serde-vars 0.3.1

Conveniently expose (environment) variables to your serde based data structures, like configurations.
Documentation 
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use serde::de;

pub fn deserialize_byte_buf<'de, D>(deserializer: D) -> Result<Vec<u8>, D::Error>
where
    D: de::Deserializer<'de>,
{
    struct Visitor;

    impl<'de> de::Visitor<'de> for Visitor {
        type Value = Vec<u8>;

        fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
            formatter.write_str("byte array")
        }

        fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(v.to_vec())
        }

        fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(v)
        }

        fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(v.as_bytes().to_vec())
        }

        fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(v.into_bytes())
        }

        fn visit_seq<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
        where
            V: de::SeqAccess<'de>,
        {
            let len = std::cmp::min(visitor.size_hint().unwrap_or(0), 4096);
            let mut bytes = Vec::with_capacity(len);

            while let Some(b) = visitor.next_element()? {
                bytes.push(b);
            }

            Ok(bytes)
        }
    }

    deserializer.deserialize_byte_buf(Visitor)
}