Title: Panic in retryDelay due to integer overflow on x86 architecture

Bug Report

Description

When using the openai-go client with a high number of retries, a panic can occur due to an integer overflow in the retryDelay function. This issue appears to be specific to the x86 architecture; it does not occur on ARM (e.g., Apple M-series chips).

The panic occurs with the message: panic: invalid argument to Int63n

Here is the stack trace from our server logs:

panic: invalid argument to Int63n

goroutine 74428 [running]:
math/rand.(*Rand).Int63n(0x6a80?, 0x3ff0000000000000?)
/root/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.1.linux-amd64/src/math/rand/rand.go:122 +0xcb
math/rand.Int63n(0xe000000000000000)
/root/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.1.linux-amd64/src/math/rand/rand.go:454 +0x25
github.com/openai/openai-go/internal/requestconfig.retryDelay(0x1cca420?, 0x23)
/root/go/pkg/mod/github.com/openai/openai-go@v1.12.0/internal/requestconfig/requestconfig.go:373 +0x91
github.com/openai/openai-go/internal/requestconfig.(*RequestConfig).Execute(0xc004e2d040)
/root/go/pkg/mod/github.com/openai/openai-go@v1.12.0/internal/requestconfig/requestconfig.go:466 +0x5a5
github.com/openai/openai-go/internal/requestconfig.ExecuteNewRequest({0x21855b0?, 0xc0046b2fc0?}, {0x1e7df52?, 0x521518?}, {0x1e98cb3?, 0x5?}, {0x1e55720?, 0xc004964c08?}, {0x19c6780, 0xc00020a0a8}, ...)
/root/go/pkg/mod/github.com/openai/openai-go@v1.12.0/internal/requestconfig/requestconfig.go:562 +0x9b
github.com/openai/openai-go.(*ChatCompletionService).New(_, {_, _}, {{0xc006281400, 0x2, 0x2}, {0xc000813590, 0xe}, {0x0, 0x0, ...}, ...}, ...)
/root/go/pkg/mod/github.com/openai/openai-go@v1.12.0/chatcompletion.go:66 +0x16a
...

Root Cause Analysis

The panic originates in the retryDelay function in internal/requestconfig/requestconfig.go:

func retryDelay(res *http.Response, retryCount int) time.Duration {
    // ...
	maxDelay := 8 * time.Second
	delay := time.Duration(0.5 * float64(time.Second) * math.Pow(2, float64(retryCount)))
	if delay > maxDelay {
		delay = maxDelay
	}

	jitter := rand.Int63n(int64(delay / 4)) // Panics here
	delay -= time.Duration(jitter)
	return delay
}

The math/rand.Int63n function panics if its argument is less than or equal to 0. The issue arises from this line:
delay := time.Duration(0.5 * float64(time.Second) * math.Pow(2, float64(retryCount)))

When retryCount is a large number (e.g., 48 or higher), math.Pow returns a very large float64. When this float is converted to time.Duration (which is an int64), the behavior differs by architecture:

• On x86 (amd64): The conversion overflows, resulting in a large negative int64 value for delay. Consequently, delay / 4 is also negative, causing rand.Int63n to panic.
• On ARM (arm64): The conversion from a large float to int64 "saturates" at math.MaxInt64 instead of overflowing. This prevents delay from becoming negative, and the code does not panic.

We encountered this in a long-running offline processing service where we set MaxRetries to a high value (e.g., 100) to ensure completion despite potential rate limiting.

Steps to Reproduce

This panic can be reliably reproduced on an x86 machine using a fuzz test.

1. Create a test file (e.g., retry_fuzz_test.go):

   package requestconfig_test
   
   import (
   	"math"
   	"math/rand"
   	"testing"
   	"time"
   )
   
   // Simplified version of the internal retryDelay for testing
   func retryDelay(t *testing.T, retryCount uint) time.Duration {
   	maxDelay := 8 * time.Second
   	// This is the problematic line
   	delay := time.Duration(0.5 * float64(time.Second) * math.Pow(2, float64(retryCount)))
   	if delay > maxDelay {
   		delay = maxDelay
   	}
   
   	if delay/4 <= 0 {
   		// This demonstrates the overflow on x86.
   		// On x86, for retryCount=48, delay becomes a large negative number.
   		t.Logf("retryCount=%d, delay=%v, delay/4=%v", retryCount, delay, delay/4)
   	}
   
   	jitter := rand.Int63n(int64(delay / 4))
   	delay -= time.Duration(jitter)
   	return delay
   }
   
   func FuzzRetryDelay(f *testing.F) {
   	f.Fuzz(func(t *testing.T, a uint) {
   		// Limit 'a' to a reasonable range to find the issue faster.
   		retryCount := a % 100 
   		retryDelay(t, retryCount)
   	})
   }

2. Run the fuzz test on an x86/amd64 machine. It will quickly fail.

   go test -fuzz=Fuzz -fuzztime=10s .

3. Failing Output (on x86):

   --- FAIL: FuzzRetryDelay (0.00s)
       --- FAIL: FuzzRetryDelay (0.00s)
           rand_fuzz_test.go:21: retryCount=48, delay=-2562047h47m16.854775808s, delay/4=-2305843009213693952
           testing.go:1693: panic: invalid argument to Int63n
               goroutine 24 [running]:
               ...
               math/rand.Int63n(0xe000000000000000)
               ...
   FAIL
   exit status 1
   

Suggested Fix

The exponential backoff calculation should guard against this overflow. A simple fix would be to cap the retryCount used in the math.Pow calculation to a safe value that won't overflow int64 when converted to nanoseconds.

For example, capping retryCount at 30 would prevent the overflow:

func retryDelay(res *http.Response, retryCount int) time.Duration {
	// ...
    effectiveRetryCount := retryCount
    // Cap retryCount to prevent int64 overflow from math.Pow
    if effectiveRetryCount > 30 {
        effectiveRetryCount = 30
    }
	delay := time.Duration(0.5 * float64(time.Second) * math.Pow(2, float64(effectiveRetryCount)))
	// ...
}

Alternatively, check if delay is negative after the cast and clamp it to maxDelay.

Environment

• openai-go version: v1.12.0
• Go version: go1.24.1
• Failing Architecture: linux/amd64
• Passing Architecture: darwin/arm64 (Apple M1/M2/M3)