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::List(_) => {
350            let array = array.as_list::<i32>();
351            NullableEncoder::new(Box::new(ListEncoder::try_new(field, array, options)?), array.nulls().cloned())
352        }
353        DataType::LargeList(_) => {
354            let array = array.as_list::<i64>();
355            NullableEncoder::new(Box::new(ListEncoder::try_new(field, array, options)?), array.nulls().cloned())
356        }
357        DataType::FixedSizeList(_, _) => {
358            let array = array.as_fixed_size_list();
359            NullableEncoder::new(Box::new(FixedSizeListEncoder::try_new(field, array, options)?), array.nulls().cloned())
360        }
361
362        DataType::Dictionary(_, _) => downcast_dictionary_array! {
363            array => {
364                NullableEncoder::new(Box::new(DictionaryEncoder::try_new(field, array, options)?), array.nulls().cloned())
365            },
366            _ => unreachable!()
367        }
368
369        DataType::Map(_, _) => {
370            let array = array.as_map();
371            NullableEncoder::new(Box::new(MapEncoder::try_new(field, array, options)?), array.nulls().cloned())
372        }
373
374        DataType::FixedSizeBinary(_) => {
375            let array = array.as_fixed_size_binary();
376            NullableEncoder::new(Box::new(BinaryEncoder::new(array)) as _, array.nulls().cloned())
377        }
378
379        DataType::Binary => {
380            let array: &BinaryArray = array.as_binary();
381            NullableEncoder::new(Box::new(BinaryEncoder::new(array)), array.nulls().cloned())
382        }
383
384        DataType::LargeBinary => {
385            let array: &LargeBinaryArray = array.as_binary();
386            NullableEncoder::new(Box::new(BinaryEncoder::new(array)), array.nulls().cloned())
387        }
388
389        DataType::Struct(fields) => {
390            let array = array.as_struct();
391            let encoders = fields.iter().zip(array.columns()).map(|(field, array)| {
392                let encoder = make_encoder(field, array, options)?;
393                Ok(FieldEncoder{
394                    field: field.clone(),
395                    encoder,
396                })
397            }).collect::<Result<Vec<_>, ArrowError>>()?;
398
399            let encoder = StructArrayEncoder{
400                encoders,
401                explicit_nulls: options.explicit_nulls(),
402                struct_mode: options.struct_mode(),
403            };
404            let nulls = array.nulls().cloned();
405            NullableEncoder::new(Box::new(encoder) as Box<dyn Encoder + 'a>, nulls)
406        }
407        DataType::Decimal32(_, _) | DataType::Decimal64(_, _) | DataType::Decimal128(_, _) | DataType::Decimal256(_, _) => {
408            let options = FormatOptions::new().with_display_error(true);
409            let formatter = JsonArrayFormatter::new(ArrayFormatter::try_new(array, &options)?);
410            NullableEncoder::new(Box::new(RawArrayFormatter(formatter)) as Box<dyn Encoder + 'a>, nulls)
411        }
412        d => match d.is_temporal() {
413            true => {
414                // Note: the implementation of Encoder for ArrayFormatter assumes it does not produce
415                // characters that would need to be escaped within a JSON string, e.g. `'"'`.
