tgstation-server 6.12.0
The /tg/station 13 server suite
|
This is a toolset to manage production DreamMaker servers. It includes the ability to update the server without having to stop or shutdown the server (the update will take effect on a "reboot" of the server), the ability to start the server and restart it if it crashes, as well as systems for managing code and game files, and locally merging GitHub Pull Requests for test deployments.
Note: If you opt to use the Windows installer, most pre-requisites for running BYOND servers (including MariaDB) are provided out of the box.
If you are running on a Windows Server OS. You might need to install the x86 Visual C++ 2015 Runtime to run BYOND.
If you wish to use OpenDream you will need to install the required dotnet SDK manually.
tgstation-server needs a relational database to store it's data.
If you're just a hobbyist server host, you can probably get away with using SQLite for this. SQLite is bundled with TGS and simply requires you to specify where on your machine you want to store the data.
HOWEVER
SQLite is not a battle-ready relational database. It doesn't scale well for any use case. TGS strongly recommends you use one of its supported standalone databases. Setting one of these up is more involved but worth the effort.
The supported standalone databases are:
TGS will require either:
Follow the instructions for your OS below.
Note that the Windows Service and installer executables require administrative privileges. These are digitally signed against the Root CA managed by Jordan Dominion. Consider installing the certificate into your Trusted Root Authorities
store for cleaner UAC prompts. The certificate can be downloaded here, please validate the thumbprint is 70176acf7ffa2898fa5b5cd6e38b43b38ea5d07f
before installing. The OCSP server for this is http://ocsp.dextraspace.net
.
Download the latest release's tgstation-server-installer.exe. Executing it will take you through the process of installing and configuring your server. The required dotnet runtime may be installed as a pre-requisite.
Note: If you use the /silent
or /passive
arguments to the installer, you will not be able to install MariaDB using it. In addition, if those arguments are present, you'll need to either pre-configure TGS or configure and start the tgstation-server
service after installing. A shortcut will be placed on your desktop and in your start menu to assist with this.
winget installed is the easiest way to install the latest version of tgstation-server (provided Microsoft has approved the most recent package manifest).
Check if you have winget
by running the following command.
If it returns an error that means you don't have winget. You can easily install it by running the following commands in an administrative Windows Powershell instance:
Once winget is installed, simply run the following commands, accepting any prompts that may appear:
The required dotnet runtime may be installed as a pre-requisite. MariaDB will not be installed.
Note: If you use the -h
or --disable-interactivity
winget arguments, you will need to either pre-configure TGS or configure and start the tgstation-server
service after installing. A shortcut will be placed on your desktop and in your start menu to assist with this.
Note: The winget
package is submitted to Microsoft for approval once TGS releases. This means the winget version may be out of date with the current release version. You can always use the TGS updater after installing. You can see the versions still awaiting approval here.
If you don't have it installed already, download and install the ASP .NET Core Runtime Hosting Bundle (>= v8.0). Ensure that the dotnet
executable file is in your system's PATH
variable (or that of the user's that will be running the server). You can test this by opening a command prompt and running dotnet --list-runtimes
.
Download the latest release .zip. Typically, you want the ServerService.zip
package in order to run TGS as a Windows service. Choose ServerConsole.zip
if you prefer to use a command line daemon.
Extract the .zip file to where you want the server to run from. Note the account running the server must have write, execute, and delete access to the lib
subdirectory.
If you wish to install the TGS as a service, run Tgstation.Server.Host.Service.exe
. It should prompt you to install it. Click Yes
and the setup wizard should run.
Should you want a clean start, be sure to first uninstall the service by running Tgstation.Server.Host.Service.exe -u
from the command line.
If using the console version, run ./tgs.bat
in the root of the installation directory. Ctrl+C will close the server, terminating all live game instances.
Installing natively is the recommended way to run tgstation-server on Linux.
You first need to add the appropriate Microsoft package repository for your distribution
Refer to the Microsoft website for steps for
After that, install TGS and all it's dependencies via our apt repository, interactively configure it, and start the service with this one-liner:
The service will execute as the newly created user: tgstation-server
. You should, ideally, store your instances somewhere under /home/tgstation-server
.
TGS supports being setup on Nix starting with version 6.12.0. Add the flake to your own system by adding the following code to your flake inputs.
