apalis-codec

apalis-codec provides encoding and decoding strategies for task arguments, results, and other values used by backends. This crate exposes a small, backend-independent [Codec] trait and optional implementations for common serialization formats.

Features

The following codecs are available behind feature flags:

• json — JSON encoding using serde_json
• msgpack — MessagePack encoding using rmp-serde
• bincode — Binary encoding using bincode

No codec implementation is enabled by default.

Codec

The [Codec] trait defines the interface between a value and its compact representation:

pub trait Codec<T> {
    /// The error type returned if encoding or decoding fails.
    type Error;

    /// The compact or encoded representation of `T`.
    type Compact;

    /// Encode a value of type `T` into its compact representation.
    fn encode(&self, val: &T) -> Result<Self::Compact, Self::Error>;

    /// Decode a compact representation back into a value of type `T`.
    fn decode(&self, val: &Self::Compact) -> Result<T, Self::Error>;
}

The Compact type is intentionally left up to the codec. Depending on the implementation, it may be a byte buffer, a string, or another representation suitable for storage or transmission.

Available Codecs

JSON

Enable the json feature:

[dependencies]
apalis-codec = { version = "...", features = ["json"] }

JSON is useful when human-readable representations or interoperability with other systems are important.

MessagePack

Enable the msgpack feature:

[dependencies]
apalis-codec = { version = "...", features = ["msgpack"] }

MessagePack provides a compact binary representation while retaining broad serialization compatibility.

Bincode

Enable the bincode feature:

[dependencies]
apalis-codec = { version = "...", features = ["bincode"] }

Bincode provides a compact binary representation suitable for applications where storage size and serialization performance are important.

Choosing a Codec

The appropriate codec depends on how tasks are stored or transported:

For distributed task queues, MessagePack or Bincode are generally preferable when compact binary representations are desired. JSON can be useful when tasks need to be inspected or consumed by systems outside the Rust ecosystem.

Serde

The codec implementations are designed around serde. Values generally need to implement the appropriate Serialize and Deserialize traits.

For example:

use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
struct Email {
    to: String,
    subject: String,
}

The same task type can then be encoded using different codecs without changing the task itself.

Feature Flags

[features]
json = ["serde_json"]
msgpack = ["rmp-serde"]
bincode = ["bincode"]

Select only the formats required by your application to avoid unnecessary dependencies.

License

Licensed under either of:

• Apache License, Version 2.0
• MIT License

at your option.