Xeoncross Xeoncross - 23 days ago 5
HTTP Question

Does Go cache DNS lookups?

I am building a test crawler and wanted to know if Go (golang) caches DNS queries. I don't see anything about caching in the dnsclient. This seems like an important thing to add to any crawler to prevent lots of extra DNS queries.

Does Go (1.4+) cache DNS lookups?

If not, does debian/ubuntu/linux, windows, or darwin/OSX do any caching at the network level Go benefits from?

Answer

The answer to your question is no. There is no built-in dns caching in the std lib resolver. Would it be helpful? Maybe in some cases. Our org runs a local dns cache on each server and points resolv.conf there. So it wouldn't necessarily help us much to have caching in the language.

There are some solutions that could help you. This package seems to have a pretty good solution. From the snippet in their readme you could even do:

http.DefaultClient.Transport = &http.Transport {
  MaxIdleConnsPerHost: 64,
  Dial: func(network string, address string) (net.Conn, error) {
    separator := strings.LastIndex(address, ":")
    ip, _ := dnscache.FetchString(address[:separator])
    return net.Dial("tcp", ip + address[separator:])
  },
}

To enable it for all http requests from http.Get and friends.