Decode images in parallel

src/main.rs

@@ -1,4 +1,5 @@
 use clap::{Parser, ValueHint};
+use image::DynamicImage;
 use log::info;
 use pdf_writer::{Content, Filter, Finish, Name, Pdf, Rect, Ref};
 use rayon::prelude::*;
@@ -56,20 +57,37 @@ struct ImageFile {
     pub data: Vec<u8>,
 }
 
+struct DecodedImageFile {
+    pub name: String,
+    pub data: Vec<u8>,
+    pub image: DynamicImage,
+}
+
+impl From<&ImageFile> for DecodedImageFile {
+    fn from(value: &ImageFile) -> Self {
+        let image = image::load_from_memory(&value.data).unwrap();
+        Self {
+            name: value.name.clone(),
+            data: value.data.clone(),
+            image,
+        }
+    }
+}
+
 fn convert_cbz(cbz_path: &Path, output_dir: &Path) -> Result<(), Box<dyn std::error::Error>> {
     info!("Converting {:?}", cbz_path);
 
     let a4 = Rect::new(0.0, 0.0, 595.0, 842.0);
 
     let mut zip = ZipArchive::new(File::open(cbz_path)?)?;
-    let mut images = Vec::new();
+    let mut files = Vec::new();
     for i in 0..zip.len() {
         let mut file = zip.by_index(i)?;
         let mut image_data = Vec::new();
         let name = file.enclosed_name().expect("Failed to read file name");
         if name.extension() == Some(OsStr::new("jpg")) {
             file.read_to_end(&mut image_data)?;
-            images.push(ImageFile {
+            files.push(ImageFile {
                 name: name
                     .file_name()
                     .expect("Failed to read file name")
@@ -80,6 +98,11 @@ fn convert_cbz(cbz_path: &Path, output_dir: &Path) -> Result<(), Box<dyn std::er
         }
     }
 
+    let mut images = Vec::new();
+    files
+        .par_iter()
+        .map(|f| DecodedImageFile::from(f))
+        .collect_into_vec(&mut images);
     images.par_sort_by_key(|img| img.name.clone());
 
     let mut pdf = Pdf::new();
@@ -98,7 +121,6 @@ fn convert_cbz(cbz_path: &Path, output_dir: &Path) -> Result<(), Box<dyn std::er
         pages.push(page_id);
         let mut page = pdf.page(page_id);
         let image_name = Name(b"Im1");
-        let dynamic = image::load_from_memory(&image.data).unwrap();
 
         page.media_box(a4);
         page.parent(page_tree_id);
@@ -108,8 +130,8 @@ fn convert_cbz(cbz_path: &Path, output_dir: &Path) -> Result<(), Box<dyn std::er
 
         let mut pdf_image = pdf.image_xobject(image_id, &image.data);
         pdf_image.filter(Filter::DctDecode);
-        pdf_image.width(dynamic.width() as i32);
-        pdf_image.height(dynamic.height() as i32);
+        pdf_image.width(image.image.width() as i32);
+        pdf_image.height(image.image.height() as i32);
         pdf_image.color_space().device_rgb();
         pdf_image.bits_per_component(8);
         pdf_image.finish();