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EmuLinker-K

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A high performance netcode server using the Kaillera protocol.

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# EmuLinker-K

EmuLinker-K (ELK) is a high-performance server that uses the Kaillera protocol to facilitate online multiplayer for
retro gaming emulators.

Built as a Kotlin rewrite of the classic [EmulinkerSF](https://github.com/God-Weapon/EmuLinkerSF), EmuLinker-K focuses
on maximizing performance and stability, patching legacy security and privacy vulnerabilities, and providing useful new
features for both server administrators and players.

Please help us translate the server into more languages by contributing to
our [CrowdIn project](https://crowdin.com/project/emulinker-k)

Feel free to file bugs and feature requests on this repository, or find our channel in the Kaillera Reborn discord:

[![Discord](https://img.shields.io/badge/Discord-%235865F2.svg?style=for-the-badge&logo=discord&logoColor=white)](https://discord.gg/MqZEph388c)

## Setting up a new server (or updating an existing one)

### Linux/MacOS

To install or update the server, simply run the following command in your terminal. If you are updating an existing
server, run the command from your `EmuLinker-K` folder:

```bash
curl -fsSL https://raw.githubusercontent.com/hopskipnfall/EmuLinker-K/master/release/setup.sh | bash
```

### Windows

Please download the `.zip` file attached to latest release on
the [Releases](https://github.com/hopskipnfall/EmuLinker-K/releases) page, extract it, and run `start-server.bat`.

### Configuration files

#### config/emulinker.cfg

This is the main configuration file for the server.

The most important settings to configure are: `emulinker.language` and `emulinker.charset`.

Here is an exhaustive list of supported options to set in `emulinker.cfg` (most of these you will not need to change):

