Added support for roundtrip extension types in parquet

src/datatypes/mod.rs

@@ -9,26 +9,17 @@ pub use schema::Schema;
 
 pub(crate) use field::{get_extension, Extension, Metadata};
 
-/// The set of datatypes that are supported by this implementation of Apache Arrow.
-///
-/// The Arrow specification on data types includes some more types.
-/// See also [`Schema.fbs`](https://github.com/apache/arrow/blob/master/format/Schema.fbs)
-/// for Arrow's specification.
-///
-/// The variants of this enum include primitive fixed size types as well as parametric or
-/// nested types.
-/// Currently the Rust implementation supports the following  nested types:
-///  - `List<T>`
-///  - `Struct<T, U, V, ...>`
-///
-/// Nested types can themselves be nested within other arrays.
-/// For more information on these types please see
-/// [the physical memory layout of Apache Arrow](https://arrow.apache.org/docs/format/Columnar.html#physical-memory-layout).
+/// The set of supported logical types.
+/// Each variant uniquely identifies a logical type, which define specific semantics to the data (e.g. how it should be represented).
+/// A [`DataType`] has an unique corresponding [`PhysicalType`], obtained via [`DataType::to_physical_type`],
+/// which uniquely identifies an in-memory representation of data.
+/// The [`DataType::Extension`] is special in that it augments a [`DataType`] with metadata to support custom types.
+/// Use `to_logical_type` to desugar such type and return its correspoding logical type.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum DataType {
-    /// Null type, representing an array without values or validity, only a length.
+    /// Null type
     Null,
-    /// A boolean datatype representing the values `true` and `false`.
+    /// `true` and `false`.
     Boolean,
     /// A signed 8-bit integer.
     Int8,
@@ -223,6 +214,17 @@ impl DataType {
             Extension(_, key, _) => key.to_physical_type(),
         }
     }
+
+    /// Returns `&self` for all but [`DataType::Extension`]. For [`DataType::Extension`],
+    /// (recursively) returns the inner [`DataType`].
+    /// Never returns the variant [`DataType::Extension`].
+    pub fn to_logical_type(&self) -> &DataType {
+        use DataType::*;
+        match self {
+            Extension(_, key, _) => key.to_logical_type(),
+            _ => self,
+        }
+    }
 }
 
 fn to_dictionary_index_type(data_type: &DataType) -> DictionaryIndexType {

src/io/parquet/read/binary/dictionary.rs

@@ -32,7 +32,7 @@ fn read_dict_optional<K, O>(
 {
     let length = indices.len() + additional;
     values.extend_from_slice(dict.values());
-    offsets.extend(
+    offsets.extend_from_trusted_len_iter(
         dict.offsets()
             .iter()
             .map(|x| O::from_usize(*x as usize).unwrap()),
@@ -152,6 +152,10 @@ where
         )?
     }
 
+    if offsets.len() == 0 {
+        // the array is empty and thus we need to push the first offset ourselves.
+        offsets.push(O::zero());
+    };
     let keys = PrimitiveArray::from_data(K::DATA_TYPE, indices.into(), validity.into());
     let data_type = DictionaryArray::<K>::get_child(&data_type).clone();
     let values = Arc::new(Utf8Array::from_data(

src/io/parquet/read/fixed_size_binary.rs

@@ -22,12 +22,11 @@ pub(crate) fn read_dict_buffer(
     validity_buffer: &[u8],
     indices_buffer: &[u8],
     additional: usize,
-    size: i32,
+    size: usize,
     dict: &FixedLenByteArrayPageDict,
     values: &mut MutableBuffer<u8>,
     validity: &mut MutableBitmap,
 ) {
-    let size = size as usize;
     let length = values.len() * size + additional;
     let dict_values = dict.values();
 
