fix exponential backoff overflow

[magras]

The backoff function's wait time calculation completely overflows time.Duration on the 55th retry (approximately after 6 hours). This results in zero wait times, leading to the uncontrolled spawn of hundreds of goroutines, which can cause memory exhaustion and OOM kill on linux.

[magras]

There is a test program that demonstrates the problem:

package main

import (
	"fmt"
	"math"
	"time"
)

func main() {
	n := 60
	for i := 0; i < n; i++ {
		x := math.Pow(2, float64(i))
		d := time.Duration(x) * time.Second
		fmt.Println(i, x, d)
	}
}

playground: https://go.dev/play/p/wBxP0SpRRkt

[magras]

Hey @hwh33, @myleshorton, @reflog, could one of you please take a look at this PR?

[reflog]

@magras I'm on it, thank you for reporting

[reflog]

There may be a subtle bug: if the first request fails before any success, nextWait starts at zero (Go's default for time.Duration):

s.nextWait = retryWaitSeconds // only set on success

On first failure → wait = 0 → immediate retry with no backoff.

Recommendation: Initialize nextWait to retryWaitSeconds in the struct or handle the zero case in backoff():

if s.nextWait == 0 {
s.nextWait = retryWaitSeconds
}

[magras]

Recommendation: Initialize nextWait to retryWaitSeconds in the struct

I don't know go, but I found no native way to achieve that.

Hence I went the second way, but slightly deviated from it: now retry timeout is clamped between min and max.

[Copilot]

Pull request overview

This PR fixes a critical exponential backoff overflow bug that could lead to memory exhaustion and OOM kill. The previous implementation used math.Pow(2, float64(failCount)) which overflows time.Duration after approximately 55 retries (6 hours), resulting in zero wait times and uncontrolled goroutine spawn.

Key Changes:

• Replaced counter-based exponential calculation with direct duration tracking to prevent overflow
• Renamed retryWaitSeconds to minRetryWait for clarity
• Changed struct field from failCount int to nextWait time.Duration

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