arrow_json/writer/
encoder.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
3// distributed with this work for additional information
4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
7// with the License.  You may obtain a copy of the License at
8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing,
12// software distributed under the License is distributed on an
13// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17use std::io::Write;
18use std::sync::Arc;
19
20use crate::StructMode;
21use arrow_array::cast::AsArray;
22use arrow_array::types::*;
23use arrow_array::*;
24use arrow_buffer::{ArrowNativeType, NullBuffer, OffsetBuffer, ScalarBuffer};
25use arrow_cast::display::{ArrayFormatter, FormatOptions};
26use arrow_schema::{ArrowError, DataType, FieldRef};
27use half::f16;
28use lexical_core::FormattedSize;
29use serde_core::Serializer;
30
31/// Configuration options for the JSON encoder.
32#[derive(Debug, Clone, Default)]
33pub struct EncoderOptions {
34    /// Whether to include nulls in the output or elide them.
35    explicit_nulls: bool,
36    /// Whether to encode structs as JSON objects or JSON arrays of their values.
37    struct_mode: StructMode,
38    /// An optional hook for customizing encoding behavior.
39    encoder_factory: Option<Arc<dyn EncoderFactory>>,
40    /// Optional date format for date arrays
41    date_format: Option<String>,
42    /// Optional datetime format for datetime arrays
43    datetime_format: Option<String>,
44    /// Optional timestamp format for timestamp arrays
45    timestamp_format: Option<String>,
46    /// Optional timestamp format for timestamp with timezone arrays
47    timestamp_tz_format: Option<String>,
48    /// Optional time format for time arrays
49    time_format: Option<String>,
50}
51
52impl EncoderOptions {
53    /// Set whether to include nulls in the output or elide them.
54    pub fn with_explicit_nulls(mut self, explicit_nulls: bool) -> Self {
55        self.explicit_nulls = explicit_nulls;
56        self
57    }
58
59    /// Set whether to encode structs as JSON objects or JSON arrays of their values.
60    pub fn with_struct_mode(mut self, struct_mode: StructMode) -> Self {
61        self.struct_mode = struct_mode;
62        self
63    }
64
65    /// Set an optional hook for customizing encoding behavior.
66    pub fn with_encoder_factory(mut self, encoder_factory: Arc<dyn EncoderFactory>) -> Self {
67        self.encoder_factory = Some(encoder_factory);
68        self
69    }
70
71    /// Get whether to include nulls in the output or elide them.
72    pub fn explicit_nulls(&self) -> bool {
73        self.explicit_nulls
74    }
75
76    /// Get whether to encode structs as JSON objects or JSON arrays of their values.
77    pub fn struct_mode(&self) -> StructMode {
78        self.struct_mode
79    }
80
81    /// Get the optional hook for customizing encoding behavior.
82    pub fn encoder_factory(&self) -> Option<&Arc<dyn EncoderFactory>> {
83        self.encoder_factory.as_ref()
84    }
85
86    /// Set the JSON file's date format
87    pub fn with_date_format(mut self, format: String) -> Self {
88        self.date_format = Some(format);
89        self
90    }
91
92    /// Get the JSON file's date format if set, defaults to RFC3339
93    pub fn date_format(&self) -> Option<&str> {
94        self.date_format.as_deref()
95    }
96
97    /// Set the JSON file's datetime format
98    pub fn with_datetime_format(mut self, format: String) -> Self {
99        self.datetime_format = Some(format);
100        self
101    }
102
103    /// Get the JSON file's datetime format if set, defaults to RFC3339
104    pub fn datetime_format(&self) -> Option<&str> {
105        self.datetime_format.as_deref()
106    }
107
108    /// Set the JSON file's time format
109    pub fn with_time_format(mut self, format: String) -> Self {
110        self.time_format = Some(format);
111        self
112    }
113
114    /// Get the JSON file's datetime time if set, defaults to RFC3339
115    pub fn time_format(&self) -> Option<&str> {
116        self.time_format.as_deref()
117    }
118
119    /// Set the JSON file's timestamp format
120    pub fn with_timestamp_format(mut self, format: String) -> Self {
121        self.timestamp_format = Some(format);
122        self
123    }
124
125    /// Get the JSON file's timestamp format if set, defaults to RFC3339
126    pub fn timestamp_format(&self) -> Option<&str> {
127        self.timestamp_format.as_deref()
128    }
129
130    /// Set the JSON file's timestamp tz format
131    pub fn with_timestamp_tz_format(mut self, tz_format: String) -> Self {
132        self.timestamp_tz_format = Some(tz_format);
133        self
134    }
135
136    /// Get the JSON file's timestamp tz format if set, defaults to RFC3339
137    pub fn timestamp_tz_format(&self) -> Option<&str> {
138        self.timestamp_tz_format.as_deref()
139    }
140}
141
142/// A trait to create custom encoders for specific data types.
