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diff --git a/meshmc/launcher/Json.cpp b/meshmc/launcher/Json.cpp
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+/* SPDX-FileCopyrightText: 2026 Project Tick
+ * SPDX-FileContributor: Project Tick
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ *   MeshMC - A Custom Launcher for Minecraft
+ *   Copyright (C) 2026 Project Tick
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  This file incorporates work covered by the following copyright and
+ *  permission notice:
+ *
+ * Copyright 2013-2021 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Json.h"
+
+#include <QFile>
+
+#include "FileSystem.h"
+#include <math.h>
+
+namespace Json
+{
+	void write(const QJsonDocument& doc, const QString& filename)
+	{
+		FS::write(filename, doc.toJson());
+	}
+	void write(const QJsonObject& object, const QString& filename)
+	{
+		write(QJsonDocument(object), filename);
+	}
+	void write(const QJsonArray& array, const QString& filename)
+	{
+		write(QJsonDocument(array), filename);
+	}
+
+	QByteArray toBinary(const QJsonObject& obj)
+	{
+		return QJsonDocument(obj).toJson(QJsonDocument::Compact);
+	}
+	QByteArray toBinary(const QJsonArray& array)
+	{
+		return QJsonDocument(array).toJson(QJsonDocument::Compact);
+	}
+	QByteArray toText(const QJsonObject& obj)
+	{
+		return QJsonDocument(obj).toJson(QJsonDocument::Compact);
+	}
+	QByteArray toText(const QJsonArray& array)
+	{
+		return QJsonDocument(array).toJson(QJsonDocument::Compact);
+	}
+
+	static bool isBinaryJson(const QByteArray& data)
+	{
+		// Binary JSON is no longer supported in Qt6
+		Q_UNUSED(data);
+		return false;
+	}
+	QJsonDocument requireDocument(const QByteArray& data, const QString& what)
+	{
+		if (isBinaryJson(data)) {
+			throw JsonException(what +
+								": Binary JSON format is no longer supported");
+		} else {
+			QJsonParseError error;
+			QJsonDocument doc = QJsonDocument::fromJson(data, &error);
+			if (error.error != QJsonParseError::NoError) {
+				throw JsonException(
+					what + ": Error parsing JSON: " + error.errorString());
+			}
+			return doc;
+		}
+	}
+	QJsonDocument requireDocument(const QString& filename, const QString& what)
+	{
+		return requireDocument(FS::read(filename), what);
+	}
+	QJsonObject requireObject(const QJsonDocument& doc, const QString& what)
+	{
+		if (!doc.isObject()) {
+			throw JsonException(what + " is not an object");
+		}
+		return doc.object();
+	}
+	QJsonArray requireArray(const QJsonDocument& doc, const QString& what)
+	{
+		if (!doc.isArray()) {
+			throw JsonException(what + " is not an array");
+		}
+		return doc.array();
+	}
+
+	void writeString(QJsonObject& to, const QString& key, const QString& value)
+	{
+		if (!value.isEmpty()) {
+			to.insert(key, value);
+		}
+	}
+
+	void writeStringList(QJsonObject& to, const QString& key,
+						 const QStringList& values)
+	{
+		if (!values.isEmpty()) {
+			QJsonArray array;
+			for (auto value : values) {
+				array.append(value);
+			}
+			to.insert(key, array);
+		}
+	}
+
+	template <> QJsonValue toJson<QUrl>(const QUrl& url)
+	{
+		return QJsonValue(url.toString(QUrl::FullyEncoded));
+	}
+	template <> QJsonValue toJson<QByteArray>(const QByteArray& data)
+	{
+		return QJsonValue(QString::fromLatin1(data.toHex()));
+	}
+	template <> QJsonValue toJson<QDateTime>(const QDateTime& datetime)
+	{
+		return QJsonValue(datetime.toString(Qt::ISODate));
+	}
+	template <> QJsonValue toJson<QDir>(const QDir& dir)
+	{
+		return QDir::current().relativeFilePath(dir.absolutePath());
+	}
+	template <> QJsonValue toJson<QUuid>(const QUuid& uuid)
+	{
+		return uuid.toString();
+	}
+	template <> QJsonValue toJson<QVariant>(const QVariant& variant)
+	{
