Crate fidl_table_validation

fidl table validation tools.

This crate’s macro generates code to validate fidl tables.

Import using fidl_table_validation::* to inherit the macro’s imports.

Basic Example

// Some fidl table defined somewhere...
struct FidlTable {
    required: Option<usize>,
    optional: Option<usize>,
    has_default: Option<usize>,
}

#[derive(ValidFidlTable)]
#[fidl_table_src(FidlHello)]
struct ValidatedFidlTable {
    // The default is #[fidl_field_type(required)]
    required: usize,
    #[fidl_field_type(optional)]
    optional: Option<usize>,
    #[fidl_field_type(default = 22)]
    has_default: usize,
}

This code generates a TryFrom implementation for ValidatedFidlTable:

pub enum FidlTableValidationError {
    MissingField(FidlTableMissingFieldError)
}

impl TryFrom<FidlTable> for ValidatedFidlTable {
    type Error = FidlTableValidationError;
    fn try_from(src: FidlTable) -> Result<ValidatedFidlTable, Self::Error> { .. }
}

and also a From implementation for FidlTable, so you can get a FidlTable using validated.into().

Custom Validations

When tables have logical relationships between fields that must be checked, you can use a custom validator:

struct FidlTableValidator;

impl Validate<ValidatedFidlTable> for FidlTableValidator {
    type Error = String; // Can be any error type.
    fn validate(candidate: &ValidatedFidlTable) -> Result<(), Self::Error> {
        match candidate.required {
            10 => {
                Err(String::from("10 is not a valid value!"))
            }
            _ => Ok(())
        }
    }
}

#[fidl_table_src(FidlHello)]
#[fidl_table_validator(FidlTableValidator)]
struct ValidFidlTable {
...

Non-literal defaults

Attribute syntax for name = value only supports literals. Another attribute for expressing defaults is used for consts. Or any type that has a Default impl can simply omit the literal.

const MY_DEFAULT: MyEnum = MyEnum::MyVariant;

#[derive(ValidFidlTable)]
#[fidl_table_src(FidlHello)]
struct ValidatedFidlTable {
    #[fidl_field_type(default)]
    has_default_impl: Vec<u32>,
    #[fidl_field_with_default(MY_DEFAULT)]
    has_default: MyEnum,
}

Custom converters

Custom converters (implementing Converter) can be used to validate the fields. A converter field type acts like required (i.e. the derive handles the optionality) and passes the unwrapped option to the given converter. An optional_converter field type acts like optional and the converter is given (and expects to generate back) Option wrapped values.

Example:

struct RequiredConverter;

impl Converter for RequiredConverter {
    type Fidl = u32;
    type Validated = NonZeroU32;
    type Error = anyhow::Error;
    fn try_from_fidl(value: Self::Fidl) -> std::result::Result<Self::Validated, Self::Error> {
       NonZeroU32::new(value).ok_or_else(|| anyhow::anyhow!("bad zero value"))
    }
    fn from_validated(validated: Self::Validated) -> Self::Fidl {
       validated.get()
    }
}

struct OptionalConverter;

enum MaybeMissing { Present(u32), Missing }

impl Converter for OptionalConverter {
   type Fidl = Option<u32>;
   type Validated = MaybeMissing;
   type Error = std::convert::Infallible;
    fn try_from_fidl(value: Self::Fidl) -> std::result::Result<Self::Validated, Self::Error> {
       Ok(match value {
          Some(v) => MaybeMissing::Present(v),
          None => MaybeMissing::Missing,
       })
    }
    fn from_validated(validated: Self::Validated) -> Self::Fidl {
       match validated {
         MaybeMissing::Present(v) => Some(v),
         MaybeMissing::Missing => None,
       }
    }
}

#[derive(ValidFidlTable)]
#[fidl_table_src(FidlHello)]
#[fidl_table_strict]
struct ValidatedFidlTable {
    #[fidl_field_type(converter = RequiredConverter)]
    foo: NonZeroU32,
    #[fidl_field_type(optional_converter = OptionalConverter)]
    bar: MaybeMissing,
}

Strict conversion

By default, this derive does not cause compilation errors if the source FIDL table has more fields than the validated struct. This behavior can be changed with the fidl_table_strict attribute. For example, the snippet below fails to compile if FidlHello has more fields than the ones in ValidatedFidlTable.

#[derive(ValidFidlTable)]
#[fidl_table_src(FidlHello)]
#[fidl_table_strict]
struct ValidatedFidlTable {
    hello: u32,
}

Fields from the FIDL table can be explicitly ignored by giving fidl_table_strict arguments:

#[derive(ValidFidlTable)]
#[fidl_table_src(FidlHello)]
#[fidl_table_strict(world)]
struct ValidatedFidlTable {
    hello: u32,
}

This adds a Logical(YourErrorType) variant to the generated error enum.

Re-exports

• pub use anyhow;

Traits

• Converter
  A converter trait that can convert from FIDL types T into a validated type Validated.
• Validate
  Validations on T that can be run during construction of a validated fidl table by adding the attribute #[fidl_table_validator(YourImpl)] to the valid struct.

Derive Macros

• ValidFidlTable