handle idempotence key error (#1200)

reading from rand can return an error and fail to read bytes, this
leads to the second component not being random.

This solution panics in that case, similar to getting a new uuid
https://github.com/google/uuid/blob/master/version4.go#L13-L15

the side effect is, in the case the second component is not random (an
error happened) we are now panicing instead of continuing

Signed-off-by: Andrew Klotz <[email protected]>

params.go

@@ -268,7 +268,9 @@ type RangeQueryParams struct {
 func NewIdempotencyKey() string {
 	now := time.Now().UnixNano()
 	buf := make([]byte, 4)
-	rand.Read(buf)
+	if _, err := rand.Read(buf); err != nil {
+		panic(err)
+	}
 	return fmt.Sprintf("%v_%v", now, base64.URLEncoding.EncodeToString(buf)[:6])
 }