footer.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::{io::Read, sync::Arc};

use crate::format::{ColumnOrder as TColumnOrder, FileMetaData as TFileMetaData};
use crate::thrift::{TCompactSliceInputProtocol, TSerializable};

use crate::basic::ColumnOrder;

use crate::errors::{ParquetError, Result};
use crate::file::{metadata::*, reader::ChunkReader, FOOTER_SIZE, PARQUET_MAGIC};

use crate::schema::types::{self, SchemaDescriptor};

/// Reads the [ParquetMetaData] from the footer of the parquet file.
///
/// # Layout of Parquet file
/// ```text
/// +---------------------------+-----+---+
/// |      Rest of file         |  B  | A |
/// +---------------------------+-----+---+
/// ```
/// where
/// * `A`: parquet footer which stores the length of the metadata.
/// * `B`: parquet metadata.
///
/// # I/O
///
/// This method first reads the last 8 bytes of the file via
/// [`ChunkReader::get_read`] to get the the parquet footer which contains the
/// metadata length.
///
/// It then issues a second `get_read` to read the encoded metadata
/// metadata.
///
/// # See Also
/// [`decode_metadata`] for decoding the metadata from the bytes.
/// [`decode_footer`] for decoding the metadata length from the footer.
pub fn parse_metadata<R: ChunkReader>(chunk_reader: &R) -> Result<ParquetMetaData> {
    // check file is large enough to hold footer
    let file_size = chunk_reader.len();
    if file_size < (FOOTER_SIZE as u64) {
        return Err(general_err!(
            "Invalid Parquet file. Size is smaller than footer"
        ));
    }

    let mut footer = [0_u8; 8];
    chunk_reader
        .get_read(file_size - 8)?
        .read_exact(&mut footer)?;

    let metadata_len = decode_footer(&footer)?;
    let footer_metadata_len = FOOTER_SIZE + metadata_len;

    if footer_metadata_len > file_size as usize {
        return Err(general_err!(
            "Invalid Parquet file. Reported metadata length of {} + {} byte footer, but file is only {} bytes",
            metadata_len,
            FOOTER_SIZE,
            file_size
        ));
    }

    let start = file_size - footer_metadata_len as u64;
    decode_metadata(chunk_reader.get_bytes(start, metadata_len)?.as_ref())
}

/// Decodes [`ParquetMetaData`] from the provided bytes.
///
/// Typically this is used to decode the metadata from the end of a parquet
/// file. The format of `buf` is the Thift compact binary protocol, as specified
/// by the [Parquet Spec].
///
/// [Parquet Spec]: https://github.com/apache/parquet-format#metadata
pub fn decode_metadata(buf: &[u8]) -> Result<ParquetMetaData> {
    // TODO: row group filtering
    let mut prot = TCompactSliceInputProtocol::new(buf);
    let t_file_metadata: TFileMetaData = TFileMetaData::read_from_in_protocol(&mut prot)
        .map_err(|e| ParquetError::General(format!("Could not parse metadata: {e}")))?;
    let schema = types::from_thrift(&t_file_metadata.schema)?;
    let schema_descr = Arc::new(SchemaDescriptor::new(schema));
    let mut row_groups = Vec::new();
    for rg in t_file_metadata.row_groups {
        row_groups.push(RowGroupMetaData::from_thrift(schema_descr.clone(), rg)?);
    }
    let column_orders = parse_column_orders(t_file_metadata.column_orders, &schema_descr);

    let file_metadata = FileMetaData::new(
        t_file_metadata.version,
        t_file_metadata.num_rows,
        t_file_metadata.created_by,
        t_file_metadata.key_value_metadata,
        schema_descr,
        column_orders,
    );
    Ok(ParquetMetaData::new(file_metadata, row_groups))
}

/// Decodes the Parquet footer returning the metadata length in bytes
///
/// A parquet footer is 8 bytes long and has the following layout:
/// * 4 bytes for the metadata length
/// * 4 bytes for the magic bytes 'PAR1'
///
/// ```text
/// +-----+--------+
/// | len | 'PAR1' |
/// +-----+--------+
/// ```
pub fn decode_footer(slice: &[u8; FOOTER_SIZE]) -> Result<usize> {
    // check this is indeed a parquet file
    if slice[4..] != PARQUET_MAGIC {
        return Err(general_err!("Invalid Parquet file. Corrupt footer"));
    }

