Dedup policy implement between grpc and proxy plugin (#3537)

Signed-off-by: zouyee <zounengren@cmss.chinamobile.com>

plugin/pkg/policy/policy.go

@@ -0,0 +1,76 @@
+package policy
+
+import (
+	"math/rand"
+	"sync/atomic"
+)
+
+// Policy defines a policy we use for selecting upstreams.
+type Policy interface {
+	List(policy ...interface{}) []interface{}
+	String() string
+}
+
+// Random is a policy that implements random upstream selection.
+type Random struct{}
+
+var _ Policy = &Random{}
+
+// String returns the name of policy Random
+func (r *Random) String() string { return "random" }
+
+// List returns a set of proxies to be used for this client depending on Random policy.
+func (r *Random) List(p ...interface{}) []interface{} {
+	switch len(p) {
+	case 1:
+		return p
+	case 2:
+		if rand.Int()%2 == 0 {
+			return []interface{}{p[1], p[0]} // swap
+		}
+		return p
+	}
+
+	perms := rand.Perm(len(p))
+	rnd := make([]interface{}, 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
+}
+
+var _ Policy = &RoundRobin{}
+
+// String returns the name of policy RoundRobin
+func (r *RoundRobin) String() string { return "round_robin" }
+
+// List returns a set of proxies to be used for this client depending on RoundRobin policy.
+func (r *RoundRobin) List(p ...interface{}) []interface{} {
+	poolLen := uint32(len(p))
+	i := atomic.AddUint32(&r.robin, 1) % poolLen
+
+	robin := []interface{}{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{}
+
+var _ Policy = &Sequential{}
+
+// String returns the name of policy Sequential
+func (r *Sequential) String() string { return "sequential" }
+
+// List returns a set of proxies without filter.
+func (r *Sequential) List(p ...interface{}) []interface{} {
+	return p
+}