[grid] Support file downloads on the node

Fixes: #9218

On the node, set the directory to where the browser 
will download files to via:

a. The CLI argument `--downloads-dir` (or)
b. via the Toml syntax of 

```
[node]
downloads-dir = "/path/to/dir/goes/here"
```

The GET end-points that will support file 
download would be:

* `/session/:sessionId:/file?filename=`
* `/session/:sessionId:/se/file?filename=`

Author: krmahadevan

java/src/org/openqa/selenium/grid/node/DownloadFile.java

@@ -0,0 +1,41 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.grid.node;
+
+import java.io.UncheckedIOException;
+import org.openqa.selenium.internal.Require;
+import org.openqa.selenium.remote.SessionId;
+import org.openqa.selenium.remote.http.HttpHandler;
+import org.openqa.selenium.remote.http.HttpRequest;
+import org.openqa.selenium.remote.http.HttpResponse;
+
+class DownloadFile implements HttpHandler {
+
+  private final Node node;
+  private final SessionId id;
+
+  DownloadFile(Node node, SessionId id) {
+    this.node = Require.nonNull("Node", node);
+    this.id = Require.nonNull("Session id", id);
+  }
+
+  @Override
+  public HttpResponse execute(HttpRequest req) throws UncheckedIOException {
+    return node.downloadFile(req, id);
+  }
+}

java/src/org/openqa/selenium/grid/node/Node.java

@@ -150,6 +150,12 @@ protected Node(Tracer tracer, NodeId id, URI uri, Secret registrationSecret) {
       post("/session/{sessionId}/se/file")
         .to(params -> new UploadFile(this, sessionIdFrom(params)))
         .with(spanDecorator("node.upload_file")),
+      get("/session/{sessionId}/file")
+        .to(params -> new DownloadFile(this, sessionIdFrom(params)))
+        .with(spanDecorator("node.download_file")),
+      get("/session/{sessionId}/se/file")
+        .to(params -> new DownloadFile(this, sessionIdFrom(params)))
+        .with(spanDecorator("node.download_file")),
       get("/se/grid/node/owner/{sessionId}")
         .to(params -> new IsSessionOwner(this, sessionIdFrom(params)))
         .with(spanDecorator("node.is_session_owner").andThen(requiresSecret)),
@@ -216,6 +222,8 @@ public TemporaryFilesystem getTemporaryFilesystem(SessionId id) throws IOExcepti
 
   public abstract HttpResponse uploadFile(HttpRequest req, SessionId id);
 
+  public abstract HttpResponse downloadFile(HttpRequest req, SessionId id);
+
   public abstract void stop(SessionId id) throws NoSuchSessionException;
 
   public abstract boolean isSessionOwner(SessionId id);

java/src/org/openqa/selenium/grid/node/config/NodeFlags.java

@@ -221,6 +221,14 @@ public class NodeFlags implements HasRoles {
     example = DEFAULT_NODE_IMPLEMENTATION)
   private String nodeImplementation = DEFAULT_NODE_IMPLEMENTATION;
 
+  @Parameter(
+    names = {"--downloads-dir"},
+    description = "The default location wherein all browser triggered file downloads would be "
+      + "available to be retrieved from. This is usually the directory that you configure in "
+      + "your browser as the default location for storing downloaded files.")
+  @ConfigValue(section = NODE_SECTION, name = "downloads-dir", example = "")
+  private String downloadsDir = "";
+
   @Override
   public Set<Role> getRoles() {
     return Collections.singleton(NODE_ROLE);

java/src/org/openqa/selenium/grid/node/config/NodeOptions.java

@@ -148,6 +148,10 @@ public Optional<URI> getPublicGridUri() {
     }
   }
 
+  public Optional<String> getDownloadsDirectory() {
+    return config.get(NODE_SECTION, "downloads-dir");
+  }
+
   public Node getNode() {
     return config.getClass(NODE_SECTION, "implementation", Node.class, DEFAULT_NODE_IMPLEMENTATION);
   }

java/src/org/openqa/selenium/grid/node/k8s/OneShotNode.java

@@ -307,6 +307,11 @@ public HttpResponse uploadFile(HttpRequest req, SessionId id) {
     return null;
   }
 
