Fix compatibility of MapBlock decoding

also properly drop support for version < 22, which hasn't worked in years
minetest · May 6, 2020 · 2979dc5 · 2979dc5
1 parent 92f6b05
commit 2979dc5
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Showing 2 changed files with 27 additions and 16 deletions.
diff --git a/BlockDecoder.cpp b/BlockDecoder.cpp
@@ -11,20 +11,18 @@ static inline uint16_t readU16(const unsigned char *data)
 	return data[0] << 8 | data[1];
 }
 
-static int readBlockContent(const unsigned char *mapData, u8 version, unsigned int datapos)
+static int readBlockContent(const unsigned char *mapData, u8 contentWidth, unsigned int datapos)
 {
-	if (version >= 24) {
+	if (contentWidth == 2) {
 		size_t index = datapos << 1;
 		return (mapData[index] << 8) | mapData[index + 1];
-	} else if (version >= 20) {
-		if (mapData[datapos] <= 0x80)
-			return mapData[datapos];
+	} else {
+		u8 param = mapData[datapos];
+		if (param <= 0x7f)
+			return param;
 		else
-			return (int(mapData[datapos]) << 4) | (int(mapData[datapos + 0x2000]) >> 4);
+			return (int(param) << 4) | (int(mapData[datapos + 0x2000]) >> 4);
 	}
-	std::ostringstream oss;
-	oss << "Unsupported map version " << version;
-	throw std::runtime_error(oss.str());
 }
 
 BlockDecoder::BlockDecoder()
@@ -39,6 +37,7 @@ void BlockDecoder::reset()
 	m_nameMap.clear();
 
 	m_version = 0;
+	m_contentWidth = 0;
 	m_mapData = ustring();
 }
 
@@ -50,25 +49,37 @@ void BlockDecoder::decode(const ustring &datastr)
 
 	uint8_t version = data[0];
 	//uint8_t flags = data[1];
+	if (version < 22) {
+		std::ostringstream oss;
+		oss << "Unsupported map version " << (int)version;
+		throw std::runtime_error(oss.str());
+	}
 	m_version = version;
 
 	size_t dataOffset = 0;
 	if (version >= 27)
-		dataOffset = 6;
-	else if (version >= 22)
 		dataOffset = 4;
 	else
 		dataOffset = 2;
 
+	uint8_t contentWidth = data[dataOffset];
+	dataOffset++;
+	uint8_t paramsWidth = data[dataOffset];
+	dataOffset++;
+	if (contentWidth != 1 && contentWidth != 2)
+		throw std::runtime_error("unsupported map version (contentWidth)");
+	if (paramsWidth != 2)
+		throw std::runtime_error("unsupported map version (paramsWidth)");
+	m_contentWidth = contentWidth;
+
+
 	ZlibDecompressor decompressor(data, length);
 	decompressor.setSeekPos(dataOffset);
 	m_mapData = decompressor.decompress();
 	decompressor.decompress(); // unused metadata
 	dataOffset = decompressor.seekPos();
 
 	// Skip unused data
-	if (version <= 21)
-		dataOffset += 2;
 	if (version == 23)
 		dataOffset += 1;
 	if (version == 24) {
@@ -92,7 +103,7 @@ void BlockDecoder::decode(const ustring &datastr)
 	dataOffset += 4; // Skip timestamp
 
 	// Read mapping
-	if (version >= 22) {
+	{
 		dataOffset++; // mapping version
 		uint16_t numMappings = readU16(data + dataOffset);
 		dataOffset += 2;
@@ -130,7 +141,7 @@ bool BlockDecoder::isEmpty() const
 std::string BlockDecoder::getNode(u8 x, u8 y, u8 z) const
 {
 	unsigned int position = x + (y << 4) + (z << 8);
-	int content = readBlockContent(m_mapData.c_str(), m_version, position);
+	int content = readBlockContent(m_mapData.c_str(), m_contentWidth, position);
 	if (content == m_blockAirId || content == m_blockIgnoreId)
 		return "";
 	NameMap::const_iterator it = m_nameMap.find(content);

diff --git a/include/BlockDecoder.h b/include/BlockDecoder.h
@@ -20,7 +20,7 @@ class BlockDecoder {
 	int m_blockAirId;
 	int m_blockIgnoreId;
 
-	u8 m_version;
+	u8 m_version, m_contentWidth;
 	ustring m_mapData;
 };