[core] make forcing cache/network only more explicit

Previously, we used the existence of a `prior*` field in the Resource object as an indication for whether we should consult the cache or not. However, this is prone to error, since a failed cache lookup won't set any prior fields. Therefore, we manually set `priorExpires` to 0. This in turn triggered another bug where generated wrong expiration timestamps when the server response we got was expired (or expired between sending and receiving).

This commit changes the flags so that we can now explicitly request CacheOnly/NetworkOnly (or All) loading methods, rather than the implicit Optional/Required naming scheme.

test/storage/default_file_source.test.cpp

@@ -251,7 +251,7 @@ TEST(DefaultFileSource, OptionalNonExpired) {
     util::RunLoop loop;
     DefaultFileSource fs(":memory:", ".");
 
-    const Resource optionalResource { Resource::Unknown, "http://127.0.0.1:3000/test", {}, Resource::Optional };
+    const Resource optionalResource { Resource::Unknown, "http://127.0.0.1:3000/test", {}, Resource::LoadingMethod::CacheOnly };
 
     using namespace std::chrono_literals;
 
@@ -281,7 +281,7 @@ TEST(DefaultFileSource, OptionalExpired) {
     util::RunLoop loop;
     DefaultFileSource fs(":memory:", ".");
 
-    const Resource optionalResource { Resource::Unknown, "http://127.0.0.1:3000/test", {}, Resource::Optional };
+    const Resource optionalResource { Resource::Unknown, "http://127.0.0.1:3000/test", {}, Resource::LoadingMethod::CacheOnly };
 
     using namespace std::chrono_literals;
 
@@ -327,7 +327,7 @@ TEST(DefaultFileSource, OptionalNotFound) {
     util::RunLoop loop;
     DefaultFileSource fs(":memory:", ".");
 
-    const Resource optionalResource { Resource::Unknown, "http://127.0.0.1:3000/test", {}, Resource::Optional };
+    const Resource optionalResource { Resource::Unknown, "http://127.0.0.1:3000/test", {}, Resource::LoadingMethod::CacheOnly };
 
     using namespace std::chrono_literals;
 
@@ -348,13 +348,13 @@ TEST(DefaultFileSource, OptionalNotFound) {
     loop.run();
 }
 
-// Test that we can make a request with etag data that doesn't first try to load
-// from cache like a regular request
+// Test that a network only request doesn't attempt to load data from the cache.
 TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheRefreshEtagNotModified)) {
     util::RunLoop loop;
     DefaultFileSource fs(":memory:", ".");
 
     Resource resource { Resource::Unknown, "http://127.0.0.1:3000/revalidate-same" };
+    resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
     resource.priorEtag.emplace("snowfall");
 
     using namespace std::chrono_literals;
@@ -383,13 +383,13 @@ TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheRefreshEtagNotModified)) {
     loop.run();
 }
 
-// Test that we can make a request with etag data that doesn't first try to load
-// from cache like a regular request
+// Test that a network only request doesn't attempt to load data from the cache.
 TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheRefreshEtagModified)) {
     util::RunLoop loop;
     DefaultFileSource fs(":memory:", ".");
 
     Resource resource { Resource::Unknown, "http://127.0.0.1:3000/revalidate-same" };
+    resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
     resource.priorEtag.emplace("sunshine");
 
     using namespace std::chrono_literals;
@@ -418,15 +418,13 @@ TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheRefreshEtagModified)) {
     loop.run();
 }
 
-// Test that we can make a request that doesn't first try to load
-// from cache like a regular request.
+// Test that a network only request doesn't attempt to load data from the cache.
 TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheFull)) {
     util::RunLoop loop;
     DefaultFileSource fs(":memory:", ".");
 
     Resource resource { Resource::Unknown, "http://127.0.0.1:3000/revalidate-same" };
-    // Setting any prior field results in skipping the cache.
-    resource.priorExpires.emplace(Seconds(0));
+    resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
 
     using namespace std::chrono_literals;
 
@@ -461,6 +459,7 @@ TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheRefreshModifiedNotModified))
     DefaultFileSource fs(":memory:", ".");
 
     Resource resource { Resource::Unknown, "http://127.0.0.1:3000/revalidate-modified" };
+    resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
     resource.priorModified.emplace(Seconds(1420070400)); // January 1, 2015
 
     using namespace std::chrono_literals;
@@ -496,6 +495,7 @@ TEST(DefaultFileSource, TEST_REQUIRES_SERVER(NoCacheRefreshModifiedModified)) {
     DefaultFileSource fs(":memory:", ".");
 
     Resource resource { Resource::Unknown, "http://127.0.0.1:3000/revalidate-modified" };
+    resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
     resource.priorModified.emplace(Seconds(1417392000)); // December 1, 2014
 
     using namespace std::chrono_literals;
@@ -578,7 +578,7 @@ TEST(DefaultFileSource, TEST_REQUIRES_SERVER(RespondToStaleMustRevalidate)) {
     DefaultFileSource fs(":memory:", ".");
 
     Resource resource { Resource::Unknown, "http://127.0.0.1:3000/revalidate-same" };
-    resource.necessity = Resource::Necessity::Optional;
+    resource.loadingMethod = Resource::LoadingMethod::CacheOnly;
 
     // using namespace std::chrono_literals;
 
@@ -621,7 +621,7 @@ TEST(DefaultFileSource, TEST_REQUIRES_SERVER(RespondToStaleMustRevalidate)) {
     // Now run this request again, with the data we gathered from the previous stale/unusable
     // request. We're replacing the data so that we can check that the DefaultFileSource doesn't
     // attempt another database access if we already have the value.
-    resource.necessity = Resource::Necessity::Required;
+    resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
     resource.priorData = std::make_shared<std::string>("Prior value");
 
     req = fs.request(resource, [&](Response res) {