inetaddress.java

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		return new Inet4Address(host, addr);
	    } else if (addr.length == Inet6Address.INADDRSZ) {
		byte[] newAddr 
		    = Inet6Address.convertFromIPv4MappedAddress(addr);
		if (newAddr != null) {
		    return new Inet4Address(host, newAddr);
		} else {
		    return new Inet6Address(host, addr);
		}
	    } 
	} 
	throw new UnknownHostException("addr is of illegal length");
    }

    /**
     * Determines the IP address of a host, given the host's name.
     *
     * <p> The host name can either be a machine name, such as
     * "<code>java.sun.com</code>", or a textual representation of its
     * IP address. If a literal IP address is supplied, only the
     * validity of the address format is checked.
     *
     * <p> For <code>host</code> specified in literal IPv6 address,
     * either the form defined in RFC 2732 or the literal IPv6 address
     * format defined in RFC 2373 is accepted.
     *
     * <p> If the host is <tt>null</tt> then an <tt>InetAddress</tt>
     * representing an address of the loopback interface is returned.
     * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>
     * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>
     * section&nbsp;2.5.3. </p>
     *
     * @param      host   the specified host, or <code>null</code>.
     * @return     an IP address for the given host name.
     * @exception  UnknownHostException  if no IP address for the
     *               <code>host</code> could be found.
     * @exception  SecurityException if a security manager exists
     *             and its checkConnect method doesn't allow the operation
     */
    public static InetAddress getByName(String host)
	throws UnknownHostException {
	return InetAddress.getAllByName(host)[0];
    }

    /**
     * Given the name of a host, returns an array of its IP addresses,
     * based on the configured name service on the system.
     * 
     * <p> The host name can either be a machine name, such as
     * "<code>java.sun.com</code>", or a textual representation of its IP
     * address. If a literal IP address is supplied, only the
     * validity of the address format is checked.
     *
     * <p> For <code>host</code> specified in literal IPv6 address,
     * either the form defined in RFC 2732 or the literal IPv6 address
     * format defined in RFC 2373 is accepted.
     *
     * <p> If the host is <tt>null</tt> then an <tt>InetAddress</tt>
     * representing an address of the loopback interface is returned.
     * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>
     * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>
     * section&nbsp;2.5.3. </p>
     *
     * <p> If there is a security manager and <code>host</code> is not 
     * null and <code>host.length() </code> is not equal to zero, the
     * security manager's
     * <code>checkConnect</code> method is called
     * with the hostname and <code>-1</code> 
     * as its arguments to see if the operation is allowed.
     *
     * @param      host   the name of the host, or <code>null</code>.
     * @return     an array of all the IP addresses for a given host name.
     * 
     * @exception  UnknownHostException  if no IP address for the
     *               <code>host</code> could be found.
     * @exception  SecurityException  if a security manager exists and its  
     *               <code>checkConnect</code> method doesn't allow the operation.
     * 
     * @see SecurityManager#checkConnect
     */
    public static InetAddress[] getAllByName(String host)
	throws UnknownHostException {

	if (host == null || host.length() == 0) {
	    InetAddress[] ret = new InetAddress[1];
	    ret[0] = impl.loopbackAddress();
	    return ret;
	}
	
	boolean ipv6Expected = false;
	if (host.charAt(0) == '[') {
	    // This is supposed to be an IPv6 litteral
	    if (host.length() > 2 && host.charAt(host.length()-1) == ']') {
		host = host.substring(1, host.length() -1);
		ipv6Expected = true;
	    } else {
		// This was supposed to be a IPv6 address, but it's not!
		throw new UnknownHostException(host);
	    }
	}

	// if host is an IP address, we won't do further lookup
	if (Character.digit(host.charAt(0), 16) != -1 
	    || (host.charAt(0) == ':')) {
	    byte[] addr = null;
	    // see if it is IPv4 address
	    addr = Inet4Address.textToNumericFormat(host);
	    if (addr == null) {
		// see if it is IPv6 address
		addr = Inet6Address.textToNumericFormat(host);
	    } else if (ipv6Expected) {
		// Means an IPv4 litteral between brackets!
		throw new UnknownHostException("["+host+"]");
	    }
	    InetAddress[] ret = new InetAddress[1];
	    if(addr != null) {
		if (addr.length == Inet4Address.INADDRSZ) {
		    ret[0] = new Inet4Address(null, addr);
		} else {
		    ret[0] = new Inet6Address(null, addr);
		}
		return ret;
	    }
	    } else if (ipv6Expected) {
		// We were expecting an IPv6 Litteral, but got something else
		throw new UnknownHostException("["+host+"]");
	    }
	return getAllByName0(host);
    }

    private static InetAddress[] getAllByName0 (String host)
	throws UnknownHostException
    {
	return getAllByName0(host, true);
    }

