Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

3 files changed, 717 insertions, 0 deletions

diff --git a/vendor/image/src/io/free_functions.rs b/vendor/image/src/io/free_functions.rs
new file mode 100644
index 0000000..d6047d7
--- /dev/null
+++ b/vendor/image/src/io/free_functions.rs
@@ -0,0 +1,312 @@
+use std::fs::File;
+use std::io::{BufRead, BufReader, BufWriter, Seek};
+use std::path::Path;
+use std::u32;
+
+use crate::codecs::*;
+
+use crate::dynimage::DynamicImage;
+use crate::error::{ImageError, ImageFormatHint, ImageResult};
+use crate::image;
+use crate::image::ImageFormat;
+#[allow(unused_imports)] // When no features are supported
+use crate::image::{ImageDecoder, ImageEncoder};
+use crate::{
+    color,
+    error::{UnsupportedError, UnsupportedErrorKind},
+    ImageOutputFormat,
+};
+
+pub(crate) fn open_impl(path: &Path) -> ImageResult<DynamicImage> {
+    let buffered_read = BufReader::new(File::open(path).map_err(ImageError::IoError)?);
+
+    load(buffered_read, ImageFormat::from_path(path)?)
+}
+
+/// Create a new image from a Reader.
+///
+/// Assumes the reader is already buffered. For optimal performance,
+/// consider wrapping the reader with a `BufReader::new()`.
+///
+/// Try [`io::Reader`] for more advanced uses.
+///
+/// [`io::Reader`]: io/struct.Reader.html
+#[allow(unused_variables)]
+// r is unused if no features are supported.
+pub fn load<R: BufRead + Seek>(r: R, format: ImageFormat) -> ImageResult<DynamicImage> {
+    load_inner(r, super::Limits::default(), format)
+}
+
+pub(crate) trait DecoderVisitor {
+    type Result;
+    fn visit_decoder<'a, D: ImageDecoder<'a>>(self, decoder: D) -> ImageResult<Self::Result>;
+}
+
+pub(crate) fn load_decoder<R: BufRead + Seek, V: DecoderVisitor>(
+    r: R,
+    format: ImageFormat,
+    limits: super::Limits,
+    visitor: V,
+) -> ImageResult<V::Result> {
+    #[allow(unreachable_patterns)]
+    // Default is unreachable if all features are supported.
+    match format {
+        #[cfg(feature = "avif-decoder")]
+        image::ImageFormat::Avif => visitor.visit_decoder(avif::AvifDecoder::new(r)?),
+        #[cfg(feature = "png")]
+        image::ImageFormat::Png => visitor.visit_decoder(png::PngDecoder::with_limits(r, limits)?),
+        #[cfg(feature = "gif")]
+        image::ImageFormat::Gif => visitor.visit_decoder(gif::GifDecoder::new(r)?),
+        #[cfg(feature = "jpeg")]
+        image::ImageFormat::Jpeg => visitor.visit_decoder(jpeg::JpegDecoder::new(r)?),
+        #[cfg(feature = "webp")]
+        image::ImageFormat::WebP => visitor.visit_decoder(webp::WebPDecoder::new(r)?),
+        #[cfg(feature = "tiff")]
+        image::ImageFormat::Tiff => visitor.visit_decoder(tiff::TiffDecoder::new(r)?),
+        #[cfg(feature = "tga")]
+        image::ImageFormat::Tga => visitor.visit_decoder(tga::TgaDecoder::new(r)?),
+        #[cfg(feature = "dds")]
+        image::ImageFormat::Dds => visitor.visit_decoder(dds::DdsDecoder::new(r)?),
+        #[cfg(feature = "bmp")]
+        image::ImageFormat::Bmp => visitor.visit_decoder(bmp::BmpDecoder::new(r)?),
+        #[cfg(feature = "ico")]
+        image::ImageFormat::Ico => visitor.visit_decoder(ico::IcoDecoder::new(r)?),
+        #[cfg(feature = "hdr")]
+        image::ImageFormat::Hdr => visitor.visit_decoder(hdr::HdrAdapter::new(BufReader::new(r))?),
+        #[cfg(feature = "exr")]
+        image::ImageFormat::OpenExr => visitor.visit_decoder(openexr::OpenExrDecoder::new(r)?),
+        #[cfg(feature = "pnm")]
+        image::ImageFormat::Pnm => visitor.visit_decoder(pnm::PnmDecoder::new(r)?),
