11 files changed, 383 insertions, 53 deletions

diff --git a/src/database/database-dummy.cpp b/src/database/database-dummy.cpp
index b56f341c5..629b2fb04 100644
--- a/src/database/database-dummy.cpp
+++ b/src/database/database-dummy.cpp
@@ -80,3 +80,41 @@ void Database_Dummy::listPlayers(std::vector<std::string> &res)
 		res.emplace_back(player);
 	}
 }
+
+bool Database_Dummy::getModEntries(const std::string &modname, StringMap *storage)
+{
+	const auto mod_pair = m_mod_meta_database.find(modname);
+	if (mod_pair != m_mod_meta_database.cend()) {
+		for (const auto &pair : mod_pair->second) {
+			(*storage)[pair.first] = pair.second;
+		}
+	}
+	return true;
+}
+
+bool Database_Dummy::setModEntry(const std::string &modname,
+	const std::string &key, const std::string &value)
+{
+	auto mod_pair = m_mod_meta_database.find(modname);
+	if (mod_pair == m_mod_meta_database.end()) {
+		m_mod_meta_database[modname] = StringMap({{key, value}});
+	} else {
+		mod_pair->second[key] = value;
+	}
+	return true;
+}
+
+bool Database_Dummy::removeModEntry(const std::string &modname, const std::string &key)
+{
+	auto mod_pair = m_mod_meta_database.find(modname);
+	if (mod_pair != m_mod_meta_database.end())
+		return mod_pair->second.erase(key) > 0;
+	return false;
+}
+
+void Database_Dummy::listMods(std::vector<std::string> *res)
+{
+	for (const auto &pair : m_mod_meta_database) {
+		res->push_back(pair.first);
+	}
+}
diff --git a/src/database/database-dummy.h b/src/database/database-dummy.h
index b69919f84..44b9e8d68 100644
--- a/src/database/database-dummy.h
+++ b/src/database/database-dummy.h
@@ -24,7 +24,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "database.h"
 #include "irrlichttypes.h"
 
-class Database_Dummy : public MapDatabase, public PlayerDatabase
+class Database_Dummy : public MapDatabase, public PlayerDatabase, public ModMetadataDatabase
 {
 public:
 	bool saveBlock(const v3s16 &pos, const std::string &data);
@@ -37,10 +37,17 @@ public:
 	bool removePlayer(const std::string &name);
 	void listPlayers(std::vector<std::string> &res);
 
+	bool getModEntries(const std::string &modname, StringMap *storage);
+	bool setModEntry(const std::string &modname,
+			const std::string &key, const std::string &value);
+	bool removeModEntry(const std::string &modname, const std::string &key);
+	void listMods(std::vector<std::string> *res);
+
 	void beginSave() {}
 	void endSave() {}
 
 private:
 	std::map<s64, std::string> m_database;
 	std::set<std::string> m_player_database;
+	std::unordered_map<std::string, StringMap> m_mod_meta_database;
 };
diff --git a/src/database/database-files.cpp b/src/database/database-files.cpp
index d9d113b4e..7c0dbac28 100644
--- a/src/database/database-files.cpp
+++ b/src/database/database-files.cpp
@@ -18,7 +18,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 */
 
