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//! Contains detailed error representation.
//!
//! See the main [`ImageError`] which contains a variant for each specialized error type. The
//! subtypes used in each variant are opaque by design. They can be roughly inspected through their
//! respective `kind` methods which work similar to `std::io::Error::kind`.
//!
//! The error interface makes it possible to inspect the error of an underlying decoder or encoder,
//! through the `Error::source` method. Note that this is not part of the stable interface and you
//! may not rely on a particular error value for a particular operation. This means mainly that
//! `image` does not promise to remain on a particular version of its underlying decoders but if
//! you ensure to use the same version of the dependency (or at least of the error type) through
//! external means then you could inspect the error type in slightly more detail.
//!
//! [`ImageError`]: enum.ImageError.html
use std::error::Error;
use std::{fmt, io};
use crate::color::ExtendedColorType;
use crate::image::ImageFormat;
/// The generic error type for image operations.
///
/// This high level enum allows, by variant matching, a rough separation of concerns between
/// underlying IO, the caller, format specifications, and the `image` implementation.
#[derive(Debug)]
pub enum ImageError {
/// An error was encountered while decoding.
///
/// This means that the input data did not conform to the specification of some image format,
/// or that no format could be determined, or that it did not match format specific
/// requirements set by the caller.
Decoding(DecodingError),
/// An error was encountered while encoding.
///
/// The input image can not be encoded with the chosen format, for example because the
/// specification has no representation for its color space or because a necessary conversion
/// is ambiguous. In some cases it might also happen that the dimensions can not be used with
/// the format.
Encoding(EncodingError),
/// An error was encountered in input arguments.
///
/// This is a catch-all case for strictly internal operations such as scaling, conversions,
/// etc. that involve no external format specifications.
Parameter(ParameterError),
/// Completing the operation would have required more resources than allowed.
///
/// Errors of this type are limits set by the user or environment, *not* inherent in a specific
/// format or operation that was executed.
Limits(LimitError),
/// An operation can not be completed by the chosen abstraction.
///
/// This means that it might be possible for the operation to succeed in general but
/// * it requires a disabled feature,
/// * the implementation does not yet exist, or
/// * no abstraction for a lower level could be found.
Unsupported(UnsupportedError),
/// An error occurred while interacting with the environment.
IoError(io::Error),
}
/// The implementation for an operation was not provided.
///
/// See the variant [`Unsupported`] for more documentation.
///
/// [`Unsupported`]: enum.ImageError.html#variant.Unsupported
#[derive(Debug)]
pub struct UnsupportedError {
format: ImageFormatHint,
kind: UnsupportedErrorKind,
}
/// Details what feature is not supported.
#[derive(Clone, Debug, Hash, PartialEq)]
#[non_exhaustive]
pub enum UnsupportedErrorKind {
/// The required color type can not be handled.
Color(ExtendedColorType),
/// An image format is not supported.
Format(ImageFormatHint),
/// Some feature specified by string.
/// This is discouraged and is likely to get deprecated (but not removed).
GenericFeature(String),
}
/// An error was encountered while encoding an image.
///
/// This is used as an opaque representation for the [`ImageError::Encoding`] variant. See its
/// documentation for more information.
///
/// [`ImageError::Encoding`]: enum.ImageError.html#variant.Encoding
#[derive(Debug)]
pub struct EncodingError {
format: ImageFormatHint,
underlying: Option<Box<dyn Error + Send + Sync>>,
}
/// An error was encountered in inputs arguments.
///
/// This is used as an opaque representation for the [`ImageError::Parameter`] variant. See its
/// documentation for more information.
///
/// [`ImageError::Parameter`]: enum.ImageError.html#variant.Parameter
#[derive(Debug)]
pub struct ParameterError {
kind: ParameterErrorKind,
underlying: Option<Box<dyn Error + Send + Sync>>,
}
/// Details how a parameter is malformed.
#[derive(Clone, Debug, Hash, PartialEq)]
#[non_exhaustive]
pub enum ParameterErrorKind {
/// The dimensions passed are wrong.
DimensionMismatch,
/// Repeated an operation for which error that could not be cloned was emitted already.
FailedAlready,
/// A string describing the parameter.
/// This is discouraged and is likely to get deprecated (but not removed).
Generic(String),
/// The end of the image has been reached.
NoMoreData,
}
/// An error was encountered while decoding an image.
///
/// This is used as an opaque representation for the [`ImageError::Decoding`] variant. See its
/// documentation for more information.
///
/// [`ImageError::Decoding`]: enum.ImageError.html#variant.Decoding
#[derive(Debug)]
pub struct DecodingError {
format: ImageFormatHint,
underlying: Option<Box<dyn Error + Send + Sync>>,
}
/// Completing the operation would have required more resources than allowed.
