postcard
A no_std, serde-compatible serializer and deserializer for Rust, designed for embedded and constrained environments.
What is postcard?
Postcard is a serializer and deserializer library for Rust that is fully compatible with the Serde framework and designed to work in `no_std` environments. It provides a stable, efficient wire format for serializing data structures, making it ideal for communication in embedded systems or other resource-constrained contexts. The library focuses on being a drop-in replacement for Serde while optimizing for memory usage, code size, and developer time.
Rust developers working on embedded systems, microcontrollers, or any constrained environment where the standard library is unavailable. It is also suitable for those needing a reliable, customizable serialization format for inter-process or network communication.
Developers choose Postcard for its seamless integration with Serde, stable wire format, and efficiency in `no_std` contexts. Its unique Flavors system allows deep customization of serialization behavior, making it versatile for bespoke protocols while maintaining low resource overhead.
Overview
A no_std + serde compatible message library for Rust
Use Cases
Best For
- Serializing data for communication between microcontrollers and desktop applications
- Building embedded systems that require efficient, stable wire formats
- Replacing Serde in no_std environments without losing functionality
- Customizing serialization behavior with combinable middleware-like Flavors
- Optimizing for code size and memory usage in resource-constrained Rust projects
- Ensuring wire format stability for long-term embedded deployments
Not Ideal For
- Projects requiring human-readable serialization formats for easy debugging, as Postcard uses a binary format.
- Systems that heavily rely on unsupported Serde attributes like flatten or skip_serializing_if, which can break serialization.
- Applications needing cross-language compatibility, since Postcard is Rust-specific and lacks native support in other languages.
- High-performance scenarios where varint encoding overhead for integers is unacceptable due to CPU constraints.
Pros & Cons
Pros
Explicitly designed for embedded and constrained environments without Rust's standard library, as stated in the design goals, making it ideal for microcontrollers.
Acts as a drop-in replacement for Serde, supporting a maximal set of its features, so developers can migrate seamlessly in no_std contexts.
Has a documented and stable wire format since v1.0.0, ensuring reliable communication for long-term deployments, as highlighted in the README.
Prioritizes low memory usage, small code size, and minimal CPU overhead, following the design goals for constrained systems.
Flavors system allows combinable plugins to modify serialization and deserialization behavior, providing flexibility for bespoke protocols.
Cons
Attributes like flatten or skip_serializing_if can break serialization, requiring extensive testing, as warned in the README's tracking issue.
Requires manual configuration in Cargo.toml, such as disabling serde's default features for no_std compatibility, adding initial overhead.
Limited to Rust; lacks built-in support for other languages, which can hinder integration in heterogeneous systems or cross-platform projects.
Varint encoding for integers larger than eight bits optimizes for size but can introduce CPU overhead compared to fixed-width encoding.
Frequently Asked Questions
Related Projects
jsonStrongly typed JSON library for Rust
prostPROST! a Protocol Buffers implementation for the Rust Language
rkyvZero-copy deserialization framework for Rust
https://github.com/ron-rs/ronRusty Object Notation
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