143///
144/// This allows overriding the default encoders for specific data types,
145/// or adding new encoders for custom data types.
146///
147/// # Examples
148///
149/// ```
150/// use std::io::Write;
151/// use arrow_array::{ArrayAccessor, Array, BinaryArray, Float64Array, RecordBatch};
152/// use arrow_array::cast::AsArray;
153/// use arrow_schema::{DataType, Field, Schema, FieldRef};
154/// use arrow_json::{writer::{WriterBuilder, JsonArray, NullableEncoder}, StructMode};
155/// use arrow_json::{Encoder, EncoderFactory, EncoderOptions};
156/// use arrow_schema::ArrowError;
157/// use std::sync::Arc;
158/// use serde_json::json;
159/// use serde_json::Value;
160///
161/// struct IntArrayBinaryEncoder<B> {
162///     array: B,
163/// }
164///
165/// impl<'a, B> Encoder for IntArrayBinaryEncoder<B>
166/// where
167///     B: ArrayAccessor<Item = &'a [u8]>,
168/// {
169///     fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
170///         out.push(b'[');
171///         let child = self.array.value(idx);
172///         for (idx, byte) in child.iter().enumerate() {
173///             write!(out, "{byte}").unwrap();
174///             if idx < child.len() - 1 {
175///                 out.push(b',');
176///             }
177///         }
178///         out.push(b']');
179///     }
180/// }
181///
182/// #[derive(Debug)]
183/// struct IntArayBinaryEncoderFactory;
184///
185/// impl EncoderFactory for IntArayBinaryEncoderFactory {
186///     fn make_default_encoder<'a>(
187///         &self,
188///         _field: &'a FieldRef,
189///         array: &'a dyn Array,
190///         _options: &'a EncoderOptions,
191///     ) -> Result<Option<NullableEncoder<'a>>, ArrowError> {
192///         match array.data_type() {
193///             DataType::Binary => {
194///                 let array = array.as_binary::<i32>();
195///                 let encoder = IntArrayBinaryEncoder { array };
196///                 let array_encoder = Box::new(encoder) as Box<dyn Encoder + 'a>;
197///                 let nulls = array.nulls().cloned();
198///                 Ok(Some(NullableEncoder::new(array_encoder, nulls)))
199///             }
200///             _ => Ok(None),
201///         }
202///     }
203/// }
204///
205/// let binary_array = BinaryArray::from_iter([Some(b"a".as_slice()), None, Some(b"b".as_slice())]);
206/// let float_array = Float64Array::from(vec![Some(1.0), Some(2.3), None]);
207/// let fields = vec![
208///     Field::new("bytes", DataType::Binary, true),
209///     Field::new("float", DataType::Float64, true),
210/// ];
211/// let batch = RecordBatch::try_new(
212///     Arc::new(Schema::new(fields)),
213///     vec![
214///         Arc::new(binary_array) as Arc<dyn Array>,
215///         Arc::new(float_array) as Arc<dyn Array>,
216///     ],
217/// )
218/// .unwrap();
219///
220/// let json_value: Value = {
221///     let mut buf = Vec::new();
222///     let mut writer = WriterBuilder::new()
223///         .with_encoder_factory(Arc::new(IntArayBinaryEncoderFactory))
224///         .build::<_, JsonArray>(&mut buf);
225///     writer.write_batches(&[&batch]).unwrap();
226///     writer.finish().unwrap();
227///     serde_json::from_slice(&buf).unwrap()
228/// };
229///
230/// let expected = json!([
231///     {"bytes": [97], "float": 1.0},
232///     {"float": 2.3},
233///     {"bytes": [98]},
234/// ]);
235///
236/// assert_eq!(json_value, expected);
237/// ```
238pub trait EncoderFactory: std::fmt::Debug + Send + Sync {
239    /// Make an encoder that overrides the default encoder for a specific field and array or provides an encoder for a custom data type.