+		return QJsonValue::fromVariant(variant);
+	}
+
+	template <>
+	QByteArray requireIsType<QByteArray>(const QJsonValue& value,
+										 const QString& what)
+	{
+		const QString string = ensureIsType<QString>(value, what);
+		// ensure that the string can be safely cast to Latin1
+		if (string != QString::fromLatin1(string.toLatin1())) {
+			throw JsonException(what + " is not encodable as Latin1");
+		}
+		return QByteArray::fromHex(string.toLatin1());
+	}
+
+	template <>
+	QJsonArray requireIsType<QJsonArray>(const QJsonValue& value,
+										 const QString& what)
+	{
+		if (!value.isArray()) {
+			throw JsonException(what + " is not an array");
+		}
+		return value.toArray();
+	}
+
+	template <>
+	QString requireIsType<QString>(const QJsonValue& value, const QString& what)
+	{
+		if (!value.isString()) {
+			throw JsonException(what + " is not a string");
+		}
+		return value.toString();
+	}
+
+	template <>
+	bool requireIsType<bool>(const QJsonValue& value, const QString& what)
+	{
+		if (!value.isBool()) {
+			throw JsonException(what + " is not a bool");
+		}
+		return value.toBool();
+	}
+
+	template <>
+	double requireIsType<double>(const QJsonValue& value, const QString& what)
+	{
+		if (!value.isDouble()) {
+			throw JsonException(what + " is not a double");
+		}
+		return value.toDouble();
+	}
+
+	template <>
+	int requireIsType<int>(const QJsonValue& value, const QString& what)
+	{
+		const double doubl = requireIsType<double>(value, what);
+		if (fmod(doubl, 1) != 0) {
+			throw JsonException(what + " is not an integer");
+		}
+		return int(doubl);
+	}
+
+	template <>
+	QDateTime requireIsType<QDateTime>(const QJsonValue& value,
+									   const QString& what)
+	{
+		const QString string = requireIsType<QString>(value, what);
+		const QDateTime datetime = QDateTime::fromString(string, Qt::ISODate);
+		if (!datetime.isValid()) {
+			throw JsonException(what +
+								" is not a ISO formatted date/time value");
+		}
+		return datetime;
+	}
+
+	template <>
+	QUrl requireIsType<QUrl>(const QJsonValue& value, const QString& what)
+	{
+		const QString string = ensureIsType<QString>(value, what);
+		if (string.isEmpty()) {
+			return QUrl();
+		}
+		const QUrl url = QUrl(string, QUrl::StrictMode);
+		if (!url.isValid()) {
+			throw JsonException(what + " is not a correctly formatted URL");
+		}
+		return url;
+	}
+
+	template <>
+	QDir requireIsType<QDir>(const QJsonValue& value, const QString& what)
+	{
+		const QString string = requireIsType<QString>(value, what);
+		// FIXME: does not handle invalid characters!
+		return QDir::current().absoluteFilePath(string);
+	}
+
+	template <>
+	QUuid requireIsType<QUuid>(const QJsonValue& value, const QString& what)
+	{
+		const QString string = requireIsType<QString>(value, what);
+		const QUuid uuid = QUuid(string);
+		if (uuid.toString() != string) // converts back => valid
+		{
+			throw JsonException(what + " is not a valid UUID");
+		}
+		return uuid;
+	}
+
+	template <>
+	QJsonObject requireIsType<QJsonObject>(const QJsonValue& value,
+										   const QString& what)
+	{
+		if (!value.isObject()) {
+			throw JsonException(what + " is not an object");
+		}
+		return value.toObject();
+	}
+
+	template <>
+	QVariant requireIsType<QVariant>(const QJsonValue& value,
+									 const QString& what)
+	{
+		if (value.isNull() || value.isUndefined()) {
+			throw JsonException(what + " is null or undefined");
+		}
+		return value.toVariant();
+	}
+
+	template <>
+	QJsonValue requireIsType<QJsonValue>(const QJsonValue& value,
+										 const QString& what)
+	{
+		if (value.isNull() || value.isUndefined()) {
+			throw JsonException(what + " is null or undefined");
+		}
+		return value;
+	}
+
+} // namespace Json