@@ -75,11 +74,10 @@ pub(crate) fn read_optional(
     validity_buffer: &[u8],
     values_buffer: &[u8],
     additional: usize,
-    size: i32,
+    size: usize,
     values: &mut MutableBuffer<u8>,
     validity: &mut MutableBitmap,
 ) {
-    let size = size as usize;
     let length = values.len() * size + additional;
 
     assert_eq!(values_buffer.len() % size, 0);
@@ -122,25 +120,27 @@ pub(crate) fn read_optional(
 pub(crate) fn read_required(
     buffer: &[u8],
     additional: usize,
-    size: i32,
+    size: usize,
     values: &mut MutableBuffer<u8>,
 ) {
-    assert_eq!(buffer.len(), additional * size as usize);
+    assert_eq!(buffer.len(), additional * size);
     values.extend_from_slice(buffer);
 }
 
 pub fn iter_to_array<I, E>(
     mut iter: I,
-    size: i32,
+    data_type: DataType,
     metadata: &ColumnChunkMetaData,
 ) -> Result<FixedSizeBinaryArray>
 where
     ArrowError: From<E>,
     E: Clone,
     I: StreamingIterator<Item = std::result::Result<DataPage, E>>,
 {
+    let size = *FixedSizeBinaryArray::get_size(&data_type) as usize;
+
     let capacity = metadata.num_values() as usize;
-    let mut values = MutableBuffer::<u8>::with_capacity(capacity * size as usize);
+    let mut values = MutableBuffer::<u8>::with_capacity(capacity * size);
     let mut validity = MutableBitmap::with_capacity(capacity);
     while let Some(page) = iter.next() {
         extend_from_page(
@@ -153,24 +153,26 @@ where
     }
 
     Ok(FixedSizeBinaryArray::from_data(
-        DataType::FixedSizeBinary(size),
+        data_type,
         values.into(),
         validity.into(),
     ))
 }
 
 pub async fn stream_to_array<I, E>(
     pages: I,
-    size: i32,
+    data_type: DataType,
     metadata: &ColumnChunkMetaData,
 ) -> Result<FixedSizeBinaryArray>
 where
     ArrowError: From<E>,
     E: Clone,
     I: Stream<Item = std::result::Result<DataPage, E>>,
 {
+    let size = *FixedSizeBinaryArray::get_size(&data_type) as usize;
+
     let capacity = metadata.num_values() as usize;
-    let mut values = MutableBuffer::<u8>::with_capacity(capacity * size as usize);
+    let mut values = MutableBuffer::<u8>::with_capacity(capacity * size);
     let mut validity = MutableBitmap::with_capacity(capacity);
 
     pin_mut!(pages); // needed for iteration
@@ -186,15 +188,15 @@ where
     }
 
     Ok(FixedSizeBinaryArray::from_data(
-        DataType::FixedSizeBinary(size),
+        data_type,
         values.into(),
         validity.into(),
     ))
 }
 
 pub(crate) fn extend_from_page(
     page: &DataPage,
-    size: i32,
+    size: usize,
     descriptor: &ColumnDescriptor,
     values: &mut MutableBuffer<u8>,
     validity: &mut MutableBitmap,

src/io/parquet/read/mod.rs

@@ -93,7 +93,7 @@ fn dict_read<
         panic!()
     };
 
-    match values_data_type {
+    match values_data_type.to_logical_type() {
         UInt8 => primitive::iter_to_dict_array::<K, _, _, _, _, _>(
             iter,
             metadata,
@@ -169,7 +169,7 @@ pub fn page_iter_to_array<
     data_type: DataType,
 ) -> Result<Box<dyn Array>> {
     use DataType::*;
-    match data_type {
+    match data_type.to_logical_type() {
         // INT32
         UInt8 => primitive::iter_to_array(iter, metadata, data_type, |x: i32| x as u8),
         UInt16 => primitive::iter_to_array(iter, metadata, data_type, |x: i32| x as u16),
@@ -207,7 +207,7 @@ pub fn page_iter_to_array<
         Binary | Utf8 => binary::iter_to_array::<i32, _, _>(iter, metadata, &data_type),
         LargeBinary | LargeUtf8 => binary::iter_to_array::<i64, _, _>(iter, metadata, &data_type),
         FixedSizeBinary(size) => Ok(Box::new(fixed_size_binary::iter_to_array(
-            iter, size, metadata,
+            iter, data_type, metadata,
         )?)),
 
