[PDF] convert JPEG non compatible with jsPDF by ourselves (#837)

* [jsPdf] workaround for non compatibles JPEG

Closes #797

web/src/engine/exporters/PortableDocumentFormatExporter.ts

@@ -18,15 +18,43 @@ export class PortableDocumentFormatExporter extends MangaExporter {
             try {
                 const { width, height } = bitmap;
                 // Conversion of unsupported images via jsPDF is slow and produces a large PDF => Using own implementation of image conversion
-                const blob = pdfImageFormats.includes(data.type) ? data : await ConvertBitmap(bitmap, 'image/jpeg', 0.95);
-                return { width, height, data: new Uint8Array(await blob.arrayBuffer()) };
+                let buffer = new Uint8Array(await data.arrayBuffer());
+                buffer = await this.CheckImageCompatibility(data.type, buffer) ? buffer : new Uint8Array(await (await ConvertBitmap(bitmap, 'image/jpeg', 0.95)).arrayBuffer());
+                return { width, height, data: buffer };
             } finally {
                 bitmap.close();
             }
         }, Priority.Normal));
         return Promise.all(promises);
     }
 
+    private async CheckImageCompatibility(mimetype: string, buffer: Uint8Array): Promise<boolean> {
+        return mimetype === 'image/jpeg' ? this.IsCompatibleJPEG(buffer) : pdfImageFormats.includes(mimetype);
+    }
+
+    /**
+     * Test if JPEG data is compatible with JsPDF "headers check"
+     * @param imageData - Image buffer as Uint8Array
+     * @returns
+     */
+    private async IsCompatibleJPEG(imageData: Uint8Array): Promise<boolean> {
+        const jsPdfJpegHeaders =
+            [[0xff, 0xd8, 0xff, 0xe0, undefined, undefined, 0x4a, 0x46, 0x49, 0x46, 0x00], //JFIF
+                [0xff, 0xd8, 0xff, 0xe1, undefined, undefined, 0x45, 0x78, 0x69, 0x66, 0x00, 0x00], //Exif
+                [0xff, 0xd8, 0xff, 0xdb], //JPEG RAW
+                [0xff, 0xd8, 0xff, 0xee] //EXIF RAW
+            ];
+
+        return jsPdfJpegHeaders.some(jpegPattern => {
+            for (let index = 0; index < jpegPattern.length; index++) {
+                if (jpegPattern[index] !== undefined && jpegPattern[index] !== imageData[index]) {
+                    return false;
+                }
+            }
+            return true;
+        });
+    }
+
     public async Export(sourceFileList: Map<number, string>, targetDirectory: FileSystemDirectoryHandle, targetBaseName: string): Promise<void> {
         const pdf = new jsPDF({ unit: 'px' });
         pdf.deletePage(1);