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OpenTTD's admin network

Last updated: 2024-03-26

Table of contents

1.0) Preface

The admin network provides a dedicated network protocol designed for other applications to communicate with OpenTTD. Connected applications can execute console commands remotely (rcon commands) with no further authentication. Furthermore information about clients and companies can be provided.

Admin applications remain connected when starting a new game or loading a saved game in contrast to normal OpenTTD clients that get disconnected.

This document describes the admin network and its protocol.

Please refer to the mentioned enums in src/network/core/tcp_admin.h

Please also note that further improvements to the admin protocol can mean that more packet types will be sent by the server. For forward compatibility it is therefore wise to ignore unknown packets. Future improvements might also add additional data to packets. This data should be ignored. Data will never be removed from packets in later versions, except the possibility that complete packets are dropped in favour of a new packet.

This though will be reflected in the protocol version as announced in the ADMIN_PACKET_SERVER_PROTOCOL in section 2.0).

A reference implementation in Java for a client connecting to the admin interface can be found at: http://dev.openttdcoop.org/projects/joan

2.0) Joining the network

Create a TCP connection to the server on port 3977. The application is expected to authenticate within 10 seconds.

To authenticate send either an ADMIN_PACKET_ADMIN_JOIN or an ADMIN_PACKET_ADMIN_JOIN_SECURE packet.

The ADMIN_PACKET_ADMIN_JOIN packet sends the password without any encryption or safeguards over the connection, and as such has been disabled by default.

The ADMIN_PACKET_ADMIN_JOIN_SECURE packet initiates a key exchange authentication schema which tells te server which methods the client supports and the server makes a choice. The server will then send an ADMIN_PACKET_SERVER_AUTH_REQUEST packet to which the client has to respond with an ADMIN_PACKET_ADMIN_AUTH_RESPONSE packet.

The current choices for secure authentication are authorized keys, where the client has a private key and the server a list of authorized public keys, and a so-called password-authenticated key exchange which allows to authenticate using a password without actually sending the password. The server falls back to password authentication when the client's key is not in the list of authorized keys.

When authentication has succeeded for either of the JOIN schemas, the server will reply with ADMIN_PACKET_SERVER_PROTOCOL followed directly by ADMIN_PACKET_SERVER_WELCOME.

ADMIN_PACKET_SERVER_PROTOCOL contains details about the protocol version. It is the job of your application to check this number and decide whether it will remain connected or not. Furthermore, this packet holds details on every AdminUpdateType and the supported AdminFrequencyTypes (bitwise representation).

ADMIN_PACKET_SERVER_WELCOME contains details on the server and the map, e.g. if the server is dedicated, its NetworkLanguage, size of the Map, etc.

Once you have received ADMIN_PACKET_SERVER_WELCOME you are connected and authorized to do your thing.

The server will not provide any game related updates unless you ask for them. There are four packets the server will none the less send, if applicable:

- ADMIN_PACKET_SERVER_ERROR
- ADMIN_PACKET_SERVER_WELCOME
- ADMIN_PACKET_SERVER_NEWGAME
- ADMIN_PACKET_SERVER_SHUTDOWN

However, ADMIN_PACKET_SERVER_WELCOME only after a ADMIN_PACKET_SERVER_NEWGAME

3.0) Asking for updates

Asking for updates is done with ADMIN_PACKET_ADMIN_UPDATE_FREQUENCY. With this packet you define which update you wish to receive at which frequency.

Note: not every update type supports every frequency. If in doubt, you can verify against the data received in ADMIN_PACKET_SERVER_PROTOCOL.

Please note the potential gotcha in the "Certain packet information" section below when using the ADMIN_UPDATE_FREQUENCY packet.

The server will not confirm your registered update. However, asking for an invalid AdminUpdateType or a not supported AdminUpdateFrequency you will be disconnected from the server with NETWORK_ERROR_ILLEGAL_PACKET.

Additional debug information can be found with a debug level of net=3.

ADMIN_UPDATE_DATE results in the server sending:

- ADMIN_PACKET_SERVER_DATE

ADMIN_UPDATE_CLIENT_INFO results in the server sending:

- ADMIN_PACKET_SERVER_CLIENT_JOIN
- ADMIN_PACKET_SERVER_CLIENT_INFO
- ADMIN_PACKET_SERVER_CLIENT_UPDATE
- ADMIN_PACKET_SERVER_CLIENT_QUIT
- ADMIN_PACKET_SERVER_CLIENT_ERROR

ADMIN_UPDATE_COMPANY_INFO results in the server sending:

- ADMIN_PACKET_SERVER_COMPANY_NEW
- ADMIN_PACKET_SERVER_COMPANY_INFO
- ADMIN_PACKET_SERVER_COMPANY_UPDATE
- ADMIN_PACKET_SERVER_COMPANY_REMOVE

ADMIN_UPDATE_COMPANY_ECONOMY results in the server sending:

- ADMIN_PACKET_SERVER_COMPANY_ECONOMY

ADMIN_UPDATE_COMPANY_STATS results in the server sending:

- ADMIN_PACKET_SERVER_COMPANY_STATS

ADMIN_UPDATE_CHAT results in the server sending:

- ADMIN_PACKET_SERVER_CHAT

ADMIN_UPDATE_CONSOLE results in the server sending:

- ADMIN_PACKET_SERVER_CONSOLE

ADMIN_UPDATE_CMD_LOGGING results in the server sending:

- ADMIN_PACKET_SERVER_CMD_LOGGING

3.1) Polling manually

Certain AdminUpdateTypes can also be polled:

- ADMIN_UPDATE_DATE
- ADMIN_UPDATE_CLIENT_INFO
- ADMIN_UPDATE_COMPANY_INFO
- ADMIN_UPDATE_COMPANY_ECONOMY
- ADMIN_UPDATE_COMPANY_STATS
- ADMIN_UPDATE_CMD_NAMES

Please note the potential gotcha in the "Certain packet information" section below when using the ADMIN_POLL packet.

ADMIN_UPDATE_CLIENT_INFO and ADMIN_UPDATE_COMPANY_INFO accept an additional parameter. This parameter is used to specify a certain client or company. Setting this parameter to UINT32_MAX (0xFFFFFFFF) will tell the server you want to receive updates for all clients or companies.

Not supported AdminUpdateType in the poll will result in the server disconnecting the application with NETWORK_ERROR_ILLEGAL_PACKET.

Additional debug information can be found with a debug level of net=3.

4.0) Sending rcon commands

Rcon runs separate from the ADMIN_UPDATE_CONSOLE AdminUpdateType. Requesting the execution of a remote console command is done with the packet ADMIN_PACKET_ADMIN_RCON.

Note: No additional authentication is required for rcon commands.

The server will reply with one or more ADMIN_PACKET_SERVER_RCON packets. Finally an ADMIN_PACKET_ADMIN_RCON_END packet will be sent. Applications will not receive the answer twice if they have asked for the AdminUpdateType ADMIN_UPDATE_CONSOLE, as the result is not printed on the servers console (just like clients rcon commands).

Furthermore, sending a say command (or any similar command) will not be sent back into the admin network. Chat from the server itself will only be sent to the admin network when it was not sent from the admin network.

Note that when content is queried or updated via rcon, the processing happens asynchronously. But the ADMIN_PACKET_ADMIN_RCON_END packet is sent already right after the content is requested as there's no immediate output. Thus other packages and the output of content rcon command may be sent at an arbitrary later time, mixing into the output of other console activity, e.g. also of possible subsequent other rcon commands sent.

5.0) Sending chat

Sending a ADMIN_PACKET_ADMIN_CHAT results in chat originating from the server.

Currently four types of chat are supported:

- NETWORK_ACTION_CHAT
- NETWORK_ACTION_CHAT_CLIENT
- NETWORK_ACTION_CHAT_COMPANY
- NETWORK_ACTION_SERVER_MESSAGE

NETWORK_ACTION_SERVER_MESSAGE can be sent to a single client or company using the respective DestType and ID. This is a message prefixed with the 3 stars, e.g. *** foo has joined the game

5.1) Receiving chat

Register ADMIN_UPDATE_CHAT at ADMIN_FREQUENCY_AUTOMATIC to receive chat. The application will be able to receive all chat the server can see.

The configuration option network.server_admin_chat specifies whether private chat for to the server is distributed into the admin network.

6.0) Disconnecting

It is a kind thing to say good bye before leaving. Do this by sending the ADMIN_PACKET_ADMIN_QUIT packet.

7.0) Certain packet information

ADMIN_PACKET_ADMIN_UPDATE_FREQUENCY and ADMIN_PACKET_ADMIN_POLL

Potential gotcha: the AdminUpdateType integer type used is a
uint16 for `UPDATE_FREQUENCY`, and a uint8 for `POLL`.
This is due to boring legacy reasons.
It is safe to cast between the two when sending
(i.e cast from a uint8 to a uint16).

All ADMIN_PACKET_SERVER_* packets have an enum value greater 100.

ADMIN_PACKET_SERVER_WELCOME

Either directly follows `ADMIN_PACKET_SERVER_PROTOCOL` or is sent
after a new game has been started or a map loaded, i.e. also
after ADMIN_PACKET_SERVER_NEWGAME.

ADMIN_PACKET_SERVER_CLIENT_JOIN and ADMIN_PACKET_SERVER_COMPANY_NEW

These packets directly follow their respective INFO packets. If you receive
a CLIENT_JOIN / COMPANY_NEW packet without having received the INFO packet
it may be a good idea to POLL for the specific ID.

ADMIN_PACKET_SERVER_CMD_NAMES and ADMIN_PACKET_SERVER_CMD_LOGGING

Data provided with these packets is not stable and will not be
treated as such. Do not rely on IDs or names to be constant
across different versions / revisions of OpenTTD.
Data provided in this packet is for logging purposes only.