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// Package forward implements a forwarding proxy. It caches an upstream net.Conn for some time, so if the same
// client returns the upstream's Conn will be precached. Depending on how you benchmark this looks to be
// 50% faster than just opening a new connection for every client. It works with UDP and TCP and uses
// inband healthchecking.
package forward
import (
"context"
"github.com/coredns/coredns/plugin/pkg/transport"
"github.com/coredns/coredns/request"
"github.com/miekg/dns"
)
// Forward forward the request in state as-is. Unlike Lookup that adds EDNS0 suffix to the message.
// Forward may be called with a nil f, an error is returned in that case.
func (f *Forward) Forward(state request.Request) (*dns.Msg, error) {
if f == nil {
return nil, ErrNoForward
}
fails := 0
var upstreamErr error
for _, proxy := range f.List() {
if proxy.Down(f.maxfails) {
fails++
if fails < len(f.proxies) {
continue
}
// All upstream proxies are dead, assume healtcheck is complete broken and randomly
// select an upstream to connect to.
proxy = f.List()[0]
}
ret, err := proxy.Connect(context.Background(), state, f.opts)
ret, err = truncated(state, ret, err)
upstreamErr = err
if err != nil {
if fails < len(f.proxies) {
continue
}
break
}
// Check if the reply is correct; if not return FormErr.
if !state.Match(ret) {
return state.ErrorMessage(dns.RcodeFormatError), nil
}
return ret, err
}
if upstreamErr != nil {
return nil, upstreamErr
}
return nil, ErrNoHealthy
}
// Lookup will use name and type to forge a new message and will send that upstream. It will
// set any EDNS0 options correctly so that downstream will be able to process the reply.
// Lookup may be called with a nil f, an error is returned in that case.
func (f *Forward) Lookup(state request.Request, name string, typ uint16) (*dns.Msg, error) {
if f == nil {
return nil, ErrNoForward
}
req := new(dns.Msg)
req.SetQuestion(name, typ)
state.SizeAndDo(req)
state2 := request.Request{W: state.W, Req: req}
return f.Forward(state2)
}
// NewLookup returns a Forward that can be used for plugin that need an upstream to resolve external names.
// Note that the caller must run Close on the forward to stop the health checking goroutines.
func NewLookup(addr []string) *Forward {
f := New()
for i := range addr {
p := NewProxy(addr[i], transport.DNS)
f.SetProxy(p)
}
return f
}
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