when influxdb server shutdown, client still send metric, the background goroutine "w.writeProc()" will crash at rand.Intn() after try 52 times

[jian2008]

Specifications

• Client Version: v2.12.0
• InfluxDB Version: v2.5.0
• Platform: Ubuntu 20.04.5 LTS

Steps to reproduce

1. influxdb server is not start, that is shutdown
2. write points using lib to send metrics to server which in fact is not started

        dbClient := influxdb2.NewClient(serverUrl, token)
	dbClient.Options().WriteOptions().SetPrecision(time.Millisecond)
	defer dbClient.Close()
        dbWriteAPI := dbClient.WriteAPI("myorg", "mybucket")
        for {
		req, ok := <-gRecvChannel
		var metricName string
		if !ok {
			break
		}
                //........code about set metricName and tags
                p := influxdb2.NewPoint(metricName, tags,
				map[string]interface{}{"value": value},
				time.UnixMilli(timestamp))
		dbWriteAPI.WritePoint(p)
      }

3. at first, only print log like "dial tcp 127.0.0.1:8086: connect: connection refused, batch kept for retrying", but finally crash

Expected behavior

at normal case, will print the follow log

2022/11/11 10:34:39 influxdb2client E! Write error: Post "http://127.0.0.1:8086/api/v2/write?bucket=mybucket&org=myorg&precision=ms": dial tcp 127.0.0.1:8086: connect: connection refused, batch kept for retrying
2022/11/11 10:34:39 influxdb2client E! Error flushing batch from retry queue: %!w(*url.Error=&{Post http://127.0.0.1:8086/api/v2/write?bucket=mybucket&org=myorg&precision=ms 0xc00022ceb0})
......
2022/11/11 10:47:09 influxdb2client E! Error flushing batch from retry queue: %!w(*url.Error=&{Post http://127.0.0.1:8086/api/v2/write?bucket=mybucket&org=myorg&precision=ms 0xc00022c1e0})
2022/11/11 10:47:24 influxdb2client E! Write error: Post "http://127.0.0.1:8086/api/v2/write?bucket=mybucket&org=myorg&precision=ms": dial tcp 127.0.0.1:8086: connect: connection refused, batch kept for retrying

Actual behavior

but after about 13 minutes, panic crash, the call stack is as follow

runtime.fatalpanic (/usr/local/go/src/runtime/panic.go:1143)
runtime.gopanic (/usr/local/go/src/runtime/panic.go:987)
math/rand.(*Rand).Intn (/usr/local/go/src/math/rand/rand.go:168)
math/rand.Intn (/usr/local/go/src/math/rand/rand.go:337)
github.com/influxdata/influxdb-client-go/v2/internal/write.(*Service).computeRetryDelay (pkg/mod/github.com/influxdata/influxdb-client-go/[email protected]/internal/write/service.go:258)
github.com/influxdata/influxdb-client-go/v2/internal/write.(*Service).HandleWrite (pkg/mod/github.com/influxdata/influxdb-client-go/[email protected]/internal/write/service.go:175)
github.com/influxdata/influxdb-client-go/v2/api.(*WriteAPIImpl).writeProc (pkg/mod/github.com/influxdata/influxdb-client-go/[email protected]/api/write.go:192)
github.com/influxdata/influxdb-client-go/v2/api.NewWriteAPI.func2 (pkg/mod/github.com/influxdata/influxdb-client-go/[email protected]/api/write.go:92)
runtime.goexit (/usr/local/go/src/runtime/asm_amd64.s:1594)

Additional info

i modify the code of function "computeRetryDelay" at Go_Path/pkg/mod/github.com/influxdata/influxdb-client-go/[email protected]/internal/write/service.go, print some logs

func (w *Service) computeRetryDelay(attempts uint) uint {
	minDelay := int(w.writeOptions.RetryInterval() * pow(w.writeOptions.ExponentialBase(), attempts))
	maxDelay := int(w.writeOptions.RetryInterval() * pow(w.writeOptions.ExponentialBase(), attempts+1))
	gTryCnt++ //added by me
	fmt.Printf("tryCnt=%5d maxDelay=%d minDelay=%d\n", gTryCnt, maxDelay, minDelay) //added by me
	retryDelay := uint(rand.Intn(maxDelay-minDelay) + minDelay)
	if retryDelay > w.writeOptions.MaxRetryInterval() {
		retryDelay = w.writeOptions.MaxRetryInterval()
	}
	return retryDelay
}