 #include <cassert>
-#include <json/json.h>
 #include "convert_json.h"
 #include "database-files.h"
 #include "remoteplayer.h"
@@ -376,3 +375,127 @@ bool AuthDatabaseFiles::writeAuthFile()
 	}
 	return true;
 }
+
+ModMetadataDatabaseFiles::ModMetadataDatabaseFiles(const std::string &savedir):
+	m_storage_dir(savedir + DIR_DELIM + "mod_storage")
+{
+}
+
+bool ModMetadataDatabaseFiles::getModEntries(const std::string &modname, StringMap *storage)
+{
+	Json::Value *meta = getOrCreateJson(modname);
+	if (!meta)
+		return false;
+
+	const Json::Value::Members attr_list = meta->getMemberNames();
+	for (const auto &it : attr_list) {
+		Json::Value attr_value = (*meta)[it];
+		(*storage)[it] = attr_value.asString();
+	}
+
+	return true;
+}
+
+bool ModMetadataDatabaseFiles::setModEntry(const std::string &modname,
+	const std::string &key, const std::string &value)
+{
+	Json::Value *meta = getOrCreateJson(modname);
+	if (!meta)
+		return false;
+
+	(*meta)[key] = Json::Value(value);
+	m_modified.insert(modname);
+
+	return true;
+}
+
+bool ModMetadataDatabaseFiles::removeModEntry(const std::string &modname,
+		const std::string &key)
+{
+	Json::Value *meta = getOrCreateJson(modname);
+	if (!meta)
+		return false;
+
+	Json::Value removed;
+	if (meta->removeMember(key, &removed)) {
+		m_modified.insert(modname);
+		return true;
+	}
+	return false;
+}
+
+void ModMetadataDatabaseFiles::beginSave()
+{
+}
+
+void ModMetadataDatabaseFiles::endSave()
+{
+	if (m_modified.empty())
+		return;
+
+	if (!fs::CreateAllDirs(m_storage_dir)) {
+		errorstream << "ModMetadataDatabaseFiles: Unable to save. '"
+				<< m_storage_dir << "' cannot be created." << std::endl;
+		return;
+	}
+	if (!fs::IsDir(m_storage_dir)) {
+		errorstream << "ModMetadataDatabaseFiles: Unable to save. '"
+				<< m_storage_dir << "' is not a directory." << std::endl;
+		return;
+	}
+
+	for (auto it = m_modified.begin(); it != m_modified.end();) {
+		const std::string &modname = *it;
+
+		const Json::Value &json = m_mod_meta[modname];
+
+		if (!fs::safeWriteToFile(m_storage_dir + DIR_DELIM + modname, fastWriteJson(json))) {
+			errorstream << "ModMetadataDatabaseFiles[" << modname
+					<< "]: failed to write file." << std::endl;
+			++it;
+			continue;
+		}
+
+		it = m_modified.erase(it);
+	}
+}
+
+void ModMetadataDatabaseFiles::listMods(std::vector<std::string> *res)
+{
+	// List in-memory metadata first.
+	for (const auto &pair : m_mod_meta) {
+		res->push_back(pair.first);
+	}
+
+	// List other metadata present in the filesystem.
+	for (const auto &entry : fs::GetDirListing(m_storage_dir)) {
+		if (!entry.dir && m_mod_meta.count(entry.name) == 0)
+			res->push_back(entry.name);
+	}
+}
+
+Json::Value *ModMetadataDatabaseFiles::getOrCreateJson(const std::string &modname)
+{
+	auto found = m_mod_meta.find(modname);
+	if (found != m_mod_meta.end())
+		return &found->second;
+
+	Json::Value meta(Json::objectValue);
+
+	std::string path = m_storage_dir + DIR_DELIM + modname;
+	if (fs::PathExists(path)) {
+		std::ifstream is(path.c_str(), std::ios_base::binary);
+
+		Json::CharReaderBuilder builder;
+		builder.settings_["collectComments"] = false;
+		std::string errs;
+
+		if (!Json::parseFromStream(builder, is, &meta, &errs)) {
+			errorstream << "ModMetadataDatabaseFiles[" << modname
+					<< "]: failed to decode data: " << errs << std::endl;
+			return nullptr;
+		}
+	}
+
+	return &(m_mod_meta[modname] = meta);
+}
diff --git a/src/database/database-files.h b/src/database/database-files.h
index e647a2e24..962e4d7bb 100644
--- a/src/database/database-files.h
+++ b/src/database/database-files.h
@@ -25,6 +25,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include "database.h"
 #include <unordered_map>
+#include <unordered_set>
+#include <json/json.h>
 
