[Json] Support FixedSizeList in json decoder

arrow-json/src/lib.rs

@@ -390,4 +390,42 @@ mod tests {
         assert_list_view_roundtrip::<i32>();
         assert_list_view_roundtrip::<i64>();
     }
+
+    #[test]
+    fn test_json_roundtrip_fixed_size_list() {
+        let inner = Arc::new(Field::new("item", DataType::Int32, true));
+        let schema = Arc::new(Schema::new(vec![
+            Field::new("flat", DataType::FixedSizeList(inner.clone(), 3), true),
+            Field::new(
+                "nested",
+                DataType::FixedSizeList(
+                    Arc::new(Field::new("item", DataType::FixedSizeList(inner, 2), true)),
+                    2,
+                ),
+                true,
+            ),
+        ]));
+
+        let input = r#"{"flat":[1,2,3],"nested":[[1,2],[3,4]]}
+{"flat":[4,null,5]}
+{"flat":[6,7,8],"nested":[[null,5],[6,null]]}
+"#
+        .as_bytes();
+
+        let batches: Vec<RecordBatch> = ReaderBuilder::new(schema.clone())
+            .with_batch_size(1024)
+            .build(Cursor::new(input))
+            .unwrap()
+            .collect::<Result<Vec<_>, _>>()
+            .unwrap();
+
+        let mut output = Vec::new();
+        let mut writer = WriterBuilder::new().build::<_, LineDelimited>(&mut output);
+        for batch in &batches {
+            writer.write(batch).unwrap();
+        }
+        writer.finish().unwrap();
+
+        assert_eq!(input, &output);
+    }
 }

arrow-json/src/reader/list_array.rs

@@ -19,7 +19,9 @@ use std::marker::PhantomData;
 use std::sync::Arc;
 
 use arrow_array::builder::BooleanBufferBuilder;
-use arrow_array::{ArrayRef, GenericListArray, GenericListViewArray, OffsetSizeTrait};
+use arrow_array::{
+    ArrayRef, FixedSizeListArray, GenericListArray, GenericListViewArray, OffsetSizeTrait,
+};
 use arrow_buffer::buffer::NullBuffer;
 use arrow_buffer::{OffsetBuffer, ScalarBuffer};
 use arrow_schema::{ArrowError, DataType, FieldRef};
@@ -134,3 +136,86 @@ impl<O: OffsetSizeTrait, const IS_VIEW: bool> ArrayDecoder for ListLikeArrayDeco
         }
     }
 }
+
+pub struct FixedSizeListArrayDecoder {
+    field: FieldRef,
+    size: i32,
+    decoder: Box<dyn ArrayDecoder>,
+    ignore_type_conflicts: bool,
+    is_nullable: bool,
+}
+
+impl FixedSizeListArrayDecoder {
+    pub fn new(
+        ctx: &DecoderContext,
+        data_type: &DataType,
+        is_nullable: bool,
+    ) -> Result<Self, ArrowError> {
+        let (field, size) = match data_type {
+            DataType::FixedSizeList(f, s) => (f, *s),
+            _ => unreachable!(),
+        };
+        let decoder = ctx.make_decoder(field.data_type(), field.is_nullable())?;
+
+        Ok(Self {
+            field: field.clone(),
+            size,
+            decoder,
+            ignore_type_conflicts: ctx.ignore_type_conflicts(),
+            is_nullable,
+        })
+    }
+}
+
+impl ArrayDecoder for FixedSizeListArrayDecoder {
+    fn decode(&mut self, tape: &Tape<'_>, pos: &[u32]) -> Result<ArrayRef, ArrowError> {
+        let expected = self.size as usize;
+        let mut child_pos = Vec::with_capacity(pos.len() * expected);
+
+        let mut nulls = self
+            .is_nullable
+            .then(|| BooleanBufferBuilder::new(pos.len()));
+
+        for p in pos {
+            let end_idx = match (tape.get(*p), nulls.as_mut()) {
+                (TapeElement::StartList(end_idx), None) => end_idx,
+                (TapeElement::StartList(end_idx), Some(nulls)) => {
+                    nulls.append(true);
+                    end_idx
+                }
+                (TapeElement::Null, Some(nulls)) => {
+                    nulls.append(false);
+                    child_pos.resize(child_pos.len() + expected, 0);
+                    continue;
+                }
+                (_, Some(nulls)) if self.ignore_type_conflicts => {
+                    nulls.append(false);
+                    child_pos.resize(child_pos.len() + expected, 0);
+                    continue;
+                }
+                _ => return Err(tape.error(*p, "[")),
+            };
+
+            let child_start = child_pos.len();
+            let mut cur_idx = *p + 1;
+            while cur_idx < end_idx {
+                child_pos.push(cur_idx);
+                cur_idx = tape.next(cur_idx, "fixed-size list value")?;
+            }
+
+            let actual = child_pos.len() - child_start;
+            if actual != expected {
+                return Err(ArrowError::JsonError(format!(
+                    "Incorrect number of elements for FixedSizeList, \
+                     expected {expected} but got {actual}"
+                )));
+            }
+        }
+
+        let values = self.decoder.decode(tape, &child_pos)?;
+        let nulls = nulls.as_mut().map(|x| NullBuffer::new(x.finish()));
+
+        let array = FixedSizeListArray::try_new(self.field.clone(), self.size, values, nulls)?;
+        Ok(Arc::new(array))
+    }
+}

