server: Keep default decision path in-sync with manager's config

This change attempts to keep the default decision path used by the server
in sync with the one defined on the manager's config. Currently the
server only updates the default decision path when it's initialized and
when there is a commit on the store. The issue happens when the default
decision path is updated via the discovered config. In this case, the
manager's config is updated but there could be no store txn. Hence
the updated value of default decision path is not taken into account by
the server.

Fixes: #6697

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>

server/server.go

@@ -1050,7 +1050,7 @@ func (s *Server) v0QueryPath(w http.ResponseWriter, r *http.Request, urlPath str
 	}
 
 	if useDefaultDecisionPath {
-		urlPath = s.defaultDecisionPath
+		urlPath = s.generateDefaultDecisionPath()
 	}
 
 	logger := s.getDecisionLogger(br)

server/server_test.go

@@ -3873,6 +3873,46 @@ func TestUnversionedPost(t *testing.T) {
 	if f.recorder.Body.String() != expectedBody {
 		t.Errorf("Expected %s got %s", expectedBody, f.recorder.Body.String())
 	}
+
+	// update the default decision path
+	s := "http/authz"
+	f.server.manager.Config.DefaultDecision = &s
+
+	f.reset()
+	f.server.Handler.ServeHTTP(f.recorder, post())
+
+	if f.recorder.Code != 404 {
+		t.Fatalf("Expected not found before policy added but got %v", f.recorder)
+	}
+
+	expectedBody = `{
+  "code": "undefined_document",
+  "message": "document missing: data.http.authz"
+}
+`
+	if f.recorder.Body.String() != expectedBody {
+		t.Fatalf("Expected %s got %s", expectedBody, f.recorder.Body.String())
+	}
+
+	module = `
+	package http.authz
+
+	agg = x {
+		sum(input.foo.bar, x)
+	}
+	`
+
+	if err := f.v1("PUT", "/policies/test", module, 200, ""); err != nil {
+		t.Fatal(err)
+	}
+
+	f.reset()
+	f.server.Handler.ServeHTTP(f.recorder, post())
+
+	expected = "{\"agg\":6}\n"
+	if f.recorder.Code != 200 || f.recorder.Body.String() != expected {
+		t.Fatalf(`Expected HTTP 200 / %v but got: %v`, expected, f.recorder)
+	}
 }
 
 func TestQueryV1Explain(t *testing.T) {