binread/
error.rs

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//! Error types and internal error handling functions
use super::*;

/// An error while parsing a BinRead type
#[non_exhaustive]
pub enum Error {
    /// The magic value did not match the provided one
    BadMagic {
        // Position in number of bytes from the start of the reader
        pos: u64,
        // The value found. Use [`Any::downcast_ref`](core::any::Any::downcast_ref) to access
        found: Box<dyn Any + Sync + Send>,
    },
    /// The condition of an assertion without a custom type failed
    AssertFail { pos: u64, message: String },
    /// An error that occured while reading from, or seeking within, the reader
    Io(io::Error),
    /// A custom error, most often given from the second value passed into an [`assert`](attribute#Assert)
    Custom {
        pos: u64,
        err: Box<dyn Any + Sync + Send>,
    },
    /// No variant in the enum was successful in parsing the data
    NoVariantMatch { pos: u64 },
    EnumErrors {
        pos: u64,
        variant_errors: Vec<(/*variant name*/ &'static str, Error)>,
    },
}

impl Error {
    /// Gets a custom error of type T from the Error. Returns `None` if the error type is not
    /// custom or if the contained error is not of the desired type.
    pub fn custom_err<T: Any>(&self) -> Option<&T> {
        if let Error::Custom { err, .. } = self {
            err.downcast_ref()
        } else {
            None
        }
    }
}

impl From<io::Error> for Error {
    fn from(err: io::Error) -> Self {
        Self::Io(err)
    }
}

#[cfg(feature = "std")]
impl std::error::Error for Error {}

use core::fmt;

impl fmt::Debug for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::BadMagic { pos, .. } => write!(f, "BadMagic {{ pos: 0x{:X} }}", pos),
            Self::AssertFail { pos, message } => {
                write!(f, "AssertFail at 0x{:X}: \"{}\"", pos, message)
            }
            Self::Io(err) => write!(f, "Io({:?})", err),
            Self::Custom { pos, err } => write!(f, "Custom {{ pos: 0x{:X}, err: {:?} }}", pos, err),
            Self::NoVariantMatch { pos } => write!(f, "NoVariantMatch {{ pos: 0x{:X} }}", pos),
            Self::EnumErrors {
                pos,
                variant_errors,
            } => write!(
                f,
                "EnumErrors {{ pos: 0x{:X}, variant_errors: {:?} }}",
                pos, variant_errors
            ),
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(self, f)
    }
}

/// Read a value then check if it is the expected value
pub fn magic<R, B>(reader: &mut R, expected: B, options: &ReadOptions) -> BinResult<()>
where
    B: BinRead<Args = ()> + PartialEq + Sync + Send + 'static,
    R: io::Read + io::Seek,
{
    let pos = reader.stream_pos()?;
    #[cfg(feature = "debug_template")]
    let options = {
        let mut options = *options;
        options.variable_name = Some("magic");
        options
    };
    let val = B::read_options(reader, &options, ())?;
    if val == expected {
        Ok(())
    } else {
        Err(Error::BadMagic {
            pos,
            found: Box::new(val) as _,
        })
    }
}

/// Assert a condition is true and if not optionally apply a function to generate the error
#[deprecated]
pub fn assert<R, E, A>(reader: &mut R, test: bool, message: &str, error: Option<E>) -> BinResult<()>
where
    R: io::Read + io::Seek,
    A: core::fmt::Debug + Sync + Send + 'static,
    E: Fn() -> A,
{
    let pos = reader.stream_pos()?;
    if test {
        Ok(())
    } else {
        error
            .map(|err| {
                Err(Error::Custom {
                    pos,
                    err: Box::new(err()),
                })
            })
            .unwrap_or_else(|| {
                Err(Error::AssertFail {
                    pos,
                    message: message.into(),
                })
            })
    }
}

pub fn read_options_then_after_parse<Args, T, R>(
    reader: &mut R,
    ro: &ReadOptions,
    args: T::Args,
) -> BinResult<T>
where
    Args: Copy + 'static,
    T: BinRead<Args = Args>,
    R: Read + Seek,
{
    let mut val = T::read_options(reader, ro, args)?;
    val.after_parse(reader, ro, args)?;
    Ok(val)
}