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    #[inline]
266    pub fn new(encoder: Box<dyn Encoder + 'a>, nulls: Option<NullBuffer>) -> Self {
267        Self { encoder, nulls }
268    }
269
270    /// Encode the value at index `idx` to `out`.
271    #[inline]
272    pub fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
273        self.encoder.encode(idx, out)
274    }
275
276    /// Returns whether the value at index `idx` is null.
277    #[inline]
278    pub fn is_null(&self, idx: usize) -> bool {
279        match self.nulls {
280            Some(ref nulls) => nulls.is_null(idx),
281            None => false,
282        }
283    }
284
285    /// Returns whether the encoder has any nulls.
286    #[inline]
287    pub fn has_nulls(&self) -> bool {
288        match self.nulls {
289            Some(ref nulls) => nulls.null_count() > 0,
290            None => false,
291        }
292    }
293}
294
295impl Encoder for NullableEncoder<'_> {
296    #[inline]
297    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
298        self.encoder.encode(idx, out)
299    }
300}
301
302/// A trait to format array values as JSON values
303///
304/// Nullability is handled by the caller to allow encoding nulls implicitly, i.e. `{}` instead of `{"a": null}`
305pub trait Encoder {
306    /// Encode the non-null value at index `idx` to `out`.
307    ///
308    /// The behaviour is unspecified if `idx` corresponds to a null index.
309    fn encode(&mut self, idx: usize, out: &mut Vec<u8>);
310}
311
312/// Creates an encoder for the given array and field.
313///
314/// This first calls the EncoderFactory if one is provided, and then falls back to the default encoders.
315pub fn make_encoder<'a>(
316    field: &'a FieldRef,
317    array: &'a dyn Array,
318    options: &'a EncoderOptions,
319) -> Result<NullableEncoder<'a>, ArrowError> {
320    macro_rules! primitive_helper {
321        ($t:ty) => {{
322            let array = array.as_primitive::<$t>();
323            let nulls = array.nulls().cloned();
324            NullableEncoder::new(Box::new(PrimitiveEncoder::new(array)), nulls)
325        }};
326    }
327
328    if let Some(factory) = options.encoder_factory()
329        && let Some(encoder) = factory.make_default_encoder(field, array, options)?
330    {
331        return Ok(encoder);
332    }
333
334    let nulls = array.nulls().cloned();
335    let encoder = downcast_integer! {
336        array.data_type() => (primitive_helper),
337        DataType::Float16 => primitive_helper!(Float16Type),
338        DataType::Float32 => primitive_helper!(Float32Type),
339        DataType::Float64 => primitive_helper!(Float64Type),
340        DataType::Boolean => {
341            let array = array.as_boolean();
342            NullableEncoder::new(Box::new(BooleanEncoder(array)), array.nulls().cloned())
343        }
344        DataType::Null => NullableEncoder::new(Box::new(NullEncoder), array.logical_nulls()),
345        DataType::Utf8 => {
346            let array = array.as_string::<i32>();
347            NullableEncoder::new(Box::new(StringEncoder(array)), array.nulls().cloned())
348        }
349        DataType::LargeUtf8 => {
350            let array = array.as_string::<i64>();
351            NullableEncoder::new(Box::new(StringEncoder(array)), array.nulls().cloned())
352        }
353        DataType::Utf8View => {
354            let array = array.as_string_view();
355            NullableEncoder::new(Box::new(StringViewEncoder(array)), array.nulls().cloned())
356        }
357        DataType::BinaryView => {
358            let array = array.as_binary_view();
359            NullableEncoder::new(Box::new(BinaryViewEncoder(array)), array.nulls().cloned())
360        }
361        DataType::List(_) => {
362            let array = array.as_list::<i32>();
363            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
364        }
365        DataType::LargeList(_) => {
366            let array = array.as_list::<i64>();