+        #[cfg(feature = "farbfeld")]
+        image::ImageFormat::Farbfeld => visitor.visit_decoder(farbfeld::FarbfeldDecoder::new(r)?),
+        #[cfg(feature = "qoi")]
+        image::ImageFormat::Qoi => visitor.visit_decoder(qoi::QoiDecoder::new(r)?),
+        _ => Err(ImageError::Unsupported(
+            ImageFormatHint::Exact(format).into(),
+        )),
+    }
+}
+
+pub(crate) fn load_inner<R: BufRead + Seek>(
+    r: R,
+    limits: super::Limits,
+    format: ImageFormat,
+) -> ImageResult<DynamicImage> {
+    struct LoadVisitor(super::Limits);
+
+    impl DecoderVisitor for LoadVisitor {
+        type Result = DynamicImage;
+
+        fn visit_decoder<'a, D: ImageDecoder<'a>>(
+            self,
+            mut decoder: D,
+        ) -> ImageResult<Self::Result> {
+            let mut limits = self.0;
+            // Check that we do not allocate a bigger buffer than we are allowed to
+            // FIXME: should this rather go in `DynamicImage::from_decoder` somehow?
+            limits.reserve(decoder.total_bytes())?;
+            decoder.set_limits(limits)?;
+            DynamicImage::from_decoder(decoder)
+        }
+    }
+
+    load_decoder(r, format, limits.clone(), LoadVisitor(limits))
+}
+
+pub(crate) fn image_dimensions_impl(path: &Path) -> ImageResult<(u32, u32)> {
+    let format = image::ImageFormat::from_path(path)?;
+    let reader = BufReader::new(File::open(path)?);
+    image_dimensions_with_format_impl(reader, format)
+}
+
+#[allow(unused_variables)]
+// fin is unused if no features are supported.
+pub(crate) fn image_dimensions_with_format_impl<R: BufRead + Seek>(
+    buffered_read: R,
+    format: ImageFormat,
+) -> ImageResult<(u32, u32)> {
+    struct DimVisitor;
+
+    impl DecoderVisitor for DimVisitor {
+        type Result = (u32, u32);
+        fn visit_decoder<'a, D: ImageDecoder<'a>>(self, decoder: D) -> ImageResult<Self::Result> {
+            Ok(decoder.dimensions())
+        }
+    }
+
+    load_decoder(buffered_read, format, super::Limits::default(), DimVisitor)
+}
+
+#[allow(unused_variables)]
+// Most variables when no features are supported
+pub(crate) fn save_buffer_impl(
+    path: &Path,
+    buf: &[u8],
+    width: u32,
+    height: u32,
+    color: color::ColorType,
+) -> ImageResult<()> {
+    let format = ImageFormat::from_path(path)?;
+    save_buffer_with_format_impl(path, buf, width, height, color, format)
+}
+
+#[allow(unused_variables)]
+// Most variables when no features are supported
+pub(crate) fn save_buffer_with_format_impl(
+    path: &Path,
+    buf: &[u8],
+    width: u32,
+    height: u32,
+    color: color::ColorType,
+    format: ImageFormat,
+) -> ImageResult<()> {
+    let buffered_file_write = &mut BufWriter::new(File::create(path)?); // always seekable
+
+    let format = match format {
+        #[cfg(feature = "pnm")]
+        image::ImageFormat::Pnm => {
+            let ext = path
+                .extension()
+                .and_then(|s| s.to_str())
+                .map_or("".to_string(), |s| s.to_ascii_lowercase());
+            ImageOutputFormat::Pnm(match &*ext {
+                "pbm" => pnm::PnmSubtype::Bitmap(pnm::SampleEncoding::Binary),
+                "pgm" => pnm::PnmSubtype::Graymap(pnm::SampleEncoding::Binary),
+                "ppm" => pnm::PnmSubtype::Pixmap(pnm::SampleEncoding::Binary),
+                "pam" => pnm::PnmSubtype::ArbitraryMap,
+                _ => {
+                    return Err(ImageError::Unsupported(
+                        ImageFormatHint::Exact(format).into(),
+                    ))
+                } // Unsupported Pnm subtype.
