Jefffrey commented on code in PR #5318:
URL: https://github.com/apache/arrow-rs/pull/5318#discussion_r1463942981
##########
arrow-json/src/writer.rs:
##########
@@ -703,7 +682,7 @@ where
format: F,
/// Whether keys with null values should be written or skipped
Review Comment:
```suggestion
/// Controls how JSON should be encoded, e.g. whether to write explicit
nulls or skip them
```
##########
arrow-json/src/writer/encoder.rs:
##########
@@ -0,0 +1,435 @@
+// 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 arrow_array::cast::AsArray;
+use arrow_array::types::*;
+use arrow_array::*;
+use arrow_buffer::{ArrowNativeType, NullBuffer, OffsetBuffer, ScalarBuffer};
+use arrow_cast::display::{ArrayFormatter, FormatOptions};
+use arrow_schema::{ArrowError, DataType, FieldRef};
+use half::f16;
+use lexical_core::FormattedSize;
+use serde::Serializer;
+use std::io::Write;
+
+#[derive(Debug, Clone, Default)]
+pub struct EncoderOptions {
+ pub explicit_nulls: bool,
+}
+
+pub trait Encoder {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>);
+}
+
+pub fn make_encoder<'a>(
+ array: &'a dyn Array,
+ options: &EncoderOptions,
+) -> Result<Box<dyn Encoder + 'a>, ArrowError> {
+ let (encoder, nulls) = make_encoder_impl(array, options)?;
+ assert!(nulls.is_none(), "root cannot be nullable");
+ Ok(encoder)
+}
+
+fn make_encoder_impl<'a>(
+ array: &'a dyn Array,
+ options: &EncoderOptions,
+) -> Result<(Box<dyn Encoder + 'a>, Option<NullBuffer>), ArrowError> {
+ macro_rules! primitive_helper {
+ ($t:ty) => {{
+ let array = array.as_primitive::<$t>();
+ let nulls = array.nulls().cloned();
+ (Box::new(PrimitiveEncoder::new(array)) as _, nulls)
+ }};
+ }
+
+ Ok(downcast_integer! {
+ array.data_type() => (primitive_helper),
+ DataType::Float16 => primitive_helper!(Float16Type),
+ DataType::Float32 => primitive_helper!(Float32Type),
+ DataType::Float64 => primitive_helper!(Float64Type),
+ DataType::Boolean => {
+ let array = array.as_boolean();
+ (Box::new(BooleanEncoder(array.clone())), array.nulls().cloned())
+ }
+ DataType::Null => (Box::new(NullEncoder), array.logical_nulls()),
+ DataType::Utf8 => {
+ let array = array.as_string::<i32>();
+ (Box::new(StringEncoder(array.clone())) as _,
array.nulls().cloned())
+ }
+ DataType::LargeUtf8 => {
+ let array = array.as_string::<i64>();
+ (Box::new(StringEncoder(array.clone())) as _,
array.nulls().cloned())
+ }
+ DataType::List(_) => {
+ let array = array.as_list::<i32>();
+ (Box::new(ListEncoder::try_new(array, options)?) as _,
array.nulls().cloned())
+ }
+ DataType::LargeList(_) => {
+ let array = array.as_list::<i64>();
+ (Box::new(ListEncoder::try_new(array, options)?) as _,
array.nulls().cloned())
+ }
+
+ DataType::Dictionary(_, _) => downcast_dictionary_array! {
+ array => (Box::new(DictionaryEncoder::try_new(array, options)?) as
_, array.logical_nulls()),
+ _ => unreachable!()
+ }
+
+ DataType::Map(_, _) => {
+ let array = array.as_map();
+ (Box::new(MapEncoder::try_new(array, options)?) as _,
array.nulls().cloned())
+ }
+
+ DataType::Struct(fields) => {
+ let array = array.as_struct();
+ let encoders = fields.iter().zip(array.columns()).map(|(field,
array)| {
+ let (encoder, nulls) = make_encoder_impl(array, options)?;
+ Ok(FieldEncoder{