367            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
368        }
369        DataType::ListView(_) => {
370            let array = array.as_list_view::<i32>();
371            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
372        }
373        DataType::LargeListView(_) => {
374            let array = array.as_list_view::<i64>();
375            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
376        }
377        DataType::FixedSizeList(_, _) => {
378            let array = array.as_fixed_size_list();
379            NullableEncoder::new(Box::new(ListLikeEncoder::try_new(field, array, options)?), array.nulls().cloned())
380        }
381
382        DataType::Dictionary(_, _) => downcast_dictionary_array! {
383            array => {
384                NullableEncoder::new(Box::new(DictionaryEncoder::try_new(field, array, options)?), array.nulls().cloned())
385            },
386            _ => unreachable!()
387        }
388
389        DataType::RunEndEncoded(_, _) => downcast_run_array! {
390            array => {
391                NullableEncoder::new(
392                    Box::new(RunEndEncodedEncoder::try_new(field, array, options)?),
393                    array.logical_nulls(),
394                )
395            },
396            _ => unreachable!()
397        }
398
399        DataType::Map(_, _) => {
400            let array = array.as_map();
401            NullableEncoder::new(Box::new(MapEncoder::try_new(field, array, options)?), array.nulls().cloned())
402        }
403
404        DataType::FixedSizeBinary(_) => {
405            let array = array.as_fixed_size_binary();
406            NullableEncoder::new(Box::new(BinaryEncoder::new(array)) as _, array.nulls().cloned())
407        }
408
409        DataType::Binary => {
410            let array: &BinaryArray = array.as_binary();
411            NullableEncoder::new(Box::new(BinaryEncoder::new(array)), array.nulls().cloned())
412        }
413
414        DataType::LargeBinary => {
415            let array: &LargeBinaryArray = array.as_binary();
416            NullableEncoder::new(Box::new(BinaryEncoder::new(array)), array.nulls().cloned())
417        }
418
419        DataType::Struct(fields) => {
420            let array = array.as_struct();
421            let encoders = fields.iter().zip(array.columns()).map(|(field, array)| {
422                let encoder = make_encoder(field, array, options)?;
423
424                // For typical ASCII names, this will be the exact length (includes 2x quotes, 1x colon).
425                let mut field_name = Vec::with_capacity(field.name().len() + 3);
426                encode_string(field.name(), &mut field_name);
427                field_name.push(b':');
428
429                Ok(FieldEncoder {
430                    field_name,
431                    encoder,
432                })
433            }).collect::<Result<Vec<_>, ArrowError>>()?;
434
435            let encoder = StructArrayEncoder{
436                encoders,
437                explicit_nulls: options.explicit_nulls(),
438                struct_mode: options.struct_mode(),
439            };
440            let nulls = array.nulls().cloned();
441            NullableEncoder::new(Box::new(encoder) as Box<dyn Encoder + 'a>, nulls)
442        }
443        DataType::Decimal32(_, _) | DataType::Decimal64(_, _) | DataType::Decimal128(_, _) | DataType::Decimal256(_, _) => {
444            let options = FormatOptions::new().with_display_error(true);
445            let formatter = JsonArrayFormatter::new(ArrayFormatter::try_new(array, &options)?);
446            NullableEncoder::new(Box::new(RawArrayFormatter(formatter)) as Box<dyn Encoder + 'a>, nulls)
447        }
448        d => match d.is_temporal() {
449            true => {
450                // Note: the implementation of Encoder for ArrayFormatter assumes it does not produce
451                // characters that would need to be escaped within a JSON string, e.g. `'"'`.
