Golang ending (Binance) web service stream using go routine - go

Question

I'm integrating Binance API into an existing system and while most parts a straight forward, the data streaming API hits my limited understanding of go-routines. I don't believe there is anything special in the golang SDK for Binance, but essentially I only need two functions, one that starts the data stream and processes events with the event handler given as a parameter and a second one that ends the data stream without actually shutting down the client as it would close all other connections. On a previous project, there were two message types for this, but the binance SDK uses an implementation that returns two go channels, one for errors and an another one, I guess from the name, for stopping the data stram.
The code I wrote for starting the data stream looks like this:
func startDataStream(symbol, interval string, wsKlineHandler futures.WsKlineHandler, errHandler futures.ErrHandler) (err error){
doneC, stopC, err := futures.WsKlineServe(symbol, interval, wsKlineHandler, errHandler)
if err != nil {
fmt.Println(err)
return err
}
return nil
}
This works as expected and streams data. A simple test verifies it:
func runWSDataTest() {
symbol := "BTCUSDT"
interval := "15m"
errHandler := func(err error) {fmt.Println(err)}
wsKlineHandler := func(event *futures.WsKlineEvent) {fmt.Println(event)}
_ = startDataStream(symbol, interval, wsKlineHandler, errHandler)
}
The thing that is not so clear to me, mainly due to incomplete understanding, really is how do I stop the stream. I think the returned stopC channel can be used to somehow issue a end singnal similar to, say, a sigterm on system level and then the stream should end.
Say, I have a stopDataStream function that takes a symbol as an argument
func stopDataStream(symbol){
}
Let's suppose I start 5 data streams for five symbols and now I want to stop just one of the streams. That begs the question of:
How do I track all those stopC channels?
Can I use a collection keyed with the symbol, pull the stopC channel, and then just issue a signal to end just that data stream?
How do I actually write into the stopC channel from the stop function?
Again, I don't think this is particularly hard, it's just I could not figure it out yet from the docs so any help would be appreciated.
Thank you

Answer 1

(Answer originally written by #Marvin.Hansen)
Turned out, just saving & closing the channel solved it all. I was really surprised how easy this is, but here is the code of the updated functions:
func startDataStream(symbol, interval string, wsKlineHandler futures.WsKlineHandler, errHandler futures.ErrHandler) (err error) {
_, stopC, err := futures.WsKlineServe(symbol, interval, wsKlineHandler, errHandler)
if err != nil {
fmt.Println(err)
return err
}
// just save the stop channel
chanMap[symbol] = stopC
return nil
}
And then, the stop function really becomes embarrassing trivial:
func stopDataStream(symbol string) {
stopC := chanMap[symbol] // load the stop channel for the symbol
close(stopC) // just close it.
}
Finally, testing it all out:
var (
chanMap map[string]chan struct{}
)
func runWSDataTest() {
chanMap = make(map[string]chan struct{})
symbol := "BTCUSDT"
interval := "15m"
errHandler := func(err error) { fmt.Println(err) }
wsKlineHandler := getKLineHandler()
println("Start stream")
_ = startDataStream(symbol, interval, wsKlineHandler, errHandler)
time.Sleep(3 * time.Second)
println("Stop stream")
stopDataStream(symbol)
time.Sleep(1 * time.Second)
}
This is it.