arrow-cast 59.2.0

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// specific language governing permissions and limitations
// under the License.

//! Functions for converting data in [`GenericBinaryArray`] such as [`StringArray`] to/from base64 encoded strings
//!
//! [`StringArray`]: arrow_array::StringArray

use arrow_array::{Array, GenericBinaryArray, GenericStringArray, OffsetSizeTrait};
use arrow_buffer::{Buffer, OffsetBuffer};
use arrow_schema::ArrowError;
use base64::encoded_len;
use base64::engine::Config;

pub use base64::prelude::*;

/// Base64 encode each element of `array` with the provided [`Engine`]
///
/// Panics if the `Engine` emits output that is not valid UTF-8. A correct
/// `Engine` never does, but it is a safe trait so a misbehaving impl could;
/// validating keeps the returned [`GenericStringArray`] sound (#10284).
pub fn b64_encode<E: Engine, O: OffsetSizeTrait>(
    engine: &E,
    array: &GenericBinaryArray<O>,
) -> GenericStringArray<O> {
    let lengths = array.offsets().windows(2).map(|w| {
        let len = w[1].as_usize() - w[0].as_usize();
        encoded_len(len, engine.config().encode_padding()).unwrap()
    });
    let offsets = OffsetBuffer::<O>::from_lengths(lengths);
    let buffer_len = offsets.last().unwrap().as_usize();
    let mut buffer = vec![0_u8; buffer_len];
    let mut offset = 0;

    for i in 0..array.len() {
        let len = engine
            .encode_slice(array.value(i), &mut buffer[offset..])
            .unwrap();
        offset += len;
    }
    assert_eq!(offset, buffer_len);

    // `try_new` validates UTF-8 instead of trusting the (safe-trait) Engine.
    GenericStringArray::try_new(offsets, Buffer::from_vec(buffer), array.nulls().cloned())
        .expect("Engine produced invalid UTF-8")
}

/// Base64 decode each element of `array` with the provided [`Engine`]
pub fn b64_decode<E: Engine, O: OffsetSizeTrait>(
    engine: &E,
    array: &GenericBinaryArray<O>,
) -> Result<GenericBinaryArray<O>, ArrowError> {
    let estimated_len = array.values().len(); // This is an overestimate
    let mut buffer = vec![0; estimated_len];

    let mut offsets = Vec::with_capacity(array.len() + 1);
    offsets.push(O::usize_as(0));
    let mut offset = 0;

    for v in array.iter() {
        if let Some(v) = v {
            let len = engine.decode_slice(v, &mut buffer[offset..]).unwrap();
            // This cannot overflow as `len` is less than `v.len()` and `a` is valid
            offset += len;
        }
        offsets.push(O::usize_as(offset));
    }

    // Safety: offsets monotonically increasing by construction
    let offsets = unsafe { OffsetBuffer::new_unchecked(offsets.into()) };

    GenericBinaryArray::try_new(offsets, Buffer::from_vec(buffer), array.nulls().cloned())
}

#[cfg(test)]
mod tests {
    use super::*;
    use arrow_array::BinaryArray;
    use rand::{Rng, rng};

    fn test_engine<E: Engine>(e: &E, a: &BinaryArray) {
        let encoded = b64_encode(e, a);
        encoded.to_data().validate_full().unwrap();

        let to_decode = encoded.into();
        let decoded = b64_decode(e, &to_decode).unwrap();
        decoded.to_data().validate_full().unwrap();

        assert_eq!(&decoded, a);
    }

    #[test]
    fn test_b64() {
        let mut rng = rng();
        let len = rng.random_range(1024..1050);
        let data: BinaryArray = (0..len)
            .map(|_| {
                let len = rng.random_range(0..16);
                Some((0..len).map(|_| rng.random::<u8>()).collect::<Vec<u8>>())
            })
            .collect();

        test_engine(&BASE64_STANDARD, &data);
        test_engine(&BASE64_STANDARD_NO_PAD, &data);
    }

    /// Safe-Rust `Engine` that writes invalid UTF-8 into the encode buffer
    /// (#10284). `b64_encode` must reject it rather than build an unsound
    /// `StringArray`.
    struct EvilEngine;

    impl Engine for EvilEngine {
        type Config = <base64::engine::GeneralPurpose as Engine>::Config;
        type DecodeEstimate = <base64::engine::GeneralPurpose as Engine>::DecodeEstimate;

        fn internal_encode(&self, input: &[u8], output: &mut [u8]) -> usize {
            BASE64_STANDARD.internal_encode(input, output)
        }
        fn internal_decoded_len_estimate(&self, input_len: usize) -> Self::DecodeEstimate {
            BASE64_STANDARD.internal_decoded_len_estimate(input_len)
        }
        fn internal_decode(
            &self,
            input: &[u8],
            output: &mut [u8],
            estimate: Self::DecodeEstimate,
        ) -> Result<base64::engine::DecodeMetadata, base64::DecodeSliceError> {
            BASE64_STANDARD.internal_decode(input, output, estimate)
        }
        fn config(&self) -> &Self::Config {
            BASE64_STANDARD.config()
        }
        fn encode_slice<T: AsRef<[u8]>>(
            &self,
            input: T,
            output_buf: &mut [u8],
        ) -> Result<usize, base64::EncodeSliceError> {
            let len = BASE64_STANDARD.encode_slice(input, output_buf)?;
            for b in output_buf[..len].iter_mut() {
                *b = 0xFF; // invalid UTF-8, but correct length
            }
            Ok(len)
        }

        fn padding(&self) -> base64::alphabet::Symbol {
            base64::alphabet::Symbol::new(b'=').unwrap()
        }
    }

    #[test]
    #[should_panic(expected = "produced invalid UTF-8")]
    fn test_b64_encode_rejects_invalid_utf8() {
        let data: BinaryArray = vec![Some(b"hello".to_vec())].into_iter().collect();
        let _ = b64_encode(&EvilEngine, &data);
    }
}