vrl 0.32.0

Vector Remap Language
Documentation 
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use crate::compiler::prelude::*;
use nom::AsBytes;

fn decode_zstd(value: Value) -> Resolved {
    let value = value.try_bytes()?;
    let result = zstd::decode_all(value.as_bytes());

    match result {
        Ok(decoded_bytes) => Ok(Value::Bytes(decoded_bytes.into())),
        Err(_) => Err("unable to decode value with Zstd decoder".into()),
    }
}

#[derive(Clone, Copy, Debug)]
pub struct DecodeZstd;

impl Function for DecodeZstd {
    fn identifier(&self) -> &'static str {
        "decode_zstd"
    }

    fn usage(&self) -> &'static str {
        "Decodes the `value` (a [Zstandard](https://facebook.github.io/zstd) string) into its original string."
    }

    fn category(&self) -> &'static str {
        Category::Codec.as_ref()
    }

    fn internal_failure_reasons(&self) -> &'static [&'static str] {
        &["`value` isn't a valid encoded Zstd string."]
    }

    fn return_kind(&self) -> u16 {
        kind::BYTES
    }

    fn examples(&self) -> &'static [Example] {
        &[example! {
            title: "Decode Zstd data",
            source: r#"decode_zstd!(decode_base64!("KLUv/QBY/QEAYsQOFKClbQBedqXsb96EWDax/f/F/z+gNU4ZTInaUeAj82KqPFjUzKqhcfDqAIsLvAsnY1bI/N2mHzDixRQA"))"#,
            result: Ok("you_have_successfully_decoded_me.congratulations.you_are_breathtaking."),
        }]
    }

    fn compile(
        &self,
        _state: &state::TypeState,
        _ctx: &mut FunctionCompileContext,
        arguments: ArgumentList,
    ) -> Compiled {
        let value = arguments.required("value");

        Ok(DecodeZstdFn { value }.as_expr())
    }

    fn parameters(&self) -> &'static [Parameter] {
        const PARAMETERS: &[Parameter] = &[Parameter::required(
            "value",
            kind::BYTES,
            "The [Zstandard](https://facebook.github.io/zstd) data to decode.",
        )];
        PARAMETERS
    }
}

#[derive(Clone, Debug)]
struct DecodeZstdFn {
    value: Box<dyn Expression>,
}

impl FunctionExpression for DecodeZstdFn {
    fn resolve(&self, ctx: &mut Context) -> Resolved {
        let value = self.value.resolve(ctx)?;

        decode_zstd(value)
    }

    fn type_def(&self, _: &state::TypeState) -> TypeDef {
        // Always fallible due to the possibility of decoding errors that VRL can't detect
        TypeDef::bytes().fallible()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::value;
    use nom::AsBytes;

    fn get_encoded_bytes(text: &str) -> Vec<u8> {
        zstd::encode_all(text.as_bytes(), 0).expect("Cannot encode bytes with Zstd encoder")
    }

    test_function![
        decode_zstd => DecodeZstd;

        right_zstd {
            args: func_args![value: value!(get_encoded_bytes("sample").as_bytes())],
            want: Ok(value!(b"sample")),
            tdef: TypeDef::bytes().fallible(),
        }

        wrong_zstd {
            args: func_args![value: value!("some_bytes")],
            want: Err("unable to decode value with Zstd decoder"),
            tdef: TypeDef::bytes().fallible(),
        }
    ];
}