DNS Lookup Cache

The dnscache package provides a DNS cache layer to Go's net.Resolver.

Install

Install using the "go get" command:

go get github.com/rs/dnscache

Usage

Create a new instance and use it in place of net.Resolver. New names will be cached. Call the Refresh method at regular interval to update cached entries and cleanup unused ones.

resolver := &dnscache.Resolver{}

// First call will cache the result
addrs, err := resolver.LookupHost("example.com")

// Subsequent calls will use the cached result
addrs, err = resolver.LookupHost("example.com")

// Call to refresh will refresh names in cache. If you pass true, it will also
// remove cached names not looked up since the last call to Refresh. It is a good idea
// to call this method on a regular interval.
go func() {
    clearUnused := true
    t := time.NewTicker(5 * time.Minute)
    defer t.Stop()
    for range t.C {
        resolver.Refresh(clearUnused)
    }
}()

If you are using an http.Transport, you can use this cache by specifying a DialContext function:

r := &Resolver{}
t := &http.Transport{
    DialContext: func(ctx context.Context, network string, addr string) (conn net.Conn, err error) {
        separator := strings.LastIndex(addr, ":")
        ips, err := r.LookupHost(ctx, addr[:separator])
        if err != nil {
            return nil, err
        }
        for _, ip := range ips {
            conn, err = net.Dial(network, ip+addr[separator:])
            if err == nil {
                break
            }
        }
        return
    },
}