consul: Support conditional policy fetch

consul/acl.go

@@ -69,7 +69,7 @@ func (s *Server) lookupACL(id, authDC string) (acl.ACL, error) {
 	}
 
 	// Attempt to refresh the policy
-	args := structs.ACLSpecificRequest{
+	args := structs.ACLPolicyRequest{
 		Datacenter: authDC,
 		ACL:        id,
 	}

consul/acl_endpoint.go

@@ -88,7 +88,7 @@ func (a *ACL) Get(args *structs.ACLSpecificRequest,
 
 // GetPolicy is used to retrieve a compiled policy object with a TTL. Does not
 // support a blocking query.
-func (a *ACL) GetPolicy(args *structs.ACLSpecificRequest, reply *structs.ACLPolicy) error {
+func (a *ACL) GetPolicy(args *structs.ACLPolicyRequest, reply *structs.ACLPolicy) error {
 	if done, err := a.srv.forward("ACL.GetPolicy", args, args, reply); done {
 		return err
 	}
@@ -99,12 +99,20 @@ func (a *ACL) GetPolicy(args *structs.ACLSpecificRequest, reply *structs.ACLPoli
 		return err
 	}
 
-	// Setup the response
+	// Generate an ETag
 	conf := a.srv.config
-	reply.Policy = policy
+	etag := fmt.Sprintf("%s:%s", conf.ACLDefaultPolicy, policy.ID)
+
+	// Setup the response
+	reply.ETag = etag
 	reply.Root = conf.ACLDefaultPolicy
 	reply.TTL = conf.ACLTTL
 	a.srv.setQueryMeta(&reply.QueryMeta)
+
+	// Only send the policy on an Etag mis-match
+	if args.ETag != etag {
+		reply.Policy = policy
+	}
 	return nil
 }
 

consul/acl_endpoint_test.go

@@ -130,7 +130,7 @@ func TestACLEndpoint_GetPolicy(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
-	getR := structs.ACLSpecificRequest{
+	getR := structs.ACLPolicyRequest{
 		Datacenter: "dc1",
 		ACL:        out,
 	}
@@ -145,6 +145,20 @@ func TestACLEndpoint_GetPolicy(t *testing.T) {
 	if acls.TTL != 30*time.Second {
 		t.Fatalf("bad: %v", acls)
 	}
+
+	// Do a conditional lookup with etag
+	getR.ETag = acls.ETag
+	var out2 structs.ACLPolicy
+	if err := client.Call("ACL.GetPolicy", &getR, &out2); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	if out2.Policy != nil {
+		t.Fatalf("Bad: %v", out2)
+	}
+	if out2.TTL != 30*time.Second {
+		t.Fatalf("bad: %v", out2)
+	}
 }
 
 func TestACLEndpoint_List(t *testing.T) {

consul/structs/structs.go

@@ -466,12 +466,26 @@ func (r *ACLSpecificRequest) RequestDatacenter() string {
 	return r.Datacenter
 }
 
+// ACLPolicyRequest is used to request an ACL by ID, conditionally
+// filtering on an ID
+type ACLPolicyRequest struct {
+	Datacenter string
+	ACL        string
+	ETag       string
+	QueryOptions
+}
+
+func (r *ACLPolicyRequest) RequestDatacenter() string {
+	return r.Datacenter
+}
+
 type IndexedACLs struct {
 	ACLs ACLs
 	QueryMeta
 }
 
 type ACLPolicy struct {
+	ETag   string
 	Root   string
 	Policy *acl.Policy
 	TTL    time.Duration