240    /// This can be used to override how e.g. binary data is encoded so that it is an encoded string or an array of integers.
241    ///
242    /// Note that the type of the field may not match the type of the array: for dictionary arrays unless the top-level dictionary is handled this
243    /// will be called again for the keys and values of the dictionary, at which point the field type will still be the outer dictionary type but the
244    /// array will have a different type.
245    /// For example, `field`` might have the type `Dictionary(i32, Utf8)` but `array` will be `Utf8`.
246    fn make_default_encoder<'a>(
247        &self,
248        _field: &'a FieldRef,
249        _array: &'a dyn Array,
250        _options: &'a EncoderOptions,
251    ) -> Result<Option<NullableEncoder<'a>>, ArrowError> {
252        Ok(None)
253    }
254}
255
256/// An encoder + a null buffer.
257/// This is packaged together into a wrapper struct to minimize dynamic dispatch for null checks.
258pub struct NullableEncoder<'a> {
259    encoder: Box<dyn Encoder + 'a>,
260    nulls: Option<NullBuffer>,
261}
262
263impl<'a> NullableEncoder<'a> {
264    /// Create a new encoder with a null buffer.
265    pub fn new(encoder: Box<dyn Encoder + 'a>, nulls: Option<NullBuffer>) -> Self {
266        Self { encoder, nulls }
267    }
268
269    /// Encode the value at index `idx` to `out`.
270    pub fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
271        self.encoder.encode(idx, out)
272    }
273
274    /// Returns whether the value at index `idx` is null.
275    pub fn is_null(&self, idx: usize) -> bool {
276        self.nulls.as_ref().is_some_and(|nulls| nulls.is_null(idx))
277    }
278
279    /// Returns whether the encoder has any nulls.
280    pub fn has_nulls(&self) -> bool {
281        match self.nulls {
282            Some(ref nulls) => nulls.null_count() > 0,
283            None => false,
284        }
285    }
286}
287
288impl Encoder for NullableEncoder<'_> {
289    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
290        self.encoder.encode(idx, out)
291    }
292}
293
294/// A trait to format array values as JSON values
295///
296/// Nullability is handled by the caller to allow encoding nulls implicitly, i.e. `{}` instead of `{"a": null}`
297pub trait Encoder {
298    /// Encode the non-null value at index `idx` to `out`.
299    ///
300    /// The behaviour is unspecified if `idx` corresponds to a null index.
301    fn encode(&mut self, idx: usize, out: &mut Vec<u8>);
302}
303
304/// Creates an encoder for the given array and field.
305///
306/// This first calls the EncoderFactory if one is provided, and then falls back to the default encoders.