 class PlayerDatabaseFiles : public PlayerDatabase
 {
@@ -69,3 +71,27 @@ private:
 	bool readAuthFile();
 	bool writeAuthFile();
 };
+
+class ModMetadataDatabaseFiles : public ModMetadataDatabase
+{
+public:
+	ModMetadataDatabaseFiles(const std::string &savedir);
+	virtual ~ModMetadataDatabaseFiles() = default;
+
+	virtual bool getModEntries(const std::string &modname, StringMap *storage);
+	virtual bool setModEntry(const std::string &modname,
+		const std::string &key, const std::string &value);
+	virtual bool removeModEntry(const std::string &modname, const std::string &key);
+	virtual void listMods(std::vector<std::string> *res);
+
+	virtual void beginSave();
+	virtual void endSave();
+
+private:
+	Json::Value *getOrCreateJson(const std::string &modname);
+	bool writeJson(const std::string &modname, const Json::Value &json);
+
+	std::string m_storage_dir;
+	std::unordered_map<std::string, Json::Value> m_mod_meta;
+	std::unordered_set<std::string> m_modified;
+};
diff --git a/src/database/database-leveldb.cpp b/src/database/database-leveldb.cpp
index 73cd63f6d..39f4c8442 100644
--- a/src/database/database-leveldb.cpp
+++ b/src/database/database-leveldb.cpp
@@ -70,11 +70,11 @@ bool Database_LevelDB::saveBlock(const v3s16 &pos, const std::string &data)
 
 void Database_LevelDB::loadBlock(const v3s16 &pos, std::string *block)
 {
-	std::string datastr;
 	leveldb::Status status = m_database->Get(leveldb::ReadOptions(),
-		i64tos(getBlockAsInteger(pos)), &datastr);
+		i64tos(getBlockAsInteger(pos)), block);
 
-	*block = (status.ok()) ? datastr : "";
+	if (!status.ok())
+		block->clear();	
 }
 
 bool Database_LevelDB::deleteBlock(const v3s16 &pos)
@@ -131,7 +131,7 @@ void PlayerDatabaseLevelDB::savePlayer(RemotePlayer *player)
 	std::string (long) serialized_inventory
 	*/
 
-	std::ostringstream os;
+	std::ostringstream os(std::ios_base::binary);
 	writeU8(os, 1);
 
 	PlayerSAO *sao = player->getPlayerSAO();
@@ -142,7 +142,7 @@ void PlayerDatabaseLevelDB::savePlayer(RemotePlayer *player)
 	writeF32(os, sao->getRotation().Y);
 	writeU16(os, sao->getBreath());
 
-	StringMap stringvars = sao->getMeta().getStrings();
+	const auto &stringvars = sao->getMeta().getStrings();
 	writeU32(os, stringvars.size());
 	for (const auto &it : stringvars) {
 		os << serializeString16(it.first);
@@ -170,7 +170,7 @@ bool PlayerDatabaseLevelDB::loadPlayer(RemotePlayer *player, PlayerSAO *sao)
 		player->getName(), &raw);
 	if (!s.ok())
 		return false;
-	std::istringstream is(raw);
+	std::istringstream is(raw, std::ios_base::binary);
 
 	if (readU8(is) > 1)
 		return false;
@@ -230,7 +230,7 @@ bool AuthDatabaseLevelDB::getAuth(const std::string &name, AuthEntry &res)
 	leveldb::Status s = m_database->Get(leveldb::ReadOptions(), name, &raw);
 	if (!s.ok())
 		return false;
-	std::istringstream is(raw);
+	std::istringstream is(raw, std::ios_base::binary);
 
 	/*
 	u8 version = 1
@@ -262,7 +262,7 @@ bool AuthDatabaseLevelDB::getAuth(const std::string &name, AuthEntry &res)
 
 bool AuthDatabaseLevelDB::saveAuth(const AuthEntry &authEntry)
 {
-	std::ostringstream os;
+	std::ostringstream os(std::ios_base::binary);
 	writeU8(os, 1);
 	os << serializeString16(authEntry.password);
 
diff --git a/src/database/database-postgresql.cpp b/src/database/database-postgresql.cpp
index e1bb39928..3469f4242 100644
--- a/src/database/database-postgresql.cpp
+++ b/src/database/database-postgresql.cpp
@@ -39,20 +39,24 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "remoteplayer.h"
 #include "server/player_sao.h"
 
