Add length limit checks for CompoundTag and TreeRoot names

I am amazed we weren't checking this already. This ensures the error shows up in the place that caused it, and not when it gets encoded.

Author: dktapps

src/TreeRoot.php

@@ -25,6 +25,9 @@
 
 use pocketmine\nbt\tag\CompoundTag;
 use pocketmine\nbt\tag\Tag;
+use pocketmine\utils\Limits;
+use function sprintf;
+use function strlen;
 
 /**
  * This class wraps around the root Tag for NBT files to avoid losing the name information.
@@ -37,6 +40,9 @@ class TreeRoot{
 	private $name;
 
 	public function __construct(Tag $root, string $name = ""){
+		if(strlen($name) > Limits::INT16_MAX){
+			throw new \InvalidArgumentException(sprintf("Tag name must be at most %d bytes, but got %d bytes", Limits::INT16_MAX, strlen($name)));
+		}
 		$this->root = $root;
 		$this->name = $name;
 	}

src/tag/CompoundTag.php

@@ -29,11 +29,14 @@
 use pocketmine\nbt\NoSuchTagException;
 use pocketmine\nbt\ReaderTracker;
 use pocketmine\nbt\UnexpectedTagTypeException;
+use pocketmine\utils\Limits;
 use function count;
 use function func_num_args;
 use function get_class;
 use function is_int;
+use function sprintf;
 use function str_repeat;
+use function strlen;
 use function strval;
 
 /**
@@ -115,6 +118,9 @@ public function getCompoundTag(string $name) : ?CompoundTag{
 	 * @return $this
 	 */
 	public function setTag(string $name, Tag $tag) : self{
+		if(strlen($name) > Limits::INT16_MAX){
+			throw new \InvalidArgumentException(sprintf("Tag name must be at most %d bytes, but got %d bytes", Limits::INT16_MAX, strlen($name)));
+		}
 		$this->value[$name] = $tag;
 		return $this;
 	}

tests/phpunit/TreeRootTest.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace pocketmine\nbt;
+
+use PHPUnit\Framework\TestCase;
+use pocketmine\nbt\tag\IntTag;
+use pocketmine\utils\Limits;
+use function str_repeat;
+
+class TreeRootTest extends TestCase{
+
+	public function testNameLength() : void{
+		new TreeRoot(new IntTag(1), str_repeat(".", Limits::INT16_MAX)); //ok
+
+		$this->expectException(\InvalidArgumentException::class);
+		new TreeRoot(new IntTag(1), str_repeat(".", Limits::INT16_MAX + 1)); //error
+	}
+}

tests/phpunit/tag/CompoundTagTest.php

@@ -24,6 +24,7 @@
 namespace pocketmine\nbt\tag;
 
 use PHPUnit\Framework\TestCase;
+use pocketmine\utils\Limits;
 use function array_fill;
 use function str_repeat;
 
@@ -184,5 +185,13 @@ public function testModificationDuringIteration() : void{
 		self::assertCount(0, $tag);
 	}
 
+	public function testNameLength() : void{
+		$tag = CompoundTag::create();
+		$tag->setTag(str_repeat(".", Limits::INT16_MAX), new IntTag(1)); //ok
+
+		$this->expectException(\InvalidArgumentException::class);
+		$tag->setTag(str_repeat(".", Limits::INT16_MAX + 1), new IntTag(1)); //error
+	}
+
 	//TODO: add more tests
 }