From 207b4d003384b048abe069e4888e980741d7bbf6 Mon Sep 17 00:00:00 2001
From: Glavo <zjx001202@gmail.com>
Date: Fri, 26 Jan 2024 21:20:29 +0800
Subject: [PATCH] Fix #2687 (#2688)

* Fix #2687

* fix checkstyle
---
 .../jackhuang/hmcl/ui/nbt/NBTFileType.java    | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/nbt/NBTFileType.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/nbt/NBTFileType.java
index 4b35a6693..02dbbb844 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/nbt/NBTFileType.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/nbt/NBTFileType.java
@@ -9,6 +9,7 @@ import org.apache.commons.compress.utils.BoundedInputStream;
 import org.jackhuang.hmcl.util.io.FileUtils;
 
 import java.io.*;
+import java.util.Arrays;
 import java.util.zip.GZIPInputStream;
 import java.util.zip.Inflater;
 import java.util.zip.InflaterInputStream;
@@ -17,8 +18,22 @@ public enum NBTFileType {
     COMPRESSED("dat", "dat_old") {
         @Override
         public Tag read(File file) throws IOException {
-            try (InputStream in = new GZIPInputStream(new FileInputStream(file))) {
-                Tag tag = NBTIO.readTag(in);
+            try (BufferedInputStream fileInputStream = new BufferedInputStream(new FileInputStream(file))) {
+                fileInputStream.mark(3);
+                byte[] header = new byte[3];
+                if (fileInputStream.read(header) < 3) {
+                    throw new IOException("File is too small");
+                }
+                fileInputStream.reset();
+
+                InputStream input;
+                if (Arrays.equals(header, new byte[]{0x1f, (byte) 0x8b, 0x08})) {
+                    input = new GZIPInputStream(fileInputStream);
+                } else {
+                    input = fileInputStream;
+                }
+
+                Tag tag = NBTIO.readTag(input);
                 if (!(tag instanceof CompoundTag))
                     throw new IOException("Unexpected tag: " + tag);
                 return tag;