    /**
     * package private so SocketPermission can call it
     */
    static InetAddress[] getAllByName0 (String host, boolean check)
	throws UnknownHostException  {
	/* If it gets here it is presumed to be a hostname */
	/* Cache.get can return: null, unknownAddress, or InetAddress[] */
        Object obj = null;
	Object objcopy = null;

	/* make sure the connection to the host is allowed, before we
	 * give out a hostname
	 */
	if (check) {
	    SecurityManager security = System.getSecurityManager();
	    if (security != null) {
		security.checkConnect(host, -1);
	    }
	}

	obj = getCachedAddress(host);

	/* If no entry in cache, then do the host lookup */
	if (obj == null) {
	    try {
	        obj = getAddressFromNameService(host);
	    } catch (UnknownHostException uhe) {
		throw new UnknownHostException(host + ": " + uhe.getMessage());
	    }
	}

	if (obj == unknown_array) 
	    throw new UnknownHostException(host);

	/* Make a copy of the InetAddress array */
	objcopy = ((InetAddress [])obj).clone();

	return (InetAddress [])objcopy;
    }

    private static Object getAddressFromNameService(String host) 
	throws UnknownHostException 
    {
	Object obj = null;
	boolean success = false;

	// Check whether the host is in the lookupTable.
	// 1) If the host isn't in the lookupTable when
	//    checkLookupTable() is called, checkLookupTable()
	//    would add the host in the lookupTable and
	//    return null. So we will do the lookup.
	// 2) If the host is in the lookupTable when
	//    checkLookupTable() is called, the current thread
	//    would be blocked until the host is removed
	//    from the lookupTable. Then this thread
	//    should try to look up the addressCache.
	//     i) if it found the address in the
	//        addressCache, checkLookupTable()  would
	//        return the address.
	//     ii) if it didn't find the address in the
	//         addressCache for any reason,
	//         it should add the host in the
	//         lookupTable and return null so the
	//         following code would do  a lookup itself.
	if ((obj = checkLookupTable(host)) == null) {
	    // This is the first thread which looks up the address 
	    // this host or the cache entry for this host has been
	    // expired so this thread should do the lookup.
	    try {
		/*
		 * Do not put the call to lookup() inside the
		 * constructor.  if you do you will still be
		 * allocating space when the lookup fails.
		 */
		byte[][] byte_array;
		byte_array = nameService.lookupAllHostAddr(host);
		InetAddress[] addr_array =
		    new InetAddress[byte_array.length];

		for (int i = 0; i < byte_array.length; i++) {
		    byte addr[] = byte_array[i];
		    if (addr.length == Inet4Address.INADDRSZ) {
			addr_array[i] = new Inet4Address(host, addr);
		    } else {
			addr_array[i] = new Inet6Address(host, addr);
		    }
		}
		obj = addr_array;
		success = true;
	    } catch (UnknownHostException uhe) {
		obj  = unknown_array; 
		success = false;
		throw uhe;
	    } finally {
		try {
		    // Cache the address.
		    cacheAddress(host, obj, success);
		} finally {
		    // Delete the host from the lookupTable, and
		    // notify all threads waiting for the monitor
		    // for lookupTable.
		    updateLookupTable(host);
		}
	    }
	}

	return obj;
    }
	
		
    private static Object checkLookupTable(String host) {
	// make sure obj  is null.
	Object obj = null;
	
	synchronized (lookupTable) {
	    // If the host isn't in the lookupTable, add it in the
	    // lookuptable and return null. The caller should do
	    // the lookup.
	    if (lookupTable.containsKey(host) == false) {
		lookupTable.put(host, null);
		return obj;
	    }

	    // If the host is in the lookupTable, it means that another
	    // thread is trying to look up the address of this host.
	    // This thread should wait.
	    while (lookupTable.containsKey(host)) {
		try {
		    lookupTable.wait();
		} catch (InterruptedException e) {
		}
	    }
	}