tryCnt= 1 maxDelay=10000 minDelay=5000
tryCnt= 2 maxDelay=20000 minDelay=10000
tryCnt= 3 maxDelay=40000 minDelay=20000
tryCnt= 4 maxDelay=80000 minDelay=40000
tryCnt= 5 maxDelay=160000 minDelay=80000
tryCnt= 6 maxDelay=320000 minDelay=160000
tryCnt= 7 maxDelay=640000 minDelay=320000
tryCnt= 8 maxDelay=1280000 minDelay=640000
tryCnt= 9 maxDelay=2560000 minDelay=1280000
tryCnt= 10 maxDelay=5120000 minDelay=2560000
tryCnt= 11 maxDelay=10240000 minDelay=5120000
tryCnt= 12 maxDelay=20480000 minDelay=10240000
tryCnt= 13 maxDelay=40960000 minDelay=20480000
tryCnt= 14 maxDelay=81920000 minDelay=40960000
tryCnt= 15 maxDelay=163840000 minDelay=81920000
tryCnt= 16 maxDelay=327680000 minDelay=163840000
tryCnt= 17 maxDelay=655360000 minDelay=327680000
tryCnt= 18 maxDelay=1310720000 minDelay=655360000
tryCnt= 19 maxDelay=2621440000 minDelay=1310720000
tryCnt= 20 maxDelay=5242880000 minDelay=2621440000
tryCnt= 21 maxDelay=10485760000 minDelay=5242880000
tryCnt= 22 maxDelay=20971520000 minDelay=10485760000
tryCnt= 23 maxDelay=41943040000 minDelay=20971520000
tryCnt= 24 maxDelay=83886080000 minDelay=41943040000
tryCnt= 25 maxDelay=167772160000 minDelay=83886080000
tryCnt= 26 maxDelay=335544320000 minDelay=167772160000
tryCnt= 27 maxDelay=671088640000 minDelay=335544320000
tryCnt= 28 maxDelay=1342177280000 minDelay=671088640000
tryCnt= 29 maxDelay=2684354560000 minDelay=1342177280000
tryCnt= 30 maxDelay=5368709120000 minDelay=2684354560000
tryCnt= 31 maxDelay=10737418240000 minDelay=5368709120000
tryCnt= 32 maxDelay=21474836480000 minDelay=10737418240000
tryCnt= 33 maxDelay=42949672960000 minDelay=21474836480000
tryCnt= 34 maxDelay=85899345920000 minDelay=42949672960000
tryCnt= 35 maxDelay=171798691840000 minDelay=85899345920000
tryCnt= 36 maxDelay=343597383680000 minDelay=171798691840000
tryCnt= 37 maxDelay=687194767360000 minDelay=343597383680000
tryCnt= 38 maxDelay=1374389534720000 minDelay=687194767360000
tryCnt= 39 maxDelay=2748779069440000 minDelay=1374389534720000
tryCnt= 40 maxDelay=5497558138880000 minDelay=2748779069440000
tryCnt= 41 maxDelay=10995116277760000 minDelay=5497558138880000
tryCnt= 42 maxDelay=21990232555520000 minDelay=10995116277760000
tryCnt= 43 maxDelay=43980465111040000 minDelay=21990232555520000
tryCnt= 44 maxDelay=87960930222080000 minDelay=43980465111040000
tryCnt= 45 maxDelay=175921860444160000 minDelay=87960930222080000
tryCnt= 46 maxDelay=351843720888320000 minDelay=175921860444160000
tryCnt= 47 maxDelay=703687441776640000 minDelay=351843720888320000
tryCnt= 48 maxDelay=1407374883553280000 minDelay=703687441776640000
tryCnt= 49 maxDelay=2814749767106560000 minDelay=1407374883553280000
tryCnt= 50 maxDelay=5629499534213120000 minDelay=2814749767106560000
tryCnt= 51 maxDelay=-7187745005283311616 minDelay=5629499534213120000
tryCnt= 52 maxDelay=4071254063142928384 minDelay=-7187745005283311616

so when maxDelay=4071254063142928384 minDelay=-7187745005283311616
maxDelay-minDelay = -7187745005283311616 < 0, so will panic at "rand.Intn()"

because https://pkg.go.dev/math/rand#Intn said:

Intn returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n) from the default Source.
It panics if n <= 0.

[vlastahajek]

@jian2008, thanks for discovering and posting the issue. I have reproduced it.