Excellent performance, no compromises!
Müsli is a flexible, fast, and generic binary serialization framework for Rust.
Encode] and [Decode], see
[derives].musli-tests].Add the following to your Cargo.toml using the format you want
to use:
toml
musli = "0.0.48"
musli-wire = "0.0.48"
The heavy lifting in user code is done through the [Encode] and [Decode]
derives which are thoroughly documented in the [derives] module. Müsli
primarily operates based on the schema types which implement these traits
imply, but self-descriptive formats are also possible (see
Formats below).
```rust use musli::{Encode, Decode};
struct Person { /* .. fields .. */ } ```
Note by default a field is identified by its numerical index which would change if they are re-ordered. Renaming fields and setting a default naming policy can be done by configuring the [
derives].
The binary serialization formats provided aim to efficiently and accurately encode every type and data structure available in Rust. Each format comes with well-documented tradeoffs and aim to be fully memory safe to use.
Internally we use the terms "encoding", "encode", and "decode" because it's
distinct from [serde]'s use of "serialization", "serialize", and
"deserialize" allowing for the ease of using both libraries side by side if
desired.
Müsli is designed on similar principles as [serde]. Relying on Rust's
powerful trait system to generate code which can largely be optimized away.
The end result should be very similar to handwritten highly optimized code.
As an example of this, these two functions both produce the same assembly on
my machine (built with --release):
```rust
const ENCODING: Encoding
pub struct Storage { left: u32, right: u32, }
fn with_musli(storage: &Storage) -> Result<[u8; 8]> { let mut array = [0; 8]; ENCODING.encode(&mut array[..], storage)?; Ok(array) }
fn withoutmusli(storage: &Storage) -> Result<[u8; 8]> { let mut array = [0; 8]; array[..4].copyfromslice(&storage.left.tonebytes()); array[4..].copyfromslice(&storage.right.tone_bytes()); Ok(array) } ```
Where Müsli differs in design philosophy is twofold:
We make use of GATs to provide tighter abstractions, which should be easier for Rust to optimize.
We make less use of the Visitor pattern in certain instances where it's deemed unnecessary, such as [when decoding collections]. The result is usually cleaner decode implementations, as shown here:
```rust use musli::de::{Decode, Decoder, SequenceDecoder}; use musli::mode::Mode;
struct MyType {
data: Vec
impl<'de, M> Decode<'de, M> for MyType where M: Mode {
fn decode
while let Some(decoder) = seq.next()? {
data.push(Decode::<M>::decode(decoder)?);
}
seq.end()?;
Ok(Self {
data
})
}
} ```
Another major aspect where Müsli differs is in the concept of
modes (note the M parameter above). Since this is a parameter of
the Encode and Decode traits it allows for the same data model to be
serialized in many different ways. This is a larger topic and is covered
further down.
Formats are currently distinguished by supporting various degrees of upgrade stability. A fully upgrade stable encoding format must tolerate that one model can add fields that an older version of the model should be capable of ignoring.
Partial upgrade stability can still be useful as is the case of the
musli-storage format below, because reading from storage only requires
decoding to be upgrade stable. So if correctly managed with
#[musli(default)] this will never result in any readers seeing unknown
fields.
The available formats and their capabilities are:
| | reorder | missing | unknown | self |
|-|-|-|-|-|
| [musli-storage] #[musli(packed)] | ✗ | ✗ | ✗ | ✗ |
| [musli-storage] | ✔ | ✔ | ✗ | ✗ |
| [musli-wire] | ✔ | ✔ | ✔ | ✗ |
| [musli-descriptive] | ✔ | ✔ | ✔ | ✔ |
reorder determines whether fields must occur in exactly the order in which
they are specified in their type. Reordering fields in such a type would
cause unknown but safe behavior of some kind. This is only suitable for
byte-oriented IPC where the data models of each client are are strictly
synchronized.
missing determines if reading can handle missing fields through something
like Option<T>. This is suitable for on-disk storage, because it means
that new optional fields can be added as the schema evolves.
unknown determines if the format can skip over unknown fields. This is
suitable for network communication. At this point you've reached upgrade
stability. Some level of introspection is possible here, because the
serialized format must contain enough information about fields to know what
to skip which usually allows for reasoning about basic types.
self determines if the format is self-descriptive. Allowing the structure
of the data to be fully reconstructed from its serialized state. These
formats do not require models to decode, and can be converted to and from
dynamic containers such as [musli-value] for introspection.