-Database_PostgreSQL::Database_PostgreSQL(const std::string &connect_string) :
+Database_PostgreSQL::Database_PostgreSQL(const std::string &connect_string,
+	const char *type) :
 	m_connect_string(connect_string)
 {
 	if (m_connect_string.empty()) {
-		throw SettingNotFoundException(
-			"Set pgsql_connection string in world.mt to "
+		// Use given type to reference the exact setting in the error message
+		std::string s = type;
+		std::string msg =
+			"Set pgsql" + s + "_connection string in world.mt to "
 			"use the postgresql backend\n"
 			"Notes:\n"
-			"pgsql_connection has the following form: \n"
-			"\tpgsql_connection = host=127.0.0.1 port=5432 user=mt_user "
-			"password=mt_password dbname=minetest_world\n"
+			"pgsql" + s + "_connection has the following form: \n"
+			"\tpgsql" + s + "_connection = host=127.0.0.1 port=5432 "
+			"user=mt_user password=mt_password dbname=minetest" + s + "\n"
 			"mt_user should have CREATE TABLE, INSERT, SELECT, UPDATE and "
-			"DELETE rights on the database.\n"
-			"Don't create mt_user as a SUPERUSER!");
+			"DELETE rights on the database. "
+			"Don't create mt_user as a SUPERUSER!";
+		throw SettingNotFoundException(msg);
 	}
 }
 
@@ -166,7 +170,7 @@ void Database_PostgreSQL::rollback()
 }
 
 MapDatabasePostgreSQL::MapDatabasePostgreSQL(const std::string &connect_string):
-	Database_PostgreSQL(connect_string),
+	Database_PostgreSQL(connect_string, ""),
 	MapDatabase()
 {
 	connectToDatabase();
@@ -270,10 +274,10 @@ void MapDatabasePostgreSQL::loadBlock(const v3s16 &pos, std::string *block)
 	PGresult *results = execPrepared("read_block", ARRLEN(args), args,
 		argLen, argFmt, false);
 
-	*block = "";
-
 	if (PQntuples(results))
-		*block = std::string(PQgetvalue(results, 0, 0), PQgetlength(results, 0, 0));
+		block->assign(PQgetvalue(results, 0, 0), PQgetlength(results, 0, 0));
+	else
+		block->clear();
 
 	PQclear(results);
 }
@@ -315,7 +319,7 @@ void MapDatabasePostgreSQL::listAllLoadableBlocks(std::vector<v3s16> &dst)
  * Player Database
  */
 PlayerDatabasePostgreSQL::PlayerDatabasePostgreSQL(const std::string &connect_string):
-	Database_PostgreSQL(connect_string),
+	Database_PostgreSQL(connect_string, "_player"),
 	PlayerDatabase()
 {
 	connectToDatabase();
@@ -492,6 +496,7 @@ void PlayerDatabasePostgreSQL::savePlayer(RemotePlayer *player)
 	execPrepared("remove_player_inventory_items", 1, rmvalues);
 
 	std::vector<const InventoryList*> inventory_lists = sao->getInventory()->getLists();
+	std::ostringstream oss;
 	for (u16 i = 0; i < inventory_lists.size(); i++) {
 		const InventoryList* list = inventory_lists[i];
 		const std::string &name = list->getName();
@@ -508,9 +513,10 @@ void PlayerDatabasePostgreSQL::savePlayer(RemotePlayer *player)
 		execPrepared("add_player_inventory", 5, inv_values);
 
 		for (u32 j = 0; j < list->getSize(); j++) {
-			std::ostringstream os;
-			list->getItem(j).serialize(os);
-			std::string itemStr = os.str(), slotId = itos(j);
+			oss.str("");
+			oss.clear();
+			list->getItem(j).serialize(oss);
+			std::string itemStr = oss.str(), slotId = itos(j);
 
 			const char* invitem_values[] = {
 				player->getName(),
@@ -637,7 +643,8 @@ void PlayerDatabasePostgreSQL::listPlayers(std::vector<std::string> &res)
 }
 