arrow-json/src/reader/mod.rs

@@ -151,7 +151,9 @@ use crate::reader::binary_array::{
 };
 use crate::reader::boolean_array::BooleanArrayDecoder;
 use crate::reader::decimal_array::DecimalArrayDecoder;
-use crate::reader::list_array::{ListArrayDecoder, ListViewArrayDecoder};
+use crate::reader::list_array::{
+    FixedSizeListArrayDecoder, ListArrayDecoder, ListViewArrayDecoder,
+};
 use crate::reader::map_array::MapArrayDecoder;
 use crate::reader::null_array::NullArrayDecoder;
 use crate::reader::primitive_array::PrimitiveArrayDecoder;
@@ -835,6 +837,7 @@ fn make_decoder(
         DataType::LargeList(_) => Ok(Box::new(ListArrayDecoder::<i64>::new(ctx, data_type, is_nullable)?)),
         DataType::ListView(_) => Ok(Box::new(ListViewArrayDecoder::<i32>::new(ctx, data_type, is_nullable)?)),
         DataType::LargeListView(_) => Ok(Box::new(ListViewArrayDecoder::<i64>::new(ctx, data_type, is_nullable)?)),
+        DataType::FixedSizeList(_, _) => Ok(Box::new(FixedSizeListArrayDecoder::new(ctx, data_type, is_nullable)?)),
         DataType::Struct(_) => Ok(Box::new(StructArrayDecoder::new(ctx, data_type, is_nullable)?)),
         DataType::Binary => Ok(Box::new(BinaryArrayDecoder::<i32>::default())),
         DataType::LargeBinary => Ok(Box::new(BinaryArrayDecoder::<i64>::default())),
@@ -2308,6 +2311,152 @@ mod tests {
         assert_read_list_view::<i64>();
     }
 
