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//! # Postcard //! //! Postcard is a `#![no_std]` focused serializer and deserializer for Serde. //! //! Postcard aims to be convenient for developers in constrained environments, while //! allowing for flexibility to customize behavior as needed. //! //! ## Design Goals //! //! 1. Design primarily for `#![no_std]` usage, in embedded or other constrained contexts //! 2. Support a maximal set of `serde` features, so `postcard` can be used as a drop in replacement //! 3. Avoid special differences in code between communication code written for a microcontroller or a desktop/server PC //! 4. Be resource efficient - memory usage, code size, developer time, and CPU time; in that order //! 5. Allow library users to customize the serialization and deserialization behavior to fit their bespoke needs //! //! ## Variable Length Data //! //! Variable length data (such as slices) are prefixed by their length. //! //! Length is encoded as a [Varint]. This is done for two reasons: to minimize wasted bytes //! on the wire when sending slices with items less than 127 items (typical for embedded), //! and to reduce compatibility issues between 32-bit and 64-bit targets due to differing sizes //! of `usize`. //! //! Similarly, `enum` descriminants are encoded as varints, meaning that any enum with less than //! 127 variants will encode its discriminant as a single byte (rather than a `u32`). //! //! Varints in `postcard` have a maximum value of the usize for that platform. In practice, this //! means that 64-bit targets should not send messages with slices containing `(2 << 32) -1` items //! to 32-bit targets, which is uncommon in practice. Enum discriminants already have a fixed //! maximum value of `(2 << 32) - 1` as currently defined in Rust. Varints larger than the current platform's //! `usize` will cause the deserialization process to return an `Err`. //! //! [Varint]: https://developers.google.com/protocol-buffers/docs/encoding //! //! ## Example - Serialization/Deserialization //! //! Postcard can serialize and deserialize messages similar to other `serde` formats. //! //! ```rust //! use core::ops::Deref; //! use serde::{Serialize, Deserialize}; //! use postcard::{from_bytes, to_vec}; //! use heapless::{Vec, consts::*}; //! //! #[derive(Serialize, Deserialize, Debug, Eq, PartialEq)] //! struct RefStruct<'a> { //! bytes: &'a [u8], //! str_s: &'a str, //! } //! let message = "hElLo"; //! let bytes = [0x01, 0x10, 0x02, 0x20]; //! let output: Vec<u8, U11> = to_vec(&RefStruct { //! bytes: &bytes, //! str_s: message, //! }).unwrap(); //! //! assert_eq!( //! &[0x04, 0x01, 0x10, 0x02, 0x20, 0x05, b'h', b'E', b'l', b'L', b'o',], //! output.deref() //! ); //! //! let out: RefStruct = from_bytes(output.deref()).unwrap(); //! assert_eq!( //! out, //! RefStruct { //! bytes: &bytes, //! str_s: message, //! } //! ); //! ``` //! //! ## Example - Flavors //! //! `postcard` supports a system called `Flavors`, which are used to modify the way //! postcard serializes or processes serialized data. These flavors act as "plugins" or "middlewares" //! during the serialization process, and can be combined to obtain complex protocol formats. //! //! Here, we serialize the given data, while simultaneously encoding it using COBS (a "modification flavor"), //! and placing the output in a byte slice (a "storage flavor"). //! //! Users of `postcard` can define their own Flavors that can be combined with existing Flavors. //! //! ```rust //! use postcard::{ //! serialize_with_flavor, //! flavors::{Cobs, Slice}, //! }; //! //! let mut buf = [0u8; 32]; //! //! let data: &[u8] = &[0x01, 0x00, 0x20, 0x30]; //! let buffer = &mut [0u8; 32]; //! let res = serialize_with_flavor::<[u8], Cobs<Slice>, &mut [u8]>( //! data, //! Cobs::try_new(Slice::new(buffer)).unwrap(), //! ).unwrap(); //! //! assert_eq!(res, &[0x03, 0x04, 0x01, 0x03, 0x20, 0x30, 0x00]); //! ``` //! //! ## 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 //! //! 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. #![cfg_attr(not(any(test, feature = "use-std")), no_std)] #![warn(missing_docs)] mod de; mod error; mod ser; mod varint; pub use de::deserializer::Deserializer; pub use de::{from_bytes, from_bytes_cobs, take_from_bytes, take_from_bytes_cobs}; pub use error::{Error, Result}; pub use ser::{ flavors, serialize_with_flavor, serializer::Serializer, to_slice, to_slice_cobs, to_vec, to_vec_cobs, };