fix: Extract filename and content type from headers in StreamReceiverHandler for XHR uploads (#22690)

StreamReceiverHandler.doHandleXhrFilePost() was using hardcoded "unknown" values for both filename and content type, even though the headers were available in the request.

This fix:
- Extracts filename from X-Filename header (with proper decoding)
- Extracts content type from Content-Type header
- Creates reusable helper methods in TransferUtil to avoid duplication with the existing XHR upload handling code (from commit 1c777e1)

Author: Artur-

flow-server/src/main/java/com/vaadin/flow/server/communication/StreamReceiverHandler.java

@@ -295,10 +295,10 @@ protected void doHandleXhrFilePost(VaadinSession session,
             StreamReceiver streamReceiver, StateNode owner, long contentLength)
             throws IOException {
 
-        // These are unknown in filexhr ATM, maybe add to Accept header that
-        // is accessible in portlets
-        final String filename = "unknown";
-        final String mimeType = filename;
+        String filename = TransferUtil.extractFilenameFromXhrRequest(request);
+        String mimeType = TransferUtil
+                .extractContentTypeFromXhrRequest(request);
+
         final InputStream stream = request.getInputStream();
 
         boolean success = false;

flow-server/src/main/java/com/vaadin/flow/server/communication/TransferUtil.java

@@ -172,21 +172,8 @@ public static void handleUpload(UploadHandler handler,
                     handler.responseHandled(false, response);
                 }
             } else {
-                // Extract filename from X-Filename header
-                // The filename is encoded using JavaScript's encodeURIComponent
-                String fileName = request.getHeader("X-Filename");
-
-                if (fileName == null || fileName.isEmpty()) {
-                    fileName = "unknown";
-                } else {
-                    // Decode the percent-encoded filename
-                    fileName = UrlUtil.decodeURIComponent(fileName);
-                }
-
-                String contentType = request.getHeader("Content-Type");
-                if (contentType == null || contentType.isEmpty()) {
-                    contentType = "unknown";
-                }
+                String fileName = extractFilenameFromXhrRequest(request);
+                String contentType = extractContentTypeFromXhrRequest(request);
 
                 UploadEvent event = new UploadEvent(request, response, session,
                         fileName, request.getContentLengthLong(), contentType,
@@ -243,6 +230,49 @@ private static boolean isMultipartContent(VaadinRequest request) {
                 && contentType.toLowerCase().startsWith("multipart/");
     }
 
+    /**
+     * Extracts the filename from an XHR upload request.
+     * <p>
+     * The filename is extracted from the X-Filename header, which is set by
+     * vaadin-upload. The filename is encoded using JavaScript's
+     * encodeURIComponent and decoded on the server using
+     * {@link UrlUtil#decodeURIComponent(String)} (RFC 3986).
+     *
+     * @param request
+     *            the request to extract the filename from
+     * @return the decoded filename, or "unknown" if not present
+     */
+    public static String extractFilenameFromXhrRequest(VaadinRequest request) {
+        String fileName = request.getHeader("X-Filename");
+
+        if (fileName == null || fileName.isEmpty()) {
+            return "unknown";
+        }
+
+        // Decode the percent-encoded filename
+        return UrlUtil.decodeURIComponent(fileName);
+    }
+
+    /**
+     * Extracts the content type from an XHR upload request.
+     * <p>
+     * The content type is extracted from the Content-Type header.
+     *
+     * @param request
+     *            the request to extract the content type from
+     * @return the content type, or "unknown" if not present
+     */
+    public static String extractContentTypeFromXhrRequest(
+            VaadinRequest request) {
+        String contentType = request.getHeader("Content-Type");
+
+        if (contentType == null || contentType.isEmpty()) {
+            return "unknown";
+        }
+
+        return contentType;
+    }
+
     /**
      * Validates upload limits for the given parts.
      *

flow-server/src/test/java/com/vaadin/flow/server/communication/StreamReceiverHandlerTest.java

@@ -103,6 +103,7 @@ public class StreamReceiverHandlerTest {
 
     private boolean isGetContentLengthLongCalled;
     private String requestCharacterEncoding;
+    private String xFilenameHeader;
 
