From 86f1ef596f596374680dd5ee76485d583ac381ea Mon Sep 17 00:00:00 2001
From: BodgeMaster <>
Date: Sat, 13 Aug 2022 15:46:06 +0200
Subject: [PATCH] lib/nbt: Begin implementing nextTagDataLength

---
 src/lib/nbt.cpp | 54 ++++++++++++++++++++++++++++++++++++++++++-------
 src/lib/nbt.hpp |  2 +-
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/src/lib/nbt.cpp b/src/lib/nbt.cpp
index b6ec029..be63d68 100644
--- a/src/lib/nbt.cpp
+++ b/src/lib/nbt.cpp
@@ -451,22 +451,62 @@ namespace NBT {
             }
         }
 
-        ErrorOr<uint32_t> nextTagDataSize(uint8_t data[], uint64_t dataSize, uint64_t currentPosition){
+        //FIXME: instead of blindly passing the error code upwards, choose
+        // one that is applicable to the situation (for example replace
+        // OUT_OF_RANGE with OVERRUN where appropriate)
+        ErrorOr<int32_t> nextTagDataLength(uint8_t data[], uint64_t dataSize, uint64_t currentPosition){
 
             uint8_t nextTag;
             if (dataSize <= currentPosition) {
-                return ErrorOr<uint32_t>(true, ErrorCodes::OVERRUN);
+                return ErrorOr<int32_t>(true, ErrorCodes::OVERRUN);
             } else {
                 nextTag = data[currentPosition];
             }
 
             // deal with compound tags separately
-            if (nextTag == TagType::COMPOUND) return ErrorOr<uint32_t>(true, ErrorCodes::NOT_YET_KNOWN);
+            if (nextTag == TagType::COMPOUND) {
+                return ErrorOr<int32_t>(true, ErrorCodes::NOT_YET_KNOWN);
+            }
+
             // deal with end tag before trying to access the name
-            if (nextTag == TagType::END) return 0;
-            //TODO: implement for all the remaining types
-            // unknown tag or parsing error
-            return ErrorOr<uint32_t>(true, ErrorCodes::UNKNOWN);
+            if (nextTag == TagType::END) {
+                return ErrorOr<int32_t>(0);
+            }
+
+            // tags that only ever hold one value
+            if (nextTag == TagType::INT8 || nextTag == TagType::INT16 || nextTag == TagType::INT32 || nextTag == TagType::INT64 || nextTag == TagType::FLOAT || nextTag == TagType::DOUBLE) {
+                return ErrorOr<int32_t>(1);
+            }
+
+            ErrorOr<int16_t> nameSize = helper::readInt16(data, dataSize, currentPosition+1);
+            if (nameSize.isError) {
+                return ErrorOr<int32_t>(true, nameSize.errorCode);
+            }
+            // add type byte and name size bytes
+            uint64_t prefixSize = (uint64_t) nameSize.value + 3;
+            switch (nextTag) {
+                case TagType::INT8_ARRAY: {
+                    return helper::readInt32(data, dataSize, currentPosition+prefixSize);
+                }
+                case TagType::STRING: {
+                    ErrorOr<int16_t> stringSize = helper::readInt16(data, dataSize, currentPosition+prefixSize);
+                    if (stringSize.isError) {
+                        return ErrorOr<int32_t>(true, stringSize.errorCode);
+                    }
+                    return ErrorOr<int32_t>((int32_t) stringSize.value);
+                }
+                case TagType::LIST: {
+                }
+                case TagType::INT32_ARRAY: {
+                    return helper::readInt32(data, dataSize, currentPosition+prefixSize);
+                }
+                case TagType::INT64_ARRAY: {
+                    return helper::readInt32(data, dataSize, currentPosition+prefixSize);
+                }
+                default:
+                    // unknown tag or parsing error
+                    return ErrorOr<int32_t>(true, ErrorCodes::UNKNOWN);
+            }
         }
     }
 
diff --git a/src/lib/nbt.hpp b/src/lib/nbt.hpp
index 578a1f2..c7174d8 100644
--- a/src/lib/nbt.hpp
+++ b/src/lib/nbt.hpp
@@ -68,7 +68,7 @@ namespace NBT {
         void writeInt64Array(std::vector<uint8_t>* destination, int64_t data[], uint32_t dataSize);
 
         ErrorOr<uint64_t> nextTagTotalSize(uint8_t data[], uint64_t dataSize, uint64_t currentPosition);
-        ErrorOr<uint32_t> nextTagDataSize(uint8_t data[], uint64_t dataSize, uint64_t currentPosition);
+        ErrorOr<int32_t> nextTagDataLength(uint8_t data[], uint64_t dataSize, uint64_t currentPosition);
     }
 
     namespace TagType {