fix: Reuse existing filesystem (#12346)

Modified cherry-pick of https://github.com/vaadin/flow/pull/11428

2 files changed, 53 insertions, 2 deletions

diff --git a/server/src/main/java/com/vaadin/server/VaadinServlet.java b/server/src/main/java/com/vaadin/server/VaadinServlet.java
index f0ec0427bf..ce69d9204c 100644
--- a/server/src/main/java/com/vaadin/server/VaadinServlet.java
+++ b/server/src/main/java/com/vaadin/server/VaadinServlet.java
@@ -39,6 +39,7 @@ import java.net.URLDecoder;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.FileSystem;
+import java.nio.file.FileSystemAlreadyExistsException;
 import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -1382,13 +1383,25 @@ public class VaadinServlet extends HttpServlet implements Constants {
                 return FileSystems.getFileSystem(resourceURI);
             }
             // Opened filesystem is for the file to get the correct provider
-            FileSystem fileSystem = FileSystems.newFileSystem(resourceURI,
-                    Collections.emptyMap());
+            FileSystem fileSystem = getNewOrExistingFileSystem(resourceURI);
             OPEN_FILE_SYSTEMS.put(fileURI, 1);
             return fileSystem;
         }
     }
 
+    private FileSystem getNewOrExistingFileSystem(URI resourceURI)
+            throws IOException {
+        try {
+            return FileSystems.newFileSystem(resourceURI,
+                    Collections.emptyMap());
+        } catch (FileSystemAlreadyExistsException fsaee) {
+            getLogger().log(Level.FINER,
+                    "Tried to get new filesystem, but it already existed for target uri.",
+                    fsaee);
+            return FileSystems.getFileSystem(resourceURI);
+        }
+    }
+
     // Package protected for feature verification purpose
     void closeFileSystem(URI resourceURI) {
         synchronized (FILE_SYSTEM_LOCK) {
diff --git a/server/src/test/java/com/vaadin/server/VaadinServletTest.java b/server/src/test/java/com/vaadin/server/VaadinServletTest.java
index 2c318e0897..4eb97d4453 100644
--- a/server/src/test/java/com/vaadin/server/VaadinServletTest.java
+++ b/server/src/test/java/com/vaadin/server/VaadinServletTest.java
@@ -10,11 +10,13 @@ import java.io.File;
 import java.io.IOException;
 import java.net.URISyntaxException;
 import java.net.URL;
+import java.nio.file.FileSystem;
 import java.nio.file.FileSystemNotFoundException;
 import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
@@ -322,6 +324,42 @@ public class VaadinServletTest {
     }
 
     @Test
+    public void openFileServerExistsForZip_openingNewDoesNotFail()
+            throws IOException, URISyntaxException {
+        assertTrue("Can not run concurrently with other test",
+                VaadinServlet.OPEN_FILE_SYSTEMS.isEmpty());
+
+        VaadinServlet servlet = new VaadinServlet();
+
+        final TemporaryFolder folder = TemporaryFolder.builder().build();
+        folder.create();
+
+        try {
+            Path tempArchive = createJAR(folder).toPath();
+
+            final FileSystem fileSystem = FileSystems
+                    .newFileSystem(
+                            new URL("jar:file:///" + tempArchive.toString()
+                                    .replaceAll("\\\\", "/") + "!/").toURI(),
+                            Collections.emptyMap());
+
+            final URL folderResourceURL = new URL("jar:file:///"
+                    + tempArchive.toString().replaceAll("\\\\", "/")
+                    + "!/VAADIN");
+
+            try {
+                servlet.getFileSystem(folderResourceURL.toURI());
+            } finally {
+                servlet.closeFileSystem(folderResourceURL.toURI());
+                fileSystem.close();
+            }
+        } finally {
+            folder.delete();
+        }
+
+    }
+
+    @Test
     public void openingJarFileSystemForDifferentFilesInSameJar_existingFileSystemIsUsed()
             throws IOException, URISyntaxException, ServletException {
         assertTrue("Can not run concurrently with other test",