+            })
+        }
+        // #[cfg(feature = "hdr")]
+        // image::ImageFormat::Hdr => hdr::HdrEncoder::new(fout).encode(&[Rgb<f32>], width, height), // usize
+        format => format.into(),
+    };
+
+    write_buffer_impl(buffered_file_write, buf, width, height, color, format)
+}
+
+#[allow(unused_variables)]
+// Most variables when no features are supported
+pub(crate) fn write_buffer_impl<W: std::io::Write + Seek>(
+    buffered_write: &mut W,
+    buf: &[u8],
+    width: u32,
+    height: u32,
+    color: color::ColorType,
+    format: ImageOutputFormat,
+) -> ImageResult<()> {
+    match format {
+        #[cfg(feature = "png")]
+        ImageOutputFormat::Png => {
+            png::PngEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "jpeg")]
+        ImageOutputFormat::Jpeg(quality) => {
+            jpeg::JpegEncoder::new_with_quality(buffered_write, quality)
+                .write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "pnm")]
+        ImageOutputFormat::Pnm(subtype) => pnm::PnmEncoder::new(buffered_write)
+            .with_subtype(subtype)
+            .write_image(buf, width, height, color),
+        #[cfg(feature = "gif")]
+        ImageOutputFormat::Gif => {
+            gif::GifEncoder::new(buffered_write).encode(buf, width, height, color)
+        }
+        #[cfg(feature = "ico")]
+        ImageOutputFormat::Ico => {
+            ico::IcoEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "bmp")]
+        ImageOutputFormat::Bmp => {
+            bmp::BmpEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "farbfeld")]
+        ImageOutputFormat::Farbfeld => {
+            farbfeld::FarbfeldEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "tga")]
+        ImageOutputFormat::Tga => {
+            tga::TgaEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "exr")]
+        ImageOutputFormat::OpenExr => {
+            openexr::OpenExrEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "tiff")]
+        ImageOutputFormat::Tiff => {
+            tiff::TiffEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "avif-encoder")]
+        ImageOutputFormat::Avif => {
+            avif::AvifEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "qoi")]
+        ImageOutputFormat::Qoi => {
+            qoi::QoiEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+        #[cfg(feature = "webp-encoder")]
+        ImageOutputFormat::WebP => {
+            webp::WebPEncoder::new(buffered_write).write_image(buf, width, height, color)
+        }
+
+        image::ImageOutputFormat::Unsupported(msg) => Err(ImageError::Unsupported(
+            UnsupportedError::from_format_and_kind(
+                ImageFormatHint::Unknown,
+                UnsupportedErrorKind::Format(ImageFormatHint::Name(msg)),
+            ),
+        )),
+    }
+}
+
+static MAGIC_BYTES: [(&[u8], ImageFormat); 23] = [
+    (b"\x89PNG\r\n\x1a\n", ImageFormat::Png),
+    (&[0xff, 0xd8, 0xff], ImageFormat::Jpeg),
+    (b"GIF89a", ImageFormat::Gif),
+    (b"GIF87a", ImageFormat::Gif),
+    (b"RIFF", ImageFormat::WebP), // TODO: better magic byte detection, see https://github.com/image-rs/image/issues/660
+    (b"MM\x00*", ImageFormat::Tiff),
+    (b"II*\x00", ImageFormat::Tiff),
+    (b"DDS ", ImageFormat::Dds),
+    (b"BM", ImageFormat::Bmp),
+    (&[0, 0, 1, 0], ImageFormat::Ico),
+    (b"#?RADIANCE", ImageFormat::Hdr),
+    (b"P1", ImageFormat::Pnm),
+    (b"P2", ImageFormat::Pnm),
+    (b"P3", ImageFormat::Pnm),
+    (b"P4", ImageFormat::Pnm),
+    (b"P5", ImageFormat::Pnm),
+    (b"P6", ImageFormat::Pnm),
+    (b"P7", ImageFormat::Pnm),
+    (b"farbfeld", ImageFormat::Farbfeld),
+    (b"\0\0\0 ftypavif", ImageFormat::Avif),
+    (b"\0\0\0\x1cftypavif", ImageFormat::Avif),
+    (&[0x76, 0x2f, 0x31, 0x01], ImageFormat::OpenExr), // = &exr::meta::magic_number::BYTES
+    (b"qoif", ImageFormat::Qoi),
+];
+
+/// Guess image format from memory block
+///
+/// Makes an educated guess about the image format based on the Magic Bytes at the beginning.
