# ![Logo](logo.svg) Modding Library (`modlib`)

Multipurpose Minetest Modding Library

## About

No dependencies. Licensed under the MIT License. Written by Lars Mueller aka LMD or appguru(eu). Notable contributions by [luk3yx](https://github.com/luk3yx) in the form of suggestions, bug reports and fixes. Another [bugfix](https://github.com/appgurueu/modlib/pull/7) by [NobWow](https://github.com/NobWow/).

### Principles

* Game-agnostic: Modlib aims to provide nothing game-specific;
* Minimal invasiveness: Modlib should not disrupt other mods;
  even at the expense of syntactic sugar, changes to the global
  environment - apart from the addition of the modlib scope - are forbidden
* Architecture: Modlib is organized hierarchically
* Performance: Modlib tries to not compromise performance for convenience; modlib loads lazily (do `_ = modlib.<module>` to avoid file load spikes at run time)

## Tests

The tests are located in a different repo, [`modlib_test`](https://github.com/appgurueu/modlib_test), as they are quite heavy due to testing the PNG reader using PngSuite. Reading the tests for examples of API usage is recommended.

## API

Mostly self-documenting code. Mod namespace is `modlib`, containing all variables & functions.

### Persistence

#### Lua Log Files

A data log file based on Lua statements. High performance. Example from `test.lua`:

```lua
local logfile = persistence.lua_log_file.new(mod.get_resource"logfile.test.lua", {})
logfile:init()
logfile.root = {}
logfile:rewrite()
logfile:set_root({a = 1}, {b = 2, c = 3})
logfile:close()
logfile:init()
assert(table.equals(logfile.root, {[{a = 1}] = {b = 2, c = 3}}))
```

Both strings and tables are stored in a reference table. Unused strings won't be garbage collected as Lua doesn't allow marking them as weak references.
This means that setting lots of temporary strings will waste memory until you call `:rewrite()` on the log file. An alternative is to set the third parameter, `reference_strings`, to `false` (default value is `true`):

```lua
persistence.lua_log_file.new(mod.get_resource"logfile.test.lua", {}, false)
```

This will prevent strings from being referenced, possibly bloating file size, but saving memory.

#### SQLite3 Database Persistence

Uses a SQLite3 database to persistently store a Lua table. **Experimental.** Obtaining it is a bit trickier, as it requires access to the `lsqlite3` library, which may be passed:

```lua
local modlib_sqlite3 = persistence.sqlite3(require"lsqlite3")
```

(assuming `require` is that of an insecure environment if Minetest is used)

Alternatively, if you are not running Minetest, mod security is disabled, you have (temporarily) provided `require` globally, or added `modlib` to `secure.trusted_mods`, you can simply do the following:

```lua
local modlib_sqlite3 = persistence.sqlite3()
```

Modlib will then simply call `require"lsqlite3"` for you.

Then, you can proceed to create a new database:

```lua
local database = persistence.modlib_sqlite3.new(mod.get_resource"database.test.sqlite3", {})
-- Create or load
database:init()
-- Use it
database:set_root("key", {nested = true})
database:close()
```

It uses a similar API to Lua log files:

* `new(filename, root)` - without `reference_strings` however (strings aren't referenced currently)
* `init`
* `set`
* `set_root`
* `rewrite`
* `close`

The advantage over Lua log files is that the SQlite3 database keeps disk usage minimal. Unused tables are dropped from the database immediately through reference counting. The downside of this is that this, combined with the overhead of using SQLite3, of course takes time, making updates on the SQLite3 database slower than Lua log file updates (which just append to an append-only file).
As simple and fast reference counting doesn't handle cycles, an additional `collectgarbage` stop-the-world method performing a full garbage collection on the database is provided which is called during `init`.
The method `defragment_ids` should not have to be used in practice (if it has to be, it happens automatically) and should be used solely for debugging purposes (neater IDs).

### Bluon

Binary Lua object notation.

#### `new(def)`

```lua
def = {
	aux_is_valid = function(object)
		return is_valid
	end,
	aux_len = function(object)
		return length_in_bytes
	end,
	-- read type byte, stream providing :read(count), map of references -> id
	aux_read = function(type, stream, references)
		... = stream:read(...)
		return object
	end,
	-- object to be written, stream providing :write(text), list of references
	aux_write = function(object, stream, references)
		stream:write(...)
	end
}
```

#### `:is_valid(object)`

Returns whether the given object can be represented by the instance as boolean.

#### `:len(object)`

Returns the expected length of the object if serialized by the current instance in bytes.

#### `:write(object, stream)`

Writes the object to a stream supporting `:write(text)`. Throws an error if invalid.

