79 lines
2.6 KiB
Markdown
79 lines
2.6 KiB
Markdown
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# DNS Lookup Cache
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[](https://raw.githubusercontent.com/rs/dnscache/master/LICENSE)
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[](https://goreportcard.com/report/github.com/rs/dnscache)
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[](https://travis-ci.org/rs/dnscache)
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[](http://gocover.io/github.com/rs/dnscache)
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[](https://godoc.org/github.com/rs/dnscache)
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The dnscache package provides a DNS cache layer to Go's `net.Resolver`.
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# Install
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Install using the "go get" command:
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```
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go get -u github.com/rs/dnscache
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```
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# Usage
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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.
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```go
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resolver := &dnscache.Resolver{}
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// First call will cache the result
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addrs, err := resolver.LookupHost(context.Background(), "example.com")
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// Subsequent calls will use the cached result
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addrs, err = resolver.LookupHost(context.Background(), "example.com")
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// Call to refresh will refresh names in cache. If you pass true, it will also
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// remove cached names not looked up since the last call to Refresh. It is a good idea
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// to call this method on a regular interval.
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go func() {
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t := time.NewTicker(5 * time.Minute)
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defer t.Stop()
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for range t.C {
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resolver.Refresh(true)
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}
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}()
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```
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If you are using an `http.Transport`, you can use this cache by specifying a `DialContext` function:
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```go
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r := &dnscache.Resolver{}
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t := &http.Transport{
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DialContext: func(ctx context.Context, network string, addr string) (conn net.Conn, err error) {
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host, port, err := net.SplitHostPort(addr)
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if err != nil {
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return nil, err
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}
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ips, err := r.LookupHost(ctx, host)
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if err != nil {
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return nil, err
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}
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for _, ip := range ips {
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var dialer net.Dialer
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conn, err = dialer.DialContext(ctx, network, net.JoinHostPort(ip, port))
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if err == nil {
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break
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}
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}
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return
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},
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}
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```
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If addition to the `Refresh` method, you can `RefreshWithOptions`. This method adds an option to persist resource records
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on failed lookups
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```go
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r := &Resolver{}
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options := dnscache.ResolverRefreshOptions{}
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options.ClearUnused = true
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options.PersistOnFailure = false
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resolver.RefreshWithOptions(options)
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```
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