created_at2017-12-06 21:31:32.039164
updated_at2024-01-14 12:41:28.475047
descriptionA fast binary serialization framework
Koute (koute)




A fast binary serialization framework


The goal of this crate is to provide fast, simple and easy binary serialization.


See rust_serialization_benchmark for benchmarks.


use std::borrow::Cow;
use speedy::{Readable, Writable, Endianness};

#[derive(PartialEq, Debug, Readable, Writable)]
enum Enum {

#[derive(PartialEq, Debug, Readable, Writable)]
struct Struct< 'a > {
    number: u64,
    string: String,
    vector: Vec< u8 >,
    cow: Cow< 'a, [i64] >,
    float: f32,
    enumeration: Enum

fn main() {
    let original = Struct {
        number: 0x12345678ABCDEF00,
        string: "A totally pointless string".to_owned(),
        vector: vec![ 1, 2, 3 ],
        cow: Cow::Borrowed( &[ 4, 5, 6 ] ),
        float: 3.1415,
        enumeration: Enum::C

    let bytes = original.write_to_vec().unwrap();
    let deserialized: Struct =
        Struct::read_from_buffer( &bytes ).unwrap();

    assert_eq!( original, deserialized );

Supported types

Out-of-box the following types are supported:

Type Serialized as
u8 as-is
u16 as-is
u32 as-is
u64 as-is
usize u64
i8 as-is
i16 as-is
i32 as-is
i64 as-is
f32 as-is
f64 as-is
bool u8, either 0 or 1
char u32
String {length: u32, bytes: [u8]}
Cow<'a, str> {length: u32, bytes: [u8]}
Vec<T> {length: u32, values: [T]}
Cow<'a, [T]> {length: u32, values: [T]}
HashMap<K, V> {length: u32, values: [K, V]}
BTreeMap<K, V> {length: u32, values: [K, V]}
HashSet<T> {length: u32, values: [T]}
BTreeSet<T> {length: u32, values: [T]}
Range<T> (T, T)
RangeInclusive<T> (T, T)
Option<T> (1_u8, T) or 0_u8
Result<T, E> (1_u8, T) or (0_u8, E)
() nothing
(T) as-is
(T, T) as-is
(T, .., T) as-is
enums {tag: u32, variant: T}
AtomicU8 u8
AtomicI8 i8
AtomicU16 u16
AtomicI16 i16
AtomicU32 u32
AtomicI32 i32
AtomicU64 u64
AtomicI64 i64
NonZeroU32 u32
std::net::Ipv4Addr u32
std::net::Ipv6Addr u128
std::net::IpAddr {is_ipv4: u8, value: {u32 or u128}}
std::time::Duration {secs: u64, subsec_nanos: u32}
std::time::SystemTime std::time::Duration since UNIX_EPOCH
uuid::Uuid [u8; 16]

These are stable and will not change in the future.

Field attributes

#[speedy(length = $expr)]

Can be used on most standard containers to specify the field's length. Can refer to any of the previous fields.

For example:

use speedy::{Readable, Writable};

#[derive(Readable, Writable)]
struct Struct {
    byte_count: u8,
    #[speedy(length = byte_count / 4)]
    data: Vec< u32 >

Before serializing you need to make sure that whatever is set as length is equal to the .len() of the field; if it's not then you will get an error when trying to serialize it.

Setting this attribute changes the serialization format as follows:

Type Serialized as
Vec<T> [T]
Cow<'a, [T]> [T]
String [u8]
Cow<'a, str> [u8]
HashMap<K, V> [K, V]
BTreeMap<K, V> [K, V]
HashSet<T> [T]
BTreeSet<T> [T]

#[speedy(length_type = $ty)]

Can be used to specify the exact size of the implicit length field of a container as it is read or written.

Possible values:

  • u7 (same as u8, but restricted to 7 bits for u64_varint compatibility)
  • u8
  • u16
  • u32 (default)
  • u64_varint


Can be used only on u64 fields. Forces the field to be serialized as a varint.


Skips a given field when reading and writing.


If an EOF is encountered when reading this field its value will be set to the default value for its type and the EOF will be ignored.

#[speedy(constant_prefix = $expr)]

Specifies a static string of bytes which will be written or has to be present when reading before a given field.

Enum attributes

#[speedy(tag_type = $ty)]

Can be used to specify the exact size of the enum's tag as it is read or written.

Possible values:

  • u7 (same as u8, but restricted to 7 bits for u64_varint compatibility)
  • u8
  • u16
  • u32 (default)
  • u64_varint


An enum marked with this attribute will not consume its tag value when reading from a stream, nor will it write its own tag when writing.

Enum variant attributes

#[speedy(tag = $expr)]

Specifies a preset tag value to be used for a given enum variant.


Licensed under either of

at your option.


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.

Commit count: 267

cargo fmt