307pub fn make_encoder<'a>(
308    field: &'a FieldRef,
309    array: &'a dyn Array,
310    options: &'a EncoderOptions,
311) -> Result<NullableEncoder<'a>, ArrowError> {
312    macro_rules! primitive_helper {
313        ($t:ty) => {{
314            let array = array.as_primitive::<$t>();
315            let nulls = array.nulls().cloned();
316            NullableEncoder::new(Box::new(PrimitiveEncoder::new(array)), nulls)
317        }};
318    }
319
320    if let Some(factory) = options.encoder_factory() {
321        if let Some(encoder) = factory.make_default_encoder(field, array, options)? {
322            return Ok(encoder);
323        }
324    }
325
326    let nulls = array.nulls().cloned();
327    let encoder = downcast_integer! {
328        array.data_type() => (primitive_helper),
329        DataType::Float16 => primitive_helper!(Float16Type),
330        DataType::Float32 => primitive_helper!(Float32Type),
331        DataType::Float64 => primitive_helper!(Float64Type),
332        DataType::Boolean => {
333            let array = array.as_boolean();
334            NullableEncoder::new(Box::new(BooleanEncoder(array)), array.nulls().cloned())
335        }
336        DataType::Null => NullableEncoder::new(Box::new(NullEncoder), array.logical_nulls()),
337        DataType::Utf8 => {
338            let array = array.as_string::<i32>();
339            NullableEncoder::new(Box::new(StringEncoder(array)), array.nulls().cloned())
340        }
341        DataType::LargeUtf8 => {
342            let array = array.as_string::<i64>();
343            NullableEncoder::new(Box::new(StringEncoder(array)), array.nulls().cloned())
344        }
345        DataType::Utf8View => {
346            let array = array.as_string_view();
347            NullableEncoder::new(Box::new(StringViewEncoder(array)), array.nulls().cloned())
348        }
349        DataType::BinaryView => {
350            let array = array.as_binary_view();
351            NullableEncoder::new(Box::new(BinaryViewEncoder(array)), array.nulls().cloned())
352        }
353        DataType::List(_) => {
354            let array = array.as_list::<i32>();
355            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
356        }
357        DataType::LargeList(_) => {
358            let array = array.as_list::<i64>();
359            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
360        }
361        DataType::ListView(_) => {
362            let array = array.as_list_view::<i32>();
363            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
364        }
365        DataType::LargeListView(_) => {
366            let array = array.as_list_view::<i64>();
367            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
368        }
369        DataType::FixedSizeList(_, _) => {
370            let array = array.as_fixed_size_list();
371            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
372        }
373
374        DataType::Dictionary(_, _) => downcast_dictionary_array! {
375            array => {
376                NullableEncoder::new(Box::new(DictionaryEncoder::try_new(field, array, options)?), array.nulls().cloned())
377            },
378            _ => unreachable!()
379        }
380
381        DataType::RunEndEncoded(_, _) => downcast_run_array! {
382            array => {
383                NullableEncoder::new(
384                    Box::new(RunEndEncodedEncoder::try_new(field, array, options)?),
385                    array.logical_nulls(),
386                )
387            },
388            _ => unreachable!()
389        }
390
391        DataType::Map(_, _) => {
392            let array = array.as_map();
393            NullableEncoder::new(Box::new(MapEncoder::try_new(field, array, options)?), array.nulls().cloned())
394        }
395
396        DataType::FixedSizeBinary(_) => {
397            let array = array.as_fixed_size_binary();
398            NullableEncoder::new(Box::new(BinaryEncoder::new(array)) as _, array.nulls().cloned())
399        }
400
401        DataType::Binary => {
402            let array: &BinaryArray = array.as_binary();
403            NullableEncoder::new(Box::new(BinaryEncoder::new(array)), array.nulls().cloned())
404        }
405
406        DataType::LargeBinary => {
407            let array: &LargeBinaryArray = array.as_binary();
408            NullableEncoder::new(Box::new(BinaryEncoder::new(array)), array.nulls().cloned())
409        }
410
411        DataType::Struct(fields) => {
412            let array = array.as_struct();
413            let encoders = fields.iter().zip(array.columns()).map(|(field, array)| {
414                let encoder = make_encoder(field, array, options)?;
415
416                // For typical ASCII names, this will be the exact length (includes 2x quotes, 1x colon).
