chore: check for magic bytes in schematic (not tested yet)

worldedit-core/src/main/java/com/fastasyncworldedit/core/extent/clipboard/io/FastSchematicWriterV2.java

@@ -103,11 +103,11 @@ public class FastSchematicWriterV2 implements ClipboardWriter {
 
         final DataOutput rawStream = outputStream.getOutputStream();
         outputStream.writeLazyCompoundTag("Schematic", out -> {
+            out.writeNamedTag("Version", CURRENT_VERSION);
             out.writeNamedTag(
                     "DataVersion",
                     WorldEdit.getInstance().getPlatformManager().queryCapability(Capability.WORLD_EDITING).getDataVersion()
             );
-            out.writeNamedTag("Version", CURRENT_VERSION);
             out.writeNamedTag("Width", (short) width);
             out.writeNamedTag("Height", (short) height);
             out.writeNamedTag("Length", (short) length);

worldedit-core/src/main/java/com/sk89q/worldedit/extent/clipboard/io/BuiltInClipboardFormat.java

@@ -50,6 +50,7 @@ import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.Arrays;
 import java.util.Locale;
 import java.util.Set;
 import java.util.zip.GZIPInputStream;
@@ -83,8 +84,13 @@ public enum BuiltInClipboardFormat implements ClipboardFormat {
 
         @Override
         public boolean isFormat(final InputStream inputStream) {
-            try (final DataInputStream stream = new DataInputStream(new FastBufferedInputStream(new GZIPInputStream(inputStream)));
+            try (final DataInputStream stream = new DataInputStream(new BufferedInputStream(new GZIPInputStream(inputStream)));
                  final NBTInputStream nbt = new NBTInputStream(stream)) {
+                stream.mark(SPONGE_V3_MAGIC.length);
+                if (Arrays.equals(stream.readNBytes(SPONGE_V3_MAGIC.length), SPONGE_V3_MAGIC)) {
+                    return stream.readInt() == FastSchematicWriterV3.CURRENT_VERSION;
+                }
+                stream.reset();
                 if (stream.readByte() != NBTConstants.TYPE_COMPOUND) {
                     return false;
                 }
@@ -394,10 +400,37 @@ public enum BuiltInClipboardFormat implements ClipboardFormat {
     };
     //FAWE end
 
+    private static final byte[] SPONGE_V2_MAGIC = new byte[]{
+            0x10, // TAG_Compound
+            0x00, 0x09, // len("Schematic") - unsigned short
+            0x53, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x74, 0x69, 0x63, // "Schematic" (modified UTF-8)
+            0x03, // TAG_INT
+            0x00, 0x07, // len("Version") - unsigned short
+            0x56, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E  // "Version" (modified UTF-8)
+    };
+
+    private static final byte[] SPONGE_V3_MAGIC = new byte[]{
+            0x10, // TAG_Compound
+            0x00, 0x00, // len("") - unsigned short (no following bytes for string because there is none)
+            0x10, // TAG_Compound
+            0x00, 0x09, // len("Schematic") - unsigned short
+            0x53, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x74, 0x69, 0x63, // "Schematic" (modified UTF-8)
+            0x03, // TAG_INT
+            0x00, 0x07, // len("Version") - unsigned short
+            0x56, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E  // "Version" (modified UTF-8)
+    };
+
     private static boolean detectOldSpongeSchematic(InputStream inputStream, int version) {
         //FAWE start - dont utilize linbus - WorldEdit approach is not really streamed
-        try (final DataInputStream stream = new DataInputStream(new FastBufferedInputStream(new GZIPInputStream(inputStream)));
+        try (final DataInputStream stream = new DataInputStream(new BufferedInputStream(new GZIPInputStream(inputStream)));
              final NBTInputStream nbt = new NBTInputStream(stream)) {
+            stream.mark(SPONGE_V2_MAGIC.length);
+            // If magic sequence found, return early (schematic was created by FAWE)
+            if (Arrays.equals(stream.readNBytes(SPONGE_V2_MAGIC.length), SPONGE_V2_MAGIC)) {
+                return stream.readInt() == version;
+            }
+            stream.reset();
+
             if (stream.readByte() != NBTConstants.TYPE_COMPOUND) {
                 return false;
             }