fix: non-leader agents return 404 on Get Intention exact api (#13179)

* fix: non-leader agents return 404 on Get Intention exact api

- rpc call method appends extra error message, so change == to
  "Strings.Contains"

Co-authored-by: Chris S. Kim <ckim@hashicorp.com>

agent/intentions_endpoint.go

@@ -324,7 +324,7 @@ func (s *HTTPHandlers) IntentionGetExact(resp http.ResponseWriter, req *http.Req
 	var reply structs.IndexedIntentions
 	if err := s.agent.RPC("Intention.Get", &args, &reply); err != nil {
 		// We have to check the string since the RPC sheds the error type
-		if err.Error() == consul.ErrIntentionNotFound.Error() {
+		if strings.Contains(err.Error(), consul.ErrIntentionNotFound.Error()) {
 			return nil, HTTPError{StatusCode: http.StatusNotFound, Reason: err.Error()}
 		}
 

agent/intentions_endpoint_test.go

@@ -1,6 +1,7 @@
 package agent
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"net/http/httptest"
@@ -314,6 +315,52 @@ func TestIntentionCheck(t *testing.T) {
 	})
 }
 
+type testSrv struct {
+	delegate
+}
+
+func (s *testSrv) RPC(method string, args interface{}, reply interface{}) error {
+	return fmt.Errorf("rpc error making call: %w", errors.New("Intention not found"))
+}
+func (s *testSrv) Shutdown() error {
+	return nil
+}
+
+func TestIntentionGetExact(t *testing.T) {
+	if testing.Short() {
+		t.Skip("too slow for testing.Short")
+	}
+
+	t.Parallel()
+
+	a := NewTestAgent(t, "")
+	defer a.Shutdown()
+	testrpc.WaitForTestAgent(t, a.RPC, "dc1")
+
+	notfound := func(t *testing.T) {
+		t.Helper()
+		req, err := http.NewRequest("GET", "/v1/connect/intentions/exact?source=foo&destination=bar", nil)
+		require.NoError(t, err)
+
+		resp := httptest.NewRecorder()
+		obj, err := a.srv.IntentionExact(resp, req)
+		testutil.RequireErrorContains(t, err, "Intention not found")
+		httpErr, ok := err.(HTTPError)
+		require.True(t, ok)
+		require.Equal(t, http.StatusNotFound, httpErr.StatusCode)
+		require.Nil(t, obj)
+	}
+
+	t.Run("not found locally", func(t *testing.T) {
+		notfound(t)
+	})
+
+	t.Run("not found by RPC", func(t *testing.T) {
+		a.delegate = &testSrv{}
+		notfound(t)
+	})
+}
+
 func TestIntentionPutExact(t *testing.T) {
 	if testing.Short() {
 		t.Skip("too slow for testing.Short")