🔊 Bus

Bus is a minimalist event/message bus implementation for internal communication. It is heavily inspired from my event_bus package for Elixir language.

API

The method names and arities/args are stable now. No change should be expected on the package for the version 2.x.x except any bug fixes.

Installation

Via go packages: go get github.com/mustafaturan/bus/v2

Usage

Configure

The package requires a unique id generator to assign ids to events. You can write your own function to generate unique ids or use a package that provides unique id generation functionality.

The bus package respect to software design choice of the packages/projects. It supports both singleton and dependency injection to init a bus instance.

Hint: Check the demo project for the singleton configuration.

Here is a sample initilization using monoton id generator:

import (
    "github.com/mustafaturan/bus/v2"
    "github.com/mustafaturan/monoton"
    "github.com/mustafaturan/monoton/sequencer"
)

func NewBus() *bus.Bus {
    // configure id generator (it doesn't have to be monoton)
    node        := uint64(1)
    initialTime := uint64(1577865600000) // set 2020-01-01 PST as initial time
    m, err := monoton.New(sequencer.NewMillisecond(), node, initialTime)
    if err != nil {
        panic(err)
    }

    // init an id generator
    var idGenerator bus.Next = (*m).Next

    // create a new bus instance
    b, err := bus.NewBus(idGenerator)
    if err != nil {
        panic(err)
    }

    // maybe register topics in here
    b.RegisterTopics("order.received", "order.fulfilled")

    return b
}

Register Event Topics

To emit events to the topics, topic names need to be registered first:

// register topics
b.RegisterTopics("order.received", "order.fulfilled")

Register Event Handlers

To receive topic events you need to register handlers; A handler basically requires two vals which are a Handle function and topic Matcher regex pattern.

handler := bus.Handler{
    Handle: func(ctx context.Context, e *bus.Event) {
        // do something
        // NOTE: Highly recommended to process the event in an async way
    },
    Matcher: ".*", // matches all topics
}
b.RegisterHandler("a unique key for the handler", &handler)

Emit Events

// if txID val is blank, bus package generates one using the id generator
ctx := context.Background()
ctx = context.WithValue(ctx, bus.CtxKeyTxID, "some-transaction-id-if-exists")

// event topic name (must be registered before)
topic := "order.received"

// interface{} data for event
order := make(map[string]string)
order["orderID"]     = "123456"
order["orderAmount"] = "112.20"
order["currency"]    = "USD"

// emit the event
event, err := b.Emit(ctx, topic, order)

if err != nil {
    // report the err
    fmt.Println(err)
}

// if the caller needs the event, a ref for the event is returning as result of
// the `Emit` call.
fmt.Println(event)

Processing Events

When an event is emitted, the topic handlers receive the event synchronously. It is highly recommended to process events asynchronous. Package leave the decision to the packages/projects to use concurrency abstractions depending on use-cases. Each handlers receive the same event as ref of bus.Event struct:

// Event data structure
type Event struct {
	ID         string      // identifier
	TxID       string      // transaction identifier
	Topic      string      // topic name
	Data       interface{} // actual event data
	OccurredAt int64       // creation time in nanoseconds
}

Sample Project

A demo project with three consumers which increments a counter for each event topic, printer consumer which prints all events and lastly calculator consumer which sums amounts.

Benchmarks

When txID specified in the context:

goos: darwin
goarch: amd64
pkg: github.com/mustafaturan/bus/v2
cpu: Intel(R) Core(TM) i5-6267U CPU @ 2.90GHz
BenchmarkEmit-4   	 5315254	       205.7 ns/op	      88 B/op	       1 allocs/op

When txID is not specified in the context (the library generates and assigns txID to the context and the event):

goos: darwin
goarch: amd64
pkg: github.com/mustafaturan/bus/v2
cpu: Intel(R) Core(TM) i5-6267U CPU @ 2.90GHz
BenchmarkEmitWithoutTxID-4   	 4044715	       285.2 ns/op	     152 B/op	       3 allocs/op

Contributing

All contributors should follow Contributing Guidelines before creating pull requests.

Credits

Mustafa Turan

License

Apache License 2.0

Copyright (c) 2021 Mustafa Turan

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.