 AuthDatabasePostgreSQL::AuthDatabasePostgreSQL(const std::string &connect_string) :
-		Database_PostgreSQL(connect_string), AuthDatabase()
+	Database_PostgreSQL(connect_string, "_auth"),
+	AuthDatabase()
 {
 	connectToDatabase();
 }
diff --git a/src/database/database-postgresql.h b/src/database/database-postgresql.h
index f47deda33..81b4a2b10 100644
--- a/src/database/database-postgresql.h
+++ b/src/database/database-postgresql.h
@@ -29,7 +29,7 @@ class Settings;
 class Database_PostgreSQL: public Database
 {
 public:
-	Database_PostgreSQL(const std::string &connect_string);
+	Database_PostgreSQL(const std::string &connect_string, const char *type);
 	~Database_PostgreSQL();
 
 	void beginSave();
diff --git a/src/database/database-redis.cpp b/src/database/database-redis.cpp
index 096ea504d..5ffff67b7 100644
--- a/src/database/database-redis.cpp
+++ b/src/database/database-redis.cpp
@@ -127,8 +127,7 @@ void Database_Redis::loadBlock(const v3s16 &pos, std::string *block)
 
 	switch (reply->type) {
 	case REDIS_REPLY_STRING: {
-		*block = std::string(reply->str, reply->len);
-		// std::string copies the memory so this won't cause any problems
+		block->assign(reply->str, reply->len);
 		freeReplyObject(reply);
 		return;
 	}
@@ -141,8 +140,7 @@ void Database_Redis::loadBlock(const v3s16 &pos, std::string *block)
 			"Redis command 'HGET %s %s' errored: ") + errstr);
 	}
 	case REDIS_REPLY_NIL: {
-		*block = "";
-		// block not found in database
+		block->clear();
 		freeReplyObject(reply);
 		return;
 	}
diff --git a/src/database/database-sqlite3.cpp b/src/database/database-sqlite3.cpp
index 4560743b9..1e63ae9d8 100644
--- a/src/database/database-sqlite3.cpp
+++ b/src/database/database-sqlite3.cpp
@@ -228,11 +228,7 @@ void MapDatabaseSQLite3::createDatabase()
 void MapDatabaseSQLite3::initStatements()
 {
 	PREPARE_STATEMENT(read, "SELECT `data` FROM `blocks` WHERE `pos` = ? LIMIT 1");
-#ifdef __ANDROID__
-	PREPARE_STATEMENT(write,  "INSERT INTO `blocks` (`pos`, `data`) VALUES (?, ?)");
-#else
 	PREPARE_STATEMENT(write, "REPLACE INTO `blocks` (`pos`, `data`) VALUES (?, ?)");
-#endif
 	PREPARE_STATEMENT(delete, "DELETE FROM `blocks` WHERE `pos` = ?");
 	PREPARE_STATEMENT(list, "SELECT `pos` FROM `blocks`");
 
@@ -265,19 +261,6 @@ bool MapDatabaseSQLite3::saveBlock(const v3s16 &pos, const std::string &data)
 {
 	verifyDatabase();
 
-#ifdef __ANDROID__
-	/**
-	 * Note: For some unknown reason SQLite3 fails to REPLACE blocks on Android,
-	 * deleting them and then inserting works.
-	 */
-	bindPos(m_stmt_read, pos);
-
-	if (sqlite3_step(m_stmt_read) == SQLITE_ROW) {
-		deleteBlock(pos);
-	}
-	sqlite3_reset(m_stmt_read);
-#endif
-
 	bindPos(m_stmt_write, pos);
 	SQLOK(sqlite3_bind_blob(m_stmt_write, 2, data.data(), data.size(), NULL),
 		"Internal error: failed to bind query at " __FILE__ ":" TOSTRING(__LINE__));
@@ -302,7 +285,10 @@ void MapDatabaseSQLite3::loadBlock(const v3s16 &pos, std::string *block)
 	const char *data = (const char *) sqlite3_column_blob(m_stmt_read, 0);
 	size_t len = sqlite3_column_bytes(m_stmt_read, 0);
 
-	*block = (data) ? std::string(data, len) : "";
+	if (data)
+		block->assign(data, len);
+	else
+		block->clear();
 
 	sqlite3_step(m_stmt_read);
 	// We should never get more than 1 row, so ok to reset
@@ -491,6 +477,7 @@ void PlayerDatabaseSQLite3::savePlayer(RemotePlayer *player)
 	sqlite3_reset(m_stmt_player_remove_inventory_items);
 
 	std::vector<const InventoryList*> inventory_lists = sao->getInventory()->getLists();
+	std::ostringstream oss;
 	for (u16 i = 0; i < inventory_lists.size(); i++) {
 		const InventoryList* list = inventory_lists[i];
 
