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// SPDX-FileCopyrightText: 2020 Ethel Morgan
//
// SPDX-License-Identifier: MIT
// Package catbus is a convenience wrapper around MQTT for use with Catbus.
package catbus
import (
"math/rand"
"sync"
"time"
mqtt "github.com/eclipse/paho.mqtt.golang"
)
type (
MessageHandler func(*Client, Message)
Message struct {
message mqtt.Message
}
Client struct {
mqtt mqtt.Client
payloadByTopicMu sync.Mutex
payloadByTopic map[string]string
onconnectTimerByTopicMu sync.Mutex
onconnectTimerByTopic map[string]*time.Timer
onconnectDelay time.Duration
onconnectJitter time.Duration
}
ClientOptions struct {
DisconnectHandler func(*Client, error)
ConnectHandler func(*Client)
// Publish previously seen or default values on connecting after OnconnectDelay ± [0,OnconnectJitter).
OnconnectDelay time.Duration
OnconnectJitter time.Duration
// DefaultPayloadByTopic are optional values to publish on connect if no prior values are seen.
// E.g. unless we've been told otherwise, assume a device is off.
DefaultPayloadByTopic map[string]string
}
// Retention is whether or not the MQTT broker should retain the message.
Retention bool
)
const (
atMostOnce byte = iota
atLeastOnce
exactlyOnce
)
const (
Retain = Retention(true)
DontRetain = Retention(false)
)
const (
DefaultOnconnectDelay = 1 * time.Minute
DefaultOnconnectJitter = 15 * time.Second
)
func NewClient(brokerURI string, options ClientOptions) *Client {
client := &Client{
payloadByTopic: map[string]string{},
onconnectTimerByTopic: map[string]*time.Timer{},
onconnectDelay: DefaultOnconnectDelay,
onconnectJitter: DefaultOnconnectJitter,
}
if options.OnconnectDelay != 0 {
client.onconnectDelay = options.OnconnectDelay
}
if options.OnconnectJitter != 0 {
client.onconnectJitter = options.OnconnectJitter
}
for topic, payload := range options.DefaultPayloadByTopic {
client.payloadByTopic[topic] = payload
}
mqttOpts := mqtt.NewClientOptions()
mqttOpts.AddBroker(brokerURI)
mqttOpts.SetAutoReconnect(true)
mqttOpts.SetOnConnectHandler(func(c mqtt.Client) {
client.stopAllTimers()
client.startAllTimers()
if options.ConnectHandler != nil {
options.ConnectHandler(client)
}
})
mqttOpts.SetConnectionLostHandler(func(c mqtt.Client, err error) {
client.stopAllTimers()
if options.DisconnectHandler != nil {
options.DisconnectHandler(client, err)
}
})
client.mqtt = mqtt.NewClient(mqttOpts)
return client
}
// Connect connects to the Catbus MQTT broker and blocks forever.
func (c *Client) Connect() error {
if err := c.mqtt.Connect().Error(); err != nil {
return err
}
select {}
}
// Subscribe subscribes to a Catbus MQTT topic.
func (c *Client) Subscribe(topic string, f MessageHandler) error {
return c.mqtt.Subscribe(topic, atLeastOnce, func(_ mqtt.Client, msg mqtt.Message) {
c.storePayload(msg.Topic(), Retention(msg.Retained()), string(msg.Payload()))
f(c, Message{msg})
}).Error()
}
// Publish publishes to a Catbus MQTT topic.
func (c *Client) Publish(topic string, retention Retention, payload string) error {
c.storePayload(topic, retention, payload)
return c.mqtt.Publish(topic, atLeastOnce, bool(retention), payload).Error()
}
func (c *Client) jitteredOnconnectDelay() time.Duration {
jitter := time.Duration(rand.Intn(int(c.onconnectJitter)))
if rand.Intn(2) == 0 {
return c.onconnectDelay + jitter
}
return c.onconnectDelay - jitter
}
func (c *Client) storePayload(topic string, retention Retention, payload string) {
c.payloadByTopicMu.Lock()
defer c.payloadByTopicMu.Unlock()
if _, ok := c.payloadByTopic[topic]; !ok && retention == DontRetain {
// If we don't have a copy, and the sender doesn't want it retained, don't retain it.
return
}
c.stopTimer(topic)
if len(payload) == 0 {
delete(c.payloadByTopic, topic)
return
}
c.payloadByTopic[topic] = payload
}
func (c *Client) stopTimer(topic string) {
c.onconnectTimerByTopicMu.Lock()
defer c.onconnectTimerByTopicMu.Unlock()
if timer, ok := c.onconnectTimerByTopic[topic]; ok {
_ = timer.Stop()
}
}
func (c *Client) stopAllTimers() {
c.onconnectTimerByTopicMu.Lock()
defer c.onconnectTimerByTopicMu.Unlock()
for _, timer := range c.onconnectTimerByTopic {
_ = timer.Stop()
}
}
func (c *Client) startAllTimers() {
c.payloadByTopicMu.Lock()
defer c.payloadByTopicMu.Unlock()
c.onconnectTimerByTopicMu.Lock()
defer c.onconnectTimerByTopicMu.Unlock()
for topic := range c.payloadByTopic {
c.onconnectTimerByTopic[topic] = time.AfterFunc(c.jitteredOnconnectDelay(), func() {
c.payloadByTopicMu.Lock()
payload, ok := c.payloadByTopic[topic]
c.payloadByTopicMu.Unlock()
if !ok {
return
}
_ = c.Publish(topic, Retain, payload)
})
}
}
func (m Message) Topic() string {
return m.message.Topic()
}
func (m Message) Payload() string {
return string(m.message.Payload())
}
func (m Message) Retained() bool {
return m.message.Retained()
}
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