Add sector offset/length helper methods in ChunkRegionHeader

Author: Glavo

src/main/java/org/glavo/nbt/chunk/ChunkRegion.java

@@ -45,7 +45,7 @@ static ChunkRegion readRegion(RawDataReader rawReader) throws IOException {
         assert rawReader.position() == fileStart + 2 * ChunkUtils.SECTOR_BYTES;
 
         for (int localIndex : header.localIndexesSortedByOffset) {
-            long sectorStart = fileStart + (long) header.getSectorOffset(localIndex) * ChunkUtils.SECTOR_BYTES;
+            long sectorStart = fileStart + header.getSectorOffsetBytes(localIndex);
             long position = rawReader.position();
             if (position != sectorStart) {
                 if (position < sectorStart) {
@@ -62,6 +62,10 @@ static ChunkRegion readRegion(RawDataReader rawReader) throws IOException {
                 throw new IOException("Invalid chunk data length: " + chunkRawLength);
             }
 
+            if (chunkRawLength + 4L > header.getSectorLengthBytes(localIndex)) {
+                throw new IOException("Invalid chunk data length: " + chunkRawLength + " (expected <= " + header.getSectorLengthBytes(localIndex) + " - 4)");
+            }
+
             long chunkRawContentLength = chunkRawLength - 1L;
 
             int compressType = rawReader.readUnsignedByte();

src/main/java/org/glavo/nbt/internal/ChunkRegionHeader.java

@@ -25,6 +25,7 @@
 import java.util.stream.IntStream;
 
 import static org.glavo.nbt.internal.ChunkUtils.CHUNKS_PRE_REGION;
+import static org.glavo.nbt.internal.ChunkUtils.SECTOR_BYTES;
 
 public final class ChunkRegionHeader {
     public static ChunkRegionHeader readHeader(DataReader reader) throws IOException {
@@ -60,4 +61,12 @@ public int getSectorOffset(int index) {
     public int getSectorLength(int index) {
         return ChunkUtils.getSectorLength(sectorInfo[index]);
     }
+
+    public long getSectorOffsetBytes(int index) {
+        return (long) getSectorOffset(index) * SECTOR_BYTES;
+    }
+
+    public long getSectorLengthBytes(int index) {
+        return (long) getSectorLength(index) * SECTOR_BYTES;
+    }
 }