Handle NPE observed in unit tests and reported on users list.

NPE occurs after an IOException on a non-container thread during
asynchronous processing.

Author: markt-asf

java/org/apache/catalina/connector/CoyoteOutputStream.java

@@ -81,8 +81,7 @@ public void write(int i) throws IOException {
         try {
             ob.writeByte(i);
         } catch (IOException ioe) {
-            ob.setErrorException(ioe);
-            throw ioe;
+            handleIOException(ioe);
         }
         if (nonBlocking) {
             checkRegisterForWrite();
@@ -102,8 +101,7 @@ public void write(byte[] b, int off, int len) throws IOException {
         try {
             ob.write(b, off, len);
         } catch (IOException ioe) {
-            ob.setErrorException(ioe);
-            throw ioe;
+            handleIOException(ioe);
         }
         if (nonBlocking) {
             checkRegisterForWrite();
@@ -121,8 +119,7 @@ public void write(ByteBuffer from) throws IOException {
         try {
             ob.write(from);
         } catch (IOException ioe) {
-            ob.setErrorException(ioe);
-            throw ioe;
+            handleIOException(ioe);
         }
         if (nonBlocking) {
             checkRegisterForWrite();
@@ -139,8 +136,7 @@ public void flush() throws IOException {
         try {
             ob.flush();
         } catch (IOException ioe) {
-            ob.setErrorException(ioe);
-            throw ioe;
+            handleIOException(ioe);
         }
         if (nonBlocking) {
             checkRegisterForWrite();
@@ -179,8 +175,7 @@ public void close() throws IOException {
         try {
             ob.close();
         } catch (IOException ioe) {
-            ob.setErrorException(ioe);
-            throw ioe;
+            handleIOException(ioe);
         }
     }
 
@@ -197,5 +192,29 @@ public boolean isReady() {
     public void setWriteListener(WriteListener listener) {
         ob.setWriteListener(listener);
     }
+
+
+    private void handleIOException(IOException ioe) throws IOException {
+        try {
+            ob.setErrorException(ioe);
+        } catch (NullPointerException npe) {
+            /*
+             * Ignore.
+             *
+             * An IOException on a non-container thread during asynchronous Servlet processing will trigger a dispatch
+             * to a container thread that will complete the asynchronous processing and recycle the request, response
+             * and associated objects including the OutputBuffer. Depending on timing it is possible that the
+             * OutputBuffer will have been cleared by the time the call above is made - resulting in an NPE.
+             *
+             * If the OutputBuffer is null then there is no need to call setErrorException(). Catching and ignoring the
+             * NPE is (for now at least) a simpler solution than adding locking to OutputBuffer to ensure it is non-null
+             * and remains non-null while setErrorException() is called.
+             *
+             * The longer term solution is likely a refactoring and clean-up of error handling for asynchronous requests
+             * but that is potentially a significant piece of work.
+             */
+        }
+        throw ioe;
+    }
 }
 

webapps/docs/changelog.xml

@@ -199,6 +199,11 @@
         control over the handling of the path used to created a
         <code>RequestDispatcher</code>. (markt)
       </add>
+      <fix>
+        Handle a potential <code>NullPointerException</code> after an
+        <code>IOException</code> occurs on a non-container thread during
+        asynchronous processing. (markt)
+      </fix>
     </changelog>
   </subsection>
   <subsection name="Coyote">