///
/// This is used as an opaque representation for the [`ImageError::Limits`] variant. See its
/// documentation for more information.
///
/// [`ImageError::Limits`]: enum.ImageError.html#variant.Limits
#[derive(Debug)]
pub struct LimitError {
kind: LimitErrorKind,
// do we need an underlying error?
}
/// Indicates the limit that prevented an operation from completing.
///
/// Note that this enumeration is not exhaustive and may in the future be extended to provide more
/// detailed information or to incorporate other resources types.
#[derive(Clone, Debug, Hash, PartialEq, Eq)]
#[non_exhaustive]
#[allow(missing_copy_implementations)] // Might be non-Copy in the future.
pub enum LimitErrorKind {
/// The resulting image exceed dimension limits in either direction.
DimensionError,
/// The operation would have performed an allocation larger than allowed.
InsufficientMemory,
/// The specified strict limits are not supported for this operation
Unsupported {
/// The given limits
limits: crate::Limits,
/// The supported strict limits
supported: crate::LimitSupport,
},
}
/// A best effort representation for image formats.
#[derive(Clone, Debug, Hash, PartialEq)]
#[non_exhaustive]
pub enum ImageFormatHint {
/// The format is known exactly.
Exact(ImageFormat),
/// The format can be identified by a name.
Name(String),
/// A common path extension for the format is known.
PathExtension(std::path::PathBuf),
/// The format is not known or could not be determined.
Unknown,
}
impl UnsupportedError {
/// Create an `UnsupportedError` for an image with details on the unsupported feature.
///
/// If the operation was not connected to a particular image format then the hint may be
/// `Unknown`.
#[must_use]
pub fn from_format_and_kind(format: ImageFormatHint, kind: UnsupportedErrorKind) -> Self {
UnsupportedError { format, kind }
}
/// Returns the corresponding `UnsupportedErrorKind` of the error.
#[must_use]
pub fn kind(&self) -> UnsupportedErrorKind {
self.kind.clone()
}
/// Returns the image format associated with this error.
#[must_use]
pub fn format_hint(&self) -> ImageFormatHint {
self.format.clone()
}
}
impl DecodingError {
/// Create a `DecodingError` that stems from an arbitrary error of an underlying decoder.
pub fn new(format: ImageFormatHint, err: impl Into<Box<dyn Error + Send + Sync>>) -> Self {
DecodingError {
format,
underlying: Some(err.into()),
}
}
/// Create a `DecodingError` for an image format.
///
/// The error will not contain any further information but is very easy to create.
#[must_use]
pub fn from_format_hint(format: ImageFormatHint) -> Self {
DecodingError {
format,
underlying: None,
}
}
/// Returns the image format associated with this error.
#[must_use]
pub fn format_hint(&self) -> ImageFormatHint {
self.format.clone()
}
}
impl EncodingError {
/// Create an `EncodingError` that stems from an arbitrary error of an underlying encoder.
pub fn new(format: ImageFormatHint, err: impl Into<Box<dyn Error + Send + Sync>>) -> Self {
EncodingError {
format,
underlying: Some(err.into()),
}
}
/// Create an `EncodingError` for an image format.
///
/// The error will not contain any further information but is very easy to create.
#[must_use]
pub fn from_format_hint(format: ImageFormatHint) -> Self {
EncodingError {
format,
underlying: None,
}
}
/// Return the image format associated with this error.
#[must_use]
pub fn format_hint(&self) -> ImageFormatHint {
self.format.clone()
}
}
impl ParameterError {
/// Construct a `ParameterError` directly from a corresponding kind.
#[must_use]
pub fn from_kind(kind: ParameterErrorKind) -> Self {
ParameterError {
kind,
underlying: None,
}
}
/// Returns the corresponding `ParameterErrorKind` of the error.
#[must_use]
pub fn kind(&self) -> ParameterErrorKind {
self.kind.clone()
}
}
impl LimitError {
/// Construct a generic `LimitError` directly from a corresponding kind.
#[must_use]
pub fn from_kind(kind: LimitErrorKind) -> Self {
LimitError { kind }
}
/// Returns the corresponding `LimitErrorKind` of the error.
