Crate facet_postcard 

Postcard binary format for facet.

This crate provides serialization and deserialization for the postcard binary format.

Serialization

Serialization supports all types that implement facet_core::Facet:

use facet::Facet;
use facet_postcard::to_vec;

#[derive(Facet)]
struct Point { x: i32, y: i32 }

let point = Point { x: 10, y: 20 };
let bytes = to_vec(&point).unwrap();

Deserialization

There are three deserialization functions:

• from_slice: Deserializes into owned types (T: Facet<'static>)
• from_slice_borrowed: Deserializes with zero-copy borrowing from the input buffer
• from_slice_with_shape: Deserializes into Value using runtime shape information

use facet_postcard::from_slice;

// Postcard encoding: [length=3, true, false, true]
let bytes = &[0x03, 0x01, 0x00, 0x01];
let result: Vec<bool> = from_slice(bytes).unwrap();
assert_eq!(result, vec![true, false, true]);

Both functions automatically select the best deserialization tier:

• Tier-2 (Format JIT): Fastest path for compatible types (primitives, structs, vecs, simple enums)
• Tier-0 (Reflection): Fallback for all other types (nested enums, complex types)

This ensures all Facet types can be deserialized.

Structs

PostcardError

Postcard parsing error with optional source context for diagnostics.

PostcardParser

Postcard parser for Tier-0 and Tier-2 deserialization.

Enums

DeserializeError

Error produced by the format deserializer.

SerializeError

Errors that can occur during postcard serialization.

Traits

Writer

A trait for writing bytes during serialization with error handling.

Functions

from_slice

Deserialize a value from postcard bytes into an owned type.

from_slice_borrowed

Deserialize a value from postcard bytes, allowing zero-copy borrowing.

from_slice_with_shape

Deserialize postcard bytes into a Value using shape information.

peek_to_vec

Serializes a Peek reference to postcard bytes.

to_vec

Serializes any Facet type to postcard bytes.

to_vec_with_shape

Serializes a dynamic value (like facet_value::Value) to postcard bytes using a target shape to guide the serialization.

to_writer_fallible

Serializes any Facet type to a custom writer implementing the fallible Writer trait.