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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.poi.util;
-
- import java.io.ByteArrayOutputStream;
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.OutputStream;
-
- public final class PngUtils {
-
- /**
- * File header for PNG format.
- */
- private static final byte[] PNG_FILE_HEADER =
- new byte[] { (byte) 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };
-
- private PngUtils() {
- // no instances of this class
- }
-
- /**
- * Checks if the offset matches the PNG header.
- *
- * @param data the data to check.
- * @param offset the offset to check at.
- * @return {@code true} if the offset matches.
- */
- public static boolean matchesPngHeader(byte[] data, int offset) {
- if (data == null || data.length - offset < PNG_FILE_HEADER.length) {
- return false;
- }
-
- for (int i = 0; i < PNG_FILE_HEADER.length; i++) {
- if (PNG_FILE_HEADER[i] != data[i + offset]) {
- return false;
- }
- }
-
- return true;
- }
- }
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