SpongeParser fails to parse valid .schematic file (no blocks detected)

[amatheo]

Description:

When loading the attached .schematic file (6901.zip), the parser detects it as SPONGE_V1 but fails to read any blocks (0 Block found).

I tested the same file with FAWE-Core and WorldEdit, and both parsed it without issue, so the file itself should not be corrupted.

After debugging, it seems that in the SpongeParser.parseBlocks method, the getByteArray step is skipped because the "BlockData" tag is not present in the file.

I’m not fully familiar with the schematic spec, so I’m unsure if the parser should handle this variant or if it’s missing support that FAWE/WE already implement.

I’m also interested in contributing a fix for this issue. Could you point me in the right direction on where to start looking in FAWE or WE’s codebase to understand how they handle this case?

[samuelh2005]

I've think I've found the problem. World Edit typically generates schematics with an extra sub-compound tag called Schematic under the root tag similar to this SNBT:

"": {
	Schematic: {
		Blocks: {
			Palette: {
				"minecraft:stone": 0
				"minecraft:cobblestone": 1
			}
			Data: bytes(...)
			BlockEntities: []
		}
		Version: 3
		Length: 33S
		Metadata: {
			WorldEdit: {
				Origin: ints(8, -60, 8)
				Platforms: {
					"enginehub:fabric": {
						Version: "7.3.16+cbf4bd5"
						Name: Fabric-Official
					}
				}
				EditingPlatform: "enginehub:fabric"
				Version: "7.3.16"
			}
			Date: 1759923072977L
		}
		Height: 1S
		DataVersion: 4440
		Width: 33S
		Offset: ints(-16, -1, -16)
	}
}

However, [SpongeParser}(https://github.com/SandroHc/schematic4j/blob/master/src/main/java/net/sandrohc/schematic4j/parser/SpongeParser.java) ingores this sub-tag alltogether and assumes all children belong to the root resulting with zero / empty data.

As a workaround one can load their schematics similar to this:

            final NamedTag rootTag = NBTUtil.Reader.read().from(...); // path, InputStream, or byte[]
            final CompoundTag nbt = rootTag!=null&& rootTag.getTag() instanceof CompoundTag? (CompoundTag) rootTag.getTag() :null;
            final CompoundTag schematicRoot = nbt.getCompoundTag("Schematic");
            Schematic schematic = SchematicLoader.parse(schematicRoot);

In addition, you may need to use a GZIPInputStream if your schematic is compressed (which is very likely).