Simple RPC

A basic client / server RPC for sending the requests over a MessagePort.

This supports Node Worker Threads, Web Workers, or anything that can provide a MessagePortLike interface.

Communication Details

The client and server communicate by sending messages over the MessagePort.

``ts
export interface RPCMessage {
sig: 'RPC0';
/**
* A Unique identifier for the request/response.
* Ideally this is a randomUUID.
*/
id: RequestID;
/**
* The type of message being sent.
*/
type: 'request' | 'response' | 'cancel' | 'canceled' | 'ok' | 'ready';
}

export type RPCRequestType = 'request' | 'cancel' | 'ok' | 'ready';

export type RPCResponseType = 'response' | 'canceled' | 'ok' | 'ready';
`

There are two types of messages: Request and Response. The client sends requests and the server sends responses.

$3

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
participant W as Worker
C->>+S: Request
S->>+W: Method
W->>-S: Result
S->>-C: Response , Result
`

$3

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
participant W as Worker
C->>+S: Request , ACK
S->>C: ACK
S->>+W: Method
W->>-S: Result
S->>-C: Response , Result
`

$3

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
participant W as Worker
C->>+S: Request , ACK
S->>C: ACK
S->>+W: Method
W->>-S: Error
S->>-C: Response , Error
`

$3

This request is used to check if the server is ok.

`mermaid
sequenceDiagram
Client->>Server: OK ?
Server->>Client: OK , Code 200
`

$3

A cancellation request is used to cancel or abort a request. The server accepts the request and acknowledges that it was received. It does not wait

#### Cancel Request: no wait

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
participant W as Worker
C->>+S: Request
S->>+W: Method
C->>S: Cancel
S->>-C: Canceled
S--xW: Cancel
W--x-S: Canceled
`

#### Cancel Request: wait

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
participant W as Worker
C->>+S: Request
S->>+W: Method
C->>S: Cancel , Wait
S--xW: Cancel
W-->>-S: Canceled
S->>-C: Canceled
`

$3

It can happen that the server needs to cancel requests. This can happen if the server is getting disposed and still has pending requests. It has a couple of ways to do this:

1. Send an Error Response
2. Send a Canceled Response

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
participant W as Worker
C->>+S: Request
S->>+W: Method
W--x-S: Canceled
S->>-C: Canceled
`

$3

An abort request is the same as a Cancel request, only the client will not wait on a response and the response will be ignored.

`mermaid
sequenceDiagram
participant C as Client
participant S as Server
C->>S: Request
C-->>S: Cancel
S--xC: Canceled
``