417                let mut field_name = Vec::with_capacity(field.name().len() + 3);
418                encode_string(field.name(), &mut field_name);
419                field_name.push(b':');
420
421                Ok(FieldEncoder {
422                    field_name,
423                    encoder,
424                })
425            }).collect::<Result<Vec<_>, ArrowError>>()?;
426
427            let encoder = StructArrayEncoder{
428                encoders,
429                explicit_nulls: options.explicit_nulls(),
430                struct_mode: options.struct_mode(),
431            };
432            let nulls = array.nulls().cloned();
433            NullableEncoder::new(Box::new(encoder) as Box<dyn Encoder + 'a>, nulls)
434        }
435        DataType::Decimal32(_, _) | DataType::Decimal64(_, _) | DataType::Decimal128(_, _) | DataType::Decimal256(_, _) => {
436            let options = FormatOptions::new().with_display_error(true);
437            let formatter = JsonArrayFormatter::new(ArrayFormatter::try_new(array, &options)?);
438            NullableEncoder::new(Box::new(RawArrayFormatter(formatter)) as Box<dyn Encoder + 'a>, nulls)
439        }
440        d => match d.is_temporal() {
441            true => {
442                // Note: the implementation of Encoder for ArrayFormatter assumes it does not produce
443                // characters that would need to be escaped within a JSON string, e.g. `'"'`.
444                // If support for user-provided format specifications is added, this assumption
445                // may need to be revisited
446                let fops = FormatOptions::new().with_display_error(true)
447                .with_date_format(options.date_format.as_deref())
448                .with_datetime_format(options.datetime_format.as_deref())
449                .with_timestamp_format(options.timestamp_format.as_deref())
450                .with_timestamp_tz_format(options.timestamp_tz_format.as_deref())
451                .with_time_format(options.time_format.as_deref());
452
453                let formatter = ArrayFormatter::try_new(array, &fops)?;
454                let formatter = JsonArrayFormatter::new(formatter);
455                NullableEncoder::new(Box::new(formatter) as Box<dyn Encoder + 'a>, nulls)
456            }
457            false => return Err(ArrowError::JsonError(format!(
458                "Unsupported data type for JSON encoding: {d:?}",
459            )))
460        }
461    };
462
463    Ok(encoder)
464}
465
466fn encode_string(s: &str, out: &mut Vec<u8>) {
467    let mut serializer = serde_json::Serializer::new(out);
468    serializer.serialize_str(s).unwrap();
469}
470
471fn encode_binary(bytes: &[u8], out: &mut Vec<u8>) {
472    out.push(b'"');
473    for byte in bytes {
474        write!(out, "{byte:02x}").unwrap();
475    }
476    out.push(b'"');
477}
478
479struct FieldEncoder<'a> {
480    field_name: Vec<u8>,
481    encoder: NullableEncoder<'a>,
482}
483
484impl FieldEncoder<'_> {
485    fn is_null(&self, idx: usize) -> bool {
486        self.encoder.is_null(idx)
487    }
488}
489
490struct StructArrayEncoder<'a> {
491    encoders: Vec<FieldEncoder<'a>>,
492    explicit_nulls: bool,
493    struct_mode: StructMode,
494}
495
496impl Encoder for StructArrayEncoder<'_> {
497    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
498        match self.struct_mode {
499            StructMode::ObjectOnly => out.push(b'{'),
500            StructMode::ListOnly => out.push(b'['),
501        }
502        let mut is_first = true;
503        // Nulls can only be dropped in explicit mode
504        let drop_nulls = (self.struct_mode == StructMode::ObjectOnly) && !self.explicit_nulls;
505
506        for field_encoder in self.encoders.iter_mut() {
507            let is_null = field_encoder.is_null(idx);
508            if is_null && drop_nulls {
509                continue;
510            }
511
512            if !is_first {
513                out.push(b',');
514            }
515            is_first = false;
516
517            if self.struct_mode == StructMode::ObjectOnly {
518                out.extend_from_slice(&field_encoder.field_name);
519            }
520
521            if is_null {
522                out.extend_from_slice(b"null");
523            } else {
524                field_encoder.encoder.encode(idx, out);
525            }
526        }
527        match self.struct_mode {
528            StructMode::ObjectOnly => out.push(b'}'),
529            StructMode::ListOnly => out.push(b']'),
530        }
531    }
532}
533
534trait PrimitiveEncode: ArrowNativeType {
535    type Buffer;
536
537    // Workaround https://github.com/rust-lang/rust/issues/61415
538    fn init_buffer() -> Self::Buffer;
539
540    /// Encode the primitive value as bytes, returning a reference to that slice.