	// The other thread has finished looking up the address of
	// the host. This thread should retry to get the address
	// from the addressCache. If it doesn't get the address from
	// the cache,  it will try to look up the address itself.
	obj = getCachedAddress(host);
	if (obj == null) {
	    synchronized (lookupTable) {
		lookupTable.put(host, null);
	    }
	}
	 
	return obj;
    }

    private static void updateLookupTable(String host) {
	synchronized (lookupTable) {
	    lookupTable.remove(host);
	    lookupTable.notifyAll();
	}
    }

    /**
     * Returns an <code>InetAddress</code> object given the raw IP address . 
     * The argument is in network byte order: the highest order
     * byte of the address is in <code>getAddress()[0]</code>.
     *
     * <p> This method doesn't block, i.e. no reverse name service lookup
     * is performed.
     *
     * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array 
     * must be 16 bytes long
     *
     * @param addr the raw IP address in network byte order
     * @return  an InetAddress object created from the raw IP address.
     * @exception  UnknownHostException  if IP address is of illegal length
     * @since 1.4
     */
    public static InetAddress getByAddress(byte[] addr) 
	throws UnknownHostException {
	return getByAddress(null, addr);
    }

    /**
     * Returns the local host.
     *
     * <p>If there is a security manager, its
     * <code>checkConnect</code> method is called
     * with the local host name and <code>-1</code> 
     * as its arguments to see if the operation is allowed. 
     * If the operation is not allowed, an InetAddress representing
     * the loopback address is returned.
     *
     * @return     the IP address of the local host.
     * 
     * @exception  UnknownHostException  if no IP address for the
     *               <code>host</code> could be found.
     * 
     * @see SecurityManager#checkConnect
     */
    public static InetAddress getLocalHost() throws UnknownHostException {

	SecurityManager security = System.getSecurityManager();
	try {
	    String local = impl.getLocalHostName();

	    if (security != null) {
		security.checkConnect(local, -1);
	    }
	    // we are calling getAddressFromNameService directly
	    // to avoid getting localHost from cache 

	    InetAddress[] localAddrs;
	    try {
		localAddrs =
		    (InetAddress[]) InetAddress.getAddressFromNameService(local);
	    } catch (UnknownHostException uhe) {
		throw new UnknownHostException(local + ": " + uhe.getMessage());
	    }
	    return localAddrs[0];
	} catch (java.lang.SecurityException e) {
	    return impl.loopbackAddress();
	}
    }


    /**
     * Perform class load-time initializations.
     */
    private static native void init();


    /*
     * Returns the InetAddress representing anyLocalAddress
     * (typically 0.0.0.0 or ::0)
     */
    static InetAddress anyLocalAddress() {
        return impl.anyLocalAddress();
    }

    /*
     * Load and instantiate an underlying impl class
     */
    static Object loadImpl(String implName) {
	Object impl;

        /*
         * Property "impl.prefix" will be prepended to the classname
         * of the implementation object we instantiate, to which we
         * delegate the real work (like native methods).  This
         * property can vary across implementations of the java.
         * classes.  The default is an empty String "".
         */
        String prefix = (String)AccessController.doPrivileged(
                      new GetPropertyAction("impl.prefix", ""));
        impl = null;
        try {
            impl = Class.forName("java.net." + prefix + implName).newInstance();
        } catch (ClassNotFoundException e) {
            System.err.println("Class not found: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        } catch (InstantiationException e) {
            System.err.println("Could not instantiate: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        } catch (IllegalAccessException e) {
            System.err.println("Cannot access class: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        }

        if (impl == null) {
            try {
                impl = Class.forName(implName).newInstance();
            } catch (Exception e) {
                throw new Error("System property impl.prefix incorrect");
            }
        }

	return impl;
    }

    /* Check java.net.preferIPv4Stack property. Used by
       init_IPv6Available() */
    private static boolean preferIPv4Stack() {
        Boolean res = (Boolean) java.security.AccessController.doPrivileged(
            new sun.security.action.GetBooleanAction(
                "java.net.preferIPv4Stack"));
        return res.booleanValue();
    }
}

/*
 * Simple factory to create the impl
 */
class InetAddressImplFactory {

    static InetAddressImpl create() {
	Object o;
	if (isIPv6Supported()) {
	    o = InetAddress.loadImpl("Inet6AddressImpl");
	} else {
	    o = InetAddress.loadImpl("Inet4AddressImpl");
	}
	return (InetAddressImpl)o;
    }

    private static native boolean isIPv6Supported();
}