/
mayqtt.go
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/
mayqtt.go
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// Copyright 2016 Michael Stapelberg and contributors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package mayqtt implements an MQTT client which receives scan requests from
// scan2drive/cmd/scan and publishes status to scan2drive/ui/status.
package mayqtt
import (
"encoding/json"
"fmt"
"log"
mqtt "github.com/eclipse/paho.mqtt.golang"
"github.com/stapelberg/scan2drive"
"golang.org/x/net/trace"
)
type scanRequest struct {
User string `json:"user"`
Source string `json:"source"`
}
type PublishRequest struct {
Topic string
Qos byte
Retained bool
Payload interface{}
}
func mqttLoop(mqttScanRequests chan *scan2drive.ScanRequest, requests <-chan PublishRequest) error {
tr := trace.New("MQTT", "Loop")
defer tr.Finish()
const broker = "tcp://dr.lan:1883"
tr.LazyPrintf("Connecting to MQTT broker %s", broker)
opts := mqtt.NewClientOptions().AddBroker(broker)
opts.SetClientID("scan2drive")
opts.SetConnectRetry(true)
opts.OnConnect = func(c mqtt.Client) {
tr.LazyPrintf("OnConnect, subscribing to scan2drive/cmd/scan")
token := c.Subscribe(
"scan2drive/cmd/scan",
0, /* qos */
func(_ mqtt.Client, m mqtt.Message) {
tr.LazyPrintf("message on topic %s: %q", m.Topic(), string(m.Payload()))
var sr scan2drive.ScanRequest
if err := json.Unmarshal(m.Payload(), &sr); err != nil {
log.Printf("error unmarshaling payload: %v", err)
}
select {
case mqttScanRequests <- &sr:
default:
// Channel full, scan request already pending; drop
}
})
if token.Wait() && token.Error() != nil {
tr.LazyPrintf("subscription failed! %v", token.Error())
}
}
mqttClient := mqtt.NewClient(opts)
if token := mqttClient.Connect(); token.Wait() && token.Error() != nil {
return fmt.Errorf("MQTT connection failed: %v", token.Error())
}
tr.LazyPrintf("Connected to MQTT broker %s", broker)
for r := range requests {
tr.LazyPrintf("publishing on topic %s: %q", r.Topic, r.Payload)
// discard Token, MQTT publishing is best-effort
_ = mqttClient.Publish(r.Topic, r.Qos, r.Retained, r.Payload)
}
return nil
}
var publish chan PublishRequest
func MQTT(scanRequests chan *scan2drive.ScanRequest) {
publish = make(chan PublishRequest)
go func() {
if err := mqttLoop(scanRequests, publish); err != nil {
log.Print(err)
}
}()
}
var lastStatus string
func Publishf(format string, args ...interface{}) {
status := fmt.Sprintf(format, args...)
// Prevent duplicate messages if status has not changed
if lastStatus == status {
return
}
lastStatus = status
select {
case publish <- PublishRequest{
Topic: "scan2drive/ui/status",
Retained: true,
Payload: []byte(status),
}:
default:
// drop message if MQTT is not connected
}
}