+  @Override
+  public HttpResponse downloadFile(HttpRequest req, SessionId id) {
+    return null;
+  }
+
   @Override
   public void stop(SessionId id) throws NoSuchSessionException {
     LOG.info("Stop has been called: " + id);

java/src/org/openqa/selenium/grid/node/local/LocalNode.java

@@ -122,6 +122,7 @@ public class LocalNode extends Node {
   private final int maxSessionCount;
   private final int configuredSessionCount;
   private final boolean cdpEnabled;
+  private final String downloadsDir;
 
   private final boolean bidiEnabled;
   private final AtomicBoolean drainAfterSessions = new AtomicBoolean();
@@ -145,7 +146,8 @@ private LocalNode(
     Duration sessionTimeout,
     Duration heartbeatPeriod,
     List<SessionSlot> factories,
-    Secret registrationSecret) {
+    Secret registrationSecret,
+    String downloadsDir) {
     super(tracer, new NodeId(UUID.randomUUID()), uri, registrationSecret);
 
     this.bus = Require.nonNull("Event bus", bus);
@@ -162,6 +164,7 @@ private LocalNode(
     this.sessionCount.set(drainAfterSessionCount);
     this.cdpEnabled = cdpEnabled;
     this.bidiEnabled = bidiEnabled;
+    this.downloadsDir = Optional.ofNullable(downloadsDir).orElse("");
 
     this.healthCheck = healthCheck == null ?
                        () -> {
@@ -176,8 +179,10 @@ private LocalNode(
       .ticker(ticker)
       .removalListener((RemovalListener<SessionId, TemporaryFilesystem>) notification -> {
         TemporaryFilesystem tempFS = notification.getValue();
-        tempFS.deleteTemporaryFiles();
-        tempFS.deleteBaseDir();
+        if (tempFS != null) {
+          tempFS.deleteTemporaryFiles();
+          tempFS.deleteBaseDir();
+        }
       })
       .build();
 
@@ -471,6 +476,49 @@ public HttpResponse executeWebDriverCommand(HttpRequest req) {
     return toReturn;
   }
 
+  @Override
+  public HttpResponse downloadFile(HttpRequest req, SessionId id) {
+    // When the session is running in a Docker container, the download file command
+    // needs to be forwarded to the container as well.
+    SessionSlot slot = currentSessions.getIfPresent(id);
+    if (slot != null && slot.getSession() instanceof DockerSession) {
+      return executeWebDriverCommand(req);
+    }
+    if (this.downloadsDir.isEmpty()) {
+      throw new WebDriverException(
+        "Please specify the directory that would contain downloaded files and restart the node.");
+    }
+    File dir = new File(this.downloadsDir);
+    if (!dir.exists()) {
+      throw new WebDriverException(
+        String.format("Cannot locate downloads directory %s.", downloadsDir));
+    }
+    if (!dir.isDirectory()) {
+      throw new WebDriverException(String.format("Invalid directory: %s.",downloadsDir));
+    }
+    String filename = req.getQueryParameter("filename");
+    try {
+      File[] allFiles = Optional.ofNullable(
+        dir.listFiles((dir1, name) -> name.equals(filename))
+      ).orElse(new File[]{});
+      if (allFiles.length == 0) {
+        throw new WebDriverException(
+          String.format("Cannot find file [%s] in directory %s.", filename, downloadsDir));
+      }
+      if (allFiles.length != 1) {
+        throw new WebDriverException(
+          String.format("Expected there to be only 1 file. There were: %s.", allFiles.length));
+      }
+      String content = Zip.zip(allFiles[0]);
+      ImmutableMap<String, Object> result = ImmutableMap.of(
+        "filename", filename,
+        "contents", content);
+      return new HttpResponse().setContent(asJson(result));
+    } catch (IOException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+
   @Override
   public HttpResponse uploadFile(HttpRequest req, SessionId id) {
 
@@ -701,6 +749,7 @@ public static class Builder {
     private Duration sessionTimeout = Duration.ofSeconds(NodeOptions.DEFAULT_SESSION_TIMEOUT);
     private HealthCheck healthCheck;
     private Duration heartbeatPeriod = Duration.ofSeconds(NodeOptions.DEFAULT_HEARTBEAT_PERIOD);
+    private String downloadsDir = "";
 
     private Builder(
       Tracer tracer,
@@ -755,6 +804,11 @@ public Builder heartbeatPeriod(Duration heartbeatPeriod) {
       return this;
     }
 
