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

arrow_json/writer/
encoder.rs
