Spin Message Trigger

A generic messaging trigger for Fermyon Spin. Note this is an experimental/work-in-progress repo, and is not production ready at this point. Also - if you have suggestions for improvements, feel free to make them in the Issues tab.

Features

• Use multipe message brokers, including (currently):
  • a simple in memory broker (with * based wildcard support)
  • redis pubsub
  • NATS
  • MQTT
• Named brokers - allowing multiple brokers of the same or different types in a single application
  • this is designed to support usecases such as separating the publishing of internal domain events & public events meant for others to consume
• an HTTP gateway server for publishing messages to the broker, as well as some request/response support
• a WebSocket server allowing subscribing to single subjects (with wildcard support, as available for the broker), as well as bi-directional socket communication
• Trigger a Spin component from a message on a subscribed channel
• Publish messages from the Spin component - defaulting to the same broker & subject, but optionally setting other defaults or manually setting the broker & subject for each message
• Run the HTTP gateway server independently of the main spin app (doesn't really work for the in memory broker, but works for others)
• Multiple message paradigms - Pub/Sub, Request/Response & Queues

Desired Features

• Additional broker support
• Support for basic event-sourcing structures
• actor style trigger options

Installation

To install the plugin, run the following command on the system running your spin deployment (or any development machine):

spin plugin install --url https://github.com/lee-orr/spin-message-trigger/releases/download/canary/trigger-message.json --yes

Quick Start

Once you've installed the plugin, you can get started quickly installing the templates and using them:

spin templates install --git https://github.com/lee-orr/spin-message-trigger --upgrade

You can then set up a new project using:

spin new message-app

Once you have that, you can use spin add to set up components, brokers and gateways. Importantly Components must be manually added to the Cargo.toml workspace once they are created. The available templates are:

Template Name	Description
message-component	This creates a component that gets triggered by a subscription.
request-response-message-component	This creates a component that gets triggered by a request-response message, with an HTTP method & path.
queue-component	This creates a component that gets subscribes to a queue - meaning only one member of the queue group will get triggered for each message. Most useful if you have multiple instances of the spin application running.
redis-broker	This connects to a redis pub-sub on the provided server
mqtt-broker	This connects to an Mqtt server
nats-broker	This connects to a Nats server or cluster
broker-gateway	This sets up an Http gateway that publishes to one of the brokers in your project

Detailed Usage

When setting up a spin application with this trigger, there are 3 parts:

• the spin application details, which are consistent with any other spin application
• the trigger definition
• the component definitions

Trigger Definition

The trigger definition object contains two fields - the type, which must be "message", and a dictionary of broker configs. Each broker config contains a broker type - a value which changes based on the message broker type - and a gateway definition.

More info on the broker types & gateway definition is below.

In the example, this section looks like this:

# Here we define the trigger message type
[trigger]
type = "message"

# This sets up a broker called "test", with the "InMemoryBroker" type.
[trigger.brokers.test]
broker_type = "InMemoryBroker"

# This sets up an HTTP gateway for the test broker on port 3005, and allowing full request/response serialization using JSON.
[trigger.brokers.test.gateway.Http]
port = 3_005
request_response = "Json"

# This sets up a broker called "secondary", which connects to a NATs server at the address "nats" (this is handled by docker compose treating that as a domain name).
[trigger.brokers.secondary.broker_type.Nats]
addresses = ["nats"]

# This sets up an HTTP gateway for the secondary broker on port 3006, and allowing websockets to subscribe to topics published on that broker.
[trigger.brokers.secondary.gateway.Http]
port = 3_006
websockets = "TextBody"

Broker Type Configuration

In Memory Broker

The in memory broker is a simple broker, primarily meant for use in single instance deployments and for testing purposes, with support for wildcard subscriptions. It's configuration is simple:

[trigger.brokers.BROKER_NAME]
broker_type = "InMemoryBroker"

Redis Broker

The Redis broker provides support for Redis channels, similar to the spin built-in redis trigger, but with additional support for wildcard subscriptions. It's configuration involves setting the redis address, like so

