Fallback-aware failure handling - make sure snippet with enabled fall…

CHANGELOG.md

@@ -6,3 +6,4 @@ List of changes that are finished but not yet released in any final version.
 
 ## 1.5.0
 Initial open source release.
+- [PR-5](https://github.com/Knotx/knotx-template-engine/pull/5) - implementation of [fallback handling](https://github.com/Cognifide/knotx/issues/466) in template engine

core/src/main/java/io/knotx/te/core/TemplateEngineKnotProxy.java

@@ -18,6 +18,7 @@
 import io.knotx.dataobjects.ClientResponse;
 import io.knotx.dataobjects.Fragment;
 import io.knotx.dataobjects.KnotContext;
+import io.knotx.exceptions.FragmentProcessingException;
 import io.knotx.knot.AbstractKnotProxy;
 import io.knotx.te.api.TemplateEngine;
 import io.knotx.te.core.exception.UnsupportedEngineException;
@@ -54,26 +55,30 @@ protected Single<KnotContext> processRequest(KnotContext knotContext) {
                 .filter(fragment -> fragment.knots().contains(SUPPORTED_FRAGMENT_ID))
                 .doOnNext(this::traceFragment)
                 .map(fragment -> FragmentContext.from(fragment, options.getDefaultEngine()))
-                .map(
-                    fragmentContext -> {
-                      final TemplateEngine templateEngine = engines
-                          .get(fragmentContext.getStrategy());
-                      if (templateEngine != null) {
-                        fragmentContext.fragment().content(
-                            templateEngine
-                                .process(fragmentContext.fragment()));
-                        return fragmentContext;
-                      } else {
-                        throw new UnsupportedEngineException(
-                            "No engine named '" + fragmentContext.getStrategy() + "' found.");
-                      }
-                    })
+                .flatMapSingle(this::processFragment)
                 .toList()
         ).orElse(Single.just(Collections.emptyList()))
         .map(result -> createSuccessResponse(knotContext))
         .onErrorReturn(error -> processError(knotContext, error));
   }
 
+  protected Single<FragmentContext> processFragment(FragmentContext fc) {
+    return Single.just(fc)
+        .map(fragmentContext -> {
+          final TemplateEngine templateEngine = engines
+              .get(fragmentContext.getStrategy());
+          if (templateEngine != null) {
+            fragmentContext.fragment().content(
+                templateEngine
+                    .process(fragmentContext.fragment()));
+            return fragmentContext;
+          } else {
+            throw new UnsupportedEngineException(
+                "No engine named '" + fragmentContext.getStrategy() + "' found.");
+          }
+        }).onErrorReturn(e -> handleFragmentError(fc, e));
+  }
+
   @Override
   protected boolean shouldProcess(Set<String> knots) {
     return knots.contains(SUPPORTED_FRAGMENT_ID);
@@ -104,4 +109,14 @@ private void traceFragment(Fragment fragment) {
       LOGGER.trace("Processing fragment {}", fragment.toJson().encodePrettily());
     }
   }
+
+  private FragmentContext handleFragmentError(FragmentContext fragmentContext, Throwable t) {
+    LOGGER.error("Fragment processing failed. Cause:{}\nFragmentContext:\n{}\n", t.getMessage(), fragmentContext);
+    fragmentContext.fragment().failure(SUPPORTED_FRAGMENT_ID, t);
+    if (fragmentContext.fragment().fallback().isPresent()) {
+      return fragmentContext;
+    } else {
+      throw new FragmentProcessingException(String.format("Fragment processing failed in %s", SUPPORTED_FRAGMENT_ID), t);
+    }
+  }
 }

it-test/src/test/java/io/knotx/te/test/integration/TemplateEngineIntegrationTest.java

@@ -3,6 +3,8 @@
 import static io.knotx.junit5.util.RequestUtil.subscribeToResult_shouldSucceed;
 import static org.hamcrest.Matchers.equalToIgnoringWhiteSpace;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertFalse;
 
 import io.knotx.dataobjects.ClientRequest;
 import io.knotx.dataobjects.Fragment;
@@ -37,11 +39,26 @@ void callTemplateEngine_validateResult(VertxTestContext context, Vertx vertx)
         knotContext -> {
           final String expectedMarkup = fileContentAsString("result/simple.txt");
           final String markup = knotContext.getFragments().iterator().next().content();
+          final boolean failed = knotContext.getFragments().iterator().next().failed();
 
+          assertFalse(failed);
           assertThat(markup, equalToIgnoringWhiteSpace(expectedMarkup));
         });
   }
 
+  @Test
+  @KnotxApplyConfiguration("templateEngineStack.conf")
+  void callTemplateEngine_validateFallback(VertxTestContext context, Vertx vertx)
+      throws IOException, URISyntaxException {
+
+    callWithAssertions(context, vertx, "snippet/simple-missing-engine.txt", "data/simple.json",
+        knotContext -> {
+          final boolean failed = knotContext.getFragments().iterator().next().failed();
+
+          assertTrue(failed);
+        });
+  }
+
   private void callWithAssertions(
       VertxTestContext context, Vertx vertx, String snippetPath, String dataPath,
       Consumer<KnotContext> onSuccess) throws IOException, URISyntaxException {
@@ -63,7 +80,8 @@ private KnotContext buildContext(String snippetPath, String dataPath)
     String fragmentContent = fileContentAsString(snippetPath);
     JsonObject data = new JsonObject(fileContentAsString(dataPath));
 
-    final Fragment fragment = Fragment
+    final Fragment fragment = fragmentContent.contains("fallback")? Fragment
+        .snippet(Collections.singletonList("te"), fragmentContent, "BLANK") :  Fragment
         .snippet(Collections.singletonList("te"), fragmentContent);
     fragment.context().mergeIn(new JsonObject(Collections.singletonMap("_result", data)));
 

it-test/src/test/resources/snippet/simple-missing-engine.txt

@@ -0,0 +1,7 @@
+<knotx:snippet knots="te"
+            te-strategy="missing-engine"
+            fallback="BLANK"
+            type="text/knotx-snippet">
+  <h2>Message - {{_result.message}}</h2>
+  <p>Info - {{_result.body.info}}</p>
+</knotx:snippet>