Discard the reference to the underlying buffer during close(), and throw…

src/main/java/com/maxmind/db/ClosedDatabaseException.java

@@ -0,0 +1,15 @@
+package com.maxmind.db;
+
+import java.io.IOException;
+
+/**
+ * Signals that the underlying database has been closed.
+ */
+public class ClosedDatabaseException extends IOException {
+
+    private static final long serialVersionUID = 1L;
+
+    ClosedDatabaseException() {
+        super("The MaxMind DB has been closed.");
+    }
+}

src/main/java/com/maxmind/db/Reader.java

@@ -6,6 +6,7 @@
 import java.io.InputStream;
 import java.net.InetAddress;
 import java.nio.ByteBuffer;
+import java.util.concurrent.atomic.AtomicReference;
 
 import com.fasterxml.jackson.databind.JsonNode;
 
@@ -21,7 +22,7 @@ public final class Reader implements Closeable {
 
     private final int ipV4Start;
     private final Metadata metadata;
-    private final BufferHolder bufferHolder;
+    private final AtomicReference<BufferHolder> bufferHolderReference;
 
     /**
      * The file mode to use when opening a MaxMind DB.
@@ -81,9 +82,9 @@ public Reader(File database, FileMode fileMode) throws IOException {
     }
 
     private Reader(BufferHolder bufferHolder, String name) throws IOException {
-        this.bufferHolder = bufferHolder;
+        this.bufferHolderReference = new AtomicReference<BufferHolder>(bufferHolder);
 
-        ByteBuffer buffer = this.bufferHolder.get();
+        ByteBuffer buffer = bufferHolder.get();
         int start = this.findMetadataStart(buffer, name);
 
         Decoder metadataDecoder = new Decoder(buffer, start);
@@ -102,14 +103,22 @@ private Reader(BufferHolder bufferHolder, String name) throws IOException {
      *             if a file I/O error occurs.
      */
     public JsonNode get(InetAddress ipAddress) throws IOException {
-        ByteBuffer buffer = this.bufferHolder.get();
+        ByteBuffer buffer = getBufferHolder().get();
         int pointer = this.findAddressInTree(buffer, ipAddress);
         if (pointer == 0) {
             return null;
         }
         return this.resolveDataPointer(buffer, pointer);
     }
 
+    private BufferHolder getBufferHolder() throws ClosedDatabaseException {
+        BufferHolder bufferHolder = bufferHolderReference.get();
+        if (bufferHolder == null) {
+            throw new ClosedDatabaseException();
+        }
+        return bufferHolder;
+    }
+
     private int findAddressInTree(ByteBuffer buffer, InetAddress address)
             throws InvalidDatabaseException {
         byte[] rawAddress = address.getAddress();
@@ -241,6 +250,6 @@ Metadata getMetadata() {
      */
     @Override
     public void close() throws IOException {
-        this.bufferHolder.close();
+        bufferHolderReference.getAndSet(null).close();
     }
 }

src/test/java/com/maxmind/db/MultiThreadedTest.java

@@ -33,7 +33,11 @@ public JsonNode call() throws UnknownHostException, IOException,
                         "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb")
                         .toURI();
                 final Reader reader = new Reader(new File(file));
-                return reader.get(InetAddress.getByName("::1.1.1.0"));
+                try {
+                    return reader.get(InetAddress.getByName("::1.1.1.0"));
+                } finally {
+                    reader.close();
+                }
             }
         };
         MultiThreadedTest.runThreads(task);
@@ -45,7 +49,11 @@ public void streamThreadTest() throws IOException, InterruptedException,
         final Reader reader = new Reader(ReaderTest.class.getResource(
                 "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb")
                 .openStream());
-        MultiThreadedTest.threadTest(reader);
+        try {
+            MultiThreadedTest.threadTest(reader);
+        } finally {
+            reader.close();
+        }
     }
 
