Expose structured JPEG XL pixel limits

crates/jxl/src/decode.rs

@@ -56,7 +56,7 @@ fn decode_inner(bytes: &[u8], limits: DecodeLimits, output_color: OutputColor) -
     }
     let pixels = u64::from(width).saturating_mul(u64::from(height));
     if pixels > limits.max_pixels {
-        return Err(Error::LimitExceeded(format!("{width}×{height} image exceeds the {} pixel limit", limits.max_pixels)));
+        return Err(Error::PixelLimitExceeded { width, height, max_pixels: limits.max_pixels });
     }
 
     // `JxlImageBuilder::read` feeds the full input. Continue in bounded chunks so trailing frame

crates/jxl/src/lib.rs

@@ -100,6 +100,16 @@ pub enum Error {
     /// The image exceeds a caller supplied size or allocation limit.
     #[error("JPEG XL: limit exceeded: {0}")]
     LimitExceeded(String),
+    /// The encoded dimensions exceed the caller's pixel-count limit.
+    #[error("JPEG XL: image dimensions {width}×{height} exceed the {max_pixels} pixel limit")]
+    PixelLimitExceeded {
+        /// Encoded image width.
+        width: u32,
+        /// Encoded image height.
+        height: u32,
+        /// Maximum accepted pixel count.
+        max_pixels: u64,
+    },
     /// The image layout or samples are unsupported.
     #[error("JPEG XL: invalid image: {0}")]
     InvalidImage(String),

crates/jxl/tests/roundtrip.rs

@@ -70,7 +70,7 @@ fn decoder_enforces_input_and_pixel_limits() {
     let input_limit = DecodeLimits { max_input_bytes: encoded.len() - 1, ..DecodeLimits::default() };
     assert!(matches!(decode(&encoded, input_limit), Err(craft_jxl::Error::LimitExceeded(_))));
     let pixel_limit = DecodeLimits { max_pixels: 0, ..DecodeLimits::default() };
-    assert!(matches!(decode(&encoded, pixel_limit), Err(craft_jxl::Error::LimitExceeded(_))));
+    assert!(matches!(decode(&encoded, pixel_limit), Err(craft_jxl::Error::PixelLimitExceeded { width: 1, height: 1, max_pixels: 0 })));
 }
 
 #[test]