452                // If support for user-provided format specifications is added, this assumption
453                // may need to be revisited
454                let fops = FormatOptions::new().with_display_error(true)
455                .with_date_format(options.date_format.as_deref())
456                .with_datetime_format(options.datetime_format.as_deref())
457                .with_timestamp_format(options.timestamp_format.as_deref())
458                .with_timestamp_tz_format(options.timestamp_tz_format.as_deref())
459                .with_time_format(options.time_format.as_deref());
460
461                let formatter = ArrayFormatter::try_new(array, &fops)?;
462                let formatter = JsonArrayFormatter::new(formatter);
463                NullableEncoder::new(Box::new(formatter) as Box<dyn Encoder + 'a>, nulls)
464            }
465            false => return Err(ArrowError::JsonError(format!(
466                "Unsupported data type for JSON encoding: {d:?}",
467            )))
468        }
469    };
470
471    Ok(encoder)
472}
473
474fn encode_string(s: &str, out: &mut Vec<u8>) {
475    let mut serializer = serde_json::Serializer::new(out);
476    serializer.serialize_str(s).unwrap();
477}
478
479fn encode_binary(bytes: &[u8], out: &mut Vec<u8>) {
480    out.push(b'"');
481    for byte in bytes {
482        write!(out, "{byte:02x}").unwrap();
483    }
484    out.push(b'"');
485}
486
487struct FieldEncoder<'a> {
488    field_name: Vec<u8>,
489    encoder: NullableEncoder<'a>,
490}
491
492impl FieldEncoder<'_> {
493    #[inline]
494    fn is_null(&self, idx: usize) -> bool {
495        self.encoder.is_null(idx)
496    }
497}
498
499struct StructArrayEncoder<'a> {
500    encoders: Vec<FieldEncoder<'a>>,
501    explicit_nulls: bool,
502    struct_mode: StructMode,
503}
504
505impl Encoder for StructArrayEncoder<'_> {
506    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
507        match self.struct_mode {
508            StructMode::ObjectOnly => out.push(b'{'),
509            StructMode::ListOnly => out.push(b'['),
510        }
511        let mut is_first = true;
512        // Nulls can only be dropped in explicit mode
513        let drop_nulls = (self.struct_mode == StructMode::ObjectOnly) && !self.explicit_nulls;
514
515        for field_encoder in self.encoders.iter_mut() {
516            let is_null = field_encoder.is_null(idx);
517            if is_null && drop_nulls {
518                continue;
519            }
520
521            if !is_first {
522                out.push(b',');
523            }
524            is_first = false;
525
526            if self.struct_mode == StructMode::ObjectOnly {
527                out.extend_from_slice(&field_encoder.field_name);
528            }
529
530            if is_null {
531                out.extend_from_slice(b"null");
532            } else {
533                field_encoder.encoder.encode(idx, out);
534            }
535        }
536        match self.struct_mode {
537            StructMode::ObjectOnly => out.push(b'}'),
538            StructMode::ListOnly => out.push(b']'),
539        }
540    }
541}
542
543trait PrimitiveEncode: ArrowNativeType {
544    type Buffer;
545
546    // Workaround https://github.com/rust-lang/rust/issues/61415
547    fn init_buffer() -> Self::Buffer;
548
549    /// Encode the primitive value as bytes, returning a reference to that slice.
550    ///
551    /// `buf` is temporary space that may be used
552    fn encode(self, buf: &mut Self::Buffer) -> &[u8];
553}
554
555macro_rules! integer_encode {
556    ($($t:ty),*) => {
557        $(
558            impl PrimitiveEncode for $t {
559                type Buffer = [u8; Self::FORMATTED_SIZE];
560
561                fn init_buffer() -> Self::Buffer {
562                    [0; Self::FORMATTED_SIZE]
563                }
564
565                fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
566                    lexical_core::write(self, buf)
567                }
568            }
569        )*
570    };
571}
572integer_encode!(i8, i16, i32, i64, u8, u16, u32, u64);
573
574macro_rules! float_encode {
575    ($($t:ty),*) => {
576        $(
577            impl PrimitiveEncode for $t {
578                type Buffer = [u8; Self::FORMATTED_SIZE];
579
580                fn init_buffer() -> Self::Buffer {
581                    [0; Self::FORMATTED_SIZE]
582                }
583
584                fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
585                    if self.is_infinite() || self.is_nan() {
586                        b"null"
587                    } else {
588                        lexical_core::write(self, buf)
589                    }
590                }
591            }
592        )*
593    };
594}
595float_encode!(f32, f64);
596
597impl PrimitiveEncode for f16 {
