From 67797138974aff5d01be137985191efc0d84f6bd Mon Sep 17 00:00:00 2001
From: trafficlunar <hello@trafficlunar.net>
Date: Thu, 23 Jan 2025 19:29:46 +0000
Subject: [PATCH] fix: decoding varint for .schem files

---
 src/components/dialogs/OpenSchematic.tsx |  9 +++---
 src/utils/varint.ts                      | 36 +++++++++++++++++++++---
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/src/components/dialogs/OpenSchematic.tsx b/src/components/dialogs/OpenSchematic.tsx
index 30ad75d..b4cc9ff 100644
--- a/src/components/dialogs/OpenSchematic.tsx
+++ b/src/components/dialogs/OpenSchematic.tsx
@@ -37,7 +37,7 @@ interface LitematicNBT extends nbt.ListTagLike {
 interface SpongeNBT extends nbt.ListTagLike {
 	Schematic: {
 		Blocks: {
-			Data: Int8Array;
+			Data: Uint8Array;
 			Palette: Record<string, number>;
 		};
 		DataVersion: number;
@@ -153,14 +153,15 @@ function OpenSchematic({ close }: DialogProps) {
 
 				// Add every block to the canvas
 				const blocks: Block[] = [];
-				let index = 0;
+				let offset = 0;
 
 				for (let y = spongeData.Height; y > 0; y--) {
 					for (let x = 0; x < spongeData.Width; x++) {
-						const paletteValue = spongeData.Blocks.Data[index];
+						// Decode varint to get the pallete value
+						const { value: paletteValue, bytesRead } = decodeVarint(spongeData.Blocks.Data, offset);
 						const paletteBlock = Object.keys(spongeData.Blocks.Palette).find((key) => spongeData.Blocks.Palette[key] == paletteValue);
 
-						index++;
+						offset += bytesRead;
 						if (!paletteBlock) continue;
 
 						const blockIdWithProperties = paletteBlock.replace("minecraft:", "");
diff --git a/src/utils/varint.ts b/src/utils/varint.ts
index 27d5888..1491572 100644
--- a/src/utils/varint.ts
+++ b/src/utils/varint.ts
@@ -1,9 +1,37 @@
-export function encodeVarint(number: number) {
+export function encodeVarint(number: number): Uint8Array {
 	const result = [];
 	while (number >= 0x80) {
-		result.push((number & 0x7f) | 0x80); // Take 7 bits and set the MSB
-		number >>>= 7; // Right shift by 7 bits (logical shift)
+		// Take 7 bits and set the MSB
+		result.push((number & 0x7f) | 0x80);
+
+		// Right shift by 7 bits (logical shift)
+		number >>>= 7;
 	}
-	result.push(number); // Last byte without MSB set
+
+	// Last byte without MSB set
+	result.push(number);
 	return new Uint8Array(result);
 }
+
+export function decodeVarint(buffer: Uint8Array, offset: number): { value: number; bytesRead: number } {
+	let value = 0;
+	let position = 0;
+	let byte: number;
+
+	do {
+		if (position > 35) {
+			throw new Error("VarInt is too big");
+		}
+
+		// Read the current byte
+		byte = buffer[offset++];
+
+		// Extract the lower 7 bits of the byte and shift them to the correct position
+		value |= (byte & 0x7f) << (position * 7);
+
+		// Increment the position for the next byte
+		position++;
+	} while ((byte & 0x80) !== 0); // Continue if the most significant bit (MSB) is set
+
+	return { value, bytesRead: position };
+}