fix: restrict thumbnail generation to images in the attachment library (#7079)

#### What type of PR is this?
/kind improvement
/area core
/milestone 2.20.x

#### What this PR does / why we need it:
限制缩略图生成仅针对附件库中的图片，防止任意 URI 的生成行为带来的潜在攻击风险

先 merge #7077 后才能合并此 PR

#### Does this PR introduce a user-facing change?

```release-note
限制缩略图生成仅针对附件库中的图片，防止任意 URI 的生成行为带来的潜在攻击风险
```

application/src/main/java/run/halo/app/content/HtmlThumbnailSrcsetInjector.java

@@ -65,7 +65,7 @@ public class HtmlThumbnailSrcsetInjector {
      */
     public static Mono<String> generateSrcset(URI src, ThumbnailService thumbnailService) {
         return Flux.fromArray(ThumbnailSize.values())
-            .flatMap(size -> thumbnailService.generate(src, size)
+            .flatMap(size -> thumbnailService.get(src, size)
                 .map(thumbnail -> thumbnail.toString() + " " + size.getWidth() + "w")
             )
             .collect(StringBuilder::new, (builder, srcsetValue) -> {

application/src/main/java/run/halo/app/core/attachment/ThumbnailService.java

@@ -18,5 +18,16 @@ public interface ThumbnailService {
      */
     Mono<URI> generate(URI imageUri, ThumbnailSize size);
 
+    /**
+     * <p>Get thumbnail by the given image uri and size.</p>
+     * <p>It depends on the {@link #generate(URI, ThumbnailSize)} method, currently the thumbnail
+     * generation is limited to the attachment service, that is, the thumbnail is strongly
+     * associated with the attachment.</p>
+     *
+     * @return if thumbnail exists, return the thumbnail uri, otherwise return the original image
+     * uri
+     */
+    Mono<URI> get(URI imageUri, ThumbnailSize size);
+
     Mono<Void> delete(URI imageUri);
 }

application/src/main/java/run/halo/app/core/attachment/impl/ThumbnailServiceImpl.java

@@ -72,6 +72,13 @@ public class ThumbnailServiceImpl implements ThumbnailService {
             });
     }
 
+    @Override
+    public Mono<URI> get(URI imageUri, ThumbnailSize size) {
+        return fetchThumbnail(imageUri, size)
+            .map(thumbnail -> URI.create(thumbnail.getSpec().getThumbnailUri()))
+            .defaultIfEmpty(imageUri);
+    }
+
     @Override
     public Mono<Void> delete(URI imageUri) {
         Assert.notNull(imageUri, "Image uri must not be null");

application/src/main/java/run/halo/app/core/endpoint/theme/ThumbnailEndpoint.java

@@ -66,7 +66,7 @@ public class ThumbnailEndpoint implements CustomEndpoint {
 
     private Mono<ServerResponse> getThumbnailByUri(ServerRequest request) {
         var query = new ThumbnailQuery(request.queryParams());
-        return thumbnailService.generate(query.getUri(), query.getSize())
+        return thumbnailService.get(query.getUri(), query.getSize())
             .filterWhen(uri -> isAccessible(request, uri))
             .defaultIfEmpty(query.getUri())
             .flatMap(uri -> ServerResponse.temporaryRedirect(uri).build());

application/src/main/java/run/halo/app/theme/finders/impl/ThumbnailFinderImpl.java

@@ -18,7 +18,7 @@ public class ThumbnailFinderImpl implements ThumbnailFinder {
     @Override
     public Mono<String> gen(String uriStr, String size) {
         return Mono.fromSupplier(() -> URI.create(uriStr))
-            .flatMap(uri -> thumbnailService.generate(uri, ThumbnailSize.fromName(size)))
+            .flatMap(uri -> thumbnailService.get(uri, ThumbnailSize.fromName(size)))
             .map(URI::toString)
             .onErrorResume(Throwable.class, e -> {
                 log.debug("Failed to generate thumbnail for [{}], error: [{}]", uriStr,

application/src/test/java/run/halo/app/core/endpoint/theme/ThumbnailEndpointTest.java

@@ -39,7 +39,7 @@ class ThumbnailEndpointTest {
 
     @Test
     void thumbnailUriNotAccessible() {
-        when(thumbnailService.generate(any(), any()))
+        when(thumbnailService.get(any(), any()))
             .thenReturn(Mono.just(URI.create("/thumbnail-not-found.png")));
         webClient.get()
             .uri("/thumbnails/-/via-uri?size=l&uri=/myavatar.png")

application/src/test/java/run/halo/app/theme/finders/impl/ThumbnailFinderImplTest.java

@@ -42,13 +42,13 @@ class ThumbnailFinderImplTest {
 
     @Test
     void shouldGenWhenUriIsValid() {
-        when(thumbnailService.generate(any(), any()))
+        when(thumbnailService.get(any(), any()))
             .thenReturn(Mono.just(URI.create("/test-thumb.jpg")));
         thumbnailFinder.gen("/test.jpg", "l")
             .as(StepVerifier::create)
             .expectNext("/test-thumb.jpg")
             .verifyComplete();
 
-        verify(thumbnailService).generate(any(), any());
+        verify(thumbnailService).get(any(), any());
     }
 }