DNS: Use cache for NXDOMAIN (rcode 3 error) #4560
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家用路由器上的dnsmasq不会面临此问题，因为它的upstream就是tcp udp 鉴于xray特有场景，应像isp的递归dns一样，防御nxdomain flood 针对nxdomain应不遵守rfc，强制缓存10或者60秒 过大的值会导致网站管理员遇到困扰不得不重启xray |
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话说我之前改 DNS 时也注意到了，ray 每多支持一种 DNS 查询方式就是 copy 整份代码，这挺劣质的，有空把它们改为复用吗？ |
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This reverts commit 1685c61
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First, I have to thank @Fangliding for his guidance on #4558 (comment).
I mistakenly think that the problem is related to log, but in fact log is just log and has nothing to do with performance.
in #3784 @Fangliding change the original code
err != errRecordNotFoundtoerr == nil || err == dns_feature.ErrEmptyResponseTo be more accurate.but in android some apps send thousands of requests in a matter of seconds, that return
NXDOMAIN.This causes performance to drop drastically, and many people have complained about this.
So I also added
NXDOMAINto the modes that should usecache.