Crate zvariant

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§zvariant

This crate provides API for encoding/decoding of data to/from D-Bus wire format. This binary wire format is simple and very efficient and hence useful outside of D-Bus context as well. A modified form of this format, GVariant is very commonly used for efficient storage of arbitrary data and is also supported by this crate.

Since version 2.0, the API is serde-based and hence you’ll find it very intuitive if you’re already familiar with serde. If you’re not familiar with serde, you may want to first read its tutorial before learning further about this crate.

Status: Stable.

§Example code

Serialization and deserialization is achieved through the toplevel functions:

use std::collections::HashMap;
use zvariant::{EncodingContext as Context, from_slice, to_bytes, Type};
use serde::{Deserialize, Serialize};
use byteorder::LE;

// All serialization and deserialization API, needs a context.
let ctxt = Context::<LE>::new_dbus(0);
// You can also use the more efficient GVariant format:
// let ctxt = Context::<LE>::new_gvariant(0);

// i16
let encoded = to_bytes(ctxt, &42i16).unwrap();
let decoded: i16 = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded, 42);

// strings
let encoded = to_bytes(ctxt, &"hello").unwrap();
let decoded: &str = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded, "hello");

// tuples
let t = ("hello", 42i32, true);
let encoded = to_bytes(ctxt, &t).unwrap();
let decoded: (&str, i32, bool) = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded, t);

// Vec
let v = vec!["hello", "world!"];
let encoded = to_bytes(ctxt, &v).unwrap();
let decoded: Vec<&str> = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded, v);

// Dictionary
let mut map: HashMap<i64, &str> = HashMap::new();
map.insert(1, "123");
map.insert(2, "456");
let encoded = to_bytes(ctxt, &map).unwrap();
let decoded: HashMap<i64, &str> = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded[&1], "123");
assert_eq!(decoded[&2], "456");

// derive macros to handle custom types.
#[derive(Deserialize, Serialize, Type, PartialEq, Debug)]
struct Struct<'s> {
    field1: u16,
    field2: i64,
    field3: &'s str,
}

assert_eq!(Struct::signature(), "(qxs)");
let s = Struct {
    field1: 42,
    field2: i64::max_value(),
    field3: "hello",
};
let ctxt = Context::<LE>::new_dbus(0);
let encoded = to_bytes(ctxt, &s).unwrap();
let decoded: Struct = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded, s);

// It can handle enums too, just that all variants must have the same number and types of fields.
// Names of fields don't matter though. You can make use of `Value` or `OwnedValue` if you want to
// encode different data in different fields.
#[derive(Deserialize, Serialize, Type, PartialEq, Debug)]
enum Enum<'s> {
    Variant1 { field1: u16, field2: i64, field3: &'s str },
    Variant2(u16, i64, &'s str),
    Variant3 { f1: u16, f2: i64, f3: &'s str },
}

// Enum encoding uses a `u32` to denote the variant index. For unit-type enums that's all that's
// needed so the signature is just `u` but complex enums are encoded as a structure whose first
// field is the variant index and the second one is the field(s).
assert_eq!(Enum::signature(), "(u(qxs))");
let e = Enum::Variant3 {
    f1: 42,
    f2: i64::max_value(),
    f3: "hello",
};
let encoded = to_bytes(ctxt, &e).unwrap();
let decoded: Enum = from_slice(&encoded, ctxt).unwrap();
assert_eq!(decoded, e);

#[derive(Deserialize, Serialize, Type, PartialEq, Debug)]
// W/o `repr` spec, `u32` is assumed.
#[repr(u8)]
enum UnitEnum {
    Variant1,
    Variant2,
    Variant3,
}

assert_eq!(UnitEnum::signature(), "y");
let encoded = to_bytes(ctxt, &UnitEnum::Variant2).unwrap();
let e: UnitEnum = from_slice(&encoded, ctxt).unwrap();
assert_eq!(e, UnitEnum::Variant2);

// Unit enums can also be (de)serialized as strings.
#[derive(Deserialize, Serialize, Type, PartialEq, Debug)]
#[zvariant(signature = "s")]
enum StrEnum {
    Variant1,
    Variant2,
    Variant3,
}

assert_eq!(StrEnum::signature(), "s");

Apart from the obvious requirement of EncodingContext instance by the main serialization and deserialization API, the type being serialized or deserialized must also implement Type trait in addition to Serialize or Deserialize, respectively. Please refer to Type module documentation for more details.

Most of the basic types of D-Bus match 1-1 with all the primitive Rust types. The only two exceptions being, Signature and ObjectPath, which are really just strings. These types are covered by the Basic trait.

Similarly, most of the container types also map nicely to the usual Rust types and collections (as can be seen in the example code above). The only note worthy exception being ARRAY type. As arrays in Rust are fixed-sized, serde treats them as tuples and so does this crate. This means they are encoded as STRUCT type of D-Bus. If you need to serialize to, or deserialize from a D-Bus array, you’ll need to use a slice (array can easily be converted to a slice), a Vec or an arrayvec::ArrayVec.

D-Bus string types, including Signature and ObjectPath, require one additional restriction that strings in Rust do not. They must not contain any interior null bytes ('\0'). Encoding/Decoding strings that contain this character will return an error.

The generic D-Bus type, VARIANT is represented by Value, an enum that holds exactly one value of any of the other types. Please refer to Value module documentation for examples.