| Config Key                              | Default Value | Description                                                                                                                                                                                                                                                                                                                                                          |
|-----------------------------------------|---------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| controllers.connect.port                | 27888         | The port used by the server for all communication. Most clients will default to 27888 as the default.                                                                                                                                                                                                                                                                |
| controllers.v086.bufferSize             | 4096          | Buffer size for v086 protocol in bytes.                                                                                                                                                                                                                                                                                                                              |
| controllers.v086.clientTypes.clientType | v086          | Comma-separated list of accepted protocols.                                                                                                                                                                                                                                                                                                                          |
| emulinker.charset                       | (required)    | The character set that matches your language region. Use `Windows-1252` for English and Western Europe, `Windows-1251` for Cyrillic, `GBK` for Simplified Chinese, `Shift_JIS` for Japanese, or `x-IBM949` for Korean. Note: Unicode (`UTF-8`) is generally not supported by clients. If text appears garbled or displays as '?', try selecting a different charset. |
| emulinker.language                      | custom        | Strict ISO 639-1 language code. Use `en` for English, `es` for Spanish, `ja` for Japanese, `ko` for Korean, `pt` for Portuguese, `ru` for Russian, or `zh` for Simplified Chinese, or `custom` if you wish to provide your own translations.                                                                                                                         |
| game.bufferSize                         | (required)    | Buffer size for the game data queue.  Increasing this will not improve performance. Should be equal to at least the largest single game packet.                                                                                                                                                                                                                      |
| game.defaultAutoFireSensitivity         | 0             | Auto-fire sensitivity. 0 (disabled) through 5 (maximum sensitivity)                                                                                                                                                                                                                                                                                                  |
| masterList.serverConnectAddress         |               | Server address for master list registration                                                                                                                                                                                                                                                                                                                          |
| masterList.serverLocation               | Unknown       | Server location for master list display                                                                                                                                                                                                                                                                                                                              |
| masterList.serverName                   | Not Set       | Name used to identify the server                                                                                                                                                                                                                                                                                                                                     |
| masterList.serverWebsite                |               | Server website URL for master list                                                                                                                                                                                                                                                                                                                                   |
| masterList.touchEmulinker               | FALSE         | Registers server with the EmuLinker master list                                                                                                                                                                                                                                                                                                                      |
| masterList.touchKaillera                | FALSE         | Registers server with the Kaillera master list                                                                                                                                                                                                                                                                                                                       |
| metrics.enabled                         | FALSE         | Enables detailed monitoring of server health                                                                                                                                                                                                                                                                                                                         |
| metrics.loggingFrequencySeconds         | 30            | How frequently to log aggregated metrics for debugging                                                                                                                                                                                                                                                                                                               |
| server.allowedConnectionTypes           | 1,2,3,4,5,6   | Comma-separated list of allowed connection types by their ID (1 = LAN, 2 = Excellent, 3 = Good, 4 = Average, 5 = Low, 6 =  Bad)                                                                                                                                                                                                                                      |
| server.allowMultipleConnections         | TRUE          | Controls whether a single IP address can be logged in multiple times at the same time                                                                                                                                                                                                                                                                                |
| server.allowSinglePlayer                | TRUE          | Whether users are allowed to start a game when no other users have joined                                                                                                                                                                                                                                                                                            |
| server.chatFloodTime                    | 2             | Minimimum time (in seconds) a user must wait between sending two chat messages                                                                                                                                                                                                                                                                                       |
| server.coreThreadpoolSize               | 5             | Core size of the thread pool for user actions.                                                                                                                                                                                                                                                                                                                       |
| server.createGameFloodTime              | 2             | Minimum time (in seconds) a user must wait between creating two games                                                                                                                                                                                                                                                                                                |
| server.idleTimeout                      | 3600          | How often a user must engage in the server before being kicked for inactivity (0 to disable)                                                                                                                                                                                                                                                                         |
| server.keepAliveTimeout                 | 190           | Amount of time (in seconds) the server will wait before deciding a client has disconnected. Note: This is not related to user inactivity                                                                                                                                                                                                                             |
| server.lagstatDurationSeconds           | 60            | Duration for lag statistics collection in seconds. This is under active development, please give feedback in the discord instead of overriding this value.                                                                                                                                                                                                           |
| server.maxChatLength                    | 150           | Maximum length of chat messages (0 to disable)                                                                                                                                                                                                                                                                                                                       |
| server.maxClientNameLength              | 127           | Maximum length of the kaillera client name (must be ≤ 127)                                                                                                                                                                                                                                                                                                           |
| server.maxGameChatLength                | 320           | Maximum length of game chat messages                                                                                                                                                                                                                                                                                                                                 |
| server.maxGameNameLength                | 127           | Maximum length of a game name (must be ≤ 127)                                                                                                                                                                                                                                                                                                                        |
| server.maxGames                         | 0             | Maximum number of games that can be created in the server simultaneously (0 to disable)                                                                                                                                                                                                                                                                              |
| server.maxPing                          | 1000          | Maximum allowed roundtrip ping in milliseconds (must be ≤ 1000)                                                                                                                                                                                                                                                                                                      |
| server.maxQuitMessageLength             | 100           | Maximum length of quit messages                                                                                                                                                                                                                                                                                                                                      |
| server.maxUserNameLength                | 30            | Maximum length of user names (must be ≤ 30)                                                                                                                                                                                                                                                                                                                          |
| server.maxUsers                         | 0             | Maximum number of concurrent users logged into the server (0 to disable)                                                                                                                                                                                                                                                                                             |
| server.switchStatusBytesForBuggyClient  | FALSE         | Switch some game/player statuses for a Japanese client "Project 64k 0.13 (01 Aug 2003)" that seems to use different values.                                                                                                                                                                                                                                          |
| twitter.auth.oAuthAccessToken           |               | Twitter OAuth access token                                                                                                                                                                                                                                                                                                                                           |
| twitter.auth.oAuthAccessTokenSecret     |               | Twitter OAuth access token secret                                                                                                                                                                                                                                                                                                                                    |
| twitter.auth.oAuthConsumerKey           |               | Twitter OAuth consumer key                                                                                                                                                                                                                                                                                                                                           |
| twitter.auth.oAuthConsumerSecret        |               | Twitter OAuth consumer secret                                                                                                                                                                                                                                                                                                                                        |
| twitter.broadcastDelaySeconds           | 15            | Delay from starting a game to when the tweet is posted                                                                                                                                                                                                                                                                                                               |
| twitter.deletePostOnClose               | FALSE         | Whether to delete Twitter posts when games close                                                                                                                                                                                                                                                                                                                     |
| twitter.enabled                         | FALSE         | Enable posting to twitter based on game activity                                                                                                                                                                                                                                                                                                                     |
| twitter.preventBroadcastNameSuffixes    |               | Comma-separated list of name suffixes appearing after a @ in the username to prevent posting to twitter                                                                                                                                                                                                                                                              |

#### config/language.properties

This file is used to customize the messages sent by the server to the clients, specifically for when users join the
server or join a game:

```properties
KailleraServerImpl.LoginMessage.1=Welcome to a new EmuLinkerSF-K Server!
KailleraServerImpl.LoginMessage.2=Here is a second message to show to users when they join.
KailleraServerImpl.JoinGameMessage.1=You joined a game!
```

If your server is in Spanish, Korean, Portuguese, Japanese, Russian, or Chinese all other messages have been translated
for you. Please contact us in the discord about adding new translations if you speak a language not represented.

