fix: image not found in README.md while mdbook build

Since commit 1ca2a86, all assets embed to top directory in book and
could not be found on reading. Another issue is not handle README.md
path correctly while applying mdbook link preprocessor.

This commit fixes above issues and update an integration test to ensure assets
is embedded to expected path.

svg image is from https://commons.wikimedia.org/wiki/File:Epub_logo.svg

src/errors.rs

@@ -1,5 +1,5 @@
-use thiserror::Error;
 use std::path::PathBuf;
+use thiserror::Error;
 
 #[derive(Error, Debug)]
 pub enum Error {
@@ -42,6 +42,9 @@ pub enum Error {
     #[error(transparent)]
     Io(#[from] std::io::Error),
 
+    #[error(transparent)]
+    AssetOutsideSrcDir(#[from] std::path::StripPrefixError),
+
     #[error(transparent)]
     Book(#[from] mdbook::errors::Error),
     #[error(transparent)]

src/resources/asset.rs

@@ -82,14 +82,7 @@ impl Asset {
             return Err(Error::AssetFile(absolute_location));
         }
         // Use filename as embedded file path with content from absolute_location.
-        let binding = utils::normalize_path(Path::new(link));
-        debug!("Extracting file name from = {:?}, binding = '{binding:?}'", &full_filename.display());
-        let filename = if cfg!(target_os = "windows") {
-            binding.as_os_str().to_os_string()
-                .into_string().expect("Error getting filename for Local Asset").replace('\\', "/")
-        } else {
-            String::from(binding.as_path().to_str().unwrap())
-        };
+        let filename = full_filename.strip_prefix(src_dir)?;
 
         let asset = Asset::new(
             filename,
@@ -112,7 +105,13 @@ impl Asset {
     pub(crate) fn compute_asset_path_by_src_and_link(link: &str, chapter_dir: &PathBuf) -> PathBuf {
         let mut reassigned_asset_root: PathBuf = PathBuf::from(chapter_dir);
         let link_string = String::from(link);
-        // if chapter is a MD file, remove if from path
+        // mdbook built-in link preprocessor have `README.md` renamed and `index.md` is not exist
+        // strip the converted filename in the path 
+        if chapter_dir.ends_with("index.md") && !chapter_dir.exists() {
+            debug!("It seems a `README.md` chapter, adjust the chapter root.");
+            reassigned_asset_root.pop();
+        }
+        // if chapter is a MD file or not exist, remove if from path
         if chapter_dir.is_file() {
             reassigned_asset_root.pop();
         }

src/resources/resource.rs

@@ -48,9 +48,15 @@ pub(crate) fn find(ctx: &RenderContext) -> Result<HashMap<String, Asset>, Error>
                     continue;
                 }
                 for link in find_assets_in_markdown(&ch.content)? {
-                    let asset = match Url::parse(&link) {
-                        Ok(url) => Asset::from_url(url, &ctx.destination),
-                        Err(_) => Asset::from_local(&link, &src_dir, ch.path.as_ref().unwrap()),
+                    let asset = if let Ok(url) = Url::parse(&link) {
+                        Asset::from_url(url, &ctx.destination)
+                    } else {
+                        let result = Asset::from_local(&link, &src_dir, ch.path.as_ref().unwrap());
+                        if let Err(Error::AssetOutsideSrcDir(_)) = result {
+                            warn!("Asset '{link}' is outside source dir '{src_dir:?}' and ignored");
+                            continue;
+                        };
+                        result
                     }?;
 
                     // that is CORRECT generation way

tests/dummy/src/02_advanced/README.md

@@ -0,0 +1,5 @@
+# README.md tests
+
+## image link
+
+![Awesome image in the same folder](Epub_logo.svg "Awesome")

tests/dummy/src/SUMMARY.md

@@ -2,3 +2,7 @@
 
 - [Chapter 1](./chapter_1.md)
   - [Getting started](01_getting_started/02_article.md)
+
+# Advanced
+
+- [README.md tests](./02_advanced/README.md)

tests/integration_tests.rs

@@ -130,12 +130,17 @@ fn look_for_chapter_1_heading() {
 fn rendered_document_contains_all_chapter_files_and_assets() {
     init_logging();
     debug!("rendered_document_contains_all_chapter_files_and_assets...");
-    let chapters = vec!["chapter_1.html", "rust-logo.png"];
+    let chapters = vec![
+        "chapter_1.html",
+        "rust-logo.png",
+        "02_advanced/README.html",
+        "02_advanced/Epub_logo.svg",
+    ];
     let mut doc = generate_epub().unwrap();
     debug!("Number of internal epub resources = {:?}", doc.0.resources);
     // number of internal epub resources for dummy test book
-    assert_eq!(10, doc.0.resources.len());
-    assert_eq!(2, doc.0.spine.len());
+    assert_eq!(12, doc.0.resources.len());
+    assert_eq!(3, doc.0.spine.len());
     assert_eq!(doc.0.mdata("title").unwrap(), "DummyBook");
     assert_eq!(doc.0.mdata("language").unwrap(), "en");
     debug!(