BaseNbtSerializer: added support for reading and writing headless tags

in the future it might be nice to make this generic, but it's not worth the effort and BC breaks right now, since we only need this in one place anyway.

src/BaseNbtSerializer.php

@@ -23,6 +23,7 @@
 
 namespace pocketmine\nbt;
 
+use pocketmine\nbt\tag\Tag;
 use pocketmine\utils\Binary;
 use pocketmine\utils\BinaryDataException;
 use pocketmine\utils\BinaryStream;
@@ -73,6 +74,24 @@ public function read(string $buffer, int &$offset = 0, int $maxDepth = 0) : Tree
 		return $data;
 	}
 
+	/**
+	 * Reads a tag without a header from the buffer and returns it. The tag does not have a name, and the type is not
+	 * specified by the binary data. Only the tag's raw binary value is present.
+	 *
+	 * This could be used if the expected root type is always the same, but it's not usually seen in the wild.
+	 * However, this is used in some places in the Minecraft: Bedrock network protocol.
+	 *
+	 * @throws NbtDataException
+	 */
+	public function readHeadless(string $buffer, int $rootType, int &$offset = 0, int $maxDepth = 0) : Tag{
+		$this->buffer = new BinaryStream($buffer, $offset);
+
+		$data = NBT::createTag($rootType, $this, new ReaderTracker($maxDepth));
+		$offset = $this->buffer->getOffset();
+
+		return $data;
+	}
+
 	/**
 	 * Decodes a list of NBT tags into objects and returns them.
 	 *
@@ -111,6 +130,18 @@ public function write(TreeRoot $data) : string{
 		return $this->buffer->getBuffer();
 	}
 
+	/**
+	 * Writes a nameless tag without any header information. The reader of the data must know what type to expect, as
+	 * it is not specified in the data.
+	 *
+	 * @see BaseNbtSerializer::readHeadless()
+	 */
+	public function writeHeadless(Tag $data) : string{
+		$this->buffer = new BinaryStream();
+		$data->write($this);
+		return $this->buffer->getBuffer();
+	}
+
 	/**
 	 * @param TreeRoot[] $data
 	 */

tests/phpunit/NbtSerializerTest.php

@@ -25,7 +25,9 @@
 
 use PHPUnit\Framework\TestCase;
 use pocketmine\nbt\tag\CompoundTag;
+use pocketmine\nbt\tag\IntTag;
 use pocketmine\nbt\tag\ListTag;
+use pocketmine\utils\Binary;
 
 class NbtSerializerTest extends TestCase{
 
@@ -73,4 +75,14 @@ public function testCompoundTagIntKeysEncode() : void{
 		$data->setInt("1", 1);
 		(new BigEndianNbtSerializer())->write(new TreeRoot($data));
 	}
+
+	public function testHeadlessDecodeEncode() : void{
+		$tag = new IntTag(123);
+		$serializer = new BigEndianNbtSerializer();
+		$raw = $serializer->writeHeadless($tag);
+		self::assertSame($raw, Binary::writeInt(123));
+
+		$tag2 = $serializer->readHeadless($raw, NBT::TAG_Int);
+		self::assertEquals($tag, $tag2);
+	}
 }