Allow simple detection of mismatched values between local file header and central directory header

Provide docs explaining how to resolve the issue as well

Author: Col-E

src/main/java/software/coley/llzip/format/model/CentralDirectoryFileHeader.java

@@ -206,7 +206,7 @@ public void setCrc32(int crc32) {
 	 * Be aware that these attributes can be falsified.
 	 * Different zip-parsing programs treat the files differently
 	 * and may not adhere to what you expect from the zip specification.
-	 * <br>
+	 * <p>
 	 * When in doubt, trust {@code data.length()} from {@link LocalFileHeader#getFileData()}.
 	 *
 	 * @return Compressed size of {@link LocalFileHeader#getFileData()}.

src/main/java/software/coley/llzip/format/model/LocalFileHeader.java

@@ -1,7 +1,8 @@
 package software.coley.llzip.format.model;
 
-import software.coley.llzip.format.compression.ZipCompressions;
 import software.coley.llzip.format.compression.Decompressor;
+import software.coley.llzip.format.compression.ZipCompressions;
+import software.coley.llzip.format.read.ZipReaderStrategy;
 import software.coley.llzip.util.ByteData;
 import software.coley.llzip.util.ByteDataUtil;
 
@@ -63,10 +64,35 @@ public void read(ByteData data, long offset) {
 		fileData = data.sliceOf(offset + 30 + fileNameLength + extraFieldLength, fileDataLength);
 	}
 
+	/**
+	 * Checks if the contents do not match those described in {@link CentralDirectoryFileHeader}.
+	 * If this is the case you will probably want to change your ZIP reading configuration.
+	 * <p>
+	 * You can override the {@link ZipReaderStrategy#postProcessLocalFileHeader(LocalFileHeader)}
+	 * to call {@link #adoptLinkedCentralDirectoryValues()}. The implementations of {@link ZipReaderStrategy}
+	 * are non-final, so you can extend them to add the override.
+	 *
+	 * @return {@code true} when the contents of this file header do not match those outlined by the associated
+	 * {@link CentralDirectoryFileHeader}.
+	 */
+	public boolean hasDifferentValuesThanCentralDirectoryHeader() {
+		if (linkedDirectoryFileHeader == null) return false;
+		if (versionNeededToExtract != linkedDirectoryFileHeader.getVersionNeededToExtract()) return true;
+		if (generalPurposeBitFlag != linkedDirectoryFileHeader.getGeneralPurposeBitFlag()) return true;
+		if (compressionMethod != linkedDirectoryFileHeader.getCompressionMethod()) return true;
+		if (lastModFileTime != linkedDirectoryFileHeader.getLastModFileTime()) return true;
+		if (lastModFileDate != linkedDirectoryFileHeader.getLastModFileDate()) return true;
+		if (crc32 != linkedDirectoryFileHeader.getCrc32()) return true;
+		if (compressedSize != linkedDirectoryFileHeader.getCompressedSize()) return true;
+		if (uncompressedSize != linkedDirectoryFileHeader.getUncompressedSize()) return true;
+		if (fileNameLength != linkedDirectoryFileHeader.getFileNameLength()) return true;
+		return !Objects.equals(getFileNameAsString(), linkedDirectoryFileHeader.getFileNameAsString());
+	}
+
 	/**
 	 * When called before being {@link #freeze() frozen} values can be adopted from the linked
 	 * {@link #getLinkedDirectoryFileHeader() CentralDirectoryFileHeader}.
-	 * <br>
+	 * <p>
 	 * In some cases the {@link LocalFileHeader} file size may be 0, but the authoritative CEN states a non-0 value,
 	 * which you may want to adopt.
 	 */
@@ -95,7 +121,7 @@ public void adoptLinkedCentralDirectoryValues() {
 
 	/**
 	 * Clears the reference to the source {@link ByteData}, preventing further modification.
-	 * <br>
+	 * <p>
 	 * Prevents usage of {@link #adoptLinkedCentralDirectoryValues()}.
 	 */
 	public void freeze() {
@@ -236,8 +262,8 @@ public void setCrc32(int crc32) {
 	 * Be aware that these attributes can be falsified.
 	 * Different zip-parsing programs treat the files differently
 	 * and may not adhere to what you expect from the zip specification.
-	 * <br>
-	 * When in doubt, trust {@code data.length()} from {@link #getFileData()}.
+	 * <p>
+	 * When in doubt, trust the length provided by the {@link #getLinkedDirectoryFileHeader()}.
 	 *
 	 * @return Compressed size of {@link #getFileData()}.
 	 */
@@ -257,6 +283,9 @@ public void setCompressedSize(long compressedSize) {
 	 * Be aware that these attributes can be falsified.
 	 * Different zip-parsing programs treat the files differently
 	 * and may not adhere to what you expect from the zip specification.
+	 * <p>
+	 * When in doubt, trust the length provided by the {@link #getLinkedDirectoryFileHeader()} or
+	 * {@code data.length()} from {@link #getFileData()}.
 	 *
 	 * @return Uncompressed size after {@link #decompress(Decompressor)} is used on {@link #getFileData()}.
 	 */

src/main/java/software/coley/llzip/format/read/ForwardScanZipReaderStrategy.java

@@ -70,8 +70,4 @@ public void read(ZipArchive zip, ByteData data) throws IOException {
 		// Sort based on order
 		zip.getParts().sort(new OffsetComparator());
 	}
-
-	protected void postProcessLocalFileHeader(LocalFileHeader file) {
-		// no-op
-	}
 }

src/main/java/software/coley/llzip/format/read/JvmZipReaderStrategy.java

@@ -20,7 +20,7 @@
 /**
  * The JVM has some edge cases in how it parses zip/jar files.
  * It allows for some tricks that most tools do not support/expect.
- * <br>
+ * <p>
  * The primary difference from {@link ForwardScanZipReaderStrategy} is that the {@link EndOfCentralDirectory}
  * is scanned from the back, rather than from the front.
  *
@@ -140,8 +140,4 @@ else if (ByteDataUtil.startsWith(data, jvmBaseFileOffset, ZipPatterns.CENTRAL_DI
 		// Sort based on order
 		zip.getParts().sort(new OffsetComparator());
 	}
-
-	protected void postProcessLocalFileHeader(LocalFileHeader file) {
-		// no-op
-	}
 }

src/main/java/software/coley/llzip/format/read/ZipReaderStrategy.java

@@ -1,5 +1,6 @@
 package software.coley.llzip.format.read;
 
+import software.coley.llzip.format.model.LocalFileHeader;
 import software.coley.llzip.format.model.ZipArchive;
 import software.coley.llzip.util.ByteData;
 
@@ -21,4 +22,8 @@ public interface ZipReaderStrategy {
 	 * 		When the data cannot be read <i>(EOF, not matching expectations, etc)</i>
 	 */
 	void read(ZipArchive zip, ByteData buffer) throws IOException;
+
+	default void postProcessLocalFileHeader(LocalFileHeader file) {
+		// no-op by default
+	}
 }