416                // If support for user-provided format specifications is added, this assumption
417                // may need to be revisited
418                let fops = FormatOptions::new().with_display_error(true)
419                .with_date_format(options.date_format.as_deref())
420                .with_datetime_format(options.datetime_format.as_deref())
421                .with_timestamp_format(options.timestamp_format.as_deref())
422                .with_timestamp_tz_format(options.timestamp_tz_format.as_deref())
423                .with_time_format(options.time_format.as_deref());
424
425                let formatter = ArrayFormatter::try_new(array, &fops)?;
426                let formatter = JsonArrayFormatter::new(formatter);
427                NullableEncoder::new(Box::new(formatter) as Box<dyn Encoder + 'a>, nulls)
428            }
429            false => return Err(ArrowError::JsonError(format!(
430                "Unsupported data type for JSON encoding: {d:?}",
431            )))
432        }
433    };
434
435    Ok(encoder)
436}
437
438fn encode_string(s: &str, out: &mut Vec<u8>) {
439    let mut serializer = serde_json::Serializer::new(out);
440    serializer.serialize_str(s).unwrap();
441}
442
443struct FieldEncoder<'a> {
444    field: FieldRef,
445    encoder: NullableEncoder<'a>,
446}
447
448impl FieldEncoder<'_> {
449    fn is_null(&self, idx: usize) -> bool {
450        self.encoder.is_null(idx)
451    }
452}
453
454struct StructArrayEncoder<'a> {
455    encoders: Vec<FieldEncoder<'a>>,
456    explicit_nulls: bool,
457    struct_mode: StructMode,
458}
459
460impl Encoder for StructArrayEncoder<'_> {
461    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
462        match self.struct_mode {
463            StructMode::ObjectOnly => out.push(b'{'),
464            StructMode::ListOnly => out.push(b'['),
465        }
466        let mut is_first = true;
467        // Nulls can only be dropped in explicit mode
468        let drop_nulls = (self.struct_mode == StructMode::ObjectOnly) && !self.explicit_nulls;
469
470        for field_encoder in self.encoders.iter_mut() {
471            let is_null = field_encoder.is_null(idx);
472            if is_null && drop_nulls {
473                continue;
474            }
475
476            if !is_first {
477                out.push(b',');
478            }
479            is_first = false;
480
481            if self.struct_mode == StructMode::ObjectOnly {
482                encode_string(field_encoder.field.name(), out);
483                out.push(b':');
484            }
485
486            if is_null {
487                out.extend_from_slice(b"null");
488            } else {
489                field_encoder.encoder.encode(idx, out);
490            }
491        }
492        match self.struct_mode {
493            StructMode::ObjectOnly => out.push(b'}'),
494            StructMode::ListOnly => out.push(b']'),
495        }
496    }
497}
498
499trait PrimitiveEncode: ArrowNativeType {
500    type Buffer;
501
502    // Workaround https://github.com/rust-lang/rust/issues/61415
503    fn init_buffer() -> Self::Buffer;
504
505    /// Encode the primitive value as bytes, returning a reference to that slice.
506    ///
507    /// `buf` is temporary space that may be used
508    fn encode(self, buf: &mut Self::Buffer) -> &[u8];
509}
510
511macro_rules! integer_encode {
512    ($($t:ty),*) => {
513        $(
514            impl PrimitiveEncode for $t {
515                type Buffer = [u8; Self::FORMATTED_SIZE];
516
517                fn init_buffer() -> Self::Buffer {
518                    [0; Self::FORMATTED_SIZE]
519                }
520
521                fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
522                    lexical_core::write(self, buf)
523                }
524            }
525        )*
526    };
527}
528integer_encode!(i8, i16, i32, i64, u8, u16, u32, u64);
529
530macro_rules! float_encode {
531    ($($t:ty),*) => {
532        $(
533            impl PrimitiveEncode for $t {
534                type Buffer = [u8; Self::FORMATTED_SIZE];
535
536                fn init_buffer() -> Self::Buffer {
537                    [0; Self::FORMATTED_SIZE]
538                }
539
540                fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
541                    if self.is_infinite() || self.is_nan() {
542                        b"null"
543                    } else {
544                        lexical_core::write(self, buf)
545                    }
546                }
547            }
548        )*
549    };
550}
551float_encode!(f32, f64);
552
553impl PrimitiveEncode for f16 {
554    type Buffer = <f32 as PrimitiveEncode>::Buffer;
555
556    fn init_buffer() -> Self::Buffer {
557        f32::init_buffer()
558    }
559
560    fn encode(self, buf: &mut Self::Buffer) -> &[u8] {
561        self.to_f32().encode(buf)