+    public Builder downloadsDirectory(String dir) {
+      this.downloadsDir = dir;
+      return this;
+    }
+
     public LocalNode build() {
       return new LocalNode(
         tracer,
@@ -770,7 +824,8 @@ public LocalNode build() {
         sessionTimeout,
         heartbeatPeriod,
         factories.build(),
-        registrationSecret);
+        registrationSecret,
+        downloadsDir);
     }
 
     public Advanced advanced() {

java/src/org/openqa/selenium/grid/node/remote/RemoteNode.java

@@ -189,6 +189,11 @@ public HttpResponse uploadFile(HttpRequest req, SessionId id) {
     return client.execute(req);
   }
 
+  @Override
+  public HttpResponse downloadFile(HttpRequest req, SessionId id) {
+    return client.execute(req);
+  }
+
   @Override
   public void stop(SessionId id) throws NoSuchSessionException {
     Require.nonNull("Session ID", id);

java/test/org/openqa/selenium/grid/distributor/AddingNodesTest.java

@@ -384,6 +384,11 @@ public HttpResponse uploadFile(HttpRequest req, SessionId id) {
       throw new UnsupportedOperationException("uploadFile");
     }
 
+    @Override
+    public HttpResponse downloadFile(HttpRequest req, SessionId id) {
+      throw new UnsupportedOperationException("uploadFile");
+    }
+
     @Override
     public Session getSession(SessionId id) throws NoSuchSessionException {
       if (running == null || !running.getId().equals(id)) {

java/test/org/openqa/selenium/grid/node/NodeTest.java

@@ -30,6 +30,8 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 
+import java.nio.file.Path;
+import java.nio.file.Paths;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.openqa.selenium.Capabilities;
@@ -115,6 +117,7 @@ public void setUp() throws URISyntaxException {
     caps = new ImmutableCapabilities("browserName", "cheese");
 
     uri = new URI("http://localhost:1234");
+    File downloadsDir = new File(System.getProperty("java.io.tmpdir"));
 
     class Handler extends Session implements HttpHandler {
       private Handler(Capabilities capabilities) {
@@ -131,6 +134,7 @@ public HttpResponse execute(HttpRequest req) throws UncheckedIOException {
         .add(caps, new TestSessionFactory((id, c) -> new Handler(c)))
         .add(caps, new TestSessionFactory((id, c) -> new Handler(c)))
         .add(caps, new TestSessionFactory((id, c) -> new Handler(c)))
+        .downloadsDirectory(downloadsDir.getAbsolutePath())
         .maximumConcurrentSessions(2)
         .build();
 
@@ -484,6 +488,27 @@ void canUploadAFile() throws IOException {
     assertThat(baseDir).doesNotExist();
   }
 
+  @Test
+  void canDownloadAFile() throws IOException {
+    Either<WebDriverException, CreateSessionResponse> response =
+      node.newSession(createSessionRequest(caps));
+    assertThatEither(response).isRight();
+    Session session = response.right().getSession();
+    String hello = "Hello, world!";
+
+    HttpRequest req = new HttpRequest(GET, String.format("/session/%s/file", session.getId()));
+    File zip = createTmpFile(hello);
+    req.addQueryParameter("filename", zip.getName());
+    HttpResponse rsp = node.execute(req);
+    node.stop(session.getId());
+    Map<String, Object> map = new Json().toType(string(rsp), Json.MAP_TYPE);
+    File baseDir = getTemporaryFilesystemBaseDir(TemporaryFilesystem.getDefaultTmpFS());
+    Zip.unzip(rsp.getContent().get(), baseDir);
+    Path path = Paths.get(baseDir.getAbsolutePath(), map.get("filename").toString());
+    String text = String.join("", Files.readAllLines(path));
+    assertThat(text).isEqualTo(hello);
+  }
+
   @Test
   void shouldNotCreateSessionIfDraining() {
     node.drain();
@@ -573,6 +598,17 @@ void shouldAllowsWebDriverCommandsForOngoingSessionIfDraining() throws Interrupt
     assertThat(latch.getCount()).isEqualTo(1);
   }
 
+  private File createFile(String content, File directory) {
+    try {
+      File f = new File(directory.getAbsolutePath(), UUID.randomUUID().toString());
+      f.deleteOnExit();
+      Files.write(directory.toPath(), content.getBytes(StandardCharsets.UTF_8));
+      return f;
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+
+  }
   private File createTmpFile(String content) {
     try {
       File f = File.createTempFile("webdriver", "tmp");