resolve hostname for the hostname column in sys.nodes

it was previously done in ES, but removed after
ES 2.0.0
elastic/elasticsearch#13014

CHANGES.txt

@@ -5,12 +5,15 @@ Changes for Crate
 Unreleased
 ==========
 
+ - Fix: the ``hostname`` column of the ``sys.nodes`` table returns a hostname
+   instead of an IP address.
+
  - Added initial experimental support for the postgres wire protocol. This is
    disabled by default.
 
  - Fixed an issue that caused select statements to get stuck if used as part of
    a bulk request. Now a proper error is raised.
-   
+
  - Updated Elasticsearch to 2.3.4
 
  - Improved the error message of `COPY FROM` statements which fail due to

sql/src/main/java/io/crate/operation/reference/sys/node/NodeHostnameExpression.java

@@ -25,6 +25,11 @@
 import org.elasticsearch.cluster.ClusterService;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.nio.charset.Charset;
+
 public class NodeHostnameExpression extends SysNodeExpression<BytesRef> {
 
     private final ClusterService clusterService;
@@ -37,9 +42,21 @@ public NodeHostnameExpression(ClusterService clusterService) {
     public BytesRef value() {
         DiscoveryNode localNode = clusterService.localNode();
         if (localNode != null) {
-            return new BytesRef(localNode.getHostName());
+            final String hostAddress = localNode.getHostAddress();
+            return new BytesRef(resolveHostname(hostAddress));
         }
         return null;
     }
 
+    private String resolveHostname(final String address) {
+        try {
+            byte[] ip = address.getBytes(Charset.forName("UTF-8"));
+            InetAddress inetAddress = InetAddress.getByAddress(ip);
+            return inetAddress.getHostName();
+        } catch (UnknownHostException e) {
+            // return an ip address, if a hostname was not resolved
+            return address;
+        }
+    }
+
 }

sql/src/test/java/io/crate/operation/reference/sys/SysNodesExpressionsTest.java

@@ -42,6 +42,7 @@
 import org.elasticsearch.common.inject.AbstractModule;
 import org.elasticsearch.common.inject.Injector;
 import org.elasticsearch.common.inject.ModulesBuilder;
+import org.elasticsearch.common.lucene.BytesRefs;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.transport.BoundTransportAddress;
 import org.elasticsearch.common.transport.InetSocketTransportAddress;
@@ -133,7 +134,7 @@ protected void configure() {
             }
 
             DiscoveryNode node = mock(DiscoveryNode.class);
-            when(node.getHostName()).thenReturn("localhost");
+            when(node.getHostAddress()).thenReturn("192.168.0.2");
             when(nodeStats.getNode()).thenReturn(node);
             when(clusterService.localNode()).thenReturn(node);
 
@@ -434,6 +435,24 @@ public void testOsInfo() throws Exception {
         assertEquals(4, cores);
     }
 
+    @Test
+    public void testHostnameExpressionIpCannotBeResolved() throws Exception {
+        ReferenceInfo refInfo = refInfo("sys.nodes.hostname", DataTypes.STRING, RowGranularity.NODE);
+        SimpleObjectExpression hostnameExpression = (SimpleObjectExpression) resolver.getImplementation(refInfo);
+        assertThat(BytesRefs.toString(hostnameExpression.value()), is("192.168.0.2"));
+    }
+
+    @Test
+    public void testHostnameExpressionResolveLocalhost() throws Exception {
+        ClusterService clusterService = mock(ClusterService.class);
+        DiscoveryNode discoveryNode = mock(DiscoveryNode.class);
+        when(discoveryNode.getHostAddress()).thenReturn("127.0.0.1");
+        when(clusterService.localNode()).thenReturn(discoveryNode);
+
+        NodeHostnameExpression expression = new NodeHostnameExpression(clusterService);
+        assertThat(BytesRefs.toString(expression.value()), is("localhost"));
+    }
+
     @Test
     public void testNestedBytesRefExpressionsString() throws Exception {
         ReferenceInfo refInfo = refInfo("sys.nodes.version", DataTypes.OBJECT, RowGranularity.NODE);