assets: custom response when asset isn't found fix #3501

Author: jknack

docs/asciidoc/static-files.adoc

@@ -221,3 +221,38 @@ specify a function via javadoc:AssetHandler[cacheControl, java.util.Function]:
       })
 }
 ----
+
+The asset handler generates a `404` response code when requested path is not found. You can change this by throwing
+an exception or generating any other content you want:
+
+
+.Custom not found:
+[source, java, role="primary"]
+----
+{
+  AssetSource www = AssetSource.create(Paths.get("www"));
+  assets("/static/*", new AssetHandler(www)
+      .notFound(ctx -> {
+        throw new MyAssetException();
+      }));
+
+  error(MyAssetException.class, (ctx, cause, code) -> {
+    // render MyAssetException as you want
+  });
+}
+----
+
+.Kotlin
+[source, kotlin, role="secondary"]
+----
+{
+  val www = AssetSource.create(Paths.get("www"))
+  assets("/static/*", AssetHandler(www)
+      .notFound { _ ->
+        throw MyAssetException()
+      })
+ error(MyAssetException::class) {
+    // render MyAssetException as you want
+ }
+}
+----

jooby/src/main/java/io/jooby/handler/AssetHandler.java

@@ -14,10 +14,8 @@
 import java.util.function.Function;
 
 import edu.umd.cs.findbugs.annotations.NonNull;
-import io.jooby.Context;
-import io.jooby.MediaType;
-import io.jooby.Route;
-import io.jooby.StatusCode;
+import edu.umd.cs.findbugs.annotations.Nullable;
+import io.jooby.*;
 
 /**
  * Handler for static resources represented by the {@link Asset} contract.
@@ -28,6 +26,8 @@
  * @since 2.0.0
  */
 public class AssetHandler implements Route.Handler {
+  private static final SneakyThrows.Consumer<Context> NOT_FOUND =
+      ctx -> ctx.send(StatusCode.NOT_FOUND);
   private static final int ONE_SEC = 1000;
 
   private final AssetSource[] sources;
@@ -41,6 +41,7 @@ public class AssetHandler implements Route.Handler {
   private Function<String, CacheControl> cacheControl = path -> defaults;
 
   private Function<Asset, MediaType> mediaTypeResolver = Asset::getContentType;
+  private SneakyThrows.Consumer<Context> notFound = NOT_FOUND;
 
   /**
    * Creates a new asset handler that fallback to the given fallback asset when the asset is not
@@ -82,7 +83,7 @@ public Object apply(@NonNull Context ctx) throws Exception {
       }
       // Still null?
       if (asset == null) {
-        ctx.send(StatusCode.NOT_FOUND);
+        notFound.accept(ctx);
         return ctx;
       } else {
         resolvedPath = fallback;
@@ -230,7 +231,19 @@ public AssetHandler cacheControl(@NonNull Function<String, CacheControl> cacheCo
     return this;
   }
 
-  private Asset resolve(String filepath) {
+  /**
+   * Sets a custom handler for <code>404</code> asset/resource. By default, generates a <code>404
+   * </code> status code response.
+   *
+   * @param handler Handler.
+   * @return This handler.
+   */
+  public AssetHandler notFound(@NonNull SneakyThrows.Consumer<Context> handler) {
+    this.notFound = handler;
+    return this;
+  }
+
+  private @Nullable Asset resolve(String filepath) {
     for (AssetSource source : sources) {
       Asset asset = source.resolve(filepath);
       if (asset != null) {
@@ -243,7 +256,7 @@ private Asset resolve(String filepath) {
   @Override
   public void setRoute(Route route) {
     List<String> keys = route.getPathKeys();
-    this.filekey = keys.size() == 0 ? route.getPattern().substring(1) : keys.get(0);
+    this.filekey = keys.isEmpty() ? route.getPattern().substring(1) : keys.get(0);
     // NOTE: It send an inputstream we don't need a renderer
     route.setReturnType(Context.class);
   }

tests/src/test/java/io/jooby/i3501/Issue3501.java

@@ -0,0 +1,47 @@
+/*
+ * Jooby https://jooby.io
+ * Apache License Version 2.0 https://jooby.io/LICENSE.txt
+ * Copyright 2014 Edgar Espina
+ */
+package io.jooby.i3501;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.jooby.handler.AssetHandler;
+import io.jooby.handler.AssetSource;
+import io.jooby.junit.ServerTest;
+import io.jooby.junit.ServerTestRunner;
+
+public class Issue3501 {
+
+  @ServerTest
+  public void assetHandlerShouldGenerateCustom404Response(ServerTestRunner runner) {
+    runner
+        .define(
+            app -> {
+              app.assets(
+                  "/issue3501/*",
+                  new AssetHandler(AssetSource.create(getClass().getClassLoader(), "/static"))
+                      .notFound(
+                          ctx -> {
+                            throw new UnsupportedOperationException();
+                          }));
+
+              app.error(
+                  UnsupportedOperationException.class,
+                  ((ctx, cause, code) -> {
+                    ctx.send(cause.getClass().getName());
+                  }));
+            })
+        .ready(
+            http -> {
+              http.get(
+                  "/issue3501/index.js",
+                  rsp -> {
+                    assertEquals(
+                        UnsupportedOperationException.class.getName(), rsp.body().string());
+                    assertEquals(500, rsp.code());
+                  });
+            });
+  }
+}