mirror of https://gitlab.com/litecord/litecord.git
199 lines
5.4 KiB
Markdown
199 lines
5.4 KiB
Markdown
# Litecord Voice Server Protocol (LVSP)
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LVSP is a protocol for Litecord to communicate with an external component
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dedicated for voice data. The voice server is responsible for the
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Voice Websocket Discord and Voice UDP connections.
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LVSP runs over a *long-lived* websocket with TLS. The encoding is JSON.
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**TODO:** common logic scenarios:
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- initializing a voice channel
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- updating a voice channel
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- destroying a voice channel
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- user joining to a voice channel
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- user joining to a voice channel (while also initializing it, e.g
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first member in the channel)
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- user leaving a voice channel
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## OP code table
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"client" is litecord. "server" is the voice server.
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| opcode | name | sent by |
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| --: | :-- | :-- |
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| 0 | HELLO | server |
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| 1 | IDENTIFY | client |
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| 2 | RESUME | client |
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| 3 | READY | server |
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| 4 | HEARTBEAT | client |
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| 5 | HEARTBEAT\_ACK | server |
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| 6 | INFO | client / server |
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## Message structure
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Message data is defined by each opcode.
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**Note:** the `snowflake` type follows the same rules as the Discord Gateway's
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snowflake type: A string encoding a Discord Snowflake.
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| field | type | description |
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| --: | :-- | :-- |
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| op | integer, opcode | operator code |
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| d | map[string, any] | message data |
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| s | Optional[int] | sequence number |
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- The `s` field is explained in the `RESUME` message.
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## High level overview
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- connect, receive HELLO
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- send IDENTIFY or RESUME
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- if RESUME, process incoming messages as they were post-ready
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- receive READY
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- start HEARTBEAT'ing
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- send INFO / VSU\_REQUEST messages as needed
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## Error codes
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| code | meaning |
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| --: | :-- |
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| 4000 | general error. Reconnect |
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| 4001 | authentication failure |
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| 4002 | decode error, given message failed to decode as json |
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## HELLO message
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Sent by the server when a connection is established.
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| field | type | description |
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| --: | :-- | :-- |
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| heartbeat\_interval | integer | amount of milliseconds to heartbeat with |
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| nonce | string | random 10-character string used in authentication |
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## IDENTIFY message
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Sent by the client to identify itself.
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| field | type | description |
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| --: | :-- | :-- |
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| token | string | `HMAC(SHA256, key=[secret shared between server and client]), message=[nonce from HELLO]` |
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## RESUME message
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Sent by the client to resume itself from a failed websocket connection.
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The server will resend its data, then send a READY message.
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| field | type | description |
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| --: | :-- | :-- |
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| token | string | same value from IDENTIFY.token |
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| seq | integer | last sequence number to resume from |
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### Sequence numbers
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Sequence numbers are used to resume a failed connection back and make the
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voice server replay its missing events to the client.
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They are **positive** integers, **starting from 0.** There is no default
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upper limit. A "long int" type in languages will probably be enough for most
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use cases.
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Replayable messages MUST have sequence numbers embedded into the message
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itself with a `s` field. The field lives at the root of the message, alongside
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`op` and `d`.
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## READY message
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- The `health` field is described with more detail in the `HEARTBEAT_ACK`
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message.
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| field | type | description |
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| --: | :-- | :-- |
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| `health` | Health | server health |
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## HEARTBEAT message
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Sent by the client as a keepalive / health monitoring method.
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The server MUST reply with a HEARTBEAT\_ACK message back in a reasonable
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time period.
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| field | type | description |
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| --: | :-- | :-- |
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| s | integer | sequence number |
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## HEARTBEAT\_ACK message
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Sent by the server in reply to a HEARTBEAT message coming from the client.
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The `health` field determines how well is the server's overall health. It is a
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float going from 0 to 1, where 0 is the worst health possible, and 1 is the
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best health possible.
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Servers SHOULD use the same algorithm to determine health, it CAN be based off:
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- Machine resource usage (RAM, CPU, etc), however they're too general and can
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be unreliable.
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- Total users connected.
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- Total bandwidth used in some X amount of time.
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Among others.
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| field | type | description |
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| --: | :-- | :-- |
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| s | integer | sequence number |
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| health | float | server health |
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## INFO message
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Sent by either client or a server to send information between eachother.
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The INFO message is extensible in which many request / response scenarios
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are laid on.
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| field | type | description |
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| --: | :-- | :-- |
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| type | InfoType | info type |
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| data | Any | info data, varies depending on InfoType |
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### InfoType Enum
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| value | name | description |
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| --: | :-- | :-- |
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| 0 | CHANNEL\_REQ | channel assignment request |
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| 1 | CHANNEL\_ASSIGN | channel assignment reply |
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| 2 | CHANNEL\_UPDATE | channel update |
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| 3 | CHANNEL\_DESTROY | channel destroy |
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| 4 | VST\_CREATE | voice state create request |
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| 5 | VST\_UPDATE | voice state update |
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| 6 | VST\_LEAVE | voice state leave |
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**TODO:** finish all infos
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### CHANNEL\_REQ
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Request a channel to be created inside the voice server.
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The Server MUST reply back with a CHANNEL\_ASSIGN when resources are
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allocated for the channel.
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**TODO:** fields
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### CHANNEL\_ASSIGN
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Sent by the Server to signal the successful creation of a voice channel.
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**TODO:** fields
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### CHANNEL\_UPDATE
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Sent by the client to signal an update to the properties of a channel,
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such as its bitrate.
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**TODO:** fields
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### CHANNEL\_DESTROY
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Sent by the client to signal the destruction of a voice channel. Be it
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a channel being deleted, or all members in it leaving.
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**TODO:** fields
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