If you choose to use "custom" translations by setting `emulinker.language=custom` in `config/emulinker.cfg`, you will
also use this file to manually
provide translations for everything listed in [messages.properties](emulinker/src/main/i18n/messages.properties).

### Enabling Twitter integration

You can have the server make a Twitter post when a user opens a game, and either delete it or reply marking it as "
closed" when the game starts. At the time of writing this, both options are supported by the Twitter API free tier.

To set it up, configure the following values in `config/emulinker.cfg`:

```
# Twitter reporting integration switch. When enabled it will
# broadcast new open games.
twitter.enabled=true

# Delay (in seconds) before sending a tweet.
twitter.broadcastDelaySeconds=20

# Comma-separated list of phrases that, if found in the name
# after a "@", will prevent tweet posting.
# Example username: nue@waiting
twitter.preventBroadcastNameSuffixes=waiting,restart
# If true, will simply delete the tweet when the game starts.
twitter.deletePostOnClose=false

# You will need to make a new Twitter API app and fill in these values.
twitter.auth.oAuthAccessToken=
twitter.auth.oAuthAccessTokenSecret=
twitter.auth.oAuthConsumerKey=
twitter.auth.oAuthConsumerSecret=
```

With these settings, users whose name ends in @waiting (meaning they are waiting for a specific person to join their
game) or @restart (meaning they are restarting the game and are waiting for the same person to join) will not have
tweets sent. Similarly, users will be notified and given 20 seconds to type `/stop` to stop the tweet from sending.
After the game starts, the account will respond to the original tweet with the text "(opponent found)".

## Server Extensions

This server extends the original Kaillera/EmuLinkerSF protocol and admin toolset with additional features. All extensions are **backwards compatible** — existing clients behave identically without needing any changes. However, some features are only accessible to users with sufficient access levels (admin, superadmin).

### Admin Commands

EmuLinker-K adds the following admin chat commands on top of the standard set. Commands are entered in the server lobby chat.

> [!NOTE]
> Optional `<reason>` arguments are **internal only** — the reason is recorded in logs and viewable via `/info`, but is never revealed to the affected user or broadcast to the server.

| Command | Access | Description |
|---|---|---|
| `/ban <UserID> <minutes> [reason]` | Moderator+ | Temporarily ban a user by UserID. The optional `reason` is recorded internally. |
| `/silence <UserID> <minutes> [reason]` | Moderator+ | Temporarily silence (mute) a user. The optional `reason` is recorded internally. |
| `/permaban <UserID> [reason]` | Admin+ | Permanently bans a user. Writes an `ipaddress,DENY` entry to `access.cfg` with a comment recording the issuer, timestamp, and optional reason. |
| `/permamute <UserID> [reason]` | Admin+ | Permanently silences a user. Writes a `silence` entry to `access.cfg` with a comment recording the issuer, timestamp, and optional reason. |
| `/clear <IP \| UserID \| Name>` | Admin+ | Clears all temporary bans and silences for a user. Accepts an IP address, UserID number, or exact username (case-insensitive). |
| `/info <IP \| UserID \| Name>` | Admin+ | Displays a user's access level and any active temporary restrictions (with issuer and reason) as private messages to the requesting admin. |

#### Backwards Compatibility Note

The `reason` parameter on `/ban` and `/silence` is optional and appended after the required arguments. Old client UIs that issue these commands automatically (e.g. `"/ban 1 10"`) will continue to work without modification.

### `access.cfg` Persistent Bans and Silences

The standard `access.cfg` format is extended with a new `silence` entry type for persistent mutes:

```
# Permanent silence issued by AdminName on 2026-01-01T00:00:00
# Reason: Hate speech
silence,10.0.0.42
```

When `/permaban` or `/permamute` is used, the server appends the appropriate rule to `access.cfg` along with a comment block. The file is automatically reloaded without a server restart.

The `access.cfg` file is monitored for changes. Any manual edits (e.g., removing a ban entry to lift a permanent ban) will take effect automatically on the next server check.

## Legal Disclaimer

Server administrators are solely responsible for ensuring that their data collection, disclosure, and retention
practices (including logs) comply with all applicable laws and regulations. The repository maintainers assume no
liability for the use of this software.

## Contributing

If you're interested in contributing to this project, please read [Contributing.md](CONTRIBUTING.md).

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