DNS hosts: Support returning RCode

[j2rong4cn]

返回指定RCode: https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-6
示例:

{
  "dns": {
    "hosts": {
      "geosite:category-ads-all": "#3"
    }
  }
}

[patterniha]

@j2rong4cn

when rcode=0, instead of RCodeError(0) it should return dns.EmptyResponse

and in other cases you should return:

errors.New("returning nil for domain ", domain).Base(err) instead of err.

[patterniha]

change "dns.go" instead to cover "errors.New("returning nil for domain ", domain).Base(err)" too.

[j2rong4cn]

@j2rong4cn

when rcode=0, instead of RCodeError(0) it should return dns.EmptyResponse

and in other cases you should return:

errors.New("returning nil for domain ", domain).Base(err) instead of err.

Thanks for the review, any other questions?

[patterniha]

change your codes base on #4702

The matched-results are appended again.

Give "#" the highest priority, meaning if one result is "#", other results will be omitted.(you should change "lookupInternal" function)

[j2rong4cn]

change your codes base on #4702

The matched-results are appended again.

Give "#" the highest priority, meaning if one result is "#", other results will be omitted.(you should change "lookupInternal" function)

我提交新代码了，你看一下对不对？

[patterniha]

In my opinion it is ok and can be merged.
But I am not the decision maker, my PRs haven't been merged yet.

[patterniha]

@j2rong4cn

LookupHosts function is removed from dns.go, change your code to resolve conflicts.

[RPRX]

需要 rebase，功能太小众，放下个版本

[patterniha]

@j2rong4cn ?

[patterniha]

@RPRX

ready to merge.

[RPRX]

DNS 最近的 new features 在下个版本可能会有变动，比如 #4666 我合并前没看，前面讨论了什么也忘了，参数可能会重新设计

[patterniha]

DNS's recent new features may change in the next version. For example, I didn't read #4666 before merging it, and I forgot what was discussed before. The parameters may be redesigned.

@RPRX

my serverless-config is almost ready, If I publish it and then make changes again, many users will be confused. The features are very simple, If possible, finalize it sooner.

[RPRX]

@patterniha 即使现在 finalize 了，近期也不会再发版了，即使以后参数改了，新旧参数都填上应该就行了

[patterniha]

@RPRX

The problems solved in these PRs(I found them) are important and should be fixed in the new version:

#4899: fix UDP dispatcher cause close connection frequently problem
#4869: fix reverse problems
#4861: fix MUX.cool problems
#4816 and #4804: fix freedom-UDP problems

I checked them all and they are OK, also @Fangliding created/approved them.

also this PR extends the features of DNS-host and It is OK too.

[patterniha]

@RPRX

Can you spare some time for my PRs?

I spent a lot of time to finding and fixing these bugs, please review them.

fang close my new PRs because I have many open PRs instead of giving the right reason !!!

[RPRX]

@patterniha 你们的 PR 会在新版本前被合并