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 is a configurable Deserializer API plus convenience 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
• from_slice_into: Deserializes into an existing Partial (type-erased, owned)
• from_slice_into_borrowed: Deserializes into an existing Partial (type-erased, zero-copy)

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

DeserializeConfig

Deserialization safety/configuration options.

DeserializeError

Error produced by the format deserializer.

Deserializer

Builder-style postcard deserializer.

PostcardError

Postcard parsing error with optional source context for diagnostics.

PostcardParser

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

ScatterPlan

A scatter/gather postcard serialization plan.

Enums

RawPostcard

Postcard-encoded opaque payload bytes.

Segment

A segment in a postcard scatter plan.

SerializeError

Errors that can occur during postcard serialization.

Constants

DEFAULT_MAX_COLLECTION_ELEMENTS

Default maximum number of elements allowed in a decoded collection.

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_into

Deserialize postcard bytes into an existing Partial.

from_slice_into_borrowed

Deserialize postcard bytes into an existing Partial, allowing zero-copy borrowing.

from_slice_with_shape

Deserialize postcard bytes into a Value using shape information.

opaque_encoded_borrowed

Builds opaque adapter serialization inputs for borrowed postcard payload bytes.

opaque_encoded_owned

Builds opaque adapter serialization inputs for owned postcard payload bytes.

peek_to_scatter_plan

Serializes a Peek into a scatter plan.

peek_to_vec

Serializes a Peek reference to postcard bytes.

to_scatter_plan

Serializes a value into a scatter plan.

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.