Subscribe API makes it impossible to match suback reasons to subscribed topics

[ewirch]

Version: 0.10.0

Client.Subscribe expects a map containing subscription topics as keys:

Subscriptions map[string]SubscribeOptions

Later, these topics are sent to MQTT broker using a for-range loop:

for t, o := range s.Subscriptions {
	writeString(t, &subs)
	subs.WriteByte(o.Pack())
}

for-range loop over a map is specified to have no consistent order ("The iteration order over maps is not specified and is not guaranteed to be the same from one iteration to the next."). Thus, the order in which topics are sent to broker is unknown. There is no way, one could correlate order of suback reasons to subscribed topics:

Suback struct {
	Properties *SubackProperties
	Reasons    []byte
}

[MattBrittan]

Closing this as the underlying issue was corrected some time ago (and included in the last release). Subscribe now contains Subscriptions []SubscribeOptions.