[trigger.brokers.BROKER_NAME]
broker_type = { Redis = "redis://redis:6379" }

NATs Broker

The NATs broker provides support for subscribing to topics on a NATs broker. It's configuration is more complex than the previous ones:

[trigger.brokers.BROKER_NAME.broker_type.NATs]
# This is required, and contains a list of addresses for the nats servers
addresses = ["nats"]

# Optional - do the servers require tls. defaults to false
tls = true

# Optional - the interval for pings, in milliseconds.
pint_interval = 10_000

# Optional - path to root certificates
root_certificate = "/path/to/root/certificate"

# Optional - paths to client certificate files
client_certificate = { certificate = "/path/to/client/cert", key = "/path/to/client/key" }

# Optional - client name
client_name = "the client name"

In addition - there are multiple optional authentication options for NATs:

# Token based auth
[trigger.brokers.BROKER_NAME.broker_type.NATs.auth]
Token = "token string"

# Username & Password authentication
[trigger.brokers.BROKER_NAME.broker_type.NATs.auth]
User = { user = "username", password = "password" }

# NKey authentication
[trigger.brokers.BROKER_NAME.broker_type.NATs.auth]
NKey = "NKey String"

# JWT auth
[trigger.brokers.BROKER_NAME.broker_type.NATs.auth]
Jwt = { nkey_seed = "nkey seed", jwt = "jwt string" }

# Credentials File
[trigger.brokers.BROKER_NAME.broker_type.NATs.auth]
CredentialsFile = "/path/to/credentials/file"

# Credentials String
[trigger.brokers.BROKER_NAME.broker_type.NATs.auth]
CredentialsString = "credentials string"

MQTT Broker

The MQTT broker provides support for MQTT compatible message brokers. Note that it traslates the topic patterns to be consistent with the other brokers - so segments of the topic will be represented with . rather than / and wildcards with * rather than +. For example, the MQTT topic my/topic would be translated into my.topic, and the subscription my/+ would be my.*.

It's configuration involves setting the redis address, like so

[trigger.brokers.BROKER_NAME.broker_type.Mqtt]
address = "mqtt://mqtt:1883"
# Optionally, you can also provide a client id. Otherwise one will be generated.
id = "my_id"
# Optionally, you can also provide the keep_alive duration, as a f32 in seconds
keep_alive = 5.0

# Optionally, you can also set up a username and password
[trigger.brokers.BROKER_NAME.broker_type.Mqtt.credentials]
username = "username"
password = "password"

Gateway Definition

Each broker can have an HTTP gateway defined for accessing it. The gateways expose 3 routes, based on the config:

• /publish/*subject* - an HTTP post to this route will send the body of the request to the subject in the route.
• /subscribe/*subject* - this is a route for WebSocket's to subscribe for updates on the subject, with support for pattern matching as provided by the broker.
• /request/*path* - this route will serialize any request sent to it into a message, publish it to a specifically formatted subject, and then recieve a response from the first published message on another specifically formatted subject.
• /ws - this is a rout for supporting bi-directional, multi-subject websocket connections.

If you wish to enable a gateway, you can define the gateway like so:

[trigger.brokers.BROKER_NAME.gateway.Http]
# The port for the Http gateway
port = 3005

# An optional configuration for websockets - enabling their use for subscribing to subjects on the broker.
websockets = "BinaryBody"

# Possible Values:

# BinaryBody - will forward the message body directly as binary data
# TextBody - will transform the message body to a utf8 string, and forward the string to the client
# Messagepack - will serialize the input message object, containing the body (a vec of u8's), subject & broker name, to Messagepack 
# Json - will serialize the input message object, containing the body (a vec of u8's), subject & broker name, to Json 

# An optional configuration for enabling request/response patterns (with the /request/ route)
request_response = "Messagepack"

# Possible Values: 

# Messagepack - this will serialize the request into a Messagepack, publish it to the broker, and rely on messagepack for the response as well
# Json - this will serialize the request into Json, publish it to the broker, and rely on json for the response as well

For request/response processes - the trigger currently publish messages to special subject names. This is a process one I'd like to change, but haven't had a chance yet. The subjects follow the following format: request.*request_id*.*method*.*path* and response.*request_id*.*method*.*path*. The request id is a Ulid generated per request.

