org.apache.catalina.util.NetMask Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.catalina.util;
import java.net.InetAddress;
import java.net.UnknownHostException;
import org.apache.tomcat.util.res.StringManager;
/**
* A class representing a CIDR netmask.
*
*
* The constructor takes a string as an argument which represents a netmask, as
* per the CIDR notation -- whether this netmask be IPv4 or IPv6. It then
* extracts the network address (before the /) and the CIDR prefix (after the
* /), and tells through the #matches() method whether a candidate
* {@link InetAddress} object fits in the recorded range.
*
*
*
* As byte arrays as returned by InetAddress.getByName() are always
* in network byte order, finding a match is therefore as simple as testing
* whether the n first bits (where n is the CIDR) are the same in both byte
* arrays (the one of the network address and the one of the candidate address).
* We do that by first doing byte comparisons, then testing the last bits if any
* (that is, if the remainder of the integer division of the CIDR by 8 is not
* 0).
*
*
*
* As a bonus, if no '/' is found in the input, it is assumed that an exact
* address match is required.
*
*/
public final class NetMask {
private static final StringManager sm = StringManager.getManager(NetMask.class);
/**
* The argument to the constructor, used for .toString()
*/
private final String expression;
/**
* The byte array representing the address extracted from the expression
*/
private final byte[] netaddr;
/**
* The number of bytes to test for equality (CIDR / 8)
*/
private final int nrBytes;
/**
* The right shift to apply to the last byte if CIDR % 8 is not 0; if it is
* 0, this variable is set to 0
*/
private final int lastByteShift;
/**
* Constructor
*
* @param input the CIDR netmask
* @throws IllegalArgumentException if the netmask is not correct (invalid
* address specification, malformed CIDR prefix, etc)
*/
public NetMask(final String input) {
expression = input;
final int idx = input.indexOf("/");
/*
* Handle the "IP only" case first
*/
if (idx == -1) {
try {
netaddr = InetAddress.getByName(input).getAddress();
} catch (UnknownHostException e) {
throw new IllegalArgumentException(sm.getString("netmask.invalidAddress", input));
}
nrBytes = netaddr.length;
lastByteShift = 0;
return;
}
/*
* OK, we do have a netmask specified, so let's extract both the address
* and the CIDR.
*/
final String addressPart = input.substring(0, idx), cidrPart = input.substring(idx + 1);
try {
/*
* The address first...
*/
netaddr = InetAddress.getByName(addressPart).getAddress();
} catch (UnknownHostException e) {
throw new IllegalArgumentException(sm.getString("netmask.invalidAddress", addressPart));
}
final int addrlen = netaddr.length * 8;
final int cidr;
try {
/*
* And then the CIDR.
*/
cidr = Integer.parseInt(cidrPart);
} catch (NumberFormatException e) {
throw new IllegalArgumentException(sm.getString("netmask.cidrNotNumeric", cidrPart));
}
/*
* We don't want a negative CIDR, nor do we want a CIDR which is greater
* than the address length (consider 0.0.0.0/33, or ::/129)
*/
if (cidr < 0) {
throw new IllegalArgumentException(sm.getString("netmask.cidrNegative", cidrPart));
}
if (cidr > addrlen) {
throw new IllegalArgumentException(
sm.getString("netmask.cidrTooBig", cidrPart, Integer.valueOf(addrlen)));
}
nrBytes = cidr / 8;
/*
* These last two lines could be shortened to:
*
* lastByteShift = (8 - (cidr % 8)) & 7;
*
* But... It's not worth it. In fact, explaining why it could work would
* be too long to be worth the trouble, so let's do it the simple way...
*/
final int remainder = cidr % 8;
lastByteShift = (remainder == 0) ? 0 : 8 - remainder;
}
/**
* Test if a given address matches this netmask.
*
* @param addr The {@link java.net.InetAddress} to test
* @return true on match, false otherwise
*/
public boolean matches(final InetAddress addr) {
final byte[] candidate = addr.getAddress();
/*
* OK, remember that a CIDR prefix tells the number of BITS which should
* be equal between this NetMask's recorded address (netaddr) and the
* candidate address. One byte is 8 bits, no matter what, and IP
* addresses, whether they be IPv4 or IPv6, are big endian, aka MSB,
* Most Significant Byte (first).
*
* We therefore need to get the byte array of the candidate address,
* compare as many bytes of the candidate address with the recorded
* address as the CIDR prefix tells us to (that is, CIDR / 8), and then
* deal with the remaining bits -- if any.
*
* But prior to that, a simple test can be done: we deal with IP
* addresses here, which means IPv4 and IPv6. IPv4 addresses are encoded
* on 4 bytes, IPv6 addresses are encoded on 16 bytes. If the candidate
* address length is different than this NetMask's address, we don't
* have a match.
*/
if (candidate.length != netaddr.length) {
return false;
}
/*
* Now do the byte-compare. The constructor has recorded the number of
* bytes to compare in nrBytes, use that. If any of the byte we have to
* compare is different than what we expect, we don't have a match.
*
* If, on the opposite, after this loop, all bytes have been deemed
* equal, then the loop variable i will point to the byte right after
* that -- which we will need...
*/
int i = 0;
for (; i < nrBytes; i++) {
if (netaddr[i] != candidate[i]) {
return false;
}
}
/*
* ... if there are bits left to test. There aren't any if lastByteShift
* is set to 0.
*/
if (lastByteShift == 0) {
return true;
}
/*
* If it is not 0, however, we must test for the relevant bits in the
* next byte (whatever is in the bytes after that doesn't matter). We do
* it this way (remember that lastByteShift contains the amount of bits
* we should _right_ shift the last byte):
*
* - grab both bytes at index i, both from the netmask address and the
* candidate address; - xor them both.
*
* After the xor, it means that all the remaining bits of the CIDR
* should be set to 0...
*/
final int lastByte = netaddr[i] ^ candidate[i];
/*
* ... Which means that right shifting by lastByteShift should be 0.
*/
return lastByte >> lastByteShift == 0;
}
@Override
public String toString() {
return expression;
}
}