svelte-websocket-stores

Synchronize primitive-typed Svelte stores across a simple WebSocket connection.

Purpose

This was originally designed to allow touch panels to use Svelte with any backend.

Usage

Initialization

import { initialize } from "svelte-websocket-stores/websocket";

initialize({
    server_address: "192.168.0.64",
    local_scope: "tp1"
});

Write-only example

<script>
    import { booleans } from "svelte-websocket-stores/store";

    let pressStore = booleans.get("myCoolButton.press");

    function press() {
        $pressStore = true;
    }

    function release() {
        $pressStore = false;
    }
</script>

<button
    on:pointerdown={press}
    on:pointerup={release}
    on:pointerout={release}>
    <slot />
</button>

Read-only exmaple

<script>
    import { numbers } from "svelte-websocket-stores/store";

    let sizeStore = numbers.get("myList.size");
</script>

<div>
    {#each { length: $sizeStore } as _, index}
        <slot />
    {/each}
</div>

WebSocket Message Format

All communication between a server and this library is over WebSocket.

All WebSocket messages are interpreted as JSON objects.

The message object is defined as:

type Message = {
    scope: string,
    id: string,
    type: string,
    value: boolean | number | string,
}

The field scope identifies the scope of the client it comes from and limits which clients receive it when coming from the server. The field type determines how the value field is interpreted as well as which of the tables (booleans, numbers, or strings) the id field will be indexing into.

Client

Message Received

1. The incoming text data is parsed as JSON.
2. The object's scope field is checked if it is global ("global") or matches the client's local scope (for example "tp1"). If it does not match, the message is discarded.
3. The object's type field is switched on with the cases "boolean", "number", and "string". If there is no match, the message is discarded.
4. The local Svelte store is indexed by the object's id field from the dictionary holding the respectively typed stores.
5. The store's value is assigned to the object's value field, cast to its respective type.

Server [^1]

Client Connected

1. Send the client messages for all the variables currently stored values

Message Received

1. The incoming text data is parsed as JSON.
2. The object's type field is switched on with the cases "boolean", "number", and "string". If there is no match, the message is discarded.
3. The variable is indexed by the object's scope and id fields from the dictionary holding the respectively typed variables.
4. The variable's value is assigned to the object's value field, cast to its respective type.
5. Send all clients a message for the new value.
6. Handle any events.

[^1]: This is the behavior expected by this WebSocket client