README.md

Serde Hooks

This crate allows you to hook into [serde] serialization. You can get callbacks for each piece of data that is being serialized, and modify serialization behavior at runtime.

For example, you can, at runtime:

• Rename or skip struct fields.
• Rename enum variants.
• Replace struct field values, map keys and values, sequence and tuple items.
• Add new entries to maps.
• Introspect serialized data structures.

"Why would I need this crate?"

You likely wouldn't.

Seriously, in the vast majority of cases, what [serde] offers out of the box is enough, and more optimal to use. Before you consider using this crate, please check serde.rs, including the examples section. After that, consider changing your data model in a way that you can use bare serde. Only then, if none of the above helps, come back for the hooks.

Some examples where having runtime control over serialization can be handy:

• You need to exclude certain fields from an API response based on permissions level. E.g. exclude salary field from Employee struct for everyone but their manager.
• You need to support different case conventions for different formats. E.g. camelCase in JSON and kebab-case in YAML.
• Your data type comes from a library you cannot change, and already has a #[derive(Serialize)]. Just not exactly with the #[serde] attributes you want there.

Obviously, all of these cases can be handled by either implementing custom serialization, or using something like #[serde(serialize_with = ...)]. But let's face it, it's not fun: you'd need to type a ton of boilerplate and the default serde derive is so much nicer to use.

In fact, this crate actually is that ton of boilerplate that just calls back to you at the right moments.

Example

This example shows conditional exclusion of a field at runtime:

use serde::Serialize;
use serde_hooks::{ser, Path};

#[derive(Serialize)]
struct Employee {
    name: String,
    salary: f64,
}

struct EmployeeHooks {
    boss_is_asking: bool,
}

impl ser::Hooks for EmployeeHooks {
    fn on_struct(&self, path: &Path, st: &mut ser::StructScope) {
        if !self.boss_is_asking {
            st.skip_field("salary");
        }
    }
}

let poor_guy = Employee {
    name: "Richie".into(),
    salary: 1_000_000.99,
};

let json = serde_json::to_string(&ser::hook(
    &poor_guy,
    &EmployeeHooks { boss_is_asking: false }
)).unwrap();
assert_eq!(json, r#"{"name":"Richie"}"#);

let json = serde_json::to_string(&ser::hook(
    &poor_guy,
    &EmployeeHooks { boss_is_asking: true }
)).unwrap();
assert_eq!(json, r#"{"name":"Richie","salary":1000000.99}"#);

More examples are available throughout the documentation and in the repository, in the examples directory.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.