#### `:read(stream)`

Reads a single bluon object from a stream supporting `:read(count)`. Throws an error if invalid bluon.

Checking whether the stream has been fully consumed by doing `assert(not stream:read(1))` is left up to the user.

#### Format

* `nil`: nothing (`""`)
* `false`: 0
* `true`: 1
* Numbers:
  * Constants: 0, nan, +inf, -inf
  * Integers: Little endian `U8`, `U16`, `U32`, `U64`, `-U8`, `-U16`, `-U32`, `-U64`
  * Floats: Little endian `F32`, `F64`
* Strings:
  * Constant: `""`
  * Length as unsigned integer: `T8`, `T16`, `T32`, `T64`
* Tables:
  * List and map part count as unsigned integers
  * `L0`, `L8`, `L16`, `L32`, `L64` times `M0`, `M8`, `M16`, `M32`, `M64`
* Reference:
  * Reference ID as unsigned integer: `R8`, `R16`, `R32`, `R64`
* Reserved types:
  * Everything <= 55 => 200 free types

#### Features

* Embeddable: Written in pure Lua
* Storage efficient: No duplication of strings or reference-equal tables
* Flexible: Can serialize circular references and strings containing null

#### Simple example

```lua
local object = ...
-- Write to file
local file = io.open(..., "wb")
modlib.bluon:write(object, file)
file:close()
-- Write to text
local rope = modlib.table.rope{}
modlib.bluon:write(object, rope)
text = rope:to_text()
-- Read from text
local inputstream = modlib.text.inputstream"\1"
assert(modlib.bluon:read(object, rope) == true)
```

#### Advanced example

```lua
-- Serializes all userdata to a constant string:
local custom_bluon = bluon.new{
	aux_is_valid = function(object)
		return type(object) == "userdata"
	end,
	aux_len = function(object)
		return 1 + ("userdata"):len())
	end,
	aux_read = function(type, stream, references)
		assert(type == 100, "unsupported type")
		assert(stream:read(("userdata"):len()) == "userdata")
		return userdata()
	end,
	-- object to be written, stream providing :write(text), list of references
	aux_write = function(object, stream, references)
		assert(type(object) == "userdata")
		stream:write"\100userdata"
	end
}
-- Write to text
local rope = modlib.table.rope{}
custom_bluon:write(userdata(), rope)
assert(rope:to_text() == "\100userdata")
```

### Schema

Place a file `schema.lua` in your mod, returning a schema table.

#### Non-string entries and `minetest.conf`

Suppose you have the following schema:

```lua
return {
	type = "table",
	entries = {
		[42] = {
			type = "boolean",
			description = "The Answer"
			default = true
		}
	}
}
```

And a user sets the following config:

```conf
mod.42 = false
```

It won't work, as the resulting table will be `{["42"] = false}` instead of `{[42] = false}`. In order to make this work, you have to convert the keys yourself:

```lua
return {
	type = "table",
	keys = {
		-- this will convert all keys to numbers
		type = "number"
	},
	entries = {
		[42] = {
			type = "boolean",
			description = "The Answer"
			default = true
		}
	}
}
```

This is best left explicit. First, you shouldn't be using numbered field keys if you want decent `minetest.conf` support, and second, `modlib`'s schema module could only guess in this case, attempting conversion to number / boolean. What if both number and string field were set as possible entries? Should the string field be deleted? And so on.

## Configuration

### Legacy

1. Configuration is loaded from `<worldpath>/config/<modname>.<extension>`, the following extensions are supported and loaded (in the given order), with loaded configurations overriding properties of previous ones:
   1. [`json`](https://json.org)
   2. [`lua`](https://lua.org)
   3. [`luon`](https://github.com/appgurueu/luon), Lua but without the `return`
   4. [`conf`](https://github.com/minetest/minetest/blob/master/doc/lua_api.txt)
2. Settings are loaded from `minetest.conf` and override configuration values

### Locations

0. Default configuration: `<modfolder>/conf.lua`
1. World configuration: `config/<modname>.<format>`
2. Mod configuration: `<modfolder>/conf.<format>`
3. Minetest configuration: `minetest.conf`

### Formats

1. [`lua`](https://lua.org)
  * Lua, with the environment being the configuration object
  * `field = value` works
  * Return new configuration object to replace
2. [`luon`](https://github.com/appgurueu/luon)
  * Single Lua literal
  * Booleans, numbers, strings and tables
3. [`conf`](https://github.com/minetest/minetest/blob/master/doc/lua_api.txt)
  * Minetest-like configuration files
4. [`json`](https://json.org)
  * Not recommended

## `minetest`

### `schematic`

A schematic format with support for metadata and baked light data.