541    ///
542    /// `buf` is temporary space that may be used
543    fn encode(self, buf: &mut Self::Buffer) -> &[u8];
544}
545
546macro_rules! integer_encode {
547    ($($t:ty),*) => {
548        $(
549            impl PrimitiveEncode for $t {
550                type Buffer = [u8; Self::FORMATTED_SIZE];
551
552                fn init_buffer() -> Self::Buffer {
553                    [0; Self::FORMATTED_SIZE]
554                }
555
556                fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
557                    lexical_core::write(self, buf)
558                }
559            }
560        )*
561    };
562}
563integer_encode!(i8, i16, i32, i64, u8, u16, u32, u64);
564
565macro_rules! float_encode {
566    ($($t:ty),*) => {
567        $(
568            impl PrimitiveEncode for $t {
569                type Buffer = [u8; Self::FORMATTED_SIZE];
570
571                fn init_buffer() -> Self::Buffer {
572                    [0; Self::FORMATTED_SIZE]
573                }
574
575                fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
576                    if self.is_infinite() || self.is_nan() {
577                        b"null"
578                    } else {
579                        lexical_core::write(self, buf)
580                    }
581                }
582            }
583        )*
584    };
585}
586float_encode!(f32, f64);
587
588impl PrimitiveEncode for f16 {
589    type Buffer = <f32 as PrimitiveEncode>::Buffer;
590
591    fn init_buffer() -> Self::Buffer {
592        f32::init_buffer()
593    }
594
595    fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
596        self.to_f32().encode(buf)
597    }
598}
599
600struct PrimitiveEncoder<N: PrimitiveEncode> {
601    values: ScalarBuffer<N>,
602    buffer: N::Buffer,
603}
604
605impl<N: PrimitiveEncode> PrimitiveEncoder<N> {
606    fn new<P: ArrowPrimitiveType<Native = N>>(array: &PrimitiveArray<P>) -> Self {
607        Self {
608            values: array.values().clone(),
609            buffer: N::init_buffer(),
610        }
611    }
612}
613
614impl<N: PrimitiveEncode> Encoder for PrimitiveEncoder<N> {
615    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
616        out.extend_from_slice(self.values[idx].encode(&mut self.buffer));
617    }
618}
619
620struct BooleanEncoder<'a>(&'a BooleanArray);
621
622impl Encoder for BooleanEncoder<'_> {
623    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
624        match self.0.value(idx) {
625            true => out.extend_from_slice(b"true"),
626            false => out.extend_from_slice(b"false"),
627        }
628    }
629}
630
631struct StringEncoder<'a, O: OffsetSizeTrait>(&'a GenericStringArray<O>);
632
633impl<O: OffsetSizeTrait> Encoder for StringEncoder<'_, O> {
634    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
635        encode_string(self.0.value(idx), out);
636    }
637}
638
639struct StringViewEncoder<'a>(&'a StringViewArray);
640
641impl Encoder for StringViewEncoder<'_> {
642    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
643        encode_string(self.0.value(idx), out);
644    }
645}
646
647struct BinaryViewEncoder<'a>(&'a BinaryViewArray);
648
649impl Encoder for BinaryViewEncoder<'_> {
650    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
651        encode_binary(self.0.value(idx), out);
652    }
653}
654
655struct ListLikeEncoder<'a, L: ListLikeArray> {
656    list_array: &'a L,
657    encoder: NullableEncoder<'a>,
658}
659
660impl<'a, L: ListLikeArray> ListLikeEncoder<'a, L> {
661    fn try_new(
662        field: &'a FieldRef,
663        array: &'a L,
664        options: &'a EncoderOptions,
665    ) -> Result<Self, ArrowError> {
