Serbia

Serde big arrays. An attribute macro to make (de)serializing big arrays painless, roughly following a design proposed by David Tolnay.

Why?

I saw the idea in request-for-implementation. Then I came up with the name.

The name was too good. I had to do it. Don't judge me.

Also: Serbia has some tasty food.

But what is it for?

Serde only implements Serialize/Deserialize for arrays of length up to 32. This is due to Rust's current limitation - we can't be generic over array length, so an arbitrary upper limit was chosen and implementations were generated only up to it.

The crate provides a macro that generates all the code you need to (de)serialize arrays bigger than that.

Status

Under development, but functional. Let me know what's missing or broken!

Usage

Just slap #[serbia] on top of your type definition. Structs and enums both work!

use serbia::serbia;

#[serbia]
#[derive(Serialize, Deserialize)]
struct S {
    arr_big: [u8; 300],     // custom serialize/deserialize code generated here
    arr_small: [u8; 8],     // no custom code - this is handled by Serde fine
}

#[serbia]
#[derive(Serialize, Deserialize)]
enum E {
    ArrBig([u8; 300]),
    ArrSmall([u8; 22]),
    Mixed([u8; 8], [i32; 44], String),
}

If Serbia sees an array length given as a constant, it will generate custom serialize/deserialize code by default, without inspecting whether the constant is larger than 32 or not. This is a limitation of macros.

const BUFSIZE: usize = 22;

#[serbia]
#[derive(Serialize, Deserialize)]
struct S {
    arr: [i32; BUFSIZE],   // custom serialize/deserialize code generated here
    foo: String,
}

Skipping fields

If for some reason you don't want Serbia to generate custom serialize/deserialize code for a field that it would normally handle, you can skip it.

const BUFSIZE: usize = 24;

#[serbia]
#[derive(Serialize, Deserialize)]
struct S {
    #[serbia(skip)]
    arr_a: [u8; BUFSIZE],
    arr_b: [u8; 42],
    arr_small: [u8; 8],
}

It's possible to be more granular if needed for some reason.

const BUFSIZE: usize = 24;

#[serbia]
#[derive(Serialize, Deserialize)]
struct S {
    #[serbia(skip_serializing, skip_deserializing)]
    arr_a: [u8; BUFSIZE],
    arr_b: [u8; 42],
    arr_small: [u8; 8],
}

Manual array length

You can use the #[serbia(bufsize = ... )] option to set an array length for a field. This can be useful to make type aliases work. Constants work here!

type BigArray = [i32; 300];

#[serbia]
#[derive(Serialize, Deserialize)]
struct S {
    #[serbia(bufsize = 300)]
    arr_a: BigArray,
    foo: String,
}

const BUFSIZE: usize = 300;
type BigArray = [i32; BUFSIZE];

#[serbia]
#[derive(Serialize, Deserialize)]
struct S {
    #[serbia(bufsize = "BUFSIZE")]
    arr_a: BigArray,
    foo: String,
}

Interaction with Serde field attributes

Serbia detects when certain Serde field attributes are used and avoids generating code that would cause a conflict, instead yielding to Serde.

    #[serbia]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    struct S {
        big_arr: [u8; 40],    // serbia generates code for this
        #[serde(serialize_with="ser", deserialize_with="de")]
        bigger_arr: [u8; 42], // serbia ignores this in favor of the (de)serializers you provided
    }

Serbia is intended to play nice with Serde field attributes. If there are problems, please create an issue or submit a PR!

What doesn't work

Nested types.

#[serbia]
#[derive(Debug, Serialize, Deserialize, PartialEq)]
struct S {
    big_arr: Option<[u8; 300]>,  // no code generated for this nested array
}

Serbia doesn't yet pick up on Serde variant attributes, so there might be conflicts there. This can probably be worked around by using #[serbia(skip)] on each field that Serbia would try to generate custom (de)serialization code for.