    // get the metadata length from the footer
    let metadata_len = u32::from_le_bytes(slice[..4].try_into().unwrap());
    // u32 won't be larger than usize in most cases
    Ok(metadata_len as usize)
}

/// Parses column orders from Thrift definition.
/// If no column orders are defined, returns `None`.
fn parse_column_orders(
    t_column_orders: Option<Vec<TColumnOrder>>,
    schema_descr: &SchemaDescriptor,
) -> Option<Vec<ColumnOrder>> {
    match t_column_orders {
        Some(orders) => {
            // Should always be the case
            assert_eq!(
                orders.len(),
                schema_descr.num_columns(),
                "Column order length mismatch"
            );
            let mut res = Vec::new();
            for (i, column) in schema_descr.columns().iter().enumerate() {
                match orders[i] {
                    TColumnOrder::TYPEORDER(_) => {
                        let sort_order = ColumnOrder::get_sort_order(
                            column.logical_type(),
                            column.converted_type(),
                            column.physical_type(),
                        );
                        res.push(ColumnOrder::TYPE_DEFINED_ORDER(sort_order));
                    }
                }
            }
            Some(res)
        }
        None => None,
    }
}

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

    use crate::basic::SortOrder;
    use crate::basic::Type;
    use crate::format::TypeDefinedOrder;
    use crate::schema::types::Type as SchemaType;

    #[test]
    fn test_parse_metadata_size_smaller_than_footer() {
        let test_file = tempfile::tempfile().unwrap();
        let reader_result = parse_metadata(&test_file);
        assert_eq!(
            reader_result.unwrap_err().to_string(),
            "Parquet error: Invalid Parquet file. Size is smaller than footer"
        );
    }

    #[test]
    fn test_parse_metadata_corrupt_footer() {
        let data = Bytes::from(vec![1, 2, 3, 4, 5, 6, 7, 8]);
        let reader_result = parse_metadata(&data);
        assert_eq!(
            reader_result.unwrap_err().to_string(),
            "Parquet error: Invalid Parquet file. Corrupt footer"
        );
    }

    #[test]
    fn test_parse_metadata_invalid_start() {
        let test_file = Bytes::from(vec![255, 0, 0, 0, b'P', b'A', b'R', b'1']);
        let reader_result = parse_metadata(&test_file);
        assert_eq!(
            reader_result.unwrap_err().to_string(),
            "Parquet error: Invalid Parquet file. Reported metadata length of 255 + 8 byte footer, but file is only 8 bytes"
        );
    }

    #[test]
    fn test_metadata_column_orders_parse() {
        // Define simple schema, we do not need to provide logical types.
        let fields = vec![
            Arc::new(
                SchemaType::primitive_type_builder("col1", Type::INT32)
                    .build()
                    .unwrap(),
            ),
            Arc::new(
                SchemaType::primitive_type_builder("col2", Type::FLOAT)
                    .build()
                    .unwrap(),
            ),
        ];
        let schema = SchemaType::group_type_builder("schema")
            .with_fields(fields)
            .build()
            .unwrap();
        let schema_descr = SchemaDescriptor::new(Arc::new(schema));

        let t_column_orders = Some(vec![
            TColumnOrder::TYPEORDER(TypeDefinedOrder::new()),
            TColumnOrder::TYPEORDER(TypeDefinedOrder::new()),
        ]);

        assert_eq!(
            parse_column_orders(t_column_orders, &schema_descr),
            Some(vec![
                ColumnOrder::TYPE_DEFINED_ORDER(SortOrder::SIGNED),
                ColumnOrder::TYPE_DEFINED_ORDER(SortOrder::SIGNED)
            ])
        );

        // Test when no column orders are defined.
        assert_eq!(parse_column_orders(None, &schema_descr), None);
    }

    #[test]
    #[should_panic(expected = "Column order length mismatch")]
    fn test_metadata_column_orders_len_mismatch() {
        let schema = SchemaType::group_type_builder("schema").build().unwrap();
        let schema_descr = SchemaDescriptor::new(Arc::new(schema));

        let t_column_orders = Some(vec![TColumnOrder::TYPEORDER(TypeDefinedOrder::new())]);

        parse_column_orders(t_column_orders, &schema_descr);
    }
}