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script: Let canvas serialization to image fail gracefully (#37184)

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Instead of panicking when serialization of canvas to image data (whether
through `toBlob()` or via `toDataURL()`), properly handle failed
serialization. This is an implementation of the appropriate error
handling from the specification text.

Testing: This change includes a new Serov-specific test, because it is
impossible to know what the canvas size limits are of all browsers.
Fixes: #36840.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This commit is contained in:
Martin Robinson 2025-05-29 18:09:05 +02:00 • committed by GitHub
parent 36e4886da1
commit 559ba4b3ee
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3 changed files with 100 additions and 40 deletions
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102
components/script/dom/htmlcanvaselement.rs
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@ -16,7 +16,7 @@ use html5ever::{LocalName, Prefix, local_name, ns};
use image::codecs::jpeg::JpegEncoder;
use image::codecs::png::PngEncoder;
use image::codecs::webp::WebPEncoder;
use image::{ColorType, ImageEncoder};
use image::{ColorType, ImageEncoder, ImageError};
#[cfg(feature = "webgpu")]
use ipc_channel::ipc::{self as ipcchan};
use js::error::throw_type_error;
@ -391,7 +391,7 @@ impl HTMLCanvasElement {
quality: Option<f64>,
snapshot: &Snapshot,
encoder: &mut W,
) {
) -> Result<(), ImageError> {
// We can't use self.Width() or self.Height() here, since the size of the canvas
// may have changed since the snapshot was created. Truncating the dimensions to a
// u32 can't panic, since the data comes from a canvas which is always smaller than
@ -404,9 +404,7 @@ impl HTMLCanvasElement {
EncodedImageType::Png => {
// FIXME(nox): https://github.com/image-rs/image-png/issues/86
// FIXME(nox): https://github.com/image-rs/image-png/issues/87
PngEncoder::new(encoder)
.write_image(canvas_data, width, height, ColorType::Rgba8)
.unwrap();
PngEncoder::new(encoder).write_image(canvas_data, width, height, ColorType::Rgba8)
},
EncodedImageType::Jpeg => {
let jpeg_encoder = if let Some(quality) = quality {
@ -424,16 +422,16 @@ impl HTMLCanvasElement {
JpegEncoder::new(encoder)
};
jpeg_encoder
.write_image(canvas_data, width, height, ColorType::Rgba8)
.unwrap();
jpeg_encoder.write_image(canvas_data, width, height, ColorType::Rgba8)
},
EncodedImageType::Webp => {
// No quality support because of https://github.com/image-rs/image/issues/1984
WebPEncoder::new_lossless(encoder)
.write_image(canvas_data, width, height, ColorType::Rgba8)
.unwrap();
WebPEncoder::new_lossless(encoder).write_image(
canvas_data,
width,
height,
ColorType::Rgba8,
)
},
}
}
@ -522,17 +520,22 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
mime_type: DOMString,
quality: HandleValue,
) -> Fallible<USVString> {
// Step 1.
// Step 1: If this canvas element's bitmap's origin-clean flag is set to false,
// then throw a "SecurityError" DOMException.
if !self.origin_is_clean() {
return Err(Error::Security);
}
// Step 2.
// Step 2: If this canvas element's bitmap has no pixels (i.e. either its
// horizontal dimension or its vertical dimension is zero), then return the string
// "data:,". (This is the shortest data: URL; it represents the empty string in a
// text/plain resource.)
if self.Width() == 0 || self.Height() == 0 {
return Ok(USVString("data:,".into()));
}
// Step 3.
// Step 3: Let file be a serialization of this canvas element's bitmap as a file,
// passing type and quality if given.
let Some(mut snapshot) = self.get_image_data() else {
return Ok(USVString("data:,".into()));
};
@ -557,12 +560,20 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
&base64::engine::general_purpose::STANDARD,
);
self.encode_for_mime_type(
&image_type,
Self::maybe_quality(quality),
&snapshot,
&mut encoder,
);
if self
.encode_for_mime_type(
&image_type,
Self::maybe_quality(quality),
&snapshot,
&mut encoder,
)
.is_err()
{
// Step 4. If file is null, then return "data:,".
return Ok(USVString("data:,".into()));
}
// Step 5. Return a data: URL representing file. [RFC2397]
encoder.into_inner();
Ok(USVString(url))
}
@ -610,26 +621,37 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
return error!("Expected blob callback, but found none!");
};
if let Some(mut snapshot) = result {
snapshot.transform(
snapshot::AlphaMode::Transparent{ premultiplied: false },
snapshot::PixelFormat::RGBA
);
// Step 4.1
// If result is non-null, then set result to a serialization of result as a file with
// type and quality if given.
let mut encoded: Vec<u8> = vec![];
this.encode_for_mime_type(&image_type, quality, &snapshot, &mut encoded);
let blob_impl = BlobImpl::new_from_bytes(encoded, image_type.as_mime_type());
// Step 4.2.1 Set result to a new Blob object, created in the relevant realm of this canvas element
let blob = Blob::new(&this.global(), blob_impl, CanGc::note());
// Step 4.2.2 Invoke callback with « result » and "report".
let _ = callback.Call__(Some(&blob), ExceptionHandling::Report, CanGc::note());
} else {
let Some(mut snapshot) = result else {
let _ = callback.Call__(None, ExceptionHandling::Report, CanGc::note());
}
return;
};
snapshot.transform(
snapshot::AlphaMode::Transparent{ premultiplied: false },
snapshot::PixelFormat::RGBA
);
// Step 4.1: If result is non-null, then set result to a serialization of
// result as a file with type and quality if given.
// Step 4.2: Queue an element task on the canvas blob serialization task
// source given the canvas element to run these steps:
let mut encoded: Vec<u8> = vec![];
let blob_impl;
let blob;
let result = match this.encode_for_mime_type(&image_type, quality, &snapshot, &mut encoded) {
Ok(..) => {
// Step 4.2.1: If result is non-null, then set result to a new Blob
// object, created in the relevant realm of this canvas element,
// representing result. [FILEAPI]
blob_impl = BlobImpl::new_from_bytes(encoded, image_type.as_mime_type());
blob = Blob::new(&this.global(), blob_impl, CanGc::note());
Some(&*blob)
}
Err(..) => None,
};
// Step 4.2.2: Invoke callback with « result » and "report".
let _ = callback.Call__(result, ExceptionHandling::Report, CanGc::note());
}));
Ok(())