Fix File resolver when classloader provides URLs for directories

src/main/java/io/vertx/core/file/impl/FileResolverImpl.java

@@ -30,6 +30,7 @@
 import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.List;
+import java.util.jar.JarFile;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 
@@ -317,6 +318,17 @@ private File unpackFromJarURL(URL url, String fileName, ClassLoader cl) {
       switch (listOfEntries.size()) {
         case 1: {
           JarURLConnection conn = (JarURLConnection) url.openConnection();
+          if (conn.getContentLength() == -1) {
+            // the entry is a directory, so, it does not really exist.
+            // which means we cannot get the JarFile from the connection.
+
+            // In general, we should not be here, as the URL should be a directory, and we should not have a JarURLConnection.
+            // However, classloader implementation may provide an URL. In this case, we should not try to get the JarFile
+            // as it does not exist (or is not valid), and it will throw an exception.
+
+            // We still retrieve it from the cache if it exists (got unzipped before or concurrently)
+            return cache.getFile(fileName);
+          }
           ZipFile zip = conn.getJarFile();
           try {
             extractFilesFromJarFile(zip, fileName);

src/test/java/io/vertx/core/file/CustomJarFileResolverTest.java

@@ -67,6 +67,16 @@ protected URLConnection openConnection(URL u) throws IOException {
                 public JarFile getJarFile() throws IOException {
                   return new JarFile(files);
                 }
+
+                @Override
+                public int getContentLength() {
+                  try {
+                    return (int) getJarFile().getJarEntry(name).getSize();
+                  } catch (IOException e) {
+                    return -1;
+                  }
+                }
+
                 @Override
                 public void connect() throws IOException {
                 }

src/test/java/io/vertx/core/file/JarFileResolverWithOddClassLoaderTest.java

@@ -0,0 +1,61 @@
+package io.vertx.core.file;
+
+import io.vertx.core.file.impl.FileResolverImpl;
+import io.vertx.core.spi.file.FileResolver;
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+
+public class JarFileResolverWithOddClassLoaderTest {
+
+  @Test
+  public void testWhenClassLoaderReturnUrlsForDirectory() throws IOException {
+    File webjar = new File("src/test/resources/jars/wc-chatbot-0.1.2.jar");
+    Assertions.assertThat(webjar).exists();
+    ClassLoader cl = new DecoratedClassLoader(new URLClassLoader(new URL[]{webjar.toURI().toURL()}, Thread.currentThread().getContextClassLoader()));
+
+    ClassLoader orig = Thread.currentThread().getContextClassLoader();
+    try (FileResolver resolver = new FileResolverImpl()) {
+      Thread.currentThread().setContextClassLoader(cl);
+      String fileName = "META-INF/resources/_static/wc-chatbot/0.1.2/LICENSE";
+      File resolved = resolver.resolveFile(fileName);
+      Assertions.assertThat(resolved).exists();
+    } finally {
+      Thread.currentThread().setContextClassLoader(orig);
+    }
+  }
+
+  /**
+   * A somewhat broken classloader returning an URL even for directory included in the given jars.
+   */
+  private static class DecoratedClassLoader extends ClassLoader {
+    private final URL[] urls;
+
+    public DecoratedClassLoader(URLClassLoader parent) {
+      super(parent);
+      this.urls = parent.getURLs();
+    }
+
+    @Override
+    protected URL findResource(String name) {
+      if (! name.contains("META-INF/resources")) {
+        return super.findResource(name);
+      }
+      for (URL url : urls) {
+        if (url.getFile().endsWith(".jar")) {
+          try {
+            return new URL("jar:" + url + "!/" + name);
+          } catch (MalformedURLException e) {
+            return super.findResource(name);
+          }
+        }
+      }
+      return super.findResource(name);
+    }
+  }
+}