#[must_use]
pub fn kind(&self) -> LimitErrorKind {
self.kind.clone()
}
}
impl From<io::Error> for ImageError {
fn from(err: io::Error) -> ImageError {
ImageError::IoError(err)
}
}
impl From<ImageFormat> for ImageFormatHint {
fn from(format: ImageFormat) -> Self {
ImageFormatHint::Exact(format)
}
}
impl From<&'_ std::path::Path> for ImageFormatHint {
fn from(path: &'_ std::path::Path) -> Self {
match path.extension() {
Some(ext) => ImageFormatHint::PathExtension(ext.into()),
None => ImageFormatHint::Unknown,
}
}
}
impl From<ImageFormatHint> for UnsupportedError {
fn from(hint: ImageFormatHint) -> Self {
UnsupportedError {
format: hint.clone(),
kind: UnsupportedErrorKind::Format(hint),
}
}
}
/// Result of an image decoding/encoding process
pub type ImageResult<T> = Result<T, ImageError>;
impl fmt::Display for ImageError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match self {
ImageError::IoError(err) => err.fmt(fmt),
ImageError::Decoding(err) => err.fmt(fmt),
ImageError::Encoding(err) => err.fmt(fmt),
ImageError::Parameter(err) => err.fmt(fmt),
ImageError::Limits(err) => err.fmt(fmt),
ImageError::Unsupported(err) => err.fmt(fmt),
}
}
}
impl Error for ImageError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
match self {
ImageError::IoError(err) => err.source(),
ImageError::Decoding(err) => err.source(),
ImageError::Encoding(err) => err.source(),
ImageError::Parameter(err) => err.source(),
ImageError::Limits(err) => err.source(),
ImageError::Unsupported(err) => err.source(),
}
}
}
impl fmt::Display for UnsupportedError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match &self.kind {
UnsupportedErrorKind::Format(ImageFormatHint::Unknown) => {
write!(fmt, "The image format could not be determined",)
}
UnsupportedErrorKind::Format(format @ ImageFormatHint::PathExtension(_)) => write!(
fmt,
"The file extension {format} was not recognized as an image format",
),
UnsupportedErrorKind::Format(format) => {
write!(fmt, "The image format {format} is not supported",)
}
UnsupportedErrorKind::Color(color) => write!(
fmt,
"The encoder or decoder for {} does not support the color type `{:?}`",
self.format, color,
),
UnsupportedErrorKind::GenericFeature(message) => match &self.format {
ImageFormatHint::Unknown => write!(
fmt,
"The decoder does not support the format feature {message}",
),
other => write!(
fmt,
"The decoder for {other} does not support the format features {message}",
),
},
}
}
}
impl Error for UnsupportedError {}
impl fmt::Display for ParameterError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match &self.kind {
ParameterErrorKind::DimensionMismatch => write!(
fmt,
"The Image's dimensions are either too \
small or too large"
),
ParameterErrorKind::FailedAlready => write!(
fmt,
"The end the image stream has been reached due to a previous error"
),
ParameterErrorKind::Generic(message) => {
write!(fmt, "The parameter is malformed: {message}",)
}
ParameterErrorKind::NoMoreData => write!(fmt, "The end of the image has been reached",),
}?;
if let Some(underlying) = &self.underlying {
write!(fmt, "\n{underlying}")?;
}
Ok(())
}
}
impl Error for ParameterError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
match &self.underlying {
None => None,
Some(source) => Some(&**source),
}
}
}
impl fmt::Display for EncodingError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match &self.underlying {
Some(underlying) => write!(
fmt,
"Format error encoding {}:\n{}",
self.format, underlying,
),
None => write!(fmt, "Format error encoding {}", self.format,),
}
}
}
impl Error for EncodingError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
match &self.underlying {
None => None,
Some(source) => Some(&**source),
}
}
}
impl fmt::Display for DecodingError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match &self.underlying {
None => match self.format {
ImageFormatHint::Unknown => write!(fmt, "Format error"),
_ => write!(fmt, "Format error decoding {}", self.format),
},
Some(underlying) => {
write!(fmt, "Format error decoding {}: {}", self.format, underlying)
}
}
}
}
impl Error for DecodingError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
match &self.underlying {
None => None,
Some(source) => Some(&**source),
}
}
}
impl fmt::Display for LimitError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match self.kind {
LimitErrorKind::InsufficientMemory => write!(fmt, "Memory limit exceeded"),
LimitErrorKind::DimensionError => write!(fmt, "Image size exceeds limit"),
LimitErrorKind::Unsupported { .. } => {
write!(fmt, "The following strict limits are specified but not supported by the opertation: ")?;
Ok(())
}
}
}
}
impl Error for LimitError {}
impl fmt::Display for ImageFormatHint {
fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match self {
ImageFormatHint::Exact(format) => write!(fmt, "{format:?}"),
ImageFormatHint::Name(name) => write!(fmt, "`{name}`"),
ImageFormatHint::PathExtension(ext) => write!(fmt, "`.{ext:?}`"),
ImageFormatHint::Unknown => write!(fmt, "`Unknown`"),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::mem::size_of;
#[allow(dead_code)]
// This will fail to compile if the size of this type is large.
const ASSERT_SMALLISH: usize = [0][(size_of::<ImageError>() >= 200) as usize];
#[test]
fn test_send_sync_stability() {
fn assert_send_sync<T: Send + Sync>() {}
assert_send_sync::<ImageError>();
}
}