+/// TGA is not supported by this function.
+/// This is not to be trusted on the validity of the whole memory block
+pub fn guess_format(buffer: &[u8]) -> ImageResult<ImageFormat> {
+    match guess_format_impl(buffer) {
+        Some(format) => Ok(format),
+        None => Err(ImageError::Unsupported(ImageFormatHint::Unknown.into())),
+    }
+}
+
+pub(crate) fn guess_format_impl(buffer: &[u8]) -> Option<ImageFormat> {
+    for &(signature, format) in &MAGIC_BYTES {
+        if buffer.starts_with(signature) {
+            return Some(format);
+        }
+    }
+
+    None
+}
diff --git a/vendor/image/src/io/mod.rs b/vendor/image/src/io/mod.rs
new file mode 100644
index 0000000..8fbc6e2
--- /dev/null
+++ b/vendor/image/src/io/mod.rs
@@ -0,0 +1,166 @@
+//! Input and output of images.
+
+use std::convert::TryFrom;
+
+use crate::{error, ImageError, ImageResult};
+
+pub(crate) mod free_functions;
+mod reader;
+
+pub use self::reader::Reader;
+
+/// Set of supported strict limits for a decoder.
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
+#[allow(missing_copy_implementations)]
+#[allow(clippy::manual_non_exhaustive)]
+pub struct LimitSupport {
+    _non_exhaustive: (),
+}
+
+#[allow(clippy::derivable_impls)]
+impl Default for LimitSupport {
+    fn default() -> LimitSupport {
+        LimitSupport {
+            _non_exhaustive: (),
+        }
+    }
+}
+
+/// Resource limits for decoding.
+///
+/// Limits can be either *strict* or *non-strict*. Non-strict limits are best-effort
+/// limits where the library does not guarantee that limit will not be exceeded. Do note
+/// that it is still considered a bug if a non-strict limit is exceeded, however as
+/// some of the underlying decoders do not support not support such limits one cannot
+/// rely on these limits being supported. For stric limits the library makes a stronger
+/// guarantee that the limit will not be exceeded. Exceeding a strict limit is considered
+/// a critical bug. If a decoder cannot guarantee that it will uphold a strict limit it
+/// *must* fail with `image::error::LimitErrorKind::Unsupported`.
+///
+/// Currently the only strict limits supported are the `max_image_width` and `max_image_height`
+/// limits, however more will be added in the future. [`LimitSupport`] will default to support
+/// being false and decoders should enable support for the limits they support in
+/// [`ImageDecoder::set_limits`].
+///
+/// The limit check should only ever fail if a limit will be exceeded or an unsupported strict
+/// limit is used.
+///
+/// [`LimitSupport`]: ./struct.LimitSupport.html
+/// [`ImageDecoder::set_limits`]: ../trait.ImageDecoder.html#method.set_limits
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
+#[allow(missing_copy_implementations)]
+#[allow(clippy::manual_non_exhaustive)]
+pub struct Limits {
+    /// The maximum allowed image width. This limit is strict. The default is no limit.
+    pub max_image_width: Option<u32>,
+    /// The maximum allowed image height. This limit is strict. The default is no limit.
+    pub max_image_height: Option<u32>,
+    /// The maximum allowed sum of allocations allocated by the decoder at any one time excluding
+    /// allocator overhead. This limit is non-strict by default and some decoders may ignore it.
+    /// The default is 512MiB.
