files. Rarely used in practice, especially in NetCDF files.

use crate::error::Result;
use crate::io::Cursor;

/// A single external file slot.
#[derive(Debug, Clone)]
pub struct ExternalFileSlot {
    /// Offset into the local heap for the file name.
    pub name_offset: u64,
    /// Byte offset into the external file where data starts.
    pub offset: u64,
    /// Number of bytes to read from the external file.
    pub size: u64,
}

/// Parsed external data files message.
#[derive(Debug, Clone)]
pub struct ExternalFilesMessage {
    /// Address of the local heap containing file names.
    pub heap_address: u64,
    /// List of external file slots.
    pub slots: Vec<ExternalFileSlot>,
}

/// Parse an external data files message.
pub fn parse(
    cursor: &mut Cursor<'_>,
    offset_size: u8,
    length_size: u8,
    msg_size: usize,
) -> Result<ExternalFilesMessage> {
    let start = cursor.position();

    let _version = cursor.read_u8()?;
    let _reserved = cursor.read_bytes(3)?;

    // Allocated slots (for pre-allocation; may differ from used slots)
    let _allocated_slots = cursor.read_u16_le()?;
    // Used slots — actual number of entries
    let used_slots = cursor.read_u16_le()? as usize;

    let heap_address = cursor.read_offset(offset_size)?;

    let mut slots = Vec::with_capacity(used_slots);
    for _ in 0..used_slots {
        let name_offset = cursor.read_length(length_size)?;
        let offset = cursor.read_length(length_size)?;
        let size = cursor.read_length(length_size)?;
        slots.push(ExternalFileSlot {
            name_offset,
            offset,
            size,
        });
    }

    let consumed = (cursor.position() - start) as usize;
    if consumed < msg_size {
        cursor.skip(msg_size - consumed)?;
    }

    Ok(ExternalFilesMessage {
        heap_address,
        slots,
    })
}