+    #[test]
+    fn test_fixed_size_list() {
+        let buf = r#"
+        {"a": [1, 2, 3]}
+        {"a": [4, 5, 6]}
+        {"a": [7, 8, 9]}
+        "#;
+
+        let field = Field::new_list_field(DataType::Int32, true);
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "a",
+            DataType::FixedSizeList(Arc::new(field), 3),
+            false,
+        )]));
+
+        let batches = do_read(buf, 1024, false, false, schema);
+        assert_eq!(batches.len(), 1);
+
+        let col = batches[0].column(0).as_fixed_size_list();
+        assert_eq!(col.len(), 3);
+        assert_eq!(col.value_length(), 3);
+
+        let values = col.values().as_primitive::<Int32Type>();
+        assert_eq!(values.values(), &[1, 2, 3, 4, 5, 6, 7, 8, 9]);
+    }
+
+    #[test]
+    fn test_fixed_size_list_nullable() {
+        let buf = r#"
+        {"a": [1, 2]}
+        {"a": null}
+        {"a": [3, null]}
+        "#;
+
+        let field = Field::new_list_field(DataType::Int32, true);
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "a",
+            DataType::FixedSizeList(Arc::new(field), 2),
+            true,
+        )]));
+
+        let batches = do_read(buf, 1024, false, false, schema);
+        assert_eq!(batches.len(), 1);
+
+        let col = batches[0].column(0).as_fixed_size_list();
+        assert_eq!(col.len(), 3);
+        assert!(col.is_valid(0));
+        assert!(col.is_null(1));
+        assert!(col.is_valid(2));
+
+        let values = col.values().as_primitive::<Int32Type>();
+        assert_eq!(values.value(0), 1);
+        assert_eq!(values.value(1), 2);
+        assert_eq!(values.value(4), 3);
+        assert!(values.is_null(5));
+    }
+
+    #[test]
+    fn test_fixed_size_list_wrong_size() {
+        let buf = r#"{"a": [1, 2, 3]}"#;
+
+        let field = Field::new_list_field(DataType::Int32, true);
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "a",
+            DataType::FixedSizeList(Arc::new(field), 2),
+            false,
+        )]));
+
+        let err = ReaderBuilder::new(schema)
+            .build(Cursor::new(buf.as_bytes()))
+            .unwrap()
+            .next()
+            .unwrap()
+            .unwrap_err();
+
+        assert!(err.to_string().contains("expected 2 but got 3"), "{}", err);
+    }
+
+    #[test]
+    fn test_fixed_size_list_nested() {
+        let buf = r#"
+        {"a": [[1, 2], [3, 4]]}
+        {"a": [[5, 6], [7, 8]]}
+        "#;
+
+        let inner_field = Field::new_list_field(DataType::Int32, true);
+        let inner_type = DataType::FixedSizeList(Arc::new(inner_field), 2);
+        let outer_field = Arc::new(Field::new_list_field(inner_type.clone(), true));
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "a",
+            DataType::FixedSizeList(outer_field, 2),
+            false,
+        )]));
+
+        let batches = do_read(buf, 1024, false, false, schema);
+        assert_eq!(batches.len(), 1);
+
+        let col = batches[0].column(0).as_fixed_size_list();
+        assert_eq!(col.len(), 2);
+        assert_eq!(col.value_length(), 2);
+
+        let inner = col.values().as_fixed_size_list();
+        assert_eq!(inner.len(), 4);
+        assert_eq!(inner.value_length(), 2);
+
+        let values = inner.values().as_primitive::<Int32Type>();
+        assert_eq!(values.values(), &[1, 2, 3, 4, 5, 6, 7, 8]);
+    }
+
+    #[test]
+    fn test_fixed_size_list_ignore_type_conflicts() {
+        let field = Field::new("item", DataType::Int32, true);
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "a",
+            DataType::FixedSizeList(Arc::new(field), 2),
+            true,
+        )]));
+
+        let json = vec![
+            json!({"a": [1, 2]}),
+            json!({"a": "not a list"}),
+            json!({"a": 42}),
+            json!({"a": [6, 7]}),
+        ];
+
+        let mut decoder = ReaderBuilder::new(schema)
+            .with_ignore_type_conflicts(true)
+            .build_decoder()
+            .unwrap();
+        decoder.serialize(&json).unwrap();
+        let batch = decoder.flush().unwrap().unwrap();
+
+        let col = batch.column(0).as_fixed_size_list();
+        assert_eq!(col.len(), 4);
+        assert!(col.is_valid(0));
+        assert!(col.is_null(1)); // string -> null
+        assert!(col.is_null(2)); // number -> null
+        assert!(col.is_valid(3));
+
+        let values = col.values().as_primitive::<Int32Type>();
+        assert_eq!(values.value(0), 1);
+        assert_eq!(values.value(1), 2);
+        assert_eq!(values.value(6), 6);
+        assert_eq!(values.value(7), 7);
+    }
+
     #[test]
     fn test_skip_empty_lines() {
         let schema = Schema::new(vec![Field::new("a", DataType::Int64, true)]);
@@ -3256,6 +3405,11 @@ mod tests {
                 DataType::List(Arc::new(Field::new("item", DataType::Int32, true))),
                 false,
             ),
+            Field::new(
+                "fixed_size_list",
+                DataType::FixedSizeList(Arc::new(Field::new("item", DataType::Int32, true)), 2),
+                false,
+            ),
             Field::new(
                 "map",
                 DataType::Map(
@@ -3312,6 +3466,11 @@ mod tests {
                 DataType::List(Arc::new(Field::new("item", DataType::Int32, true))),
                 true,
             ),
+            Field::new(
+                "fixed_size_list",
+                DataType::FixedSizeList(Arc::new(Field::new("item", DataType::Int32, true)), 2),
+                true,
+            ),
             Field::new(
                 "map",
                 DataType::Map(