YARN-3148. Allow CORS related headers to passthrough in

WebAppProxyServlet. Contributed by Varun Saxena.

hadoop-yarn-project/CHANGES.txt

@@ -309,6 +309,9 @@ Release 2.8.0 - UNRELEASED
     YARN-3789. Improve logs for LeafQueue#activateApplications().
     (Bibin A Chundatt via devaraj)
 
+    YARN-3148. Allow CORS related headers to passthrough in WebAppProxyServlet.
+    (Varun Saxena via devaraj)
+
   OPTIMIZATIONS
 
     YARN-3339. TestDockerContainerExecutor should pull a single image and not

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/main/java/org/apache/hadoop/yarn/server/webproxy/WebAppProxyServlet.java

@@ -81,7 +81,10 @@ public class WebAppProxyServlet extends HttpServlet {
         "Accept-Encoding",
         "Accept-Language",
         "Accept-Charset",
-        "Content-Type"));
+        "Content-Type",
+        "Origin",
+        "Access-Control-Request-Method",
+        "Access-Control-Request-Headers"));
 
   public static final String PROXY_USER_COOKIE_NAME = "proxy-user";
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/test/java/org/apache/hadoop/yarn/server/webproxy/TestWebAppProxyServlet.java

@@ -31,6 +31,7 @@ import java.net.HttpCookie;
 import java.net.HttpURLConnection;
 import java.net.URI;
 import java.net.URL;
+import java.util.Enumeration;
 import java.util.List;
 import java.util.Map;
 
@@ -72,6 +73,10 @@ public class TestWebAppProxyServlet {
 
   private static Server server;
   private static int originalPort = 0;
+  private static int numberOfHeaders = 0;
+  private static final String UNKNOWN_HEADER = "Unknown-Header";
+  private static boolean hasUnknownHeader = false;
+
 
   /**
    * Simple http server. Server should send answer with status 200
@@ -88,6 +93,9 @@ public class TestWebAppProxyServlet {
     originalPort = server.getConnectors()[0].getLocalPort();
     LOG.info("Running embedded servlet container at: http://localhost:"
         + originalPort);
+    // This property needs to be set otherwise CORS Headers will be dropped
+    // by HttpUrlConnection
+    System.setProperty("sun.net.http.allowRestrictedHeaders", "true");
   }
 
   @SuppressWarnings("serial")
@@ -96,6 +104,18 @@ public class TestWebAppProxyServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp)
         throws ServletException, IOException {
+      int numHeaders = 0;
+      hasUnknownHeader = false;
+      @SuppressWarnings("unchecked")
+      Enumeration<String> names = req.getHeaderNames();
+      while(names.hasMoreElements()) {
+        String headerName = names.nextElement();
+        if (headerName.equals(UNKNOWN_HEADER)) {
+          hasUnknownHeader = true;
+        }
+        ++numHeaders;
+      }
+      numberOfHeaders = numHeaders;
       resp.setStatus(HttpServletResponse.SC_OK);
     }
 
@@ -206,6 +226,43 @@ public class TestWebAppProxyServlet {
     }
   }
 
+  @Test(timeout=5000)
+  public void testWebAppProxyPassThroughHeaders() throws Exception {
+    Configuration configuration = new Configuration();
+    configuration.set(YarnConfiguration.PROXY_ADDRESS, "localhost:9091");
+    configuration.setInt("hadoop.http.max.threads", 5);
+    WebAppProxyServerForTest proxy = new WebAppProxyServerForTest();
+    proxy.init(configuration);
+    proxy.start();
+
+    int proxyPort = proxy.proxy.proxyServer.getConnectorAddress(0).getPort();
+
+    try {
+      URL url = new URL("http://localhost:" + proxyPort + "/proxy/application_00_1");
+      HttpURLConnection proxyConn = (HttpURLConnection) url.openConnection();
+      // set headers
+      proxyConn.addRequestProperty("Origin", "http://www.someurl.com");
+      proxyConn.addRequestProperty("Access-Control-Request-Method", "GET");
+      proxyConn.addRequestProperty(
+          "Access-Control-Request-Headers", "Authorization");
+      proxyConn.addRequestProperty(UNKNOWN_HEADER, "unknown");
+      // Verify if four headers mentioned above have been added
+      assertEquals(proxyConn.getRequestProperties().size(), 4);
+      proxyConn.connect();
+      assertEquals(HttpURLConnection.HTTP_OK, proxyConn.getResponseCode());
+      // Verify if number of headers received by end server is 8.
+      // Eight headers include Accept, Host, Connection, User-Agent, Cookie,
+      // Origin, Access-Control-Request-Method and
+      // Access-Control-Request-Headers. Pls note that Unknown-Header is dropped
+      // by proxy as it is not in the list of allowed headers.
+      assertEquals(numberOfHeaders, 8);
+      assertFalse(hasUnknownHeader);
+    } finally {
+      proxy.close();
+    }
+  }
+
+
   /**
    * Test main method of WebAppProxyServer
    */