§no-std

While std is currently a hard requirement, optional no-std support is planned in the future. On the other hand, noalloc support is not planned as it will be extremely difficult to accomplish. However, community contribution can change that. 😊

§Optional features

Feature	Description
arrayvec	Implement `Type` for `arrayvec::ArrayVec` and `arrayvec::ArrayString`
enumflags2	Implement `Type` for `enumflags2::BitFlags<F>`

Modules§

dbus

Structs§

Array: A helper type to wrap arrays in a Value.
ArraySeed: Use this to deserialize an Array.
DeserializeValue: A wrapper to deserialize a value to T: Type + Deserialize.
Dict: A helper type to wrap dictionaries in a Value.
EncodingContext: The encoding context to use with the serialization and deserialization API.
Fd: A RawFd wrapper.
ObjectPath: String that identifies objects at a given destination on the D-Bus bus.
Optional: An optional value.
OwnedFd: An owned RawFd wrapper.
OwnedObjectPath: Owned ObjectPath
OwnedSignature: Owned Signature
OwnedValue: Owned Value
SerializeValue: A wrapper to serialize T: Type + Serialize as a value.
Signature: String that identifies the type of an encoded value.
Str: A string wrapper.
Structure: A helper type to wrap structs in Value.
StructureBuilder: Use this to efficiently build a Structure.
StructureSeed: Use this to deserialize a Structure.

Enums§

Deserializer: Our deserialization implementation.
EncodingFormat: The encoding format.
Error: Error type used by zvariant API.
MaxDepthExceeded: Enum representing the max depth exceeded error.
Serializer: Our serialization implementation.
Value: A generic container, in the form of an enum that holds exactly one value of any of the other types.

Constants§

ARRAY_SIGNATURE_CHAR: The prefix of ARRAY type signature, as a character. Provided for manual signature creation.
ARRAY_SIGNATURE_STR: The prefix of ARRAY type signature, as a string. Provided for manual signature creation.
DICT_ENTRY_SIG_END_CHAR: The closing character of DICT_ENTRY type signature. Provided for manual signature creation.
DICT_ENTRY_SIG_END_STR: The closing character of DICT_ENTRY type signature, as a string. Provided for manual signature creation.
DICT_ENTRY_SIG_START_CHAR: The opening character of DICT_ENTRY type signature. Provided for manual signature creation.
DICT_ENTRY_SIG_START_STR: The opening character of DICT_ENTRY type signature, as a string. Provided for manual signature creation.
STRUCT_SIG_END_CHAR: The closing character of STRUCT type signature. Provided for manual signature creation.
STRUCT_SIG_END_STR: The closing character of STRUCT type signature, as a string. Provided for manual signature creation.
STRUCT_SIG_START_CHAR: The opening character of STRUCT type signature. Provided for manual signature creation.
STRUCT_SIG_START_STR: The opening character of STRUCT type signature, as a string. Provided for manual signature creation.
VARIANT_SIGNATURE_CHAR: The VARIANT type signature. Provided for manual signature creation.
VARIANT_SIGNATURE_STR: The VARIANT type signature, as a string. Provided for manual signature creation.

Traits§

Basic: Trait for basic types.
DynamicDeserialize: Types that deserialize based on dynamic signatures.
DynamicType: Types with dynamic signatures.
NoneValue: Type that uses a special value to be used as none.
Type: Trait implemented by all serializable types.

Functions§

from_slice: Deserialize T from a given slice of bytes.
from_slice_fds: Deserialize T from a given slice of bytes, containing file descriptor indices.
from_slice_fds_for_dynamic_signature: Deserialize T from a given slice of bytes containing file descriptor indices, with the given signature.
from_slice_fds_for_signature: Deserialize T from a given slice of bytes containing file descriptor indices, with the given signature.
from_slice_fds_with_seed: Deserialize T from a given slice of bytes containing file descriptor indices, using the given seed.
from_slice_for_dynamic_signature: Deserialize T from a given slice of bytes containing file descriptor indices, with the given signature.
from_slice_for_signature: Deserialize T from a given slice of bytes with the given signature.
from_slice_with_seed: Deserialize T from a given slice of bytes containing file descriptor indices, using the given seed.
serialized_size: Calculate the serialized size of T.
serialized_size_fds: Calculate the serialized size of T that (potentially) contains FDs.
to_bytes: Serialize T as a byte vector.
to_bytes_fds: Serialize T that (potentially) contains FDs, as a byte vector.
to_bytes_fds_for_signature: Serialize T that (potentially) contains FDs and has the given signature, to a new byte vector.
to_bytes_for_signature: Serialize T that has the given signature, to a new byte vector.
to_writer: Serialize T to the given writer.
to_writer_fds: Serialize T that (potentially) contains FDs, to the given writer.
to_writer_fds_for_signature: Serialize T that (potentially) contains FDs and has the given signature, to the given writer.
to_writer_for_signature: Serialize T that has the given signature, to the given writer.

Type Aliases§

Result: Alias for a Result with the error type zvariant::Error.

Derive Macros§

DeserializeDict: Adds Deserialize implementation to structs to be deserialized from a{sv} type.
OwnedValue: Implements conversions for your type to/from OwnedValue.
SerializeDict: Adds Serialize implementation to structs to be serialized as a{sv} type.
Type: Derive macro to add Type implementation to structs and enums.
TypeDict: Derive macro to add Type implementation to structs serialized as a{sv} type.
Value: Implements conversions for your type to/from Value.

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