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package forward
import (
"sync/atomic"
"time"
"github.com/coredns/coredns/plugin/pkg/proxy"
"github.com/coredns/coredns/plugin/pkg/rand"
)
// Policy defines a policy we use for selecting upstreams.
type Policy interface {
List([]*proxy.Proxy) []*proxy.Proxy
String() string
}
// random is a policy that implements random upstream selection.
type random struct{}
func (r *random) String() string { return "random" }
func (r *random) List(p []*proxy.Proxy) []*proxy.Proxy {
switch len(p) {
case 1:
return p
case 2:
if rn.Int()%2 == 0 {
return []*proxy.Proxy{p[1], p[0]} // swap
}
return p
}
perms := rn.Perm(len(p))
rnd := make([]*proxy.Proxy, len(p))
for i, p1 := range perms {
rnd[i] = p[p1]
}
return rnd
}
// roundRobin is a policy that selects hosts based on round robin ordering.
type roundRobin struct {
robin uint32
}
func (r *roundRobin) String() string { return "round_robin" }
func (r *roundRobin) List(p []*proxy.Proxy) []*proxy.Proxy {
poolLen := uint32(len(p))
i := atomic.AddUint32(&r.robin, 1) % poolLen
robin := []*proxy.Proxy{p[i]}
robin = append(robin, p[:i]...)
robin = append(robin, p[i+1:]...)
return robin
}
// sequential is a policy that selects hosts based on sequential ordering.
type sequential struct{}
func (r *sequential) String() string { return "sequential" }
func (r *sequential) List(p []*proxy.Proxy) []*proxy.Proxy {
return p
}
var rn = rand.New(time.Now().UnixNano())
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