canadensis_codegen_rust: A Rust code generator for Cyphal data types

This application reads Cyphal data structure description language (DSDL) files. It generates Rust code to represent the Cyphal data types, serialize them, and deserialize them.

Usage

Compiling a DSDL package

canadensis_codegen_rust compile -o output-file input-directory..

Specify an output file where the code will be written, and one or more input directories that contain DSDL files. The compiler will read all DSDL files in the input directories and put code for all the data types in the output file.

Example

Clone the Cyphal public regulated data types repository and run canadensis_codegen_rust compile -o lib.rs public_regulated_data_types.

For easier viewing, you may want to use rustfmt to reformat the generated code.

Using the generated code

The compiler produces only one .rs file. To compile it, you will need to put it in some Cargo package. The file can be in a submodule along with other code, or in the root of a library.

The generated code is compatible with no_std, so if necessary you can include #![no_std] in the lib.rs file.

The generated code depends on a few external libraries for data types and serialization. Run canadensis_codegen_rust print-dependencies to show the dependency specifications. You should include the output in the package's Cargo.toml file.

Formatting

By default, the generated code does not have consistent formatting. To format it, add the --rustfmt option when running canadensis_codegen_rust. This option requires a preinstalled rustfmt binary in the default path.

External modules

For motivation, suppose you have this file depends_on_prdt/canadensis/test/ContainsHealth.1.0.uavcan:

uavcan.node.Health.1.0 health0
uavcan.node.Health.1.0 health1

@sealed

This data type depends on the Health type from the Cyphal public regulated data types. Normally, you would need to compile both packages together: canadensis_codegen_rust compile -o lib.rs public_regulated_data_types depends_on_prdt. That would generate a file with all the public regulated data types and the ContainsHealth type.

However, if your code already depends on canadensis_data_types, you would need to compile all the public regulated data types twice and the generated ContainsHealth code would not be compatible with canadensis_data_types.

Instead, you can mark the uavcan and reg packages as external, and refer to the pre-generated code in canadensis_data_types with this command: canadensis_codegen_rust compile public_regulated_data_types depends_on_prdt --external-package uavcan,canadensis_data_types::uavcan --external-package reg,canadensis_data_types::reg -o lib.rs

That command will produce this code:

#[cfg(not(target_endian = "little"))]
compile_error!("Zero-copy serialization requires a little-endian target");
#[allow(unused_variables, unused_braces, unused_parens)]
#[deny(unaligned_references)]
pub mod canadensis {
    pub mod test {
        pub mod contains_health_0_1 {
            /// `canadensis.test.ContainsHealth.0.1`
            ///
            /// Fixed size 2 bytes
            pub struct ContainsHealth {
                /// `uavcan.node.Health.1.0`
                ///
                /// Always aligned
                /// Size 8 bits
                pub health0: ::canadensis_data_types::uavcan::node::health_1_0::Health,
                /// `uavcan.node.Health.1.0`
                ///
                /// Always aligned
                /// Size 8 bits
                pub health1: ::canadensis_data_types::uavcan::node::health_1_0::Health,
            }
            impl ::canadensis_encoding::DataType for ContainsHealth {
                const EXTENT_BYTES: Option<u32> = None;
            }
            impl ::canadensis_encoding::Message for ContainsHealth {}
            impl ContainsHealth {}
            impl ::canadensis_encoding::Serialize for ContainsHealth {
                fn size_bits(&self) -> usize {
                    16
                }
                fn serialize(&self, cursor: &mut ::canadensis_encoding::WriteCursor<'_>) {
                    cursor.write_composite(&self.health0);
                    cursor.write_composite(&self.health1);
                }
            }
            impl ::canadensis_encoding::Deserialize for ContainsHealth {
                fn deserialize(
                    cursor: &mut ::canadensis_encoding::ReadCursor<'_>,
                ) -> ::core::result::Result<Self, ::canadensis_encoding::DeserializeError>
                where
                    Self: Sized,
                {
                    Ok(ContainsHealth {
                        health0: { cursor.read_composite()? },
                        health1: { cursor.read_composite()? },
                    })
                }
            }
        }
    }
}

Note that this file contains only the custom ContainsHealth type, and refers to the existing Health type canadensis_data_types::uavcan::node::health_1_0::Health.

Generating enums

All non-union DSDL types normally get converted into Rust structs. Some DSDL types are better represented as Rust enums because they have a single integer field that is allowed to have certain predefined values. Two examples of this are uavcan.node.Health.1.0 and uavcan.diagnostic.Severity.1.0.

This software does not currently automatically produce enums for non-union DSDL types. Instead, a DSDL type (message, request, or response) can be marked with a #[canadensis(enum)] comment to enable enum generation. The # must be at the beginning of the line for the comment to be recognized. The comment should be before the first field.

For a DSDL type to produce a Rust enum, it must follow all the following rules:

• The type is not a union
• The type has exactly one field, and that field has an unsigned integer type
• If the type has any constants, each constant has the same type as the field
• No two constants in the type have the same value

Any type marked with #[canadensis(enum)] that does not follow the rules will cause a code generation error.

In the generated code, each constant becomes an enum variant. The normal Rust enum limitations apply. When deserializing, any value that is not equal to one of the DSDL constants will cause an error.

Example

DSDL:

#[canadensis(enum)]
uint1 value

uint1 BUTTERCREAM = 0
uint1 PASTRY_CREAM = 1

@sealed

Generated code:

/// `canadensis.Uint1Exhaustive.1.0`
///
/// Fixed size 1 bytes
///
#[cfg_attr(not(doctest), doc = "[canadensis(enum)]")]
pub enum Uint1Exhaustive {
    Buttercream,
    PastryCream,
}

Limitations

• Types that support zero-copy serialization/deserialization are always labeled #[repr(C, packed), but sometimes they don't need to be packed and #[repr(C)] would be sufficient. Packed structs are not fun to work with because references to their fields are not allowed and derives can't be used on them.
• Some generated serialization/deserialization code does not take full advantage of fields that are always aligned