@@ -503,9 +490,10 @@ void PlayerDatabaseSQLite3::savePlayer(RemotePlayer *player)
 		sqlite3_reset(m_stmt_player_add_inventory);
 
 		for (u32 j = 0; j < list->getSize(); j++) {
-			std::ostringstream os;
-			list->getItem(j).serialize(os);
-			std::string itemStr = os.str();
+			oss.str("");
+			oss.clear();
+			list->getItem(j).serialize(oss);
+			std::string itemStr = oss.str();
 
 			str_to_sqlite(m_stmt_player_add_inventory_items, 1, player->getName());
 			int_to_sqlite(m_stmt_player_add_inventory_items, 2, i);
@@ -774,3 +762,108 @@ void AuthDatabaseSQLite3::writePrivileges(const AuthEntry &authEntry)
 		sqlite3_reset(m_stmt_write_privs);
 	}
 }
+
+ModMetadataDatabaseSQLite3::ModMetadataDatabaseSQLite3(const std::string &savedir):
+	Database_SQLite3(savedir, "mod_storage"), ModMetadataDatabase()
+{
+}
+
+ModMetadataDatabaseSQLite3::~ModMetadataDatabaseSQLite3()
+{
+	FINALIZE_STATEMENT(m_stmt_remove)
+	FINALIZE_STATEMENT(m_stmt_set)
+	FINALIZE_STATEMENT(m_stmt_get)
+}
+
+void ModMetadataDatabaseSQLite3::createDatabase()
+{
+	assert(m_database); // Pre-condition
+
+	SQLOK(sqlite3_exec(m_database,
+		"CREATE TABLE IF NOT EXISTS `entries` (\n"
+			"	`modname` TEXT NOT NULL,\n"
+			"	`key` BLOB NOT NULL,\n"
+			"	`value` BLOB NOT NULL,\n"
+			"	PRIMARY KEY (`modname`, `key`)\n"
+			");\n",
+		NULL, NULL, NULL),
+		"Failed to create database table");
+}
+
+void ModMetadataDatabaseSQLite3::initStatements()
+{
+	PREPARE_STATEMENT(get, "SELECT `key`, `value` FROM `entries` WHERE `modname` = ?");
+	PREPARE_STATEMENT(set,
+		"REPLACE INTO `entries` (`modname`, `key`, `value`) VALUES (?, ?, ?)");
+	PREPARE_STATEMENT(remove, "DELETE FROM `entries` WHERE `modname` = ? AND `key` = ?");
+}
+
+bool ModMetadataDatabaseSQLite3::getModEntries(const std::string &modname, StringMap *storage)
+{
+	verifyDatabase();
+
+	str_to_sqlite(m_stmt_get, 1, modname);
+	while (sqlite3_step(m_stmt_get) == SQLITE_ROW) {
+		const char *key_data = (const char *) sqlite3_column_blob(m_stmt_get, 0);
+		size_t key_len = sqlite3_column_bytes(m_stmt_get, 0);
+		const char *value_data = (const char *) sqlite3_column_blob(m_stmt_get, 1);
+		size_t value_len = sqlite3_column_bytes(m_stmt_get, 1);
+		(*storage)[std::string(key_data, key_len)] = std::string(value_data, value_len);
+	}
+	sqlite3_vrfy(sqlite3_errcode(m_database), SQLITE_DONE);
+
+	sqlite3_reset(m_stmt_get);
+
+	return true;
+}
+
+bool ModMetadataDatabaseSQLite3::setModEntry(const std::string &modname,
+	const std::string &key, const std::string &value)
+{
+	verifyDatabase();
+
+	str_to_sqlite(m_stmt_set, 1, modname);
+	SQLOK(sqlite3_bind_blob(m_stmt_set, 2, key.data(), key.size(), NULL),
+		"Internal error: failed to bind query at " __FILE__ ":" TOSTRING(__LINE__));
+	SQLOK(sqlite3_bind_blob(m_stmt_set, 3, value.data(), value.size(), NULL),
+		"Internal error: failed to bind query at " __FILE__ ":" TOSTRING(__LINE__));
+	SQLRES(sqlite3_step(m_stmt_set), SQLITE_DONE, "Failed to set mod entry")
+
+	sqlite3_reset(m_stmt_set);
+
+	return true;
+}
+
+bool ModMetadataDatabaseSQLite3::removeModEntry(const std::string &modname,