666        let encoder = make_encoder(field, array.values().as_ref(), options)?;
667        Ok(Self {
668            list_array: array,
669            encoder,
670        })
671    }
672}
673
674impl<L: ListLikeArray> Encoder for ListLikeEncoder<'_, L> {
675    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
676        let range = self.list_array.element_range(idx);
677        let start = range.start;
678        let end = range.end;
679        out.push(b'[');
680        if self.encoder.has_nulls() {
681            for idx in start..end {
682                if idx != start {
683                    out.push(b',')
684                }
685                if self.encoder.is_null(idx) {
686                    out.extend_from_slice(b"null");
687                } else {
688                    self.encoder.encode(idx, out);
689                }
690            }
691        } else {
692            for idx in start..end {
693                if idx != start {
694                    out.push(b',')
695                }
696                self.encoder.encode(idx, out);
697            }
698        }
699        out.push(b']');
700    }
701}
702
703struct DictionaryEncoder<'a, K: ArrowDictionaryKeyType> {
704    keys: ScalarBuffer<K::Native>,
705    encoder: NullableEncoder<'a>,
706}
707
708impl<'a, K: ArrowDictionaryKeyType> DictionaryEncoder<'a, K> {
709    fn try_new(
710        field: &'a FieldRef,
711        array: &'a DictionaryArray<K>,
712        options: &'a EncoderOptions,
713    ) -> Result<Self, ArrowError> {
714        let encoder = make_encoder(field, array.values().as_ref(), options)?;
715
716        Ok(Self {
717            keys: array.keys().values().clone(),
718            encoder,
719        })
720    }
721}
722
723impl<K: ArrowDictionaryKeyType> Encoder for DictionaryEncoder<'_, K> {
724    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
725        self.encoder.encode(self.keys[idx].as_usize(), out)
726    }
727}
728
729struct RunEndEncodedEncoder<'a, R: RunEndIndexType> {
730    run_array: &'a RunArray<R>,
731    encoder: NullableEncoder<'a>,
732}
733
734impl<'a, R: RunEndIndexType> RunEndEncodedEncoder<'a, R> {
735    fn try_new(
736        field: &'a FieldRef,
737        array: &'a RunArray<R>,
738        options: &'a EncoderOptions,
739    ) -> Result<Self, ArrowError> {
740        let encoder = make_encoder(field, array.values().as_ref(), options)?;
741        Ok(Self {
742            run_array: array,
743            encoder,
744        })
745    }
746}
747
748impl<R: RunEndIndexType> Encoder for RunEndEncodedEncoder<'_, R> {
749    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
750        let physical_idx = self.run_array.get_physical_index(idx);
751        self.encoder.encode(physical_idx, out)
752    }
753}
754
755/// A newtype wrapper around [`ArrayFormatter`] to keep our usage of it private and not implement `Encoder` for the public type
756struct JsonArrayFormatter<'a> {
757    formatter: ArrayFormatter<'a>,
758}
759
760impl<'a> JsonArrayFormatter<'a> {
761    fn new(formatter: ArrayFormatter<'a>) -> Self {
762        Self { formatter }
763    }
764}
765
766impl Encoder for JsonArrayFormatter<'_> {
767    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
768        out.push(b'"');
769        // Should be infallible
770        // Note: We are making an assumption that the formatter does not produce characters that require escaping
771        let _ = write!(out, "{}", self.formatter.value(idx));
772        out.push(b'"')
773    }
774}
775
776/// A newtype wrapper around [`JsonArrayFormatter`] that skips surrounding the value with `"`
777struct RawArrayFormatter<'a>(JsonArrayFormatter<'a>);
778