For every feature you drop, the format becomes more compact and efficient.
[musli-storage] using #[musli(packed)] for example is roughly as compact
as [bincode] while [musli-wire] is comparable in size to something like
[protobuf]. All formats are primarily byte-oriented, but some might
perform [bit packing] if the benefits are obvious.
The following is an example of full upgrade stability using
[musli-wire]. Note how Version1 can be decoded from an instance of
Version2 because it understands how to skip fields which are part of
Version2. We're also explicitly #[musli(rename = ..)] the fields to
ensure that they don't change in case they are re-ordered.
```rust use musli::{Encode, Decode};
struct Version1 { #[musli(rename = 0)] name: String, }
struct Version2 {
#[musli(rename = 0)]
name: String,
#[musli(default, rename = 1)]
age: Option
let version2 = musliwire::tobuffer(&Version2 { name: String::from("Aristotle"), age: Some(62), })?;
let version1: Version1 = musliwire::decode(version2.asslice())?; ```
The following is an example of partial upgrade stability using
[musli-storage] on the same data models. Note how Version2 can be
decoded from Version1 but not the other way around. That's why it's
suitable for on-disk storage the schema can evolve from older to newer
versions.
```rust use musli::{Encode, Decode};
let version2 = muslistorage::tobuffer(&Version2 { name: String::from("Aristotle"), age: Some(62), })?;
assert!(muslistorage::decode::<_, Version1>(version2.asslice()).is_err());
let version1 = muslistorage::tobuffer(&Version1 { name: String::from("Aristotle"), })?;
let version2: Version2 = muslistorage::decode(version1.asslice())?; ```
In Müsli the same model can be serialized in different ways. Instead of requiring the use of multiple models, we instead support each model implementing different modes.
A mode allows for different encoding attributes to apply depending on which mode something is performed in. A mode can apply to any musli parameter giving you a lot of flexibility.
If a mode is not specified, an implementation will apply to all modes (M:
Mode), if at least one mode is specified it will be implemented for all
modes which are present in a model and [DefaultMode]. This way, an
encoding which uses DefaultMode (which it does by default) should always
work.
For more information on how to configure modes, see the [derives] module.
Below is a simple example of how we can use two modes to provide two
different kinds of serialization to a single struct.
```rust use musli::mode::{DefaultMode, Mode}; use musli::{Decode, Encode}; use musli_json::Encoding;
enum Alt {} impl Mode for Alt {}
struct Word<'a> { text: &'a str, teineigo: bool, }
let CONFIG: Encoding
let word = Word { text: "あります", teineigo: true, };
let out = CONFIG.tostring(&word)?; asserteq!(out, r#"{"text":"あります","teineigo":true}"#);
let out = ALTCONFIG.tostring(&word)?; assert_eq!(out, r#"["あります",true]"#); ```
This is a non-exhaustive list of unsafe use in this crate, and why they are used:
A mem::transcode in Tag::kind. Which guarantees that converting into
the Kind enum which is #[repr(u8)] is as efficient as possible.
A largely unsafe SliceReader which provides more efficient reading than
the default Reader impl for &[u8] does. Since it can perform most of
the necessary comparisons directly on the pointers.
Some unsafety related to UTF-8 handling in musli_json, because we check
UTF-8 validity internally ourselves (like serde_json).
FixedBytes<N> is a stack-based container that can operate over
uninitialized data. Its implementation is largely unsafe. With it
stack-based serialization can be performed which is useful in no-std
environments.
Some unsafe is used for owned String decoding in all binary formats to
support faster string processing using [simdutf8]. Disabling the
simdutf8 feature (enabled by default) removes the use of this unsafe.
To ensure this library is correctly implemented with regards to memory
safety, extensive testing is performed using miri. For more information on
this, see [musli-tests] for more information on this.
The following are the results of preliminary benchmarking and should be taken with a big grain of 🧂.
The two benchmark suites portrayed are:
* rt-prim - which is a small object containing one of each primitive type
and a string and a byte array.
* rt-lg - which is roundtrip encoding of a large object, containing
vectors and maps of other objects.