     @Test
@@ -54,7 +62,11 @@ public void mmapThreadTest() throws IOException, InterruptedException,
         URI file = ReaderTest.class.getResource(
                 "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb").toURI();
         final Reader reader = new Reader(new File(file));
-        MultiThreadedTest.threadTest(reader);
+        try {
+            MultiThreadedTest.threadTest(reader);
+        } finally {
+            reader.close();
+        }
     }
 
     private static void threadTest(final Reader reader) throws InterruptedException,

src/test/java/com/maxmind/db/ReaderTest.java

@@ -16,6 +16,8 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -27,6 +29,20 @@
 public class ReaderTest {
     private final ObjectMapper om = new ObjectMapper();
 
+    private Reader testReader;
+
+    @Before
+    public void setupReader() {
+        testReader = null;
+    }
+
+    @After
+    public void teardownReader() throws IOException {
+        if (testReader != null) {
+            testReader.close();
+        }
+    }
+
     @Test
     public void test() throws IOException, URISyntaxException {
         for (long recordSize : new long[] { 24, 28, 32 }) {
@@ -37,15 +53,14 @@ public void test() throws IOException, URISyntaxException {
                 Reader reader = new Reader(new File(file));
                 try {
                     this.testMetadata(reader, ipVersion, recordSize);
+                    if (ipVersion == 4) {
+                        this.testIpV4(reader, file);
+                    } else {
+                        this.testIpV6(reader, file);
+                    }
                 } finally {
                     reader.close();
                 }
-
-                if (ipVersion == 4) {
-                    this.testIpV4(reader, file);
-                } else {
-                    this.testIpV6(reader, file);
-                }
             }
         }
     }
@@ -57,8 +72,8 @@ public void testNoIpV4SearchTreeFile() throws IOException,
                 "/maxmind-db/test-data/MaxMind-DB-no-ipv4-search-tree.mmdb")
                 .toURI();
 
-        Reader reader = new Reader(new File(file));
-        this.testNoIpV4SearchTree(reader);
+        testReader = new Reader(new File(file));
+        this.testNoIpV4SearchTree(testReader);
     }
 
     @Test
@@ -67,8 +82,8 @@ public void testNoIpV4SearchTreeURL() throws IOException,
         InputStream stream = ReaderTest.class.getResource(
                 "/maxmind-db/test-data/MaxMind-DB-no-ipv4-search-tree.mmdb")
                 .openStream();
-        Reader reader = new Reader(stream);
-        this.testNoIpV4SearchTree(reader);
+        testReader = new Reader(stream);
+        this.testNoIpV4SearchTree(testReader);
     }
 
     private void testNoIpV4SearchTree(Reader reader) throws IOException,
@@ -85,8 +100,8 @@ public void testDecodingTypesFile() throws URISyntaxException, IOException {
         URI file = ReaderTest.class.getResource(
                 "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb").toURI();
 
-        Reader reader = new Reader(new File(file));
-        this.testDecodingTypes(reader);
+        testReader = new Reader(new File(file));
+        this.testDecodingTypes(testReader);
     }
 
     @Test
@@ -95,8 +110,8 @@ public void testDecodingTypesURL() throws URISyntaxException, IOException {
                 "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb")
                 .openStream();
 
-        Reader reader = new Reader(stream);
-        this.testDecodingTypes(reader);
+        testReader = new Reader(stream);
+        this.testDecodingTypes(testReader);
     }
 
     private void testDecodingTypes(Reader reader) throws URISyntaxException,
@@ -148,8 +163,8 @@ public void testZerosFile() throws URISyntaxException, IOException {
         URI file = ReaderTest.class.getResource(
                 "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb").toURI();
 
-        Reader reader = new Reader(new File(file));
-        this.testZeros(reader);
+        testReader = new Reader(new File(file));
+        this.testZeros(testReader);
     }
 
     @Test
@@ -158,8 +173,8 @@ public void testZerosURL() throws URISyntaxException, IOException {
                 "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb")
                 .openStream();
 
