I’m implementing a unified parameter extractor Params for axum that can handle parameters from Path/Query/Form/Multipart. I have a custom DOM-like type that stores both JSON data and uploaded files:

pub struct UploadFile {
    pub file_name: String,
    pub temp_file: Arc<NamedTempFile>,
}

pub enum ParamsValue {
    Object(HashMap<String, ParamsValue>),
    Array(Vec<ParamsValue>),
    Json(serde_json::Value),
    UploadFile(Box<UploadFile>),
}

I need to deserialize ParamsValue into a struct like this:

#[derive(Deserialize)]
struct FileUploadParams {
    title: String,
    file: UploadFile,
}

I know it can’t be serialize to and deserialize from bytes likes JSON, I just wan’t use it to ser/de between DOM and struct.

The challenge is that the UploadFile field(or just temp_file field) needs to be assigned directly from ParamsValue::UploadFile variant rather than being deserialized. I’ve tried implementing Deserialize/Deserializer traits for both ParamsValue and FileUpload, but can’t get it working.
Any suggestions on how to implement this custom deserialization properly?