Where version
is the latest major TGS version you wish to use.
Note that changing this version does not change the core version of TGS used after the first launch. Instead, have TGS self-update via its API.
For maximum game server uptime, do NOT modify this version unless you are doing a major TGS version update in which case it is a requirement.
Configure TGS by setting up its service definition:
Refer to tgstation-server.nix for the full list of available configuration options.
The following dependencies are required.
Ubuntu/Debian Package
section)Download the latest release .zip. Choose ServerConsole
.
If you have SystemD installed, we recommend installing the service unit here. It assumes TGS is installed into /opt/tgstation-server
, it is executing as the user tgstation-server
, and you will be using the console runner, but feel free to adjust it to your needs. Note that the server will need to have it's configuration file setup before running with SystemD.
Alternatively, to launch the server in the current shell, run ./tgs.sh
in the root of the installation directory. The process will run in a blocking fashion. SIGQUIT will close the server, terminating all live game instances.
tgstation-server supports running in a docker container. The official image repository is located at https://hub.docker.com/r/tgstation/server. It can also be built locally by running docker build . -f build/Dockerfile -t <your tag name>
in the repository root.
To create a container run
with any additional options you desire (i.e. You'll have to expose more game ports in order to host more than one instance).
When launching the container for the first time, you'll be prompted with the setup wizard and then the container will exit. Start the container again to launch the server.
Important note about port exposure: The internal port used by DreamDaemon MUST match the port you want users to connect on. If it doesn't, you'll still be able to have them connect HOWEVER links from the BYOND hub will point at what DreamDaemon thinks the port is (the internal port).
Note although /app/lib
is specified as a volume mount point in the Dockerfile
, unless you REALLY know what you're doing. Do not mount any volumes over this for fear of breaking your container.
The configuration option General:ValidInstancePaths
will be preconfigured to point to /tgs_instances
. It is recommended you don't change this.
Note that this container is meant to be long running. Updates are handled internally as opposed to at the container level.
Note that automatic configuration reloading is currently not supported in the container. See #1143
If using manual configuration, before starting your container make sure the aforementioned appsettings.Production.yml
is setup properly. See below
In order for TGS to use OpenDream, it requires the full .NET SDK to build whichever version your servers target. Whatever that is, it must be available using the dotnet
command for whichever user runs TGS.
OpenDream currently requires .NET SDK 8.0 at the time of this writing. You must install this manually outside of TGS (i.e. using your package manager).
On Linux, as long as OpenDream and TGS do not use the same .NET major version, you cannot achieve this with the package manager as they will conflict. For example, the 7.0 SDK can be added to an 8.0 runtime installation via the following steps.
tgstation-server
using any of the above methods.dotnet
executable, LICENSE.txt
, and ThirdPartyNotices.txt
in the .tar.gz
on top of the existing installation directory /usr/share/dotnet/
sudo chown -R root /usr/share/dotnet
You should now be able to run the dotnet --list-sdks
command and see an entry for 7.0.XXX [/usr/share/dotnet/sdk]
.
The first time you run TGS you should be prompted with a configuration wizard which will guide you through setting up your appsettings.Production.yml
This wizard will, generally, run whenever the server is launched without detecting the config yml. Follow the instructions below to perform this process manually.
There are 3 primary supported ways to configure TGS:
appsettings.Production.yml
file (Recommended).Section__Subsection=value
or Section__ArraySubsection__0=value
for arrays.--Section:Subsection=value
or --Section:ArraySubsection:0=value
for arrays.The latter two are not recommended as they cannot be dynamically changed at runtime. See more on ASP.NET core configuration here.