-        Reader reader = new Reader(stream);
-        this.testZeros(reader);
+        testReader = new Reader(stream);
+        this.testZeros(testReader);
     }
 
     private void testZeros(Reader reader) throws URISyntaxException,
@@ -197,8 +212,8 @@ public void testBrokenDatabaseFile() throws URISyntaxException, IOException {
                         "/maxmind-db/test-data/GeoIP2-City-Test-Broken-Double-Format.mmdb")
                 .toURI();
 
-        Reader reader = new Reader(new File(file));
-        this.testBrokenDatabase(reader);
+        testReader = new Reader(new File(file));
+        this.testBrokenDatabase(testReader);
     }
 
     @Test
@@ -208,8 +223,8 @@ public void testBrokenDatabaseURL() throws URISyntaxException, IOException {
                         "/maxmind-db/test-data/GeoIP2-City-Test-Broken-Double-Format.mmdb")
                 .openStream();
 
-        Reader reader = new Reader(stream);
-        this.testBrokenDatabase(reader);
+        testReader = new Reader(stream);
+        this.testBrokenDatabase(testReader);
     }
 
     private void testBrokenDatabase(Reader reader) throws URISyntaxException,
@@ -230,8 +245,8 @@ public void testBrokenSearchTreePointerFile() throws URISyntaxException,
                         "/maxmind-db/test-data/MaxMind-DB-test-broken-pointers-24.mmdb")
                 .toURI();
 
-        Reader reader = new Reader(new File(file));
-        this.testBrokenSearchTreePointer(reader);
+        testReader = new Reader(new File(file));
+        this.testBrokenSearchTreePointer(testReader);
     }
 
     @Test
@@ -242,8 +257,8 @@ public void testBrokenSearchTreePointerURL() throws URISyntaxException,
                         "/maxmind-db/test-data/MaxMind-DB-test-broken-pointers-24.mmdb")
                 .openStream();
 
-        Reader reader = new Reader(stream);
-        this.testBrokenSearchTreePointer(reader);
+        testReader = new Reader(stream);
+        this.testBrokenSearchTreePointer(testReader);
     }
 
     private void testBrokenSearchTreePointer(Reader reader)
@@ -264,8 +279,8 @@ public void testBrokenDataPointerFile() throws IOException,
                         "/maxmind-db/test-data/MaxMind-DB-test-broken-pointers-24.mmdb")
                 .toURI();
 
-        Reader reader = new Reader(new File(file));
-        this.testBrokenDataPointer(reader);
+        testReader = new Reader(new File(file));
+        this.testBrokenDataPointer(testReader);
     }
 
     @Test
@@ -276,8 +291,8 @@ public void testBrokenDataPointerURL() throws IOException,
                         "/maxmind-db/test-data/MaxMind-DB-test-broken-pointers-24.mmdb")
                 .openStream();
 
-        Reader reader = new Reader(stream);
-        this.testBrokenDataPointer(reader);
+        testReader = new Reader(stream);
+        this.testBrokenDataPointer(testReader);
     }
 
     private void testBrokenDataPointer(Reader reader) throws IOException,
@@ -290,6 +305,19 @@ private void testBrokenDataPointer(Reader reader) throws IOException,
         reader.get(InetAddress.getByName("1.1.1.16"));
     }
 
+    @Test
+    public void testClosedReaderThrowsException() throws IOException, URISyntaxException {
+        URI file = ReaderTest.class.getResource(
+                "/maxmind-db/test-data/MaxMind-DB-test-decoder.mmdb").toURI();
+        Reader reader = new Reader(new File(file));
+
+        this.thrown.expect(ClosedDatabaseException.class);
+        this.thrown.expectMessage("The MaxMind DB has been closed.");
+
+        reader.close();
+        reader.get(InetAddress.getByName("1.1.1.16"));
+    }
+
     private void testMetadata(Reader reader, int ipVersion, long recordSize) {
 
         Metadata metadata = reader.getMetadata();