Mute 'Broken pipe' IOExceptions

Closes #38

Author: eperott

common/src/main/java/com/zegelin/cassandra/exporter/netty/Server.java

@@ -54,7 +54,8 @@ public void initChannel(final SocketChannel ch) {
                     .addLast(new HttpObjectAggregator(1048576))
                     .addLast(new HttpContentCompressor())
                     .addLast(new ChunkedWriteHandler())
-                    .addLast(new HttpHandler(harvester, helpExposition));
+                    .addLast(new HttpHandler(harvester, helpExposition))
+                    .addLast(new SuppressingExceptionHandler());
         }
     }
 

common/src/main/java/com/zegelin/cassandra/exporter/netty/SuppressingExceptionHandler.java

@@ -0,0 +1,26 @@
+package com.zegelin.cassandra.exporter.netty;
+
+import io.netty.channel.ChannelHandlerAdapter;
+import io.netty.channel.ChannelHandlerContext;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+public class SuppressingExceptionHandler extends ChannelHandlerAdapter {
+    private static final Logger logger = LoggerFactory.getLogger(SuppressingExceptionHandler.class);
+
+    @Override
+    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
+        if (brokenPipeException(cause)) {
+            logger.debug("Exception while processing scrape request: {}", cause.getMessage());
+        } else {
+            ctx.fireExceptionCaught(cause);
+        }
+    }
+
+    private boolean brokenPipeException(Throwable cause) {
+        return cause instanceof IOException
+                && "Broken pipe".equals(cause.getMessage());
+    }
+}

common/src/test/java/com/zegelin/cassandra/exporter/netty/TestSuppressingExceptionHandler.java

@@ -0,0 +1,44 @@
+package com.zegelin.cassandra.exporter.netty;
+
+import io.netty.channel.ChannelHandlerContext;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.Test;
+
+import java.io.IOException;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+public class TestSuppressingExceptionHandler {
+    @Mock
+    private ChannelHandlerContext context;
+
+    private SuppressingExceptionHandler handler;
+
+    @BeforeMethod
+    public void before() {
+        MockitoAnnotations.initMocks(this);
+        handler = new SuppressingExceptionHandler();
+    }
+
+    @Test
+    public void testBrokenPipeIoExceptionIsMuted() throws Exception {
+        handler.exceptionCaught(context, new IOException("Broken pipe"));
+        verify(context, times(0)).fireExceptionCaught(any());
+    }
+
+    @Test
+    public void testOtherIoExceptionIsPropagated() throws Exception {
+        handler.exceptionCaught(context, new IOException("Other"));
+        verify(context, times(1)).fireExceptionCaught(any());
+    }
+
+    @Test
+    public void testOtherExceptionIsPropagated() throws Exception {
+        handler.exceptionCaught(context, new NullPointerException());
+        verify(context, times(1)).fireExceptionCaught(any());
+    }
+}