Registering
-----------
The idea is that game servers push their server info to the
masterservers every 15 seconds or when the server info changes, but not
more than once per second.
The game servers do not support the old registering protocol anymore,
the backward compatibility is handled by the masterserver.
The register call is a HTTP POST to a URL like
`https://master1.ddnet.tw/ddnet/15/register` and looks like this:
```json
POST /ddnet/15/register HTTP/1.1
Address: tw-0.6+udp://connecting-address.invalid:8303
Secret: 81fa3955-6f83-4290-818d-31c0906b1118
Challenge-Secret: 81fa3955-6f83-4290-818d-31c0906b1118:tw0.6/ipv6
Info-Serial: 0
{
"max_clients": 64,
"max_players": 64,
"passworded": false,
"game_type": "TestDDraceNetwork",
"name": "My DDNet server",
"map": {
"name": "dm1",
"sha256": "0b0c481d77519c32fbe85624ef16ec0fa9991aec7367ad538bd280f28d8c26cf",
"size": 5805
},
"version": "0.6.4, 16.0.3",
"clients": []
}
```
The `Address` header declares that the server wants to register itself as
a `tw-0.6+udp` server, i.e. a server speaking a Teeworlds-0.6-compatible
protocol.
The free-form `Secret` header is used as a server identity, the server
list will be deduplicated via this secret.
The free-form `Challenge-Secret` is sent back via UDP for a port forward
check. This might have security implications as the masterserver can be
asked to send a UDP packet containing some user-controlled bytes. This
is somewhat mitigated by the fact that it can only go to an
attacker-controlled IP address.
The `Info-Serial` header is an integer field that should increase each
time the server info (in the body) changes. The masterserver uses that
field to ensure that it doesn't use old server infos.
The body is a free-form JSON object set by the game server. It should
contain certain keys in the correct form to be accepted by clients. The
body is optional if the masterserver already confirmed the reception of
the info with the given `Info-Serial`.
Not shown in this payload is the `Connless-Token` header that is used
for Teeworlds 0.7 style communication.
Also not shown is the `Challenge-Token` that should be included once the
server receives the challenge token via UDP.
The masterserver responds with a `200 OK` with a body like this:
```
{"status":"success"}
```
The `status` field can be `success` if the server was successfully
registered on the masterserver, `need_challenge` if the masterserver
wants the correct `Challenge-Token` header before the register process
is successful, `need_info` if the server sent an empty body but the
masterserver doesn't actually know the server info.
It can also be `error` if the request was malformed, only in this case
an HTTP status code except `200 OK` is sent.
Synchronization
---------------
The masterserver keeps state and outputs JSON files every second.
```json
{
"servers": [
{
"addresses": [
"tw-0.6+udp://127.0.0.1:8303",
"tw-0.6+udp://[::1]:8303"
],
"info_serial": 0,
"info": {
"max_clients": 64,
"max_players": 64,
"passworded": false,
"game_type": "TestDDraceNetwork",
"name": "My DDNet server",
"map": {
"name": "dm1",
"sha256": "0b0c481d77519c32fbe85624ef16ec0fa9991aec7367ad538bd280f28d8c26cf",
"size": 5805
},
"version": "0.6.4, 16.0.3",
"clients": []
}
}
]
}
```
`servers.json` (or configured by `--out`) is a server list that is
compatible with DDNet 15.5+ clients. It is a JSON object containing a
single key `servers` with a list of game servers. Each game server is
represented by a JSON object with an `addresses` key containing a list
of all known addresses of the server and an `info` key containing the
free-form server info sent by the game server. The free-form `info` JSON
object re-encoded by the master server and thus canonicalized and
stripped of any whitespace characters outside strings.