Component Definitions

The component definition contains a trigger secion, which contains information used to determine triggering & responses for this component. Specifically - the broker field takes the name of the broker this compoment gets triggered by, and the subscription field, which takes an object configuring the subscription.

A component can either subscribe to a Topic, a Request or a Queue.

General Configuration

The main portion of the general configuration is setting the broker you wish to subscribe to, along with any other common spin component configuration options.

[[component]]
id = "hello"
source = "./target/wasm32-wasi/release/example_app.wasm"
allowed_http_hosts = []
[component.trigger]
# Here we set up the broker we want to subscribe to
broker = "test"
[component.build]
command = "cargo build --target wasm32-wasi --release -p example-app"

Topic Subscriptions

A Topic subscription takes a topic string representing the topic being subscribed to - based on the conventions of the specific broker, and an optional result field that allows setting up a defaults for published result messages, allowing them to target a different default broker and subject.

Here is one of the component definitions in the example:

[component.trigger.subscription.Topic]
# Here we set up the topic
topic = "hello.*"
# Here we set up alternative default publishing targets for this component - so by default it sends messages to the "good.bye" subject on the "secondary" broker
result = { default_broker = "secondary", default_subject = "good.bye" }

Request / Response

A Request requires a path & an optional method, similar to an HTTP router.

[component.trigger.subscription.Request]
path = "test/*/hello"
method = "POST"

Note that the path supports segment wildcards, but not variables at the moment.

Queues

A Queue requires a topic to subscribe to, and a group which names the queue for which only one subscriber will receive each message.

[component.trigger.subscription.Queue]
topic = "test"
group = "queue"

Run the Gateway Independently

You can build the gateway independantly using cargo build -b gateway and run it uusing cargo run -b gateway. However, it cannot parse the gateway definitions from the spin toml, since it's built primarily for situations where you might host the gateway separately from the actual spin app.

As such - you configure it via the cli arguments. To get the up-to-date arguments, run cargo run --bin gateway -- -h. It's important to note that the broker is parsed as a query string. As such - a redis broker might be: cargo run --bin gateway -- --broker Redis=redis://redis:6379 while a nats broker might be: cargo run --bin gateway -- --broker Nats[addresses][0]="nats". It defaults to port 3015.

Bi-Directional Websockets

Bi-directional websockets rely on a simple protocol, encoded in either Json or Msgpack (based on whether websocket subscriptions rely on binary or text).

To subscribe to a topic, the client should send a message with the following structure:

{
    "Subscribe": "good.*" 
}

The client will receive messages encoding the following structure:

{
    message: Array<u8>, // an array representing the contents of the message
    subject: String, // the subject the message was published on
    broker: String, // the name of the broker in the config file
    response_subject: Option<String> // if it is a request/response, send the response to this subject
}

The client can also publish messages with the following structure:

{
    "Publish": {
        "message": Array<u8>,
        "subject": "good.test",
        "response_subject": Option<String>
    }
}

Development

This repository is set up to function as either a Dev Container (using VsCode). This means you can use Github workspaces to get it set up automatically, or use VSCodes "Clone Repository into Volume" option to clone the repo & build the dev environment for you.

Once you are running, you can use the "update-plugin.sh" script to build the plugin and install it on spin. Then - run "spin build" & "spin up" in the workspace root to launch it

If you are using VS Code, you'll notice there are two extensions installed:

• Thunder client, which lets you make HTTP requests.
  • you should see, under "Collections" an example app collection with an example request
• WebSocket, which lets you connect to websockets.
  • you should be able to connect to "ws://localhost:3006/subscribe/good.*"
  • When you send the example request in thunder client, you should see a "Goodbye" message arrive in the websocket client

Repo Structure

• The trigger-message crate contains the spin plugin, including the message broker interfaces
• The spin-message-types crate contains the .wit definition, some shared file types to allow for easy creation of messages, and a #[message_component] macro for setting up the trigger in your app
• The example-app create demonstrates simple use, and showcasing the use of multiple brokers within a single file
• the request-response-demo crate demonstrates creation of a json-based http request/response handler (the body is still a vec<u8>)