FileDownloader for starting downloads with any component (#9524)

* Based on patch by Pekka Hyvönen

Change-Id: I9263078ffc624f9cabec6c25264920dfdb430efe

1 files changed, 127 insertions, 0 deletions

diff --git a/server/src/com/vaadin/server/FileDownloader.java b/server/src/com/vaadin/server/FileDownloader.java
new file mode 100644
index 0000000000..a07c0d3ed1
--- /dev/null
+++ b/server/src/com/vaadin/server/FileDownloader.java
@@ -0,0 +1,127 @@
+package com.vaadin.server;
+
+import java.io.IOException;
+
+import com.vaadin.ui.AbstractComponent;
+
+/**
+ * Extension that starts a download when the extended component is clicked. This
+ * is used to overcome two challenges:
+ * <ul>
+ * <li>Resource should be bound to a component to allow it to be garbage
+ * collected when there are no longer any ways of reaching the resource.</li>
+ * <li>Download should be started directly when the user clicks e.g. a Button
+ * without going through a server-side click listener to avoid triggering
+ * security warnings in some browsers.</li>
+ * </ul>
+ * <p>
+ * Please note that the download will be started in an iframe, which means that
+ * care should be taken to avoid serving content types that might make the
+ * browser attempt to show the content using a plugin instead of downloading it.
+ * Connector resources (e.g. {@link FileResource} and {@link ClassResource})
+ * will automatically be served using a
+ * <code>Content-Type: application/octet-stream</code> header unless
+ * {@link #setOverrideContentType(boolean)} has been set to <code>false</code>
+ * while files served in other ways, (e.g. {@link ExternalResource} or
+ * {@link ThemeResource}) will not automatically get this treatment.
+ * </p>
+ * 
+ * @author Vaadin Ltd
+ * @since 7.0.0
+ */
+public class FileDownloader extends AbstractExtension {
+
+    private boolean overrideContentType = true;
+
+    /**
+     * Creates a new file downloader for the given resource. To use the
+     * downloader, you should also {@link #extend(AbstractClientConnector)} the
+     * component.
+     * 
+     * @param resource
+     *            the resource to download when the user clicks the extended
+     *            component.
+     */
+    public FileDownloader(Resource resource) {
+        if (resource == null) {
+            throw new IllegalArgumentException("resource may not be null");
+        }
+        setResource("dl", resource);
+    }
+
+    public void extend(AbstractComponent target) {
+        super.extend(target);
+    }
+
+    /**
+     * Gets the resource set for download.
+     * 
+     * @return the resource that will be downloaded if clicking the extended
+     *         component
+     */
+    public Resource getFileDownloadResource() {
+        return getResource("dl");
+    }
+
+    /**
+     * Sets whether the content type of served resources should be overriden to
+     * <code>application/octet-stream</code> to reduce the risk of a browser
+     * plugin choosing to display the resource instead of downloading it. This
+     * is by default set to <code>true</code>.
+     * <p>
+     * Please note that this only affects Connector resources (e.g.
+     * {@link FileResource} and {@link ClassResource}) but not other resource
+     * types (e.g. {@link ExternalResource} or {@link ThemeResource}).
+     * </p>
+     * 
+     * @param overrideContentType
+     *            <code>true</code> to override the content type if possible;
+     *            <code>false</code> to use the original content type.
+     */
+    public void setOverrideContentType(boolean overrideContentType) {
+        this.overrideContentType = overrideContentType;
+    }
+
+    /**
+     * Checks whether the content type should be overridden.
+     * 
+     * @see #setOverrideContentType(boolean)
+     * 
+     * @return <code>true</code> if the content type will be overridden when
+     *         possible; <code>false</code> if the original content type will be
+     *         used.
+     */
+    public boolean isOverrideContentType() {
+        return overrideContentType;
+    }
+
+    @Override
+    public boolean handleConnectorRequest(VaadinRequest request,
+            VaadinResponse response, String path) throws IOException {
+        if (!path.matches("dl(/.*)?")) {
+            // Ignore if it isn't for us
+            return false;
+        }
+
+        Resource resource = getFileDownloadResource();
+        if (resource instanceof ConnectorResource) {
+            DownloadStream stream = ((ConnectorResource) resource).getStream();
+
+            if (stream.getParameter("Content-Disposition") == null) {
+                // Content-Disposition: attachment generally forces download
+                stream.setParameter("Content-Disposition",
+                        "attachment; filename=\"" + stream.getFileName() + "\"");
+            }
+
+            // Content-Type to block eager browser plug-ins from hijacking the
+            // file
+            if (isOverrideContentType()) {
+                stream.setContentType("application/octet-stream;charset=UTF-8");
+            }
+            stream.writeResponse(request, response);
+            return true;
+        } else {
+            return false;
+        }
+    }
+}