```json
{
"kind": "mastersrv",
"now": 1816002,
"secrets": {
"tw-0.6+udp://127.0.0.1:8303": {
"ping_time": 1811999,
"secret": "42d8f991-f2fa-46e5-a9ae-ebcc93846feb"
},
"tw-0.6+udp://[::1]:8303": {
"ping_time": 1811999,
"secret": "42d8f991-f2fa-46e5-a9ae-ebcc93846feb"
}
},
"servers": {
"42d8f991-f2fa-46e5-a9ae-ebcc93846feb": {
"info_serial": 0,
"info": {
"max_clients": 64,
"max_players": 64,
"passworded": false,
"game_type": "TestDDraceNetwork",
"name": "My DDNet server",
"map": {
"name": "dm1",
"sha256": "0b0c481d77519c32fbe85624ef16ec0fa9991aec7367ad538bd280f28d8c26cf",
"size": 5805
},
"version": "0.6.4, 16.0.3",
"clients": []
}
}
}
}
```
`--write-dump` outputs a JSON file compatible with `--read-dump-dir`,
this can be used to synchronize servers across different masterservers.
`--read-dump-dir` is also used to ingest servers from the backward
compatibility layer that pings each server for their server info using
the old protocol.
The `kind` field describe that this is `mastersrv` output and not from a
`backcompat`. This is used for prioritizing `mastersrv` information over
`backcompat` information.
The `now` field contains an integer describing the current time in
milliseconds relative an unspecified epoch that is fixed for each JSON
file. This is done instead of using the current time as the epoch for
better compression of non-changing data.
`secrets` is a map from each server address and to a JSON object
containing the last ping time (`ping_time`) in milliseconds relative to
the same epoch as before, and the server secret (`secret`) that is used
to unify server infos from different addresses of the same logical
server.
`servers` is a map from the aforementioned `secret`s to the
corresponding `info_serial` and `info`.
```json
[
"tw-0.6+udp://127.0.0.1:8303",
"tw-0.6+udp://[::1]:8303"
]
```
`--write-addresses` outputs a JSON file containing all addresses
corresponding to servers that are registered to HTTP masterservers. It
does not contain the servers that are obtained via backward
compatibility measures.
This file can be used by an old-style masterserver to also list
new-style servers without the game servers having to register there.
An implementation of this can be found at
https://github.com/heinrich5991/teeworlds/tree/mastersrv_6_backcompat
for Teeworlds 0.5/0.6 masterservers and at
https://github.com/heinrich5991/teeworlds/tree/mastersrv_7_backcompat
for Teeworlds 0.7 masterservers.
All these JSON files can be sent over the network in an efficient way
using https://github.com/heinrich5991/twmaster-collect. It establishes a
zstd-compressed TCP connection authenticated by a string token that is
sent in plain-text. It watches the specified file and transmits it every
time it changes. Due to the zstd-compression, the data sent over the
network is similar to the size of a diff.
Implementation
--------------
The masterserver implementation was done in Rust.
The current gameserver register implementation doesn't support more than
one masterserver for registering.
These diagnostics are supposed to guide the user to problem resolution.
They're displayed if no packet is received from the server within one
second of connecting.
No message if we don't have STUN servers.
"Trying to determine UDP connectivity..." if no answer has been received
from the STUN server yet and it hasn't timed out yet.
"UDP seems to be filtered." if the STUN request has timed out.
"UDP and TCP IP addresses seem to be different. Try disabling VPN,
proxy or network accelerators." if the STUN request has returned an IP
address different from the one obtained via HTTP from info2.ddnet.tw.
"No answer from server yet." otherwise, if the STUN request has returned
no interesting data, indicating that it's likely the game server's
fault.
Purely automatic change. In case of conflict with this change, apply the
other change and rerun the formatting to restore it:
$ python scripts/fix_style.py
This means that we have a reliable and fast way to query for extended info,
while also not wasting network bandwidth.
The protocol is designed to be extensible, there's four bytes space for
encoding more request types (currently zeroed), and there's one string in each
response packet and one string for each player available (currently the empty
string).
The protocol itself has no problems with more than 64 players, although the
current client implementation will drop the player info after the 64th player,
because it uses a static array for storage.
Also fixes#130, the player list is just sorted each time new player info
arrives.
ChillerDragon
