Add DNS based discovery. Patch from John Sample. Resolves issue 18.

Rename IRCPeers to PrintPeers, add DNS, add timing measurements.

src/com/google/bitcoin/core/DnsDiscovery.java

@@ -0,0 +1,106 @@
+/**
+ * Copyright 2011 John Sample
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.bitcoin.core;
+
+import java.net.*;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.Vector;
+
+/**
+ * Supports peer discovery through DNS.<p>
+ *
+ * This class does not support the testnet as currently there are no DNS servers providing testnet hosts.
+ * If this class is being used for testnet you must specify the hostnames to use.<p>
+ * 
+ * Failure to resolve individual host names will not cause an Exception to be thrown.
+ * However, if all hosts passed fail to resolve a PeerDiscoveryException will be thrown during getPeers().
+ */
+public class DnsDiscovery implements PeerDiscovery {
+    private String[] hostNames;
+    private NetworkParameters netParams;
+    private static final String[] defaultHosts = new String[] {"bitseed.xf2.org","bitseed.bitcoin.org.uk"};
+    
+    /**
+     * Supports finding peers through DNS A records. Community run DNS entry points will be used.
+     * 
+     * @param netParams Network parameters to be used for port information.
+     */
+    public DnsDiscovery(NetworkParameters netParams)
+    {
+        this(getDefaultHostNames(), netParams);
+    }
+    
+    /**
+     * Supports finding peers through DNS A records.
+     * 
+     * @param hostNames Host names to be examined for seed addresses.
+     * @param netParams Network parameters to be used for port information.
+     */
+    public DnsDiscovery(String[] hostNames, NetworkParameters netParams)
+    {
+        this.hostNames = hostNames;
+        this.netParams = netParams;
+    }
+
+    public InetSocketAddress[] getPeers() throws PeerDiscoveryException {
+        Set<InetSocketAddress> addresses = new HashSet<InetSocketAddress>();
+
+        /*
+         * Keep track of how many lookups failed vs. succeeded.
+         * We'll throw an exception only if all the lookups fail.
+         * We don't want to throw an exception if only one of many lookups fails.
+         */
+        int failedLookups = 0;
+        
+        for (String hostName : hostNames) {
+            try {
+                InetAddress[] hostAddresses = InetAddress.getAllByName(hostName);
+                
+                for (InetAddress inetAddress : hostAddresses) {
+                    // DNS isn't going to provide us with the port.
+                    // Grab the port from the specified NetworkParameters.
+                    InetSocketAddress socketAddress = new InetSocketAddress(inetAddress, netParams.port);
+                    
+                    // Only add the new address if it's not already in the combined list.
+                    if (!addresses.contains(socketAddress)) {
+                        addresses.add(socketAddress);
+                    }
+                }
+            } catch (Exception e) {
+                failedLookups++;
+                Utils.LOG("DNS lookup for " + hostName + " failed.");
+                
+                if (failedLookups == hostNames.length) {
+                    // All the lookups failed.
+                    // Throw the discovery exception and include the last inner exception.
+                    throw new PeerDiscoveryException("DNS resolution for all hosts failed.", e);
+                }
+            }
+        }
+        return addresses.toArray(new InetSocketAddress[]{});
+    }
+    
+    /**
+     * Returns the well known discovery host names on the production network.
+     */
+    public static String[] getDefaultHostNames()
+    {
+        return defaultHosts;
+    }
+
+}

src/com/google/bitcoin/examples/PrintPeers.java

@@ -23,24 +23,47 @@ import com.google.bitcoin.core.*;
 /**
  * Prints a list of IP addresses connected to the rendezvous point on the LFnet IRC channel.
  */
-public class IRCPeers {
-    public static void main(String[] args) throws PeerDiscoveryException {
-        IrcDiscovery d = new IrcDiscovery("#bitcoin") {
-            @Override
-            protected void onIRCReceive(String message) {
-                System.out.println(message);
-            }
+public class PrintPeers {
+    private static void printElapsed(long start) {
+        long now = System.currentTimeMillis();
+        System.out.println(String.format("Took %.2f seconds", (now - start) / 1000.0));
+    }
 
-            @Override
-            protected void onIRCSend(String message) {
-                System.out.println(message);
-            }
-        };
-
-        InetSocketAddress[] addresses = d.getPeers();
+    private static void printPeers(InetSocketAddress[] addresses) {
         for (InetSocketAddress address : addresses) {
             String hostAddress = address.getAddress().getHostAddress();
             System.out.println(String.format("%s:%d", hostAddress.toString(), address.getPort()));
         }
     }
+
+    private static void printIRC() throws PeerDiscoveryException {
+        long start = System.currentTimeMillis();
+        IrcDiscovery d = new IrcDiscovery("#bitcoin") {
+            @Override
+            protected void onIRCReceive(String message) {
+                System.out.println("<- " + message);
+            }
+
+            @Override
+            protected void onIRCSend(String message) {
+                System.out.println("-> " + message);
+            }
+        };
+        printPeers(d.getPeers());
+        printElapsed(start);
+    }
+
+    private static void printDNS() throws PeerDiscoveryException {
+        long start = System.currentTimeMillis();
+        DnsDiscovery dns = new DnsDiscovery(NetworkParameters.prodNet());
+        printPeers(dns.getPeers());
+        printElapsed(start);
+    }
+
+    public static void main(String[] args) throws PeerDiscoveryException {
+        System.out.println("=== IRC ===");
+        printIRC();
+        System.out.println("=== DNS ===");
+        printDNS();
+    }
 }