| /* |
| * Copyright 2016-present Open Networking Laboratory |
| * |
| * 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 org.onosproject.isis.io.util; |
| |
| |
| import java.util.Arrays; |
| |
| /** |
| * Calculates checksum for ISIS LSP packets. |
| */ |
| public class ChecksumCalculator { |
| |
| /** |
| * Verifies the checksum is valid in given LSP packet bytes. |
| * |
| * @param lspPacket lsp as byte array |
| * @param lspChecksumPos1 position of checksum bit in packet |
| * @param lspChecksumPos2 position of checksum bit in packet |
| * @return true if valid else false |
| */ |
| public boolean validateLspCheckSum(byte[] lspPacket, int lspChecksumPos1, int lspChecksumPos2) { |
| |
| byte[] checksum = calculateLspChecksum(lspPacket, lspChecksumPos1, lspChecksumPos2); |
| if (lspPacket[lspChecksumPos1] == checksum[0] && lspPacket[lspChecksumPos2] == checksum[1]) { |
| return true; |
| } |
| return false; |
| } |
| |
| |
| /** |
| * Calculates the LSP checksum. |
| * |
| * @param lspBytes as byte array |
| * @param lspChecksumPos1 position of checksum bit in packet |
| * @param lspChecksumPos2 position of checksum bit in packet |
| * @return checksum bytes |
| */ |
| public byte[] calculateLspChecksum(byte[] lspBytes, int lspChecksumPos1, int lspChecksumPos2) { |
| |
| byte[] tempLsaByte = Arrays.copyOf(lspBytes, lspBytes.length); |
| |
| int[] checksumOut = {0, 0}; |
| tempLsaByte[lspChecksumPos1] = 0; |
| tempLsaByte[lspChecksumPos2] = 0; |
| byte[] byteCheckSum = {0, 0}; |
| if (lspBytes != null) { |
| for (int i = 12; i < tempLsaByte.length; i++) { |
| checksumOut[0] = checksumOut[0] + ((int) tempLsaByte[i] & 0xFF); |
| checksumOut[1] = checksumOut[1] + checksumOut[0]; |
| } |
| checksumOut[0] = checksumOut[0] % 255; |
| checksumOut[1] = checksumOut[1] % 255; |
| } |
| int byte1 = (int) ((tempLsaByte.length - lspChecksumPos1 - 1) * checksumOut[0] - checksumOut[1]) % 255; |
| if (byte1 <= 0) { |
| byte1 += 255; |
| } |
| int byte2 = 510 - checksumOut[0] - byte1; |
| if (byte2 > 255) { |
| byte2 -= 255; |
| } |
| |
| byteCheckSum[0] = (byte) byte1; |
| byteCheckSum[1] = (byte) byte2; |
| |
| return byteCheckSum; |
| } |
| } |