+		const std::string &key)
+{
+	verifyDatabase();
+
+	str_to_sqlite(m_stmt_remove, 1, modname);
+	SQLOK(sqlite3_bind_blob(m_stmt_remove, 2, key.data(), key.size(), NULL),
+		"Internal error: failed to bind query at " __FILE__ ":" TOSTRING(__LINE__));
+	sqlite3_vrfy(sqlite3_step(m_stmt_remove), SQLITE_DONE);
+	int changes = sqlite3_changes(m_database);
+
+	sqlite3_reset(m_stmt_remove);
+
+	return changes > 0;
+}
+
+void ModMetadataDatabaseSQLite3::listMods(std::vector<std::string> *res)
+{
+	verifyDatabase();
+
+	char *errmsg;
+	int status = sqlite3_exec(m_database,
+		"SELECT `modname` FROM `entries` GROUP BY `modname`;",
+		[](void *res_vp, int n_col, char **cols, char **col_names) -> int {
+			((decltype(res)) res_vp)->emplace_back(cols[0]);
+			return 0;
+		}, (void *) res, &errmsg);
+	if (status != SQLITE_OK) {
+		DatabaseException e(std::string("Error trying to list mods with metadata: ") + errmsg);
+		sqlite3_free(errmsg);
+		throw e;
+	}
+}
diff --git a/src/database/database-sqlite3.h b/src/database/database-sqlite3.h
index d7202a918..5e3d7c96c 100644
--- a/src/database/database-sqlite3.h
+++ b/src/database/database-sqlite3.h
@@ -232,3 +232,28 @@ private:
 	sqlite3_stmt *m_stmt_delete_privs = nullptr;
 	sqlite3_stmt *m_stmt_last_insert_rowid = nullptr;
 };
+
+class ModMetadataDatabaseSQLite3 : private Database_SQLite3, public ModMetadataDatabase
+{
+public:
+	ModMetadataDatabaseSQLite3(const std::string &savedir);
+	virtual ~ModMetadataDatabaseSQLite3();
+
+	virtual bool getModEntries(const std::string &modname, StringMap *storage);
+	virtual bool setModEntry(const std::string &modname,
+		const std::string &key, const std::string &value);
+	virtual bool removeModEntry(const std::string &modname, const std::string &key);
+	virtual void listMods(std::vector<std::string> *res);
+
+	virtual void beginSave() { Database_SQLite3::beginSave(); }
+	virtual void endSave() { Database_SQLite3::endSave(); }
+
+protected:
+	virtual void createDatabase();
+	virtual void initStatements();
+
+private:
+	sqlite3_stmt *m_stmt_get = nullptr;
+	sqlite3_stmt *m_stmt_set = nullptr;
+	sqlite3_stmt *m_stmt_remove = nullptr;
+};
diff --git a/src/database/database.h b/src/database/database.h
index b7d551935..fbb5befea 100644
--- a/src/database/database.h
+++ b/src/database/database.h
@@ -25,6 +25,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "irr_v3d.h"
 #include "irrlichttypes.h"
 #include "util/basic_macros.h"
+#include "util/string.h"
 
 class Database
 {
@@ -84,3 +85,15 @@ public:
 	virtual void listNames(std::vector<std::string> &res) = 0;
 	virtual void reload() = 0;
 };
+
+class ModMetadataDatabase : public Database
+{
+public:
+	virtual ~ModMetadataDatabase() = default;
+
+	virtual bool getModEntries(const std::string &modname, StringMap *storage) = 0;
+	virtual bool setModEntry(const std::string &modname,
+		const std::string &key, const std::string &value) = 0;
+	virtual bool removeModEntry(const std::string &modname, const std::string &key) = 0;
+	virtual void listMods(std::vector<std::string> *res) = 0;
+};