562    }
563}
564
565struct PrimitiveEncoder<N: PrimitiveEncode> {
566    values: ScalarBuffer<N>,
567    buffer: N::Buffer,
568}
569
570impl<N: PrimitiveEncode> PrimitiveEncoder<N> {
571    fn new<P: ArrowPrimitiveType<Native = N>>(array: &PrimitiveArray<P>) -> Self {
572        Self {
573            values: array.values().clone(),
574            buffer: N::init_buffer(),
575        }
576    }
577}
578
579impl<N: PrimitiveEncode> Encoder for PrimitiveEncoder<N> {
580    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
581        out.extend_from_slice(self.values[idx].encode(&mut self.buffer));
582    }
583}
584
585struct BooleanEncoder<'a>(&'a BooleanArray);
586
587impl Encoder for BooleanEncoder<'_> {
588    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
589        match self.0.value(idx) {
590            true => out.extend_from_slice(b"true"),
591            false => out.extend_from_slice(b"false"),
592        }
593    }
594}
595
596struct StringEncoder<'a, O: OffsetSizeTrait>(&'a GenericStringArray<O>);
597
598impl<O: OffsetSizeTrait> Encoder for StringEncoder<'_, O> {
599    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
600        encode_string(self.0.value(idx), out);
601    }
602}
603
604struct StringViewEncoder<'a>(&'a StringViewArray);
605
606impl Encoder for StringViewEncoder<'_> {
607    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
608        encode_string(self.0.value(idx), out);
609    }
610}
611
612struct ListEncoder<'a, O: OffsetSizeTrait> {
613    offsets: OffsetBuffer<O>,
614    encoder: NullableEncoder<'a>,
615}
616
617impl<'a, O: OffsetSizeTrait> ListEncoder<'a, O> {
618    fn try_new(
619        field: &'a FieldRef,
620        array: &'a GenericListArray<O>,
621        options: &'a EncoderOptions,
622    ) -> Result<Self, ArrowError> {
623        let encoder = make_encoder(field, array.values().as_ref(), options)?;
624        Ok(Self {
625            offsets: array.offsets().clone(),
626            encoder,
627        })
628    }
629}
630
631impl<O: OffsetSizeTrait> Encoder for ListEncoder<'_, O> {
632    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
633        let end = self.offsets[idx + 1].as_usize();
634        let start = self.offsets[idx].as_usize();
635        out.push(b'[');
636
637        if self.encoder.has_nulls() {
638            for idx in start..end {
639                if idx != start {
640                    out.push(b',')
641                }
642                if self.encoder.is_null(idx) {
643                    out.extend_from_slice(b"null");
644                } else {
645                    self.encoder.encode(idx, out);
646                }
647            }
648        } else {
649            for idx in start..end {
650                if idx != start {
651                    out.push(b',')
652                }
653                self.encoder.encode(idx, out);
654            }
655        }
656        out.push(b']');
657    }
658}
659
660struct FixedSizeListEncoder<'a> {
661    value_length: usize,
662    encoder: NullableEncoder<'a>,
663}
664
665impl<'a> FixedSizeListEncoder<'a> {
666    fn try_new(
667        field: &'a FieldRef,
668        array: &'a FixedSizeListArray,
669        options: &'a EncoderOptions,
670    ) -> Result<Self, ArrowError> {
671        let encoder = make_encoder(field, array.values().as_ref(), options)?;
672        Ok(Self {
673            encoder,
674            value_length: array.value_length().as_usize(),
675        })
676    }
677}
678
679impl Encoder for FixedSizeListEncoder<'_> {
680    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
681        let start = idx * self.value_length;
682        let end = start + self.value_length;
683        out.push(b'[');
684        if self.encoder.has_nulls() {
685            for idx in start..end {
686                if idx != start {
687                    out.push(b',')
688                }
689                if self.encoder.is_null(idx) {
690                    out.extend_from_slice(b"null");
691                } else {
692                    self.encoder.encode(idx, out);
693                }
694            }
695        } else {
696            for idx in start..end {
697                if idx != start {
698                    out.push(b',')
699                }
700                self.encoder.encode(idx, out);
701            }
702        }
703        out.push(b']');
704    }
705}
706
707struct DictionaryEncoder<'a, K: ArrowDictionaryKeyType> {
708    keys: ScalarBuffer<K::Native>,
709    encoder: NullableEncoder<'a>,
710}
711
712impl<'a, K: ArrowDictionaryKeyType> DictionaryEncoder<'a, K> {
713    fn try_new(
714        field: &'a FieldRef,
715        array: &'a DictionaryArray<K>,
716        options: &'a EncoderOptions,
717    ) -> Result<Self, ArrowError> {
718        let encoder = make_encoder(field, array.values().as_ref(), options)?;