Create an appsettings.Production.yml
file next to appsettings.yml
. This will override the default settings in appsettings.yml
with your production settings. There are a few keys meant to be changed by hosts. The configuration is only read after server statup. To reload it you must restart TGS. This can be done while your game servers are running by using the Administrative restart function (as opposed to an OS service restart). Note these are all case-sensitive:
General:ConfigVersion
: Suppresses warnings about out of date config versions. You should change this after updating TGS to one with a new config version. The current version can be found on the releases page for your server version.General:MinimumPasswordLength
: Minimum password length requirement for database usersGeneral:ValidInstancePaths
: Array meant to limit the directories in which instances may be created.General:UserLimit
: Maximum number of users that may be createdGeneral:InstanceLimit
: Maximum number of instances that may be createdGeneral:GitHubAccessToken
: Specify a classic GitHub personal access token with no scopes here to highly mitigate the possiblity of 429 response codes from GitHub requestsGeneral:SkipAddingByondFirewallException
: Set to true
if you have Windows firewall disabledGeneral:AdditionalEventScriptsDirectories
: An array of directories that are considered to contain EventScripts alongside instance directories. Working directory for executed scripts will remain the instance EventScripts directory.Session:HighPriorityLiveDreamDaemon
: Boolean controlling if live DreamDaemon instances get set to above normal priority processes.Session:LowPriorityDeploymentProcesses
: Boolean controlling if DreamMaker and API validation DreamDaemon instances get set to below normal priority processes.FileLogging:Directory
: Override the default directory where server logs are stored. Default is C:/ProgramData/tgstation-server/logs
on Windows, /usr/share/tgstation-server/logs
otherwiseFileLogging:LogLevel
: Can be one of Trace
, Debug
, Information
, Warning
, Error
, or Critical
. Restricts what is put into the log files. Currently Debug
is reccommended for help with error reporting.FileLogging:ProviderNetworkDebug
: Boolean controlling whether or not Chat bot providers should log their raw network traffic. Currently only applies to IrcProvider.Kestrel:Endpoints:Http:Url
: The URL (i.e. interface and ports) your application should listen on. General use case should be http://localhost:<port>
for restricted local connections. See the Remote Access section for configuring public access to the World Wide Web. This doesn't need to be changed using the docker setup and should be mapped with the -p
option insteadDatabase:DatabaseType
: Can be one of SqlServer
, MariaDB
, MySql
, PostgresSql
, or Sqlite
.Database:ServerVersion
: The version of the database server. Used by the MySQL/MariaDB and Postgres providers for selection of certain features, ignore at your own risk. A string in the form <major>.<minor>.<patch>
for MySQL/MariaDB or <major>.<minor>
for PostgresSQL.Database:ConnectionString
: Connection string for your database. Click here for an SQL Server generator, or see here for a Postgres guide or here for a MySQL guide (You should probably use '127.0.0.1' instead of 'localhost'). Sqlite connection strings should be in the format Data Source=<PATH TO DATABASE FILE>;Mode=ReadWriteCreate
.ControlPanel:Enable
: Enable the javascript based control panel to be served from the server via /index.htmlControlPanel:AllowAnyOrigin
: Set the Access-Control-Allow-Origin header to * for all responses (also enables all headers and methods)ControlPanel:AllowedOrigins
: Set the Access-Control-Allow-Origin headers to this list of origins for all responses (also enables all headers and methods). This is overridden by ControlPanel:AllowAnyOrigin
ControlPanel:PublicPath
: URL from which the webpanel can be accessed, defaults to "/app/". Must be an absolute path (https://example.org/path/to/webpanel) or a path starting from root (/path/to/webpanel). Note that this option does not relocate the webpanel for you; you will need a reverse proxy to relocate the webpanelElasticsearch
: tgstation-server also supports automatically ingesting its logs to ElasticSearch. You can set this up in the setup wizard, or with the following configuration: Swarm
: This section should be left empty unless using the server swarm system. If this is to happen, ensure all swarm servers are set to connect to the same database.Swarm:PrivateKey
: Must be a secure string set identically on all swarmed servers.Swarm:ControllerAddress
: Must be set on all swarmed servers that are not the controller server and should be an address the controller server may be reached at.Swarm:Address
: Must be set on all swarmed servers. Should be an address the server can be reached at by other servers in the swarm.Swarm:PublicAddress
: Should be set on all swarmed servers. Should be an address the server can be reached at by other servers in the swarm.Swarm:Identifier
: Must be set uniquely on all swarmed servers. Used to identify the current server. This is also used to select which instances exist on the current machine and should not be changed post-setup.Swarm:UpdateRequiredNodeCount
: Should be set to the total number of servers in your swarm minus 1. Prevents updates from occurring unless the non-controller server count in the swarm is greater than or equal to this value.Security:OAuth:<Provider Name>
: Sets the OAuth client ID and secret for a given <Provider Name>
. The currently supported providers are Keycloak
, GitHub
, Discord
, InvisionCommunity
and TGForums
. Setting these fields to null
disables logins AND gateway auth with the provider, but does not stop users from associating their accounts using the API. Sample Entry: RedirectUrl
setting:The following providers use the ServerUrl
setting:
Gateway auth simply allows the users to authenticate with the service using the configuration you provide and have their impersonation token passed back to the client. An example of this is using GitHub gateway auth to allow clients to enumerate pull requests without getting rate limited.