+    pub max_alloc: Option<u64>,
+    _non_exhaustive: (),
+}
+
+impl Default for Limits {
+    fn default() -> Limits {
+        Limits {
+            max_image_width: None,
+            max_image_height: None,
+            max_alloc: Some(512 * 1024 * 1024),
+            _non_exhaustive: (),
+        }
+    }
+}
+
+impl Limits {
+    /// Disable all limits.
+    pub fn no_limits() -> Limits {
+        Limits {
+            max_image_width: None,
+            max_image_height: None,
+            max_alloc: None,
+            _non_exhaustive: (),
+        }
+    }
+
+    /// This function checks that all currently set strict limits are supported.
+    pub fn check_support(&self, _supported: &LimitSupport) -> ImageResult<()> {
+        Ok(())
+    }
+
+    /// This function checks the `max_image_width` and `max_image_height` limits given
+    /// the image width and height.
+    pub fn check_dimensions(&self, width: u32, height: u32) -> ImageResult<()> {
+        if let Some(max_width) = self.max_image_width {
+            if width > max_width {
+                return Err(ImageError::Limits(error::LimitError::from_kind(
+                    error::LimitErrorKind::DimensionError,
+                )));
+            }
+        }
+
+        if let Some(max_height) = self.max_image_height {
+            if height > max_height {
+                return Err(ImageError::Limits(error::LimitError::from_kind(
+                    error::LimitErrorKind::DimensionError,
+                )));
+            }
+        }
+
+        Ok(())
+    }
+
+    /// This function checks that the current limit allows for reserving the set amount
+    /// of bytes, it then reduces the limit accordingly.
+    pub fn reserve(&mut self, amount: u64) -> ImageResult<()> {
+        if let Some(max_alloc) = self.max_alloc.as_mut() {
+            if *max_alloc < amount {
+                return Err(ImageError::Limits(error::LimitError::from_kind(
+                    error::LimitErrorKind::InsufficientMemory,
+                )));
+            }
+
+            *max_alloc -= amount;
+        }
+
+        Ok(())
+    }
+
+    /// This function acts identically to [`reserve`], but takes a `usize` for convenience.
+    pub fn reserve_usize(&mut self, amount: usize) -> ImageResult<()> {
+        match u64::try_from(amount) {
+            Ok(n) => self.reserve(n),
+            Err(_) if self.max_alloc.is_some() => Err(ImageError::Limits(
+                error::LimitError::from_kind(error::LimitErrorKind::InsufficientMemory),
+            )),
+            Err(_) => {
+                // Out of bounds, but we weren't asked to consider any limit.
+                Ok(())
+            }
+        }
+    }
+
+    /// This function increases the `max_alloc` limit with amount. Should only be used
+    /// together with [`reserve`].
+    ///
+    /// [`reserve`]: #method.reserve
+    pub fn free(&mut self, amount: u64) {
+        if let Some(max_alloc) = self.max_alloc.as_mut() {
+            *max_alloc = max_alloc.saturating_add(amount);
+        }
+    }
+
+    /// This function acts identically to [`free`], but takes a `usize` for convenience.
+    pub fn free_usize(&mut self, amount: usize) {
+        match u64::try_from(amount) {
+            Ok(n) => self.free(n),
+            Err(_) if self.max_alloc.is_some() => {
+                panic!("max_alloc is set, we should have exited earlier when the reserve failed");
+            }
+            Err(_) => {
+                // Out of bounds, but we weren't asked to consider any limit.
+            }
+        }
+    }
+}
diff --git a/vendor/image/src/io/reader.rs b/vendor/image/src/io/reader.rs
new file mode 100644
index 0000000..660780f
--- /dev/null
+++ b/vendor/image/src/io/reader.rs
@@ -0,0 +1,239 @@
+use std::fs::File;
+use std::io::{self, BufRead, BufReader, Cursor, Read, Seek, SeekFrom};
+use std::path::Path;
+
+use crate::dynimage::DynamicImage;
+use crate::error::{ImageFormatHint, UnsupportedError, UnsupportedErrorKind};
+use crate::image::ImageFormat;
+use crate::{ImageError, ImageResult};
+
+use super::free_functions;
+
+/// A multi-format image reader.