719
720        Ok(Self {
721            keys: array.keys().values().clone(),
722            encoder,
723        })
724    }
725}
726
727impl<K: ArrowDictionaryKeyType> Encoder for DictionaryEncoder<'_, K> {
728    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
729        self.encoder.encode(self.keys[idx].as_usize(), out)
730    }
731}
732
733/// A newtype wrapper around [`ArrayFormatter`] to keep our usage of it private and not implement `Encoder` for the public type
734struct JsonArrayFormatter<'a> {
735    formatter: ArrayFormatter<'a>,
736}
737
738impl<'a> JsonArrayFormatter<'a> {
739    fn new(formatter: ArrayFormatter<'a>) -> Self {
740        Self { formatter }
741    }
742}
743
744impl Encoder for JsonArrayFormatter<'_> {
745    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
746        out.push(b'"');
747        // Should be infallible
748        // Note: We are making an assumption that the formatter does not produce characters that require escaping
749        let _ = write!(out, "{}", self.formatter.value(idx));
750        out.push(b'"')
751    }
752}
753
754/// A newtype wrapper around [`JsonArrayFormatter`] that skips surrounding the value with `"`
755struct RawArrayFormatter<'a>(JsonArrayFormatter<'a>);
756
757impl Encoder for RawArrayFormatter<'_> {
758    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
759        let _ = write!(out, "{}", self.0.formatter.value(idx));
760    }
761}
762
763struct NullEncoder;
764
765impl Encoder for NullEncoder {
766    fn encode(&mut self, _idx: usize, _out: &mut Vec<u8>) {
767        unreachable!()
768    }
769}
770
771struct MapEncoder<'a> {
772    offsets: OffsetBuffer<i32>,
773    keys: NullableEncoder<'a>,
774    values: NullableEncoder<'a>,
775    explicit_nulls: bool,
776}
777
778impl<'a> MapEncoder<'a> {
779    fn try_new(
780        field: &'a FieldRef,
781        array: &'a MapArray,
782        options: &'a EncoderOptions,
783    ) -> Result<Self, ArrowError> {
784        let values = array.values();
785        let keys = array.keys();
786
787        if !matches!(keys.data_type(), DataType::Utf8 | DataType::LargeUtf8) {
788            return Err(ArrowError::JsonError(format!(
789                "Only UTF8 keys supported by JSON MapArray Writer: got {:?}",
790                keys.data_type()
791            )));
792        }
793
794        let keys = make_encoder(field, keys, options)?;
795        let values = make_encoder(field, values, options)?;
796
797        // We sanity check nulls as these are currently not enforced by MapArray (#1697)
798        if keys.has_nulls() {
799            return Err(ArrowError::InvalidArgumentError(
800                "Encountered nulls in MapArray keys".to_string(),
801            ));
802        }
803
804        if array.entries().nulls().is_some_and(|x| x.null_count() != 0) {
805            return Err(ArrowError::InvalidArgumentError(
806                "Encountered nulls in MapArray entries".to_string(),
807            ));
808        }
809
810        Ok(Self {
811            offsets: array.offsets().clone(),
812            keys,
813            values,
814            explicit_nulls: options.explicit_nulls(),
815        })
816    }
817}
818
819impl Encoder for MapEncoder<'_> {
820    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
821        let end = self.offsets[idx + 1].as_usize();
822        let start = self.offsets[idx].as_usize();
823
824        let mut is_first = true;
825
826        out.push(b'{');
827
828        for idx in start..end {
829            let is_null = self.values.is_null(idx);
830            if is_null && !self.explicit_nulls {
831                continue;
832            }
833
834            if !is_first {
835                out.push(b',');
836            }
837            is_first = false;
838
839            self.keys.encode(idx, out);
840            out.push(b':');
841
842            if is_null {
843                out.extend_from_slice(b"null");
844            } else {
845                self.values.encode(idx, out);
846            }
847        }
848        out.push(b'}');
849    }
850}
851
852/// New-type wrapper for encoding the binary types in arrow: `Binary`, `LargeBinary`
853/// and `FixedSizeBinary` as hex strings in JSON.
854struct BinaryEncoder<B>(B);
855
856impl<'a, B> BinaryEncoder<B>
857where
858    B: ArrayAccessor<Item = &'a [u8]>,
859{
860    fn new(array: B) -> Self {
861        Self(array)
862    }
863}
864
865impl<'a, B> Encoder for BinaryEncoder<B>
866where
867    B: ArrayAccessor<Item = &'a [u8]>,
868{
869    fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
870        out.push(b'"');
871        for byte in self.0.value(idx) {
872            // this write is infallible
873            write!(out, "{byte:02x}").unwrap();
874        }
875        out.push(b'"');
876    }
877}
arrow_json/writer/encoder.rs

arrow_json/writer/
encoder.rs
