# Custom de/serialization functions for Rust's [serde](https://serde.rs) [![crates.io badge](https://img.shields.io/crates/v/serde_with.svg)](https://crates.io/crates/serde_with/) [![Build Status](https://github.com/jonasbb/serde_with/workflows/Rust%20CI/badge.svg)](https://github.com/jonasbb/serde_with) [![codecov](https://codecov.io/gh/jonasbb/serde_with/branch/master/graph/badge.svg)](https://codecov.io/gh/jonasbb/serde_with) [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/4322/badge)](https://bestpractices.coreinfrastructure.org/projects/4322) [![Rustexplorer](https://img.shields.io/badge/Try%20on-rustexplorer-lightgrey?logo=rust&logoColor=orange)](https://www.rustexplorer.com/b/py7ida) --- This crate provides custom de/serialization helpers to use in combination with [serde's `with` annotation][with-annotation] and with the improved [`serde_as`][as-annotation]-annotation. Some common use cases are: * De/Serializing a type using the `Display` and `FromStr` traits, e.g., for `u8`, `url::Url`, or `mime::Mime`. Check [`DisplayFromStr`] for details. * Support for arrays larger than 32 elements or using const generics. With `serde_as` large arrays are supported, even if they are nested in other types. `[bool; 64]`, `Option<[u8; M]>`, and `Box<[[u8; 64]; N]>` are all supported, as [this examples shows](#large-and-const-generic-arrays). * Skip serializing all empty `Option` types with [`#[skip_serializing_none]`][skip_serializing_none]. * Apply a prefix to each field name of a struct, without changing the de/serialize implementations of the struct using [`with_prefix!`][]. * Deserialize a comma separated list like `#hash,#tags,#are,#great` into a `Vec<String>`. Check the documentation for [`serde_with::StringWithSeparator::<CommaSeparator, T>`][StringWithSeparator]. ### Getting Help **Check out the [user guide][user guide] to find out more tips and tricks about this crate.** For further help using this crate, you can [open a new discussion](https://github.com/jonasbb/serde_with/discussions/new) or ask on [users.rust-lang.org](https://users.rust-lang.org/). For bugs, please open a [new issue](https://github.com/jonasbb/serde_with/issues/new) on GitHub. ## Use `serde_with` in your Project ```bash # Add the current version to your Cargo.toml cargo add serde_with ``` The crate contains different features for integration with other common crates. Check the [feature flags][] section for information about all available features. ## Examples Annotate your struct or enum to enable the custom de/serializer. The `#[serde_as]` attribute must be placed *before* the `#[derive]`. The `as` is analogous to the `with` attribute of serde. You mirror the type structure of the field you want to de/serialize. You can specify converters for the inner types of a field, e.g., `Vec<DisplayFromStr>`. The default de/serialization behavior can be restored by using `_` as a placeholder, e.g., `BTreeMap<_, DisplayFromStr>`. ### `DisplayFromStr` [![Rustexplorer](https://img.shields.io/badge/Try%20on-rustexplorer-lightgrey?logo=rust&logoColor=orange)](https://www.rustexplorer.com/b/py7ida) ```rust #[serde_as] #[derive(Deserialize, Serialize)] struct Foo { // Serialize with Display, deserialize with FromStr #[serde_as(as = "DisplayFromStr")] bar: u8, } // This will serialize Foo {bar: 12} // into this JSON {"bar": "12"} ``` ### Large and const-generic arrays serde does not support arrays with more than 32 elements or using const-generics. The `serde_as` attribute allows circumventing this restriction, even for nested types and nested arrays. On top of it, `[u8; N]` (aka, bytes) can use the specialized `"Bytes"` for efficiency much like the `serde_bytes` crate. [![Rustexplorer](https://img.shields.io/badge/Try%20on-rustexplorer-lightgrey?logo=rust&logoColor=orange)](https://www.rustexplorer.com/b/um0xyi) ```rust #[serde_as] #[derive(Deserialize, Serialize)] struct Arrays<const N: usize, const M: usize> { #[serde_as(as = "[_; N]")] constgeneric: [bool; N], #[serde_as(as = "Box<[[_; 64]; N]>")] nested: Box<[[u8; 64]; N]>, #[serde_as(as = "Option<[_; M]>")] optional: Option<[u8; M]>, #[serde_as(as = "Bytes")] bytes: [u8; M], } // This allows us to serialize a struct like this let arrays: Arrays<100, 128> = Arrays { constgeneric: [true; 100], nested: Box::new([[111; 64]; 100]), optional: Some([222; 128]), bytes: [0x42; 128], }; assert!(serde_json::to_string(&arrays).is_ok()); ``` ### `skip_serializing_none` This situation often occurs with JSON, but other formats also support optional fields. If many fields are optional, putting the annotations on the structs can become tedious. The `#[skip_serializing_none]` attribute must be placed *before* the `#[derive]`. [![Rustexplorer](https://img.shields.io/badge/Try%20on-rustexplorer-lightgrey?logo=rust&logoColor=orange)](https://www.rustexplorer.com/b/xr1tm0) ```rust #[skip_serializing_none] #[derive(Deserialize, Serialize)] struct Foo { a: Option<usize>, b: Option<usize>, c: Option<usize>, d: Option<usize>, e: Option<usize>, f: Option<usize>, g: Option<usize>, } // This will serialize Foo {a: None, b: None, c: None, d: Some(4), e: None, f: None, g: Some(7)} // into this JSON {"d": 4, "g": 7} ``` ### Advanced `serde_as` usage This example is mainly supposed to highlight the flexibility of the `serde_as` annotation compared to [serde's `with` annotation][with-annotation]. More details about `serde_as` can be found in the [user guide]. ```rust use std::time::Duration; #[serde_as] #[derive(Deserialize, Serialize)] enum Foo { Durations( // Serialize them into a list of number as seconds #[serde_as(as = "Vec<DurationSeconds>")] Vec<Duration>, ), Bytes { // We can treat a Vec like a map with duplicates. // JSON only allows string keys, so convert i32 to strings // The bytes will be hex encoded #[serde_as(as = "Map<DisplayFromStr, Hex>")] bytes: Vec<(i32, Vec<u8>)>, } } // This will serialize Foo::Durations( vec![Duration::new(5, 0), Duration::new(3600, 0), Duration::new(0, 0)] ) // into this JSON { "Durations": [5, 3600, 0] } // and serializes Foo::Bytes { bytes: vec![ (1, vec![0, 1, 2]), (-100, vec![100, 200, 255]), (1, vec![0, 111, 222]), ], } // into this JSON { "Bytes": { "bytes": { "1": "000102", "-100": "64c8ff", "1": "006fde" } } } ``` [`DisplayFromStr`]: https://docs.rs/serde_with/3.11.0/serde_with/struct.DisplayFromStr.html [`with_prefix!`]: https://docs.rs/serde_with/3.11.0/serde_with/macro.with_prefix.html [feature flags]: https://docs.rs/serde_with/3.11.0/serde_with/guide/feature_flags/index.html [skip_serializing_none]: https://docs.rs/serde_with/3.11.0/serde_with/attr.skip_serializing_none.html [StringWithSeparator]: https://docs.rs/serde_with/3.11.0/serde_with/struct.StringWithSeparator.html [user guide]: https://docs.rs/serde_with/3.11.0/serde_with/guide/index.html [with-annotation]: https://serde.rs/field-attrs.html#with [as-annotation]: https://docs.rs/serde_with/3.11.0/serde_with/guide/serde_as/index.html ## License Licensed under either of * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0) * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT) at your option. ## Contribution For detailed contribution instructions please read [`CONTRIBUTING.md`]. Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual-licensed as above, without any additional terms or conditions. [`CONTRIBUTING.md`]: https://github.com/jonasbb/serde_with/blob/master/CONTRIBUTING.md