Add iteration mechanism

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

@@ -0,0 +1,9 @@
+package com.maxmind.db;
+
+import java.net.InetAddress;
+
+public class BadVersionException extends Exception {
+    public BadVersionException(InetAddress ip) {
+        super("you attempted to use an IPv6 network in an IPv4-only database: " + ip.toString());
+    }
+}

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

@@ -0,0 +1,196 @@
+package com.maxmind.db;
+
+import java.io.IOException;
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+
+public class Networks<T> implements Iterator<DatabaseRecord<T>> {
+    private final Reader reader;
+    private ArrayList<NetworkNode> nodes;
+    private NetworkNode lastNode;
+    private boolean skipAliasedNetworks;
+    private Exception err;
+    private ByteBuffer buffer; /* Stores the buffer for Next() calls */
+    private Class<T> typeParameterClass;
+
+    /**
+     * Constructs a Networks instance.
+     * @param reader The reader object.
+     * @param skipAliasedNetworks The boolean to skip aliased networks.
+     * @throws ClosedDatabaseException Exception for a closed database.
+     */
+    Networks(Reader reader, boolean skipAliasedNetworks) 
+        throws ClosedDatabaseException {
+        this(reader, skipAliasedNetworks, new NetworkNode[]{});
+    }
+
+    /**
+     * Constructs a Networks instance.
+     * @param reader The reader object.
+     * @param skipAliasedNetworks The boolean to skip aliased networks.
+     * @param nodes The initial nodes array to start Networks iterator with.
+     * @throws ClosedDatabaseException Exception for a closed database.
+     */
+    Networks(Reader reader, boolean skipAliasedNetworks, NetworkNode[] nodes) 
+        throws ClosedDatabaseException {
+        this.reader = reader;
+        this.skipAliasedNetworks = skipAliasedNetworks;
+        this.nodes = new ArrayList<NetworkNode>(Arrays.asList(nodes));
+        this.buffer = reader.getBufferHolder().get();
+    }
+
+    /**
+     * Constructs a Networks instance with skipAliasedNetworks set to false by default.
+     * @param reader The reader object.
+     */
+    Networks(Reader reader) throws ClosedDatabaseException {
+        this(reader, false);
+    }
+
+    /**
+     * Returns if Networks had any errors.
+     * @return Exception The exception to the Networks iteration.
+     */
+    public Exception getErr() {
+        return this.err;
+    }
+
+    /**
+     * Sets the Class for the data type in DataRecord.
+     * @param cls The class object. ( For example, Map.class )
+     */
+    public void setDataClass(Class<T> cls) {
+        this.typeParameterClass = cls;
+    }
+
+    /**
+     * Returns the next NetworksItem. You need to set the class using
+     * prepareForClass before calling next. 
+     * For example,
+     *  networks.prepareForClass(Map.Class);
+     *  Map test = networks.next();
+     */
+    @Override
+    public DatabaseRecord<T> next() {
+        if (this.err != null) {
+            return null;
+        } 
+
+        try {
+            T data = this.reader.resolveDataPointer(
+                this.buffer, this.lastNode.pointer, this.typeParameterClass);
+
+            byte[] ip = this.lastNode.ip;
+            int prefixLength = this.lastNode.prefix;
+
+            // We do this because uses of SkipAliasedNetworks expect the IPv4 networks
+            // to be returned as IPv4 networks. If we are not skipping aliased
+            // networks, then the user will get IPv4 networks from the ::FFFF:0:0/96
+            // network.
+            if (this.skipAliasedNetworks && isInIpv4Subtree(ip)) {
+                ip = Arrays.copyOfRange(ip, 12, ip.length);
+                prefixLength -= 96;
+            }
+
+            // If the ip is in ipv6 form, drop the prefix manually
+            // as InetAddress converts it to ipv4.
+            InetAddress ipAddr = InetAddress.getByAddress(ip);
+            if (ipAddr instanceof Inet4Address && ip.length > 4
+                    && ip[10] == -1 && ip[11] == -1 && prefixLength > 32) {
+                prefixLength -= 96;
+            }
+
+            return new DatabaseRecord<T>(data, InetAddress.getByAddress(ip), prefixLength);
+        } catch (IOException e) {
+            this.err = e;
+            return null;
+        }
+    }
+
+    public boolean isInIpv4Subtree(byte[] ip) {
+        if (ip.length != 16) {
+            return false;
+        }
+        for (int i = 0; i < 12; i++) {
+            if (ip[i] != 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /*
+    * Next prepares the next network for reading with the Network method. It
+    * returns true if there is another network to be processed and false if there
+    * are no more networks or if there is an error.
+    */
+    @Override
+    public boolean hasNext()  {
+        if (this.err != null) {
+            return false;
+        }
+        while (!this.nodes.isEmpty()) {
+            // Pop the last one.
+            NetworkNode node = this.nodes.remove(this.nodes.size() - 1);
+
+            // Next until we don't have data.
+            while (node.pointer != this.reader.getMetadata().getNodeCount()) {
+                // This skips IPv4 aliases without hardcoding the networks that the writer
+                // currently aliases.
+                if (this.skipAliasedNetworks && this.reader.getIpv4Start() != 0
+                        && node.pointer == this.reader.getIpv4Start()
+                        && !isInIpv4Subtree(node.ip)) {
+                    break;
+                }
+
+                if (node.pointer > this.reader.getMetadata().getNodeCount()) {
+                    this.lastNode = node;
+                    return true;
+                }
+
+                byte[] ipRight = Arrays.copyOf(node.ip, node.ip.length);
+                if (ipRight.length <= (node.prefix >> 3)) {
+                    this.err = new InvalidDatabaseException("Invalid search tree");
+                    return false;
+                }
+
+                ipRight[node.prefix >> 3] |= 1 << (7 - (node.prefix % 8));
+
+                try {
+                    int rightPointer = this.reader.readNode(this.buffer, node.pointer, 1);
+                    node.prefix++;
+
+                    this.nodes.add(new NetworkNode(ipRight, node.prefix, rightPointer));
+                    node.pointer = this.reader.readNode(this.buffer, node.pointer, 0);
+                } catch (InvalidDatabaseException e) {
+                    this.err = e;
+                    return false;
+                }
+            }
+        }
+        return false;
+    }
+
+    protected static class NetworkNode {
+        public byte[] ip;
+        public int prefix;
+        public int pointer;
+
+        /**
+         * Constructs a network node for internal use.
+         * @param ip The ip address of the node.
+         * @param prefix The prefix of the node.
+         * @param pointer The node number
+         */
+        public NetworkNode(byte[] ip, int prefix, int pointer) {
+            this.ip = ip;
+            this.prefix = prefix;
+            this.pointer = pointer;
+        }
+    }
+
+}