Fix fhirweb diff template error (#4721)

* Add test to check template returned is not empty

* Check operation is diff so web template does not error

* Refactor for clarity

* add changelog

---------

Co-authored-by: David Chen <david.chen@smilecdr.com>

hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/6_6_0/4721-fix-fhirweb-diff-template-error.yaml

@@ -0,0 +1,5 @@
+---
+type: fix
+issue: 4721
+title: "Previously, clicking the '$diff' button on FHIRweb module would direct the user to an empty page. Now it 
+   displays the correct page."

hapi-fhir-testpage-overlay/src/main/java/ca/uhn/fhir/to/BaseController.java

@@ -485,6 +485,8 @@ public class BaseController {
 						} else if (theResultType == ResultType.BUNDLE) {
 							resultDescription.append("JSON bundle");
 							riBundle = context.newJsonParser().parseResource(resultBody);
+						} else if (theResultType == ResultType.PARAMETERS) {
+							resultDescription.append("JSON parameters");
 						}
 						break;
 					case XML:
@@ -494,6 +496,8 @@ public class BaseController {
 						} else if (theResultType == ResultType.BUNDLE) {
 							resultDescription.append("XML bundle");
 							riBundle = context.newXmlParser().parseResource(resultBody);
+						} else if (theResultType == ResultType.PARAMETERS) {
+							resultDescription.append("XML parameters");
 						}
 						break;
 				}
@@ -549,7 +553,7 @@ public class BaseController {
 	}
 
 	protected enum ResultType {
-		BUNDLE, NONE, RESOURCE, TAGLIST
+		BUNDLE, NONE, RESOURCE, TAGLIST, PARAMETERS
 	}
 
 	public static class CaptureInterceptor implements IClientInterceptor {

hapi-fhir-testpage-overlay/src/main/java/ca/uhn/fhir/to/Controller.java

@@ -45,6 +45,7 @@ import org.springframework.ui.ModelMap;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.annotation.RequestMapping;
 
+import javax.annotation.Nullable;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import java.io.IOException;
@@ -52,8 +53,10 @@ import java.io.StringWriter;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import java.util.TreeSet;
 
+import static ca.uhn.fhir.rest.server.provider.ProviderConstants.DIFF_OPERATION_NAME;
 import static ca.uhn.fhir.util.UrlUtil.sanitizeUrlPart;
 import static org.apache.commons.lang3.StringUtils.defaultIfEmpty;
 import static org.apache.commons.lang3.StringUtils.defaultString;
@@ -622,7 +625,7 @@ public class Controller extends BaseController {
 		Class<? extends IBaseParameters> parametersType = (Class<? extends IBaseParameters>) getContext(theRequest).getResourceDefinition("Parameters").getImplementingClass();
 
 		StopWatch sw = new StopWatch();
-		ResultType returnsResource = ResultType.BUNDLE;
+		ResultType returnsResource = getReturnedTypeBasedOnOperation(operationName);
 		try {
 			client
 				.operation()
@@ -646,6 +649,9 @@ public class Controller extends BaseController {
 		return "result";
 	}
 
+	private static ResultType getReturnedTypeBasedOnOperation(@Nullable String operationName) {
+		return DIFF_OPERATION_NAME.equals(operationName) ? ResultType.PARAMETERS : ResultType.BUNDLE;
+	}
 
 
 	private void doActionHistory(HttpServletRequest theReq, HomeRequest theRequest, BindingResult theBindingResult, ModelMap theModel, String theMethod, String theMethodDescription) {

hapi-fhir-testpage-overlay/src/test/java/ca/uhn/fhir/jpa/test/WebTest.java

@@ -28,9 +28,12 @@ import org.eclipse.jetty.servlet.ServletHolder;
 import org.hl7.fhir.instance.model.api.IIdType;
 import org.hl7.fhir.r4.model.