         List(ref inner) => match inner.data_type() {
@@ -247,7 +247,7 @@ pub fn page_iter_to_array<
                 binary::iter_to_array_nested::<i64, _, _>(iter, metadata, data_type)
             }
             other => Err(ArrowError::NotYetImplemented(format!(
-                "The conversion of {:?} to arrow still not implemented",
+                "Reading {:?} from parquet still not implemented",
                 other
             ))),
         },
@@ -265,7 +265,7 @@ pub fn page_iter_to_array<
         },
 
         other => Err(ArrowError::NotYetImplemented(format!(
-            "The conversion of {:?} to arrow still not implemented",
+            "Reading {:?} from parquet still not implemented",
             other
         ))),
     }
@@ -278,7 +278,7 @@ pub async fn page_stream_to_array<I: Stream<Item = std::result::Result<DataPage,
     data_type: DataType,
 ) -> Result<Box<dyn Array>> {
     use DataType::*;
-    match data_type {
+    match data_type.to_logical_type() {
         // INT32
         UInt8 => primitive::stream_to_array(pages, metadata, data_type, |x: i32| x as u8).await,
         UInt16 => primitive::stream_to_array(pages, metadata, data_type, |x: i32| x as u16).await,
@@ -321,7 +321,7 @@ pub async fn page_stream_to_array<I: Stream<Item = std::result::Result<DataPage,
             binary::stream_to_array::<i64, _, _>(pages, metadata, &data_type).await
         }
         FixedSizeBinary(size) => Ok(Box::new(
-            fixed_size_binary::stream_to_array(pages, size, metadata).await?,
+            fixed_size_binary::stream_to_array(pages, data_type, metadata).await?,
         )),
         other => Err(ArrowError::NotYetImplemented(format!(
             "Async conversion of {:?}",

src/io/parquet/write/dictionary.rs

@@ -136,7 +136,7 @@ where
     match encoding {
         Encoding::PlainDictionary | Encoding::RleDictionary => {
             // write DictPage
-            let dict_page = match array.values().data_type() {
+            let dict_page = match array.values().data_type().to_logical_type() {
                 DataType::Int8 => dyn_prim!(i8, i32, array),
                 DataType::Int16 => dyn_prim!(i16, i32, array),
                 DataType::Int32 | DataType::Date32 | DataType::Time32(_) => {

src/io/parquet/write/mod.rs

@@ -141,7 +141,7 @@ pub fn array_to_page(
         )));
     }
 
-    match data_type {
+    match data_type.to_logical_type() {
         DataType::Boolean => {
             boolean::array_to_page(array.as_any().downcast_ref().unwrap(), options, descriptor)
         }

src/io/parquet/write/schema.rs

@@ -45,7 +45,7 @@ pub fn to_parquet_type(field: &Field) -> Result<ParquetType> {
         Repetition::Required
     };
     // create type from field
-    match field.data_type() {
+    match field.data_type().to_logical_type() {
         DataType::Null => Ok(ParquetType::try_from_primitive(
             name,
             PhysicalType::Int32,

tests/it/io/parquet/mod.rs

@@ -458,6 +458,12 @@ fn roundtrip_100_dict() -> Result<()> {
     test_file("1.0.0-bigendian", "generated_dictionary")
 }
 
+#[test]
+fn roundtrip_100_extension() -> Result<()> {
+    test_file("1.0.0-littleendian", "generated_extension")?;
+    test_file("1.0.0-bigendian", "generated_extension")
+}
+
 /// Tests that when arrow-specific types (Duration and LargeUtf8) are written to parquet, we can rountrip its
 /// logical types.
 #[test]