hdf5-pure-rust 0.2.2

Pure Rust implementation of the HDF5 file format. No C dependencies.
Documentation 
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use crate::error::{Error, Result};

/// Dataspace type.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum DataspaceType {
    Scalar,
    Simple,
    Null,
}

/// Parsed Dataspace message (type 0x0001).
#[derive(Debug, Clone)]
pub struct DataspaceMessage {
    pub version: u8,
    pub space_type: DataspaceType,
    pub ndims: u8,
    /// Current dimension sizes.
    pub dims: Vec<u64>,
    /// Maximum dimension sizes (None means same as current).
    pub max_dims: Option<Vec<u64>>,
}

impl DataspaceMessage {
    pub fn decode(data: &[u8]) -> Result<Self> {
        if data.len() < 4 {
            return Err(Error::InvalidFormat("dataspace message too short".into()));
        }

        let version = data[0];
        let ndims = data[1];

        match version {
            1 => Self::decode_v1(data, ndims),
            2 => Self::decode_v2(data, ndims),
            _ => {
                // Some embedded dataspaces (in attribute messages) may not have
                // a standard version byte. Try to parse as v2 with what we have.
                // If ndims is 0 and the data is very short, it might be a scalar.
                if data.len() <= 4 {
                    Ok(Self {
                        version,
                        space_type: DataspaceType::Scalar,
                        ndims: 0,
                        dims: vec![],
                        max_dims: None,
                    })
                } else {
                    // Try as v1
                    Self::decode_v1(data, ndims)
                }
            }
        }
    }

    fn decode_v1(data: &[u8], ndims: u8) -> Result<Self> {
        let flags = data[2];
        // v1: reserved bytes [3..8], then dimensions
        let has_max = flags & 0x01 != 0;

        let mut pos = 8; // skip 5 reserved bytes after version(1)+ndims(1)+flags(1)

        let dims = read_dims(data, &mut pos, ndims as usize);
        let max_dims = if has_max {
            Some(read_dims(data, &mut pos, ndims as usize))
        } else {
            None
        };

        // Permutation indices (deprecated, skip if present)
        // flags & 0x02 != 0 means permutation present

        let space_type = if ndims == 0 {
            DataspaceType::Scalar
        } else {
            DataspaceType::Simple
        };

        Ok(Self {
            version: 1,
            space_type,
            ndims,
            dims,
            max_dims,
        })
    }

    fn decode_v2(data: &[u8], ndims: u8) -> Result<Self> {
        let flags = data[2];
        let space_type_val = data[3];

        let space_type = match space_type_val {
            0 => DataspaceType::Scalar,
            1 => DataspaceType::Simple,
            2 => DataspaceType::Null,
            _ => {
                return Err(Error::InvalidFormat(format!(
                    "unknown dataspace type {space_type_val}"
                )))
            }
        };

        let has_max = flags & 0x01 != 0;
        let mut pos = 4;

        let dims = read_dims(data, &mut pos, ndims as usize);
        let max_dims = if has_max {
            Some(read_dims(data, &mut pos, ndims as usize))
        } else {
            None
        };

        Ok(Self {
            version: 2,
            space_type,
            ndims,
            dims,
            max_dims,
        })
    }
}

fn read_dims(data: &[u8], pos: &mut usize, count: usize) -> Vec<u64> {
    let mut dims = Vec::with_capacity(count);
    for _ in 0..count {
        if *pos + 8 > data.len() {
            break;
        }
        let val = read_le_u64(&data[*pos..], 8);
        *pos += 8;
        dims.push(val);
    }
    dims
}

fn read_le_u64(data: &[u8], size: usize) -> u64 {
    let mut val = 0u64;
    for i in 0..size.min(data.len()).min(8) {
        val |= (data[i] as u64) << (i * 8);
    }
    val
}