Telemetry:DisableVersionReporting
: Prevents you installation and the version you're using from being reported on the source repository's deployments listTelemetry:ServerFriendlyName
: Prevents anonymous TGS version usage statistics from being sent to be displayed on the repository.Telemetry:VersionReportingRepositoryId
: The repository telemetry is sent to. For security reasons, this is not the main TGS repo. See the tgstation-server-deployments repository for more information.If using a MariaDB/MySQL server, our client library recommends you set 'utf8mb4' as your default charset disregard at your own risk.
The user created for the application will need the privilege to create databases on the first run, do not create the database for it. Once the initial set of migrations is run, the create right may be revoked. The user should maintain DDL rights though for applying future migrations
Note that the ratio of application installations to databases is 1:1. Do not attempt to share a database amongst multiple TGS installations.
For the Windows service version start the tgstation-server
service. If it fails to start, check the Windows event log under Windows/Application for entries from tgstation-server for errors.
For the console version run dotnet Tgstation.Server.Host.Console.dll
in the installation directory. The tgs.bat
and tgs.sh
shell scripts are shortcuts for this. If on Windows, you must do this as admin to give the server permission to install the required DirectX dependency for certain 512 BYOND versions as well as create symlinks.
For the docker version run docker start <your container name>
Test your server is running by visiting the local port in your browser. You should receive a 401 Unauthorized response (You may need to view the developer console). Otherwise an error page will be present.
Normally stopping TGS will terminate DreamDaemon processes. If you need a graceful detach, send command 130
to the Windows service or signal SIGUSR2
to the Linux dotnet process. Detaching with the Windows console runner is currently not officially supported.
For the Windows service version stop the tgstation-server
service.
For the SystemD managed service, use systemctl stop tgstation-server
. DO NOT USE systemctl kill
as this can create orphaned processes while leaving TGS running.
For the console version press Ctrl+C
or send a SIGQUIT to the ORIGINAL dotnet process.
For the docker version run docker stop <your container name>
.
tgstation-server provides the DMAPI which can be be integrated into any BYOND codebase for heavily enhanced functionality. The integration process is a fairly simple set of code changes.
tgs.dm
can be seperated from the tgs
folder, but do not modify or move the contents of the tgs
folder.dme
(s) to include the tgs.dm
and tgs/includes.dm
files (ORDER OF APPEARANCE IS MANDATORY)tgs.dm
to integrate the API with your codebase.The DMAPI is fully backwards compatible and should function with any tgstation-server version to date. Updates can be performed in the same manner. Using the TGS_EXTERNAL_CONFIGURATION
is recommended in order to make the process as easy as replacing tgs.dm
and the tgs
folder with a newer version
Here is a bare minimum example project that implements the essential code changes for integrating the DMAPI
Before tgs.dm
:
Anywhere else:
tgstation-server is an ASP.Net Core app based on the Kestrel web server. This section is meant to serve as a general use case overview, but the entire Kestrel configuration can be modified to your liking with the configuration YAML. See the official documentation for details.
Exposing the builtin Kestrel server to the internet directly over HTTP is highly not reccommended due to the lack of security. The recommended way to expose tgstation-server to the internet is to host it through a reverse proxy with HTTPS support. Here are some step by step examples to achieve this for major web servers.
System administrators will most likely have their own configuration plans, but here are some basic guides for beginners.
Once complete, test that your configuration worked by visiting your proxy site from a browser on a different computer. You should receive a 401 Unauthorized response.
NOTE: Your reverse proxy setup may interfere with SSE (Server-Sent Events) which is used for real-time job updates. If you find this to be the case, please open an issue describing what you did to fix it as there may be a way for us to bypass the need for a workaround from our end.
Require Server Name Indication
if you want to limit requests to a specific URL prefix. Do not use the same port as the one TGS is running on.URL Rewrite
moduleActions
Pane on the right click Add Rule(s)...