598    type Buffer = <f32 as PrimitiveEncode>::Buffer;
599
600    fn init_buffer() -> Self::Buffer {
601        f32::init_buffer()
602    }
603
604    fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
605        self.to_f32().encode(buf)
606    }
607}
608
609struct PrimitiveEncoder<N: PrimitiveEncode> {
610    values: ScalarBuffer<N>,
611    buffer: N::Buffer,
612}
613
614impl<N: PrimitiveEncode> PrimitiveEncoder<N> {
615    fn new<P: ArrowPrimitiveType<Native = N>>(array: &PrimitiveArray<P>) -> Self {
616        Self {
617            values: array.values().clone(),
618            buffer: N::init_buffer(),
619        }
620    }
621}
622
623impl<N: PrimitiveEncode> Encoder for PrimitiveEncoder<N> {
624    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
625        out.extend_from_slice(self.values[idx].encode(&mut self.buffer));
626    }
627}
628
629struct BooleanEncoder<'a>(&'a BooleanArray);
630
631impl Encoder for BooleanEncoder<'_> {
632    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
633        match self.0.value(idx) {
634            true => out.extend_from_slice(b"true"),
635            false => out.extend_from_slice(b"false"),
636        }
637    }
638}
639
640struct StringEncoder<'a, O: OffsetSizeTrait>(&'a GenericStringArray<O>);
641
642impl<O: OffsetSizeTrait> Encoder for StringEncoder<'_, O> {
643    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
644        encode_string(self.0.value(idx), out);
645    }
646}
647
648struct StringViewEncoder<'a>(&'a StringViewArray);
649
650impl Encoder for StringViewEncoder<'_> {
651    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
652        encode_string(self.0.value(idx), out);
653    }
654}
655
656struct BinaryViewEncoder<'a>(&'a BinaryViewArray);
657
658impl Encoder for BinaryViewEncoder<'_> {
659    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
660        encode_binary(self.0.value(idx), out);
661    }
662}
663
664struct ListLikeEncoder<'a, L: ListLikeArray> {
665    list_array: &'a L,
666    encoder: NullableEncoder<'a>,
667}
668
669impl<'a, L: ListLikeArray> ListLikeEncoder<'a, L> {
670    fn try_new(
671        field: &'a FieldRef,
672        array: &'a L,
673        options: &'a EncoderOptions,
674    ) -> Result<Self, ArrowError> {
675        let encoder = make_encoder(field, array.values().as_ref(), options)?;
676        Ok(Self {
677            list_array: array,
678            encoder,
679        })
680    }
681}
682
683impl<L: ListLikeArray> Encoder for ListLikeEncoder<'_, L> {
684    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
685        let range = self.list_array.element_range(idx);
686        let start = range.start;
687        let end = range.end;
688        out.push(b'[');
689        if self.encoder.has_nulls() {
690            for idx in start..end {
691                if idx != start {
692                    out.push(b',')
693                }
694                if self.encoder.is_null(idx) {
695                    out.extend_from_slice(b"null");
696                } else {
697                    self.encoder.encode(idx, out);
698                }
699            }
700        } else {
701            for idx in start..end {
702                if idx != start {
703                    out.push(b',')
704                }
705                self.encoder.encode(idx, out);
706            }
707        }
708        out.push(b']');
709    }
710}
711
712struct DictionaryEncoder<'a, K: ArrowDictionaryKeyType> {
713    keys: ScalarBuffer<K::Native>,
714    encoder: NullableEncoder<'a>,
715}
716
717impl<'a, K: ArrowDictionaryKeyType> DictionaryEncoder<'a, K> {
718    fn try_new(
719        field: &'a FieldRef,
720        array: &'a DictionaryArray<K>,
721        options: &'a EncoderOptions,
722    ) -> Result<Self, ArrowError> {
723        let encoder = make_encoder(field, array.values().as_ref(), options)?;
724
725        Ok(Self {
726            keys: array.keys().values().clone(),
727            encoder,
728        })
729    }
730}
731
732impl<K: ArrowDictionaryKeyType> Encoder for DictionaryEncoder<'_, K> {
733    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
734        self.encoder.encode(self.keys[idx].as_usize(), out)
735    }
736}
737
738struct RunEndEncodedEncoder<'a, R: RunEndIndexType> {
739    run_array: &'a RunArray<R>,
740    encoder: NullableEncoder<'a>,
741}
742
743impl<'a, R: RunEndIndexType> RunEndEncodedEncoder<'a, R> {
744    fn try_new(
745        field: &'a FieldRef,
746        array: &'a RunArray<R>,
747        options: &'a EncoderOptions,
748    ) -> Result<Self, ArrowError> {
749        let encoder = make_encoder(field, array.values().as_ref(), options)?;
750        Ok(Self {
751            run_array: array,
752            encoder,
753        })
754    }
755}
756
757impl<R: RunEndIndexType> Encoder for RunEndEncodedEncoder<'_, R> {