+ field: field.clone(),
+ encoder, nulls
+ })
+ }).collect::<Result<Vec<_>, ArrowError>>()?;
+
+ let encoder = StructArrayEncoder{
+ encoders,
+ explicit_nulls: options.explicit_nulls,
+ };
+ (Box::new(encoder) as _, array.nulls().cloned())
+ }
+ d => match d.is_temporal() {
+ true => {
+ // Note: the implementation assumes that escaping is not
necessary
+ // If this is extended to support user-provided format
specifications
+ // this assumption may need to be revisited
+ let options = FormatOptions::new().with_display_error(true);
+ let formatter = ArrayFormatter::try_new(array, &options)?;
+ (Box::new(formatter) as _, array.nulls().cloned())
+ }
+ false => return Err(ArrowError::InvalidArgumentError(format!("JSON
Writer does not support data type: {d}"))),
+ }
+ })
+}
+
+fn encode_string(s: &str, out: &mut Vec<u8>) {
+ let mut serializer = serde_json::Serializer::new(out);
+ serializer.serialize_str(s).unwrap();
+}
+
+struct FieldEncoder<'a> {
+ field: FieldRef,
+ encoder: Box<dyn Encoder + 'a>,
+ nulls: Option<NullBuffer>,
+}
+
+struct StructArrayEncoder<'a> {
+ encoders: Vec<FieldEncoder<'a>>,
+ explicit_nulls: bool,
+}
+
+impl<'a> Encoder for StructArrayEncoder<'a> {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ out.push(b'{');
+ let mut is_first = true;
+ for field_encoder in &mut self.encoders {
+ let is_null = field_encoder.nulls.as_ref().is_some_and(|n|
n.is_null(idx));
+ if is_null && !self.explicit_nulls {
+ continue;
+ }
+
+ if !is_first {
+ out.push(b',');
+ }
+ is_first = false;
+
+ encode_string(field_encoder.field.name(), out);
+ out.push(b':');
+
+ match is_null {
+ true => out.extend_from_slice(b"null"),
+ false => field_encoder.encoder.encode(idx, out),
+ }
+ }
+ out.push(b'}');
+ }
+}
+
+trait PrimitiveEncode: ArrowNativeType {
+ type Buffer;
+
+ // Workaround https://github.com/rust-lang/rust/issues/61415
+ fn init_buffer() -> Self::Buffer;
+
+ fn encode(self, buf: &mut Self::Buffer) -> &[u8];
+}
+
+macro_rules! integer_encode {
+ ($($t:ty),*) => {
+ $(
+ impl PrimitiveEncode for $t {
+ type Buffer = [u8; Self::FORMATTED_SIZE];
+
+ fn init_buffer() -> Self::Buffer {
+ [0; Self::FORMATTED_SIZE]
+ }
+
+ fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
+ lexical_core::write(self, buf)
+ }
+ }
+ )*
+ };
+}
+integer_encode!(i8, i16, i32, i64, u8, u16, u32, u64);
+
+macro_rules! float_encode {
+ ($($t:ty),*) => {
+ $(
+ impl PrimitiveEncode for $t {
+ type Buffer = [u8; Self::FORMATTED_SIZE];
+
+ fn init_buffer() -> Self::Buffer {
+ [0; Self::FORMATTED_SIZE]
+ }
+
+ fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
+ if self.is_infinite() || self.is_nan() {
+ b"null"
+ } else {
+ lexical_core::write(self, buf)
+ }
+ }
+ }
+ )*
+ };
+}
+float_encode!(f32, f64);
+
+impl PrimitiveEncode for f16 {
+ type Buffer = <f64 as PrimitiveEncode>::Buffer;
+
+ fn init_buffer() -> Self::Buffer {
+ f64::init_buffer()
+ }
+
+ fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
+ self.to_f64().encode(buf)
+ }
+}
+
+struct PrimitiveEncoder<N: PrimitiveEncode> {
+ values: ScalarBuffer<N>,
+ buffer: N::Buffer,
+}
+
+impl<N: PrimitiveEncode> PrimitiveEncoder<N> {
+ fn new<P: ArrowPrimitiveType<Native = N>>(array: &PrimitiveArray<P>) ->
Self {
+ Self {
+ values: array.values().clone(),
