activitypub-federation-rust/src/deser/helpers.rs

use serde::{Deserialize, Deserializer};

/// Deserialize either a single json value, or a json array. In either case, the items are returned
/// as an array.
///
/// Usage:
/// `#[serde(deserialize_with = "deserialize_one_or_many")]`
pub fn deserialize_one_or_many<'de, T, D>(deserializer: D) -> Result<Vec<T>, D::Error>
where
    T: Deserialize<'de>,
    D: Deserializer<'de>,
{
    #[derive(Deserialize)]
    #[serde(untagged)]
    enum OneOrMany<T> {
        One(T),
        Many(Vec<T>),
    }

    let result: OneOrMany<T> = Deserialize::deserialize(deserializer)?;
    Ok(match result {
        OneOrMany::Many(list) => list,
        OneOrMany::One(value) => vec![value],
    })
}

/// Deserialize either a single json value, or a json array with one element. In both cases it
/// returns an array with a single element.
///
/// Usage:
/// `#[serde(deserialize_with = "deserialize_one")]`
pub fn deserialize_one<'de, T, D>(deserializer: D) -> Result<[T; 1], D::Error>
where
    T: Deserialize<'de>,
    D: Deserializer<'de>,
{
    #[derive(Deserialize)]
    #[serde(untagged)]
    enum MaybeArray<T> {
        Simple(T),
        Array([T; 1]),
    }

    let result: MaybeArray<T> = Deserialize::deserialize(deserializer)?;
    Ok(match result {
        MaybeArray::Simple(value) => [value],
        MaybeArray::Array(value) => value,
    })
}

/// Attempts to deserialize the item. If any error happens, its ignored and the type's default
/// value is returned.
///
/// Usage:
/// `#[serde(deserialize_with = "deserialize_skip_error")]`
pub fn deserialize_skip_error<'de, T, D>(deserializer: D) -> Result<T, D::Error>
where
    T: Deserialize<'de> + Default,
    D: Deserializer<'de>,
{
    let value = serde_json::Value::deserialize(deserializer)?;
    let inner = T::deserialize(value).unwrap_or_default();
    Ok(inner)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_deserialize_skip_error() {
        #[derive(Debug, Deserialize)]
        pub struct MyData {
            #[serde(deserialize_with = "deserialize_skip_error")]
            pub data: Option<String>,
        }
        // data has type object
        let _: MyData = serde_json::from_str(r#"{ "data": {} }"#).unwrap();

        // data has type array
        let _: MyData = serde_json::from_str(r#"{"data": []}"#).unwrap();
    }
}