Race condition when sending messages with the MQTT protocol #1093
Description
I launched 10 goroutines to send messages using the MQTT protocol. After a while, it might throw an error like this:
Code to reproduce the issue:
for i := 0; i < count; i++ {
go func() {
for {
e := cloudevents.NewEvent()
e.SetID(uuid.New().String())
e.SetType("com.cloudevents.sample.sent")
e.SetSource("https://github.com/cloudevents/sdk-go/samples/mqtt/sender")
err = e.SetData(cloudevents.ApplicationJSON, map[string]interface{}{
"id": rand.Intn(100), // generates a random int between 0 and 99
"message": "Hello, World!",
})
if err != nil {
log.Printf("failed to set data: %v", err)
}
if result := c.Send(
cecontext.WithTopic(ctx, "test-topic"),
e,
); cloudevents.IsUndelivered(result) {
log.Printf("failed to send: %v", result)
} else {
log.Printf("sent: %d, accepted: %t", i, cloudevents.IsACK(result))
}
time.Sleep(time.Second)
}
}()
time.Sleep(1 * time.Second)
}
<-ctx.Done()Error message:
panic: runtime error: growslice: len out of range [recovered]
panic: bytes.Buffer: too large
goroutine 9 [running]:
bytes.growSlice.func1()
/usr/local/go/src/bytes/buffer.go:232 +0x45
panic({0x725280?, 0x813980?})
/usr/local/go/src/runtime/panic.go:914 +0x21f
bytes.growSlice({0xc000500bc0, 0x16, 0x44df49?}, 0x40?)
/usr/local/go/src/bytes/buffer.go:249 +0x8e
bytes.(*Buffer).grow(0xc0007119c8, 0x101000000000000)
/usr/local/go/src/bytes/buffer.go:151 +0x13d
bytes.(*Buffer).WriteString(0xc0007119c8, {0x0, 0x101000000000000})
/usr/local/go/src/bytes/buffer.go:191 +0x59
github.com/eclipse/paho.golang/packets.writeString({0x0, 0x101000000000000}, 0x4f66ab?)
/home/myan/go/pkg/mod/github.com/eclipse/paho.golang@v0.12.0/packets/packets.go:437 +0x3c
github.com/eclipse/paho.golang/packets.(*Properties).Pack(0xc000724780, 0x3)
/home/myan/go/pkg/mod/github.com/eclipse/paho.golang@v0.12.0/packets/properties.go:388 +0x865
github.com/eclipse/paho.golang/packets.(*Publish).Buffers(0xc000090880)
/home/myan/go/pkg/mod/github.com/eclipse/paho.golang@v0.12.0/packets/publish.go:70 +0x7b
github.com/eclipse/paho.golang/packets.(*ControlPacket).WriteTo(0xc000711b60, {0x814ac0, 0xc000182238})
/home/myan/go/pkg/mod/github.com/eclipse/paho.golang@v0.12.0/packets/packets.go:317 +0x84
github.com/eclipse/paho.golang/packets.(*Publish).WriteTo(0xc0001c6580?, {0x814ac0?, 0xc000182238?})
/home/myan/go/pkg/mod/github.com/eclipse/paho.golang@v0.12.0/packets/publish.go:78 +0x6a
github.com/eclipse/paho.golang/paho.(*Client).Publish(0xc0001ea140, {0x818708, 0xc0004370b0}, 0xc0001c6580)
/home/myan/go/pkg/mod/github.com/eclipse/paho.golang@v0.12.0/paho/client.go:797 +0x2bb
github.com/cloudevents/sdk-go/protocol/mqtt_paho/v2.(*Protocol).Send(0xc0001c6600, {0x818708, 0xc0004370b0}, {0x8189a8?, 0xc000480a00}, {0x0, 0x0, 0x0})
/home/myan/workspace/cloudevents-sdk-go/protocol/mqtt_paho/v2/protocol.go:105 +0x270
github.com/cloudevents/sdk-go/v2/client.(*ceClient).Send(0xc0000a6000, {0x818708, 0xc0004370b0}, {{0x81cb20, 0xc000659180}, {0xc00049e510, 0x22, 0x30}, 0x0, 0x0})
/home/myan/workspace/cloudevents-sdk-go/v2/client/client.go:138 +0x2dc
main.main.func1()
/home/myan/workspace/cloudevents-sdk-go/samples/mqtt/sender/main.go:68 +0x411
created by main.main in goroutine 1
/home/myan/workspace/cloudevents-sdk-go/samples/mqtt/sender/main.go:55 +0x445
exit status 2The root cause is that these goroutines use the same object to load events. To resolve this, we must avoid using the same object in multiple goroutines.