Reverse Proxy
under Inbound and Outbound Rules
and click OK
OK
Inbound Rules
textbox to the URL of your tgstation-server i.e. localhost:5000
. Ensure Enable SSL Offloading
is checked, then click OK
ControlPanel:PublicPath
needs to be blank. If you have a path in PublicPath
, it needs to be in "reverse_proxy PublicPathHere localhost:5000".See https://caddyserver.com/docs/caddyfile/directives/reverse_proxy
See https://docs.nginx.com/nginx/admin-guide/web-server/reverse-proxy/
mod_proxy
extension is installed.See https://httpd.apache.org/docs/2.4/howto/reverse_proxy.html
Example VirtualHost Entry
Multiple tgstation-servers can be linked together in a swarm. The main benefit of this is allowing for users, groups, and permissions to be shared across the servers. Servers in a swarm must connect to the same database, use the same tgstation-server version, and have their own unique names.
In a swarm, one server is designated the 'controller'. This is the server other 'node's in the swarm communicate with and coordinates group updates. Issuing an update command to one server in a swarm will update them all to the specified version.
Instances can be either part of a swarm or not. Once in the database they cannot switch between these states. In order to brin a non-swarmed instance into a swarmed server or vice-versa follow these steps.
tgstation-server is controlled via a RESTful HTTP json API. Documentation on this API can be found here. This section serves to document the concepts of the server. The API is versioned separately from the release version. A specification for it can be found in the api-vX.X.X git releases/tags.
TGS can self update without stopping your DreamDaemon servers. Releases made to this repository are bound by a contract that allows changes of the runtime assemblies without stopping your servers. Database migrations are automatically applied as well. Reverting to lower versions works but only works so far back in time, do so at your own risk (check changes made to /src/Tgstation.Server.Host/Models/Migrations
).
Major version updates may require additional action on the part of the user (apart from the configuration changes).
If TGS was installed via a package manager, using the TGS self updater will cause the version to change without notifying said package manager. This is not necessarily a problem if you're okay with the deviation.
To avoid this, use the package manager to update TGS. It is just as seamless as the self-updater.
If a server update is available, it will be indicated in the response from the GET /Administration endpoint and shown as a green exclamation mark in the webpanel navbar. For more active notifications, you can subscribe to this GitHub discussion.
All actions apart from logging in must be taken by a user. TGS installs with one default user whose credentials can be found here. It is recommended to disable this user ASAP as it is used to create Jobs that are started by the server itself. If access to all users is lost, the default user can be reset using the Database:ResetAdminPassword
configuration setting.
Users can be enabled/disabled and have a very granular set of rights associated to them that determine the actions they are allowed to take (i.e. Modify the user list or create instances). Users can be database based or system based. Database users are your standard web users with a username and password. System users, on the otherhand, are authenticated with the host OS. These users cannot have their password or names changed by TGS as they are managed by the system (and in reverse, login tokens don't expire when their password changes). The benefit to having these users is it allows the use of system ACLs for static file control. More on that later.
A TGS deployment is made up with a set of instances, which each represent a production BYOND server. As many instances as desired can be created. Be aware, however, due to the nature of BYOND, this will quickly result in system resource exhaustion.
An instance is stored in a single folder anywhere on a system and is made up of several components: The source code git repository, the BYOND installations, the compiler, the watchdog, chat bots, and static file management systems.
All users with access to an instance have an InstanceUser object associated with the two that defines more rights specific to that instance (i.e. Deploy code, modify bots, edit other InstanceUsers).
The Repository
folder is a git repository containing the code of the game you wish to host. It can be cloned from any public or private remote repository and has capabilities to affect changes back to it. All the standard benefits of git are utilized (i.e. check out any revision or reference).
Additional features become available if the remote repository is hosted on https://github.com/. Namely the Test Merge feature, which allows you to take a pull request opened on the repository and compile it into a game deployment for testing. Information about test merges is available in game via the DMAPI and via the main API as well. These require a valid personal access token with repo
scope or an installed GitHub App with the following permissions: contents: write
, pull_requests: write
, and deployments: write
.
Manual operations on the repository while an instance is running may lead to git data corruption. Thankfully, it's simple enough to delete and reclone the repository via the API.
The Byond
folder contains installations of BYOND or OpenDream versions. The version which is used by your game code can be changed on a whim (Note that only versions >= 511.1385 have been thouroughly tested. Lower versions should work but if one doesn't function, please open an issue report) and the server will take care of installing it.