+ buffer: N::init_buffer(),
+ }
+ }
+}
+
+impl<N: PrimitiveEncode> Encoder for PrimitiveEncoder<N> {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ out.extend_from_slice(self.values[idx].encode(&mut self.buffer));
+ }
+}
+
+struct BooleanEncoder(BooleanArray);
+
+impl Encoder for BooleanEncoder {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ match self.0.value(idx) {
+ true => out.extend_from_slice(b"true"),
+ false => out.extend_from_slice(b"false"),
+ }
+ }
+}
+
+struct StringEncoder<O: OffsetSizeTrait>(GenericStringArray<O>);
+
+impl<O: OffsetSizeTrait> Encoder for StringEncoder<O> {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ encode_string(self.0.value(idx), out);
+ }
+}
+
+struct ListEncoder<'a, O: OffsetSizeTrait> {
+ offsets: OffsetBuffer<O>,
+ nulls: Option<NullBuffer>,
+ encoder: Box<dyn Encoder + 'a>,
+}
+
+impl<'a, O: OffsetSizeTrait> ListEncoder<'a, O> {
+ fn try_new(
+ array: &'a GenericListArray<O>,
+ options: &EncoderOptions,
+ ) -> Result<Self, ArrowError> {
+ let (encoder, nulls) = make_encoder_impl(array.values().as_ref(),
options)?;
+ Ok(Self {
+ offsets: array.offsets().clone(),
+ encoder,
+ nulls,
+ })
+ }
+}
+
+impl<'a, O: OffsetSizeTrait> Encoder for ListEncoder<'a, O> {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ let end = self.offsets[idx + 1].as_usize();
+ let start = self.offsets[idx].as_usize();
+ out.push(b'[');
+ match self.nulls.as_ref() {
+ Some(n) => (start..end).for_each(|idx| {
+ if idx != start {
+ out.push(b',')
+ }
+ match n.is_null(idx) {
+ true => out.extend_from_slice(b"null"),
+ false => self.encoder.encode(idx, out),
+ }
+ }),
+ None => (start..end).for_each(|idx| {
+ if idx != start {
+ out.push(b',')
+ }
+ self.encoder.encode(idx, out);
+ }),
+ }
+ out.push(b']');
+ }
+}
+
+struct DictionaryEncoder<'a, K: ArrowDictionaryKeyType> {
+ keys: ScalarBuffer<K::Native>,
+ encoder: Box<dyn Encoder + 'a>,
+}
+
+impl<'a, K: ArrowDictionaryKeyType> DictionaryEncoder<'a, K> {
+ fn try_new(
+ array: &'a DictionaryArray<K>,
+ options: &EncoderOptions,
+ ) -> Result<Self, ArrowError> {
+ let encoder = make_encoder(array.values().as_ref(), options)?;
+
+ Ok(Self {
+ keys: array.keys().values().clone(),
+ encoder,
+ })
+ }
+}
+
+impl<'a, K: ArrowDictionaryKeyType> Encoder for DictionaryEncoder<'a, K> {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ self.encoder.encode(self.keys[idx].as_usize(), out)
+ }
+}
+
+impl<'a> Encoder for ArrayFormatter<'a> {
+ fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
+ out.push(b'"');
+ // Should be infallible
+ // Note: We are making an assumption that the formatter does not
produce characters that require escaping
Review Comment:
Could you expand on this a little? I'm not sure I follow :thinking:
##########
arrow-json/src/writer.rs:
##########
@@ -1564,9 +1575,9 @@ mod tests {
r#"{"a":{"list":[1,2]},"b":{"list":[1,2]}}
{"a":{"list":[null]},"b":{"list":[null]}}
{"a":{"list":[]},"b":{"list":[]}}
-{"a":null,"b":{"list":[3,null]}}
+{"b":{"list":[3,null]}}
Review Comment:
This does seem like it was a bug previously, I'm just racking my brain to
remember if I was aware of this before or not, if there was a reason for this
:thinking:
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