758    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
759        let physical_idx = self.run_array.get_physical_index(idx);
760        self.encoder.encode(physical_idx, out)
761    }
762}
763
764/// A newtype wrapper around [`ArrayFormatter`] to keep our usage of it private and not implement `Encoder` for the public type
765struct JsonArrayFormatter<'a> {
766    formatter: ArrayFormatter<'a>,
767}
768
769impl<'a> JsonArrayFormatter<'a> {
770    fn new(formatter: ArrayFormatter<'a>) -> Self {
771        Self { formatter }
772    }
773}
774
775impl Encoder for JsonArrayFormatter<'_> {
776    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
777        out.push(b'"');
778        // Should be infallible
779        // Note: We are making an assumption that the formatter does not produce characters that require escaping
780        let _ = write!(out, "{}", self.formatter.value(idx));
781        out.push(b'"')
782    }
783}
784
785/// A newtype wrapper around [`JsonArrayFormatter`] that skips surrounding the value with `"`
786struct RawArrayFormatter<'a>(JsonArrayFormatter<'a>);
787
788impl Encoder for RawArrayFormatter<'_> {
789    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
790        let _ = write!(out, "{}", self.0.formatter.value(idx));
791    }
792}
793
794struct NullEncoder;
795
796impl Encoder for NullEncoder {
797    fn encode(&mut self, _idx: usize, _out: &mut Vec<u8>) {
798        unreachable!()
799    }
800}
801
802struct MapEncoder<'a> {
803    offsets: OffsetBuffer<i32>,
804    keys: NullableEncoder<'a>,
805    values: NullableEncoder<'a>,
806    explicit_nulls: bool,
807}
808
809impl<'a> MapEncoder<'a> {
810    fn try_new(
811        field: &'a FieldRef,
812        array: &'a MapArray,
813        options: &'a EncoderOptions,
814    ) -> Result<Self, ArrowError> {
815        let values = array.values();
816        let keys = array.keys();
817
818        if !matches!(
819            keys.data_type(),
820            DataType::Utf8 | DataType::LargeUtf8 | DataType::Utf8View
821        ) {
822            return Err(ArrowError::JsonError(format!(
823                "Only UTF8 keys supported by JSON MapArray Writer: got {:?}",
824                keys.data_type()
825            )));
826        }
827
828        let keys = make_encoder(field, keys, options)?;
829        let values = make_encoder(field, values, options)?;
830
831        // We sanity check nulls as these are currently not enforced by MapArray (#1697)
832        if keys.has_nulls() {
833            return Err(ArrowError::InvalidArgumentError(
834                "Encountered nulls in MapArray keys".to_string(),
835            ));
836        }
837
838        if array.entries().nulls().is_some_and(|x| x.null_count() != 0) {
839            return Err(ArrowError::InvalidArgumentError(
840                "Encountered nulls in MapArray entries".to_string(),
841            ));
842        }
843
844        Ok(Self {
845            offsets: array.offsets().clone(),
846            keys,
847            values,
848            explicit_nulls: options.explicit_nulls(),
849        })
850    }
851}
852
853impl Encoder for MapEncoder<'_> {
854    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
855        let end = self.offsets[idx + 1].as_usize();
856        let start = self.offsets[idx].as_usize();
857
858        let mut is_first = true;
859
860        out.push(b'{');
861
862        for idx in start..end {
863            let is_null = self.values.is_null(idx);
864            if is_null && !self.explicit_nulls {
865                continue;
866            }
867
868            if !is_first {
869                out.push(b',');
870            }
871            is_first = false;
872
873            self.keys.encode(idx, out);
874            out.push(b':');
875
876            if is_null {
877                out.extend_from_slice(b"null");
878            } else {
879                self.values.encode(idx, out);
880            }
881        }
882        out.push(b'}');
883    }
884}
885
886/// New-type wrapper for encoding the binary types in arrow: `Binary`, `LargeBinary`
887/// and `FixedSizeBinary` as hex strings in JSON.
888struct BinaryEncoder<B>(B);
889
890impl<'a, B> BinaryEncoder<B>
891where
892    B: ArrayAccessor<Item = &'a [u8]>,
893{
894    fn new(array: B) -> Self {
895        Self(array)
896    }
897}
898
899impl<'a, B> Encoder for BinaryEncoder<B>
900where
901    B: ArrayAccessor<Item = &'a [u8]>,
902{
903    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
904        out.push(b'"');
905        for byte in self.0.value(idx) {
906            // this write is infallible
907            write!(out, "{byte:02x}").unwrap();
908        }
909        out.push(b'"');
910    }
911}
arrow_json/writer/encoder.rs

arrow_json/writer/
encoder.rs
