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+package org.apache.hadoop.net;
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+
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+import java.io.IOException;
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+import java.net.InetAddress;
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+import java.net.NetworkInterface;
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+import java.net.SocketException;
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+import java.net.UnknownHostException;
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+import java.util.Enumeration;
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+import java.util.Vector;
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+
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+import javax.naming.NamingException;
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+import javax.naming.directory.Attributes;
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+import javax.naming.directory.DirContext;
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+import javax.naming.directory.InitialDirContext;
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+
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+/**
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+ *
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+ * A class that provides direct and reverse lookup functionalities, allowing
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+ * the querying of specific network interfaces or nameservers.
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+ *
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+ * @author Lorenzo Thione
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+ *
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+ */
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+public class DNS {
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+
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+ /**
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+ * Returns the hostname associated with the specified IP address by the
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+ * provided nameserver.
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+ *
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+ * @param hostIp
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+ * The address to reverse lookup
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+ * @param ns
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+ * The host name of a reachable DNS server
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+ * @return The host name associated with the provided IP
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+ * @throws NamingException
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+ * If a NamingException is encountered
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+ */
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+ public static String reverseDns(InetAddress hostIp, String ns)
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+ throws NamingException {
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+ //
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+ // Builds the reverse IP lookup form
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+ // This is formed by reversing the IP numbers and appending in-addr.arpa
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+ //
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+ String[] parts = hostIp.getHostAddress().split("\\.");
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+ String reverseIP = parts[3] + "." + parts[2] + "." + parts[1] + "."
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+ + parts[0] + ".in-addr.arpa";
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+
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+ DirContext ictx = new InitialDirContext();
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+ Attributes attribute =
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+ ictx.getAttributes("dns://" // Use "dns:///" if the default
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+ + ((ns == null) ? "" : ns) +
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+ // nameserver is to be used
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+ "/" + reverseIP, new String[] { "PTR" });
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+ ictx.close();
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+
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+ return attribute.get("PTR").get().toString();
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+ }
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+
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+ /**
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+ * Returns all the IPs associated with the provided interface, if any, in
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+ * textual form.
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+ *
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+ * @param strInterface
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+ * The name of the network interface to query (e.g. eth0)
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+ * @return A string vector of all the IPs associated with the provided
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+ * interface
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+ * @throws UnknownHostException
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+ * If an UnknownHostException is encountered in querying the
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+ * default interface
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+ *
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+ */
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+ public static String[] getIPs(String strInterface)
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+ throws UnknownHostException {
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+ try {
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+ NetworkInterface netIF = NetworkInterface.getByName(strInterface);
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+ if (netIF == null)
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+ return new String[] { InetAddress.getLocalHost()
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+ .getHostAddress() };
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+ else {
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+ Vector ips = new Vector();
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+ Enumeration e = netIF.getInetAddresses();
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+ while (e.hasMoreElements())
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+ ips.add(((InetAddress) e.nextElement()).getHostAddress());
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+ return (String[]) ips.toArray(new String[] {});
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+ }
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+ } catch (SocketException e) {
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+ return new String[] { InetAddress.getLocalHost().getHostAddress() };
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+ }
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+ }
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+
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+ /**
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+ * Returns the first available IP address associated with the provided
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+ * network interface
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+ *
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+ * @param strInterface
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+ * The name of the network interface to query (e.g. eth0)
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+ * @return The IP address in text form
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+ * @throws UnknownHostException
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+ * If one is encountered in querying the default interface
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+ */
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+ public static String getDefaultIP(String strInterface)
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+ throws UnknownHostException {
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+ String[] ips = getIPs(strInterface);
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+ return ips[0];
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+ }
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+
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+ /**
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+ * Returns all the host names associated by the provided nameserver with the
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+ * address bound to the specified network interface
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+ *
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+ * @param strInterface
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+ * The name of the network interface to query (e.g. eth0)
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+ * @param nameserver
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+ * The DNS host name
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+ * @return A string vector of all host names associated with the IPs tied to
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+ * the specified interface
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+ * @throws UnknownHostException
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+ */
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+ public static String[] getHosts(String strInterface, String nameserver)
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+ throws UnknownHostException {
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+ String[] ips = getIPs(strInterface);
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+ Vector hosts = new Vector();
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+ for (int ctr = 0; ctr < ips.length; ctr++)
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+ try {
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+ hosts.add(reverseDns(InetAddress.getByName(ips[ctr]),
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+ nameserver));
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+ } catch (Exception e) {
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+ }
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+
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+ if (hosts.size() == 0)
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+ return new String[] { InetAddress.getLocalHost().getHostName() };
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+ else
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+ return (String[]) hosts.toArray(new String[] {});
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+ }
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+
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+ /**
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+ * Returns all the host names associated by the default nameserver with the
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+ * address bound to the specified network interface
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+ *
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+ * @param strInterface
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+ * The name of the network interface to query (e.g. eth0)
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+ * @return The list of host names associated with IPs bound to the network
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+ * interface
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+ * @throws UnknownHostException
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+ * If one is encountered while querying the deault interface
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+ *
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+ */
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+ public static String[] getHosts(String strInterface)
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+ throws UnknownHostException {
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+ return getHosts(strInterface, null);
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+ }
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+
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+ /**
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+ * Returns the default (first) host name associated by the provided
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+ * nameserver with the address bound to the specified network interface
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+ *
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+ * @param strInterface
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+ * The name of the network interface to query (e.g. eth0)
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+ * @param nameserver
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+ * The DNS host name
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+ * @return The default host names associated with IPs bound to the network
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+ * interface
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+ * @throws UnknownHostException
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+ * If one is encountered while querying the deault interface
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+ */
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+ public static String getDefaultHost(String strInterface, String nameserver)
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+ throws UnknownHostException {
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+ if (strInterface.equals("default"))
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+ return InetAddress.getLocalHost().getHostName();
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+
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+ if (nameserver.equals("default"))
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+ return getDefaultHost(strInterface);
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+
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+ String[] hosts = getHosts(strInterface, nameserver);
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+ return hosts[0];
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+ }
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+
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+ /**
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+ * Returns the default (first) host name associated by the default
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+ * nameserver with the address bound to the specified network interface
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+ *
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+ * @param strInterface
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+ * The name of the network interface to query (e.g. eth0)
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+ * @return The default host name associated with IPs bound to the network
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+ * interface
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+ * @throws UnknownHostException
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+ * If one is encountered while querying the deault interface
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+ */
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+ public static String getDefaultHost(String strInterface)
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+ throws UnknownHostException {
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+ return getDefaultHost(strInterface, null);
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+ }
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+
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+}
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Doug Cutting