hdf5-pure-rust 0.2.0

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

/// Parsed Attribute message (type 0x000C).
#[derive(Debug, Clone)]
pub struct AttributeMessage {
    pub version: u8,
    pub name: String,
    pub datatype: DatatypeMessage,
    pub dataspace: DataspaceMessage,
    /// Raw attribute data bytes.
    pub data: Vec<u8>,
}

impl AttributeMessage {
    pub fn decode(raw: &[u8]) -> Result<Self> {
        if raw.len() < 6 {
            return Err(Error::InvalidFormat("attribute message too short".into()));
        }

        let version = raw[0];
        match version {
            1 => Self::decode_v1(raw),
            2 => Self::decode_v2(raw),
            3 => Self::decode_v3(raw),
            _ => Err(Error::Unsupported(format!(
                "attribute message version {version}"
            ))),
        }
    }

    fn decode_v1(raw: &[u8]) -> Result<Self> {
        // v1: version(1) + reserved(1) + name_size(2) + datatype_size(2) + dataspace_size(2)
        let name_size = u16::from_le_bytes([raw[2], raw[3]]) as usize;
        let dt_size = u16::from_le_bytes([raw[4], raw[5]]) as usize;
        let ds_size = u16::from_le_bytes([raw[6], raw[7]]) as usize;
        let mut pos = 8;

        // Name (null-padded to 8-byte boundary)
        let name_end = raw[pos..pos + name_size]
            .iter()
            .position(|&b| b == 0)
            .unwrap_or(name_size);
        let name = String::from_utf8_lossy(&raw[pos..pos + name_end]).to_string();
        let name_padded = (name_size + 7) & !7;
        pos += name_padded;

        // Datatype (padded to 8-byte boundary)
        let datatype = DatatypeMessage::decode(&raw[pos..pos + dt_size])?;
        let dt_padded = (dt_size + 7) & !7;
        pos += dt_padded;

        // Dataspace (padded to 8-byte boundary)
        let dataspace = DataspaceMessage::decode(&raw[pos..pos + ds_size])?;
        let ds_padded = (ds_size + 7) & !7;
        pos += ds_padded;

        // Data
        let data = raw[pos..].to_vec();

        Ok(Self {
            version: 1,
            name,
            datatype,
            dataspace,
            data,
        })
    }

    fn decode_v2(raw: &[u8]) -> Result<Self> {
        // v2: version(1) + flags(1) + name_size(2) + datatype_size(2) + dataspace_size(2)
        let name_size = u16::from_le_bytes([raw[2], raw[3]]) as usize;
        let dt_size = u16::from_le_bytes([raw[4], raw[5]]) as usize;
        let ds_size = u16::from_le_bytes([raw[6], raw[7]]) as usize;
        let mut pos = 8;

        // Name (NOT padded in v2)
        let name_end = raw[pos..pos + name_size]
            .iter()
            .position(|&b| b == 0)
            .unwrap_or(name_size);
        let name = String::from_utf8_lossy(&raw[pos..pos + name_end]).to_string();
        pos += name_size;

        // Datatype (NOT padded in v2)
        let datatype = DatatypeMessage::decode(&raw[pos..pos + dt_size])?;
        pos += dt_size;

        // Dataspace (NOT padded in v2)
        let dataspace = DataspaceMessage::decode(&raw[pos..pos + ds_size])?;
        pos += ds_size;

        let data = raw[pos..].to_vec();

        Ok(Self {
            version: 2,
            name,
            datatype,
            dataspace,
            data,
        })
    }

    fn decode_v3(raw: &[u8]) -> Result<Self> {
        // v3: version(1) + flags(1) + name_size(2) + datatype_size(2) + dataspace_size(2) + encoding(1)
        let _flags = raw[1];
        let name_size = u16::from_le_bytes([raw[2], raw[3]]) as usize;
        let dt_size = u16::from_le_bytes([raw[4], raw[5]]) as usize;
        let ds_size = u16::from_le_bytes([raw[6], raw[7]]) as usize;
        let _encoding = raw[8]; // character encoding: 0=ASCII, 1=UTF-8
        let mut pos = 9;

        let name_end = raw[pos..pos + name_size]
            .iter()
            .position(|&b| b == 0)
            .unwrap_or(name_size);
        let name = String::from_utf8_lossy(&raw[pos..pos + name_end]).to_string();
        pos += name_size;

        let datatype = DatatypeMessage::decode(&raw[pos..pos + dt_size])?;
        pos += dt_size;

        let dataspace = DataspaceMessage::decode(&raw[pos..pos + ds_size])?;
        pos += ds_size;

        let data = raw[pos..].to_vec();

        Ok(Self {
            version: 3,
            name,
            datatype,
            dataspace,
            data,
        })
    }

    /// Get total number of elements.
    pub fn num_elements(&self) -> u64 {
        if self.dataspace.dims.is_empty() {
            1 // scalar
        } else {
            self.dataspace.dims.iter().product()
        }
    }

    /// Get total data size in bytes.
    pub fn data_size(&self) -> usize {
        self.num_elements() as usize * self.datatype.size as usize
    }
}