Add random default for client ID

README.md

@@ -35,7 +35,7 @@ mqcontrol --help
   -h string
         Address and port of MQTT broker (default "127.0.0.1:1883")
   -i string
-        ID to use for this client
+        ID to use for this client (default "mqcontrol-{randomString}")
   -t string
         Topic to subscribe to (default "computer/command")
   -u string
@@ -46,31 +46,31 @@ mqcontrol --help
 
 ### Examples
 
-* Make a topic to hibernate your PC
+- Make a topic to hibernate your PC
 
-    ```bash
-    mqcontrol -i mqc -c "systemctl hibernate" -t desktop/command/hibernate
-    ```
+  ```bash
+  mqcontrol -c "systemctl hibernate" -t desktop/command/hibernate
+  ```
 
-* Dim laptop screen when the lights are turned off
+- Dim laptop screen when the lights are turned off
 
-    ```bash
-    mqcontrol -i mqc -c "brightnessctl 50%-" -t lights/bedroom/turnoff
-    ```
+  ```bash
+  mqcontrol -c "brightnessctl 50%-" -t lights/bedroom/turnoff
+  ```
 
-* Close gzdoom when the office door is opened
+- Close gzdoom when the office door is opened
 
-    ```bash
-    mqcontrol -i mqc -c "killall gzdoom" -t work/office/door/open
-    ```
+  ```bash
+  mqcontrol -c "killall gzdoom" -t work/office/door/open
+  ```
 
 ### Notes
 
 - The command argument does not include any shell processing. If you're having problems getting commands to run or want them to run in a shell, specify the shell in the command. For example:
 
-    ```bash
-    mqcontrol -i mqc -c "/bin/sh -c \"echo message received\"" -t desktop/command/hibernate
-    ```
+  ```bash
+  mqcontrol -c "/bin/sh -c \"echo message received\"" -t desktop/command/hibernate
+  ```
 
 - An error in the executed command will cause the entire program to terminate. Stderr and an exit code from the executed command will be available.
 
@@ -80,27 +80,27 @@ Get then run with Go:
 
 ```bash
 go get github.com/albertnis/mqcontrol
-go run github.com/albertnis/mqcontrol -i mqc -c "echo Message received"
+go run github.com/albertnis/mqcontrol -c "echo Message received"
 ```
 
 Run with Go in cloned repo:
 
 ```bash
-go run main.go -i mqc -c "echo Message received"
+go run main.go -c "echo Message received"
 ```
 
 With Docker (BuildKit):
 
 ```bash
 DOCKER_BUILDKIT=1 docker build -t mqcontrol .
-docker run -it --rm --network=host mqcontrol -i mqc -c "echo Message received"
+docker run -it --rm --network=host mqcontrol -c "echo Message received"
 ```
 
 With docker-compose (BuildKit):
 
 ```bash
 COMPOSE_DOCKER_CLI_BUILD=1 DOCKER_BUILDKIT=1 docker-compose build
-docker-compose run mqcontrol -i mqc -c "echo Message received"
+docker-compose run mqcontrol -c "echo Message received"
 ```
 
 ## Run it at startup
@@ -118,21 +118,21 @@ docker-compose run mqcontrol -i mqc -c "echo Message received"
 
 1. Create a systemd unit file as below, customise the `ExecStart` line, then save it at `/usr/lib/systemd/system/mqcontrol.service`:
 
-      ```service
-      [Unit]
-      Description=mqcontrol remote control
+   ```service
+   [Unit]
+   Description=mqcontrol remote control
 
-      [Service]
-      Type=simple
-      ExecStart=/home/user/go/bin/mqcontrol -i mqclinux -c "systemctl hibernate" -h 192.168.1.110:1883
+   [Service]
+   Type=simple
+   ExecStart=/home/user/go/bin/mqcontrol -i mqclinux -c "systemctl hibernate" -h 192.168.1.110:1883
 
-      [Install]
-      WantedBy=multi-user.target
-      ```
+   [Install]
+   WantedBy=multi-user.target
+   ```
 
 1. Start and enable the `mqcontrol` service
 
-      ```sh
-      systemctl start mqcontrol
-      systemctl enable mqcontrol
-      ```
+   ```sh
+   systemctl start mqcontrol
+   systemctl enable mqcontrol
+   ```

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"crypto/rand"
 	"encoding/csv"
 	"flag"
 	"fmt"
@@ -24,6 +25,16 @@ type config struct {
 	Password string
 }
 
+func randomString(n int) string {
+	const alphanum = "ABCDEFGHJKMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz"
+	var bytes = make([]byte, n)
+	rand.Read(bytes)
+	for i, b := range bytes {
+		bytes[i] = alphanum[b%byte(len(alphanum))]
+	}
+	return string(bytes)
+}
+
 func subscribe(client MQTT.Client, topic string, msg chan []byte) {
 	handler := MQTT.MessageHandler(func(client MQTT.Client, message MQTT.Message) {
 		payload := message.Payload()
@@ -74,7 +85,7 @@ func main() {
 	commandPtr := flag.String("c", "", "Command to run when any message received on topic")
 	topicPtr := flag.String("t", "computer/command", "Topic to subscribe to")
 	brokerPtr := flag.String("h", "127.0.0.1:1883", "Address and port of MQTT broker")
-	clientIDPtr := flag.String("i", "", "ID to use for this client")
+	clientIDPtr := flag.String("i", "mqcontrol-{randomString}", "ID to use for this client")
 	userPtr := flag.String("u", "", "Username for MQTT connection")
 	passwordPtr := flag.String("p", "", "Password for MQTT connection")
 
@@ -102,11 +113,15 @@ func main() {
 		os.Exit(1)
 	}
 	if conf.ClientID == "" {
-		fmt.Println("No client ID argument provided")
+		fmt.Println("Empty client ID argument provided")
 		fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
 		flag.PrintDefaults()
 		os.Exit(1)
 	}
+	if conf.ClientID == "mqcontrol-{randomString}" {
+		conf.ClientID = "mqcontrol-" + randomString(8)
+		fmt.Println("No client ID argument provided. Using randomly-generated client ID " + conf.ClientID)
+	}
 
 	r := csv.NewReader(strings.NewReader(conf.Command))
 	r.Comma = ' '