@truffle/dashboard-message-bus
The @truffle/dashboard-message-bus manages the communication between the Truffle Dashboard and any other Truffle components via a specialized proxy RPC server instance.
Installation
End users should never have to install this message bus as it is used under the hood by other packages. If you are building a package that needs to interface with the Dashboard or message bus, you can install this package from NPM.
npm install @truffle/dashboard-message-bus
yarn add @truffle/dashboard-message-bus
Usage
A new message bus can be started by instantiating a new DashboardMessageBus and calling the start() function on it. This should almost always be done in combination with starting a new dashboard, so you probably don't want to do this directly. Instead you should start a new dashboard, which automatically starts its corresponding message bus.
The @truffle/dashboard-message-bus does contain a bunch of exported utilities used for connecting and communicating with the message bus that can be used directly by other packages, although this should still only be used when developing new packages that interface with the dashboard, rather than end-user applications.
Development
Architecture
The message bus works by running two separate WebSocket servers. One server is for publishers to connect to and send requests, while the other server is for subscribers (dashboards) to connect to and receive requests. The subscribers respond to these requests by sending a message to the message bus with an ID that corresponds to the request. Any requests from publishers are sent to all subscribers, but only the first response will be returned to the publisher. When new subscribers connect, any "unfulfilled" requests will be sent to the newly connected subscribers as well. The message bus stays running as long as there is at least one publisher or subscriber connected. As soon as the last one disconnects, the message bus shuts down.
Testing
This package is meant to be used with the @truffle/dashboard package. So manual testing is most likely done through the dashboard package. Some automated tests are defined in the test/ folder, but these still need to be expanded.
Adding new message types
Right now there are very few message types. The most important one is "provider", which sends RPC requests to the @truffle/dashboard so that they can be handled by the injected web3 provider that your wallet (e.g. MetaMask) providers. Other message types are "invalidate", which can be sent to invalidate earlier messages, and "log", which is sent by the message bus to send log messages over the wire. See the @truffle/dashboard-message-bus-common README for details about adding new message types.