lib/nbt: Prevent addition of additional end tags to compounds

src/lib/error.hpp

@@ -70,13 +70,10 @@ namespace ErrorCodes {
     // Ahh yes, very useful.
     const uint8_t SUCCESS = 0;
 
-    // IndexOutOfRangeException equivalent
     const uint8_t OUT_OF_RANGE = 1;
-
-    // when going out of bounds in a non-predetermined way
+    // like OUT_OF_RANGE but when going out of bounds in a non-predetermined way
     const uint8_t OVERRUN = 2;
 
-    // when checking for presence of something, for example CLI arguments
     const uint8_t NOT_PRESENT = 3;
 
     const uint8_t WRONG_USAGE = 4;
@@ -94,6 +91,10 @@ namespace ErrorCodes {
     const uint8_t FILE_NOT_OPEN = 9;
     const uint8_t FILE_NOT_FOUND = 10;
 
+    // when performing an operation that would technically be valid but must
+    // never be performed (like deleting an end tag from an NBT compound)
+    const uint8_t NOT_ALLOWED = 11;
+
     const uint8_t UNIMPLEMENTED = 254;
 
     const uint8_t UNKNOWN = 255;

src/lib/nbt.cpp

@@ -940,23 +940,27 @@ namespace NBT {
 
         Compound::Compound() {
             this->type = TagType::COMPOUND;
+            this->endPointer = new End();
         }
 
         Compound::Compound(tiny_utf8::string name) {
             this->type = TagType::COMPOUND;
             this->name = name;
+            this->endPointer = new End();
         }
 
         Compound::Compound(tiny_utf8::string name, std::vector<Generic*> data) {
             this->type = TagType::COMPOUND;
             this->name = name;
             this->tags = data;
+            this->endPointer = new End();
         }
 
         Compound::~Compound() {
             for (uint64_t i=0; i<this->tags.size(); i++) {
                 delete this->tags.at(i);
             }
+            delete this->endPointer;
         }
 
         ErrorOrVoid Compound::serializeWithoutHeader(std::vector<uint8_t>* rawData) {
@@ -966,20 +970,36 @@ namespace NBT {
                     return result;
                 }
             }
+            this->endPointer->serialize(rawData);
 
             return ErrorOrVoid();
         }
 
         ErrorOr<Generic*> Compound::getElementPointer(uint64_t position) {
-            if (position >= this->tags.size()) {
+            if (position > this->tags.size()) {
                 return ErrorOr<Generic*>(true, ErrorCodes::OUT_OF_RANGE);
             }
 
+            if (position == this->tags.size()) {
+                return this->endPointer;
+            }
+
             return ErrorOr<Generic*>(this->tags.at(position));
         }
 
         ErrorOrVoid Compound::setElementPointerAt(uint64_t position, Generic* pointer) {
-            if (position >= this->tags.size()) {
+            if (position == this->tags.size() || pointer->getTagType() == TagType::END) {
+                if (position == this->tags.size() && pointer->getTagType() == TagType::END) {
+                    delete pointer;
+                    // do nothing, already have one of those
+                } else {
+                    delete pointer;
+                    // End tags may only go at the end and
+                    // the end may only hold an end tag.
+                    return ErrorOrVoid(true, ErrorCodes::NOT_ALLOWED);
+                }
+            }
+            if (position > this->tags.size()) {
                 return ErrorOrVoid(true, ErrorCodes::OUT_OF_RANGE);
             }
 
@@ -989,12 +1009,20 @@ namespace NBT {
             return ErrorOrVoid();
         }
 
-        void Compound::appendPointer(Generic* pointer) {
+        ErrorOrVoid Compound::appendPointer(Generic* pointer) {
+            if (pointer->getTagType() == TagType::END) {
+                return ErrorOrVoid(true, ErrorCodes::NOT_ALLOWED);
+            }
             this->tags.push_back(pointer);
+            return ErrorOrVoid();
         }
 
         ErrorOrVoid Compound::deleteElement(uint64_t position) {
-            if (position >= this->tags.size()) {
+            // built-in end tag
+            if (position == this->tags.size()) {
+                return ErrorOrVoid(true, ErrorCodes::NOT_ALLOWED);
+            }
+            if (position > this->tags.size()) {
                 return ErrorOrVoid(true, ErrorCodes::OUT_OF_RANGE);
             }
 
@@ -1005,7 +1033,8 @@ namespace NBT {
         }
 
         uint64_t Compound::length() {
-            return this->tags.size();
+            // account for built-in end tag
+            return this->tags.size()+1;
         }
 
         Int32Array::Int32Array() {

src/lib/nbt.hpp

@@ -244,6 +244,8 @@ namespace NBT {
         class Compound: public Generic {
             private:
                 std::vector<Generic*> tags;
+                // built-in end tag
+                End* endPointer;
             public:
                 Compound();
                 Compound(tiny_utf8::string name);
@@ -255,7 +257,7 @@ namespace NBT {
 
                 ErrorOr<Generic*> getElementPointer(uint64_t position);
                 ErrorOrVoid setElementPointerAt(uint64_t position, Generic* pointer);
-                void appendPointer(Generic* pointer);
+                ErrorOrVoid appendPointer(Generic* pointer);
                 ErrorOrVoid deleteElement(uint64_t position);
                 uint64_t length();
         };