Supports legacy lz4 decompression

src/compression.rs

@@ -188,6 +188,20 @@ pub fn decompress(compression: Compression, input_buf: &[u8], output_buf: &mut [
             crate::error::Feature::Lz4,
             "decompress with lz4".to_string(),
         )),
+
+        #[cfg(any(feature = "lz4_flex", feature = "lz4"))]
+        Compression::Lz4 => try_decompress_hadoop(input_buf, output_buf).or_else(|_| {
+            decompress_to_buffer(input_buf, Some(output_buf.len() as i32), output_buf)
+                .map(|_| {})
+        }
+        ),
+
+        #[cfg(all(not(feature = "lz4_flex"), not(feature = "lz4")))]
+        Compression::Lz4 => Err(Error::FeatureNotActive(
+            crate::error::Feature::Lz4,
+            "decompress with legacy lz4".to_string(),
+        )),
+
         #[cfg(feature = "zstd")]
         Compression::Zstd => {
             use std::io::Read;
@@ -209,6 +223,88 @@ pub fn decompress(compression: Compression, input_buf: &[u8], output_buf: &mut [
     }
 }
 
+/// Try to decompress the buffer as if it was compressed with the Hadoop Lz4Codec.
+/// Translated from the apache arrow c++ function [TryDecompressHadoop](https://github.com/apache/arrow/blob/bf18e6e4b5bb6180706b1ba0d597a65a4ce5ca48/cpp/src/arrow/util/compression_lz4.cc#L474).
+/// Returns error if decompression failed.
+#[cfg(any(feature = "lz4", feature = "lz4_flex"))]
+fn try_decompress_hadoop(input_buf: &[u8], output_buf: &mut [u8]) -> Result<()> {
+    // Parquet files written with the Hadoop Lz4Codec use their own framing.
+    // The input buffer can contain an arbitrary number of "frames", each
+    // with the following structure:
+    // - bytes 0..3: big-endian uint32_t representing the frame decompressed size
+    // - bytes 4..7: big-endian uint32_t representing the frame compressed size
+    // - bytes 8...: frame compressed data
+    //
+    // The Hadoop Lz4Codec source code can be found here:
+    // https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-nativetask/src/main/native/src/codec/Lz4Codec.cc
+
+    const SIZE_U32: usize = std::mem::size_of::<u32>();
+    const PREFIX_LEN: usize = SIZE_U32 * 2;
+    let mut input_len = input_buf.len();
+    let mut input = input_buf;
+    let mut output_len = output_buf.len();
+    let mut output: &mut [u8] = output_buf;
+    while input_len >= PREFIX_LEN {
+        let mut bytes = [0; SIZE_U32];
+        bytes.copy_from_slice(&input[0..4]);
+        let expected_decompressed_size = u32::from_be_bytes(bytes);
+        let mut bytes = [0; SIZE_U32];
+        bytes.copy_from_slice(&input[4..8]);
+        let expected_compressed_size = u32::from_be_bytes(bytes);
+        input = &input[PREFIX_LEN..];
+        input_len -= PREFIX_LEN;
+
+        if input_len < expected_compressed_size as usize {
+            return Err(general_err!("Not enough bytes for Hadoop frame".to_owned()));
+        }
+
+        if output_len < expected_decompressed_size as usize {
+            return Err(general_err!(
+                "Not enough bytes to hold advertised output".to_owned()
+            ));
+        }
+        let decompressed_size = decompress_to_buffer(
+            &input[..expected_compressed_size as usize],
+            Some(output_len as i32),
+            output,
+        )?;
+        if decompressed_size != expected_decompressed_size as usize {
+            return Err(general_err!("unexpected decompressed size"));
+        }
+        if input_len > expected_compressed_size as usize {
+            input = &input[expected_compressed_size as usize..];
+            input_len -= expected_compressed_size as usize;
+            output = &mut output[expected_decompressed_size as usize..];
+            output_len -= expected_decompressed_size as usize;
+        } else {
+            break;
+        }
+    }
+    Ok(())
+}
+
+#[cfg(all(feature = "lz4", not(feature = "lz4_flex")))]
+#[inline]
+fn decompress_to_buffer(
+    src: &[u8],
+    uncompressed_size: Option<i32>,
+    buffer: &mut [u8],
+) -> Result<usize> {
+    let size = lz4::block::decompress_to_buffer(src, uncompressed_size, buffer)?;
+    Ok(size)
+}
+
+#[cfg(all(feature = "lz4_flex", not(feature = "lz4")))]
+#[inline]
+fn decompress_to_buffer(
+    src: &[u8],
+    _uncompressed_size: Option<i32>,
+    buffer: &mut [u8],
+) -> Result<usize> {
+    let size = lz4_flex::block::decompress_into(src, buffer)?;
+    Ok(size)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

tests/it/read/lz4_legacy.rs

@@ -0,0 +1,67 @@
+use crate::get_path;
+use crate::read::get_column;
+use crate::Array;
+use parquet2::error::Result;
+
+fn verify_column_data(column: &str) -> Array {
+    match column {
+        "c0" => {
+            let expected = vec![1593604800, 1593604800, 1593604801, 1593604801];
+            let expected = expected.into_iter().map(Some).collect::<Vec<_>>();
+            Array::Int64(expected)
+        }
+        "c1" => {
+            let expected = vec!["abc", "def", "abc", "def"];
+            let expected = expected
+                .into_iter()
+                .map(|v| Some(v.as_bytes().to_vec()))
+                .collect::<Vec<_>>();
+            Array::Binary(expected)
+        }
+        "v11" => {
+            let expected = vec![42_f64, 7.7, 42.125, 7.7];
+            let expected = expected.into_iter().map(Some).collect::<Vec<_>>();
+            Array::Float64(expected)
+        }
+        _ => unreachable!(),
+    }
+}
+
+#[test]
+fn test_lz4_inference() -> Result<()> {
+
+    // - file "hadoop_lz4_compressed.parquet" is compressed using the hadoop Lz4Codec
+    // - file "non_hadoop_lz4_compressed.parquet" is "the LZ4 block format without the custom Hadoop header".
+    //    see https://github.com/apache/parquet-testing/pull/14
+
+    // Those two files, are all marked as compressed as Lz4, the decompressor should
+    // be able to distinguish them from each other.
+
+    let files = ["hadoop_lz4_compressed.parquet", "non_hadoop_lz4_compressed.parquet"];
+    let columns = ["c0", "c1", "v11"];
+    for file in files {
+        let mut path = get_path();
+        path.push(file);
+        let path = path.to_str().unwrap();
+        for column in columns {
+            let (result, _statistics) = get_column(path, column)?;
+            assert_eq!(result, verify_column_data(column), "of file {}", file);
+        }
+    }
+    Ok(())
+}
+
+#[test]
+fn test_lz4_large_file() -> Result<()> {
+
+    //File "hadoop_lz4_compressed_larger.parquet" is compressed using the hadoop Lz4Codec,
+    //which contains 10000 rows.
+
+    let mut path = get_path();
+    let file = "hadoop_lz4_compressed_larger.parquet";
+    path.push(file);
+    let path = path.to_str().unwrap();
+    let (result, _statistics) = get_column(path, "a")?;
+    assert_eq!(result.len(), 10000);
+    Ok(())
+}

tests/it/read/mod.rs

@@ -11,6 +11,9 @@ mod primitive_nested;
 mod struct_;
 mod utils;
 
+#[cfg(any(feature = "lz4", feature = "lz4_flex"))]
+mod lz4_legacy;
+
 use std::fs::File;
 
 use futures::StreamExt;