+///
+/// Wraps an input reader to facilitate automatic detection of an image's format, appropriate
+/// decoding method, and dispatches into the set of supported [`ImageDecoder`] implementations.
+///
+/// ## Usage
+///
+/// Opening a file, deducing the format based on the file path automatically, and trying to decode
+/// the image contained can be performed by constructing the reader and immediately consuming it.
+///
+/// ```no_run
+/// # use image::ImageError;
+/// # use image::io::Reader;
+/// # fn main() -> Result<(), ImageError> {
+/// let image = Reader::open("path/to/image.png")?
+///     .decode()?;
+/// # Ok(()) }
+/// ```
+///
+/// It is also possible to make a guess based on the content. This is especially handy if the
+/// source is some blob in memory and you have constructed the reader in another way. Here is an
+/// example with a `pnm` black-and-white subformat that encodes its pixel matrix with ascii values.
+///
+/// ```
+/// # use image::ImageError;
+/// # use image::io::Reader;
+/// # fn main() -> Result<(), ImageError> {
+/// use std::io::Cursor;
+/// use image::ImageFormat;
+///
+/// let raw_data = b"P1 2 2\n\
+///     0 1\n\
+///     1 0\n";
+///
+/// let mut reader = Reader::new(Cursor::new(raw_data))
+///     .with_guessed_format()
+///     .expect("Cursor io never fails");
+/// assert_eq!(reader.format(), Some(ImageFormat::Pnm));
+///
+/// # #[cfg(feature = "pnm")]
+/// let image = reader.decode()?;
+/// # Ok(()) }
+/// ```
+///
+/// As a final fallback or if only a specific format must be used, the reader always allows manual
+/// specification of the supposed image format with [`set_format`].
+///
+/// [`set_format`]: #method.set_format
+/// [`ImageDecoder`]: ../trait.ImageDecoder.html
+pub struct Reader<R: Read> {
+    /// The reader. Should be buffered.
+    inner: R,
+    /// The format, if one has been set or deduced.
+    format: Option<ImageFormat>,
+    /// Decoding limits
+    limits: super::Limits,
+}
+
+impl<R: Read> Reader<R> {
+    /// Create a new image reader without a preset format.
+    ///
+    /// Assumes the reader is already buffered. For optimal performance,
+    /// consider wrapping the reader with a `BufReader::new()`.
+    ///
+    /// It is possible to guess the format based on the content of the read object with
+    /// [`with_guessed_format`], or to set the format directly with [`set_format`].
+    ///
+    /// [`with_guessed_format`]: #method.with_guessed_format
+    /// [`set_format`]: method.set_format
+    pub fn new(buffered_reader: R) -> Self {
+        Reader {
+            inner: buffered_reader,
+            format: None,
+            limits: super::Limits::default(),
+        }
+    }
+
+    /// Construct a reader with specified format.
+    ///
+    /// Assumes the reader is already buffered. For optimal performance,
+    /// consider wrapping the reader with a `BufReader::new()`.
+    pub fn with_format(buffered_reader: R, format: ImageFormat) -> Self {
+        Reader {
+            inner: buffered_reader,
+            format: Some(format),
+            limits: super::Limits::default(),
+        }
+    }
+
+    /// Get the currently determined format.
+    pub fn format(&self) -> Option<ImageFormat> {
+        self.format
+    }
+
+    /// Supply the format as which to interpret the read image.
+    pub fn set_format(&mut self, format: ImageFormat) {
+        self.format = Some(format);
+    }
+
+    /// Remove the current information on the image format.
+    ///
+    /// Note that many operations require format information to be present and will return e.g. an
+    /// `ImageError::Unsupported` when the image format has not been set.
+    pub fn clear_format(&mut self) {
+        self.format = None;
+    }
+
+    /// Disable all decoding limits.
+    pub fn no_limits(&mut self) {
+        self.limits = super::Limits::no_limits();
+    }
+
+    /// Set a custom set of decoding limits.
+    pub fn limits(&mut self, limits: super::Limits) {
+        self.limits = limits;
+    }
+
+    /// Unwrap the reader.