You can specify additional environment variables to launch your server/compiler with by adding server.env
/compiler.env
to your engine installation directory (i.e. <instance>/Byond/515.1530/server.env
). These are .env files.
The compiler deploys code from the Repository
folder to the Game
folder and compiles it either by autodetecting the .dme
or having it set by configuration. Several other step are also run such as validating the DMAPI version and creating symlinks for static files are done at this point. The compiler also applies server side code modifications and duplicates compiled code for the watchdog as well (See following section).
The watchdog is responsible for starting and keeping your server running. It functions by launching two servers which are hot-swapped on /world/Reboot
s and during crashes to prevent downtime. This hot swapping feature is also what allows TGS to deploy updates to live servers without bringing them down.
DreamDaemon can be finicky and will crash with several high load games or bad DM code. The watchdog has several failure prevention methods to keep at least one server running while these issues are sorted out.
TGS supports creating infinite chat bots for notifying staff or players of things like code deployments and uptime in. Currently the following providers are supported
More can be added by providing a new implementation of the IProvider interface
Bots have a set of built-in commands that can be triggered via !tgs
, mentioning, or private messaging them. Along with these, custom commands can be defined using the DMAPI by creating a subtype of the /datum/tgs_chat_command
type (See tgs.dm
for details). Invocation for custom commands can be restricted to certain channels.
All files in game code deployments are considered transient by default, meaning when new code is deployed, changes will be lost. Static files allow you to specify which files and folders stick around throughout all deployments.
The StaticFiles
folder contains 3 root folders which cannot be deleted and operate under special rules
CodeModifications
EventScripts
GameStaticFiles
These files can be modified either in host mode or system user mode. In host mode, TGS itself is responsible for reading and writing the files. In system user mode read and write actions are performed using the system account of the logged on User, enabling the use of ACLs to control access to files. Database users will not be able to use the static file system if this mode is configured for an instance.
This folder may be freely modified manually just beware this may cause in-progress deployments to error if done on Windows systems.
When a deployment is made by the compiler, all the contents of this folder are copied over the repository contents. Then one of two code change modes are selected based on the prescense of certain files.
If <target dme>.dme
is present, that .dme will be used instead of the repository's .dme
Otherwise the files HeadInclude.dm
and TailInclude.dm
are searched for and added as include lines to the top and bottom of the target .dme
repsectively if they exist. These files can contain any valid DreamMaker code (Including #include
ing other .dm
files!) allowing you to modify the a repository's code on a per instance basis
This folder can contain anything. But, when certain events occur in the instance, TGS will look here for .bat
or .sh
files with the same name and run those with corresponding arguments. List of supported events can be found here.
Any files and folders contained in this root level of this folder will be symbolically linked to all deployments at the time they are created. This allows persistent game data (BYOND .sav
s or code configuration files for example) to persist across all deployments. This folder contains a .tgsignore file which can be used to prevent symlinks from being generated by entering the names of files and folders (1 per line).
This functionality has the following prerequisites:
OR
Trusted
security level.OR
GameStaticFiles
directory are on the same filesystem as the instance's Game
directory.OR
Trusted
security level.Here are tools for interacting with the TGS web API
Contact project maintainers to get your client added to this list
Note that tgstation-server is NOT a backup solution, the onus is on the server runners.
The Repository
folder should be backed up on the remote server, do not rely on the instance copy to store changes.
The BYOND
and Game
folders should never be backed up due to being intertwined with instance data.
The Configuration
folder should be fully backed up.
The database should be fully backed up.
To restore an installation from backups, first restore the instance Configuration
folder in its new home. Then restore the database, modifying the Path
column in the Instances
table where necessary to point to the new instances. Then start the server pointed at the new database.
Should you end up with a lost database for some reason or want to reattach a detached instance you can reattach an existing folder by creating an empty file named TGS4_ALLOW_INSTANCE_ATTACH
inside it (This is automatically created when detaching instances). Then create a new instance with that path, this will bypass the empty folder check. Note that this will not restore things such as user permissions, server config options, or deployment metadata. Those must be reconfigured manually.
Feel free to ask for help on the discussions page.
See the files in the /src/DMAPI
tree for the MIT license