     @Before
     public void setup() throws Exception {
@@ -178,6 +179,12 @@ public String getHeader(String name) {
                 if ("content-length".equals(name.toLowerCase())) {
                     return contentLength;
                 }
+                if ("x-filename".equals(name.toLowerCase())) {
+                    return xFilenameHeader;
+                }
+                if ("content-type".equals(name.toLowerCase())) {
+                    return contentType;
+                }
                 return super.getHeader(name);
             }
 
@@ -468,4 +475,90 @@ public void doHandleMultipartFileUpload_IOExceptionIsThrown_exceptionIsNotRethro
         Mockito.verifyNoInteractions(errorHandler);
     }
 
+    @Test
+    public void doHandleXhrFilePost_filenameFromHeader_extractedCorrectly()
+            throws IOException {
+        xFilenameHeader = "test.txt";
+        outputStream = new ByteArrayOutputStream();
+
+        handler.doHandleXhrFilePost(session, request, response, streamReceiver,
+                stateNode, 6);
+
+        ArgumentCaptor<StreamVariable.StreamingEndEvent> endEventCaptor = ArgumentCaptor
+                .forClass(StreamVariable.StreamingEndEvent.class);
+        Mockito.verify(streamVariable)
+                .streamingFinished(endEventCaptor.capture());
+        Assert.assertEquals("test.txt",
+                endEventCaptor.getValue().getFileName());
+    }
+
+    @Test
+    public void doHandleXhrFilePost_encodedFilename_decodedCorrectly()
+            throws IOException {
+        // encodeURIComponent("my file åäö.txt") in JavaScript
+        xFilenameHeader = "my%20file%20%C3%A5%C3%A4%C3%B6.txt";
+        outputStream = new ByteArrayOutputStream();
+
+        handler.doHandleXhrFilePost(session, request, response, streamReceiver,
+                stateNode, 6);
+
+        ArgumentCaptor<StreamVariable.StreamingEndEvent> endEventCaptor = ArgumentCaptor
+                .forClass(StreamVariable.StreamingEndEvent.class);
+        Mockito.verify(streamVariable)
+                .streamingFinished(endEventCaptor.capture());
+        Assert.assertEquals("my file åäö.txt",
+                endEventCaptor.getValue().getFileName());
+    }
+
+    @Test
+    public void doHandleXhrFilePost_contentTypeFromHeader_extractedCorrectly()
+            throws IOException {
+        xFilenameHeader = "test.txt";
+        contentType = "text/plain";
+        outputStream = new ByteArrayOutputStream();
+
+        handler.doHandleXhrFilePost(session, request, response, streamReceiver,
+                stateNode, 6);
+
+        ArgumentCaptor<StreamVariable.StreamingEndEvent> endEventCaptor = ArgumentCaptor
+                .forClass(StreamVariable.StreamingEndEvent.class);
+        Mockito.verify(streamVariable)
+                .streamingFinished(endEventCaptor.capture());
+        Assert.assertEquals("text/plain",
+                endEventCaptor.getValue().getMimeType());
+    }
+
+    @Test
+    public void doHandleXhrFilePost_missingContentTypeHeader_defaultsToUnknown()
+            throws IOException {
+        xFilenameHeader = "test.txt";
+        contentType = null;
+        outputStream = new ByteArrayOutputStream();
+
+        handler.doHandleXhrFilePost(session, request, response, streamReceiver,
+                stateNode, 6);
+
+        ArgumentCaptor<StreamVariable.StreamingEndEvent> endEventCaptor = ArgumentCaptor
+                .forClass(StreamVariable.StreamingEndEvent.class);
+        Mockito.verify(streamVariable)
+                .streamingFinished(endEventCaptor.capture());
+        Assert.assertEquals("unknown", endEventCaptor.getValue().getMimeType());
+    }
+
+    @Test
+    public void doHandleXhrFilePost_missingFilenameHeader_defaultsToUnknown()
+            throws IOException {
+        xFilenameHeader = null;
+        outputStream = new ByteArrayOutputStream();
+
+        handler.doHandleXhrFilePost(session, request, response, streamReceiver,
+                stateNode, 6);
+
+        ArgumentCaptor<StreamVariable.StreamingEndEvent> endEventCaptor = ArgumentCaptor
+                .forClass(StreamVariable.StreamingEndEvent.class);
+        Mockito.verify(streamVariable)
+                .streamingFinished(endEventCaptor.capture());
+        Assert.assertEquals("unknown", endEventCaptor.getValue().getFileName());
+    }
+
 }