779impl Encoder for RawArrayFormatter<'_> {
780    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
781        let _ = write!(out, "{}", self.0.formatter.value(idx));
782    }
783}
784
785struct NullEncoder;
786
787impl Encoder for NullEncoder {
788    fn encode(&mut self, _idx: usize, _out: &mut Vec<u8>) {
789        unreachable!()
790    }
791}
792
793struct MapEncoder<'a> {
794    offsets: OffsetBuffer<i32>,
795    keys: NullableEncoder<'a>,
796    values: NullableEncoder<'a>,
797    explicit_nulls: bool,
798}
799
800impl<'a> MapEncoder<'a> {
801    fn try_new(
802        field: &'a FieldRef,
803        array: &'a MapArray,
804        options: &'a EncoderOptions,
805    ) -> Result<Self, ArrowError> {
806        let values = array.values();
807        let keys = array.keys();
808
809        if !matches!(
810            keys.data_type(),
811            DataType::Utf8 | DataType::LargeUtf8 | DataType::Utf8View
812        ) {
813            return Err(ArrowError::JsonError(format!(
814                "Only UTF8 keys supported by JSON MapArray Writer: got {:?}",
815                keys.data_type()
816            )));
817        }
818
819        let keys = make_encoder(field, keys, options)?;
820        let values = make_encoder(field, values, options)?;
821
822        // We sanity check nulls as these are currently not enforced by MapArray (#1697)
823        if keys.has_nulls() {
824            return Err(ArrowError::InvalidArgumentError(
825                "Encountered nulls in MapArray keys".to_string(),
826            ));
827        }
828
829        if array.entries().nulls().is_some_and(|x| x.null_count() != 0) {
830            return Err(ArrowError::InvalidArgumentError(
831                "Encountered nulls in MapArray entries".to_string(),
832            ));
833        }
834
835        Ok(Self {
836            offsets: array.offsets().clone(),
837            keys,
838            values,
839            explicit_nulls: options.explicit_nulls(),
840        })
841    }
842}
843
844impl Encoder for MapEncoder<'_> {
845    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
846        let end = self.offsets[idx + 1].as_usize();
847        let start = self.offsets[idx].as_usize();
848
849        let mut is_first = true;
850
851        out.push(b'{');
852
853        for idx in start..end {
854            let is_null = self.values.is_null(idx);
855            if is_null && !self.explicit_nulls {
856                continue;
857            }
858
859            if !is_first {
860                out.push(b',');
861            }
862            is_first = false;
863
864            self.keys.encode(idx, out);
865            out.push(b':');
866
867            if is_null {
868                out.extend_from_slice(b"null");
869            } else {
870                self.values.encode(idx, out);
871            }
872        }
873        out.push(b'}');
874    }
875}
876
877/// New-type wrapper for encoding the binary types in arrow: `Binary`, `LargeBinary`
878/// and `FixedSizeBinary` as hex strings in JSON.
879struct BinaryEncoder<B>(B);
880
881impl<'a, B> BinaryEncoder<B>
882where
883    B: ArrayAccessor<Item = &'a [u8]>,
884{
885    fn new(array: B) -> Self {
886        Self(array)
887    }
888}
889
890impl<'a, B> Encoder for BinaryEncoder<B>
891where
892    B: ArrayAccessor<Item = &'a [u8]>,
893{
894    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
895        out.push(b'"');
896        for byte in self.0.value(idx) {
897            // this write is infallible
898            write!(out, "{byte:02x}").unwrap();
899        }
900        out.push(b'"');
901    }
902}
arrow_json/writer/encoder.rs

arrow_json/writer/
encoder.rs
