PrintSocketClient: Attempt to gracefully handle StaticException and closed sessions when calling send()

Author: tresf

src/qz/ws/ClosedSocketException.java

@@ -0,0 +1,61 @@
+package qz.ws;
+
+import org.eclipse.jetty.util.StaticException;
+
+import java.io.IOException;
+import java.nio.channels.ClosedChannelException;
+import java.util.Locale;
+
+/**
+ * <code>ClosedChannelException</code> wrapper class for handling edge-cases where Jetty nests or hides
+ * the underlying <code>Exception</code> cause.  Inspired by #1300 and #1414
+ */
+public class ClosedSocketException extends ClosedChannelException {
+    public ClosedSocketException(String message) {
+        super();
+        this.initCause(new IOException(message));
+    }
+
+    public ClosedSocketException(Throwable t) {
+        super();
+        this.initCause(t);
+    }
+
+    public static void filter(Throwable t) throws ClosedChannelException {
+        Throwable throwable = t;
+        while(true) {
+            if(throwable instanceof ClosedChannelException) {
+                throw (ClosedChannelException)throwable;
+            }
+            if(throwable != null) {
+                throwable = throwable.getCause();
+            } else {
+                break;
+            }
+        }
+
+        if (messageMatchesClosed(t)) {
+            throw new ClosedSocketException(t);
+        }
+    }
+
+    /**
+     * Check if a <code>Throwable</code> or its cause matches a <code>StaticException</code>
+     * with "closed" in the message string.
+     */
+    private static boolean messageMatchesClosed(Throwable t) {
+        Throwable throwable = t;
+        while(true) {
+            if(throwable == null) {
+                return false;
+            } else if(!(throwable instanceof StaticException)) {
+                // go deeper
+                throwable = throwable.getCause();
+            } else {
+                break;
+            }
+        }
+        StaticException staticException = (StaticException)throwable;
+        return staticException.getMessage() != null && staticException.getMessage().toLowerCase(Locale.ENGLISH).contains("closed");
+    }
+}

src/qz/ws/PrintSocketClient.java

@@ -828,14 +828,14 @@ public static void sendStream(Session session, StreamEvent event, Runnable close
      */
     private static synchronized void send(Session session, JSONObject reply) throws WebSocketException, ClosedChannelException {
         try {
-            session.getRemote().sendString(reply.toString());
+            if(session.isOpen()) {
+                session.getRemote().sendString(reply.toString());
+            } else {
+                throw new ClosedSocketException("Channel was closed before message could be sent");
+            }
         }
         catch(IOException e) {
-            if(e instanceof ClosedChannelException) {
-                throw (ClosedChannelException)e;
-            } else if(e.getCause() instanceof ClosedChannelException) {
-                throw (ClosedChannelException)e.getCause();
-            }
+            ClosedSocketException.filter(e); // Explicitly detect and re-throw ClosedChannelExceptions
             log.error("Could not send message", e);
         }
     }