+    pub fn into_inner(self) -> R {
+        self.inner
+    }
+}
+
+impl Reader<BufReader<File>> {
+    /// Open a file to read, format will be guessed from path.
+    ///
+    /// This will not attempt any io operation on the opened file.
+    ///
+    /// If you want to inspect the content for a better guess on the format, which does not depend
+    /// on file extensions, follow this call with a call to [`with_guessed_format`].
+    ///
+    /// [`with_guessed_format`]: #method.with_guessed_format
+    pub fn open<P>(path: P) -> io::Result<Self>
+    where
+        P: AsRef<Path>,
+    {
+        Self::open_impl(path.as_ref())
+    }
+
+    fn open_impl(path: &Path) -> io::Result<Self> {
+        Ok(Reader {
+            inner: BufReader::new(File::open(path)?),
+            format: ImageFormat::from_path(path).ok(),
+            limits: super::Limits::default(),
+        })
+    }
+}
+
+impl<R: BufRead + Seek> Reader<R> {
+    /// Make a format guess based on the content, replacing it on success.
+    ///
+    /// Returns `Ok` with the guess if no io error occurs. Additionally, replaces the current
+    /// format if the guess was successful. If the guess was unable to determine a format then
+    /// the current format of the reader is unchanged.
+    ///
+    /// Returns an error if the underlying reader fails. The format is unchanged. The error is a
+    /// `std::io::Error` and not `ImageError` since the only error case is an error when the
+    /// underlying reader seeks.
+    ///
+    /// When an error occurs, the reader may not have been properly reset and it is potentially
+    /// hazardous to continue with more io.
+    ///
+    /// ## Usage
+    ///
+    /// This supplements the path based type deduction from [`open`](Reader::open) with content based deduction.
+    /// This is more common in Linux and UNIX operating systems and also helpful if the path can
+    /// not be directly controlled.
+    ///
+    /// ```no_run
+    /// # use image::ImageError;
+    /// # use image::io::Reader;
+    /// # fn main() -> Result<(), ImageError> {
+    /// let image = Reader::open("image.unknown")?
+    ///     .with_guessed_format()?
+    ///     .decode()?;
+    /// # Ok(()) }
+    /// ```
+    pub fn with_guessed_format(mut self) -> io::Result<Self> {
+        let format = self.guess_format()?;
+        // Replace format if found, keep current state if not.
+        self.format = format.or(self.format);
+        Ok(self)
+    }
+
+    fn guess_format(&mut self) -> io::Result<Option<ImageFormat>> {
+        let mut start = [0; 16];
+
+        // Save current offset, read start, restore offset.
+        let cur = self.inner.stream_position()?;
+        let len = io::copy(
+            // Accept shorter files but read at most 16 bytes.
+            &mut self.inner.by_ref().take(16),
+            &mut Cursor::new(&mut start[..]),
+        )?;
+        self.inner.seek(SeekFrom::Start(cur))?;
+
+        Ok(free_functions::guess_format_impl(&start[..len as usize]))
+    }
+
+    /// Read the image dimensions.
+    ///
+    /// Uses the current format to construct the correct reader for the format.
+    ///
+    /// If no format was determined, returns an `ImageError::Unsupported`.
+    pub fn into_dimensions(mut self) -> ImageResult<(u32, u32)> {
+        let format = self.require_format()?;
+        free_functions::image_dimensions_with_format_impl(self.inner, format)
+    }
+
+    /// Read the image (replaces `load`).
+    ///
+    /// Uses the current format to construct the correct reader for the format.
+    ///
+    /// If no format was determined, returns an `ImageError::Unsupported`.
+    pub fn decode(mut self) -> ImageResult<DynamicImage> {
+        let format = self.require_format()?;
+        free_functions::load_inner(self.inner, self.limits, format)
+    }
+
+    fn require_format(&mut self) -> ImageResult<ImageFormat> {
+        self.format.ok_or_else(|| {
+            ImageError::Unsupported(UnsupportedError::from_format_and_kind(
+                ImageFormatHint::Unknown,
+                UnsupportedErrorKind::Format(ImageFormatHint::Unknown),
+            ))
+        })
+    }
+}