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Websocket Protocol

This document details the expected data structure of information sent down the websocket.

Contents

Wrapper

Every message across the WebSocket must be contained in the following wrapper's payload field:

Client -> server

{
  "event": "",
  "payload": {event data}
}

Server -> client

{
  "event": "",
  "time": 1582128345655,
  "payload": {event data}
}

The server will be in charge of dating events as it receives them.

time is in UNIX time to millisecond precision.

Payloads

init - Joining a room

{
  "RoomID": "id",
  "RoomName": "default",
  "Public": true,
  "UserIndex": 1,
  "Users": ["Eddie", null, "Josho", null, null, "Martin", "Elle", null],
}

Users has length equal to the max number of users in a room. Colours are assigned using the index of the user. You have the index UserIndex in the array. The RoomID is the value for /room/RoomID and serves as the link for inviting friends to the room.

user - User join/leave

User join:

{
  "UserIndex": 1,
  "UserName":"Jordie",
  "Users": ["Eddie", "Jordie", "Josho", null, null, "Martin", "Elle", null],
}

User leave:

{
  "UserIndex": 1,
  "UserName":"Jordie",
  "Users": ["Eddie", null, "Josho", null, null, "Martin", "Elle", null],
}

Including UserName may seem a bit redundant but it is necessary in the case of cached join/leave events.

message - Client Message

Client -> Server:

{
  "Data": [255, 255, ...],
  "Span": 192
}

Server -> Client:

{
  "ColourIndex": 2,
  "Sender": "Josh",
  "Data": "///...",
  "Span": 192
}

ColourIndex was the index of the user that sent the message in the users array when they sent it, it differs from UserIndex in that there may or may not be the same user that sent the message in that index in the Users array.

See the Message Encoding section for a description of the Data field.

announcement - message from server

Server -> Client:

{
  "Announcement": "Welcome to Picto!",
}

rename - Rename Room

Client -> server

{
  "RoomName": "Denver Airport"
}

Server -> client

{
  "UserName": "Josj",
  "RoomName": "Denver Airport"
}

rename events are ignored in static rooms.

Error Codes

Code Description
4400 Invalid username provided (too long/empty string etc).
4404 The server can't find the room specified.
4409 The server can't add the client to the room (the name is already taken or the room is full).
4503 The server can't create a room (has reached maximum rooms capacity).
4666 If this happens, an error isn't being handled appropriately by the server.

Message Encoding

A byte is used per pixel.

Range Use
0 Transparent
1 Black
2-3 Greyscale (2 = light grey, 3 = dark grey)
4-62 Rainbow colours
63 RLE encoding start character

RLE encoding is 255 [counts] 0 [value] where the total count is the sum of counts, plus 4 (if four or less characters are repeated they're not RLE'd as it'd be less efficient, and 0 is an illegal character in [counts], so we know there's at least 5). The sum of [counts] is used as opposed to a product as to avoid having to complicate message checking for illegally large images.

The RLE decoder will cut off as soon as the current count sums to more than the canvas size, or the image length becomes longer than the canvas size.