JSON field names with serde

Hello there! I'm sorry if this has been already asked before but I just want to get confirmation if what I want to do is currently possible with serde or not. For that I'll use an example similar to what I have now:

Basically I have an actix endpoint that receives a request with the following definition:

struct EndpointPayload {
    #[serde(deserialize_with = "option_date_time_iso8601_deserializer")]
    from_date: Option<chrono::NaiveDateTime>,
    #[serde(deserialize_with = "option_date_time_iso8601_deserializer")]
    to_date: Option<chrono::NaiveDateTime>,

pub fn option_date_time_iso8601_deserializer<'de, D>(deserializer: D) -> Result<Option<chrono::NaiveDateTime>, D::Error>
    D: Deserializer<'de>,
    match Option::deserialize(deserializer)? {
        Some(x) => Ok(Some(
            deserialize_string_to_naive_date_time(x).map_err(|_| D::Error::custom("Couldn't deserialize NaiveDateTime from string"))?,
        None => Ok(None),

fn deserialize_string_to_naive_date_time(s: &str) -> chrono::ParseResult<chrono::NaiveDateTime> {
    let date_format = "%Y-%m-%dT%H:%M:%S%.3fZ";
    chrono::NaiveDateTime::parse_from_str(s, &date_format)

Now, as you can see basically the endpoint receives a JSON body where the dates are strings in an ISO8601 format, now my problem is that sometimes the date may not be properly formatted, that makes my parsing code in deserialize_string_to_naive_date_time which is fine, but I would like to get the name of the JSON field that provoked that error.

I've searched both the source of serde_json and some topics around but I don't think it is something that can currently be done, at least not without changing serde_json itself.

TLDR: Is there a way to get the name of the JSON fields in a custom deserialization function?

I'm not aware of any way to do this in the deserialize function. To get the path to fields you can use

Hello @jonasbb thanks for your reply!

I did check that crate you've mentioned, what I've seen though is that you can only get the path if the deserializer fails, which is not exactly my case since the error happens in the deserialize_string_to_naive_date_time

Of course then I convert that error so that the deserialization fails, but in the end the one doing calling the deserializer is actix not me, so the moment I leave the option_date_time_iso8601_deserializer function I cannot control how the error will be treated.

Maybe I should simply implement my own deserializer that consumes the one actix passes to me as parameter so that I can then either use the aforementioned crate, or directly implement the logic myself.

The problem is that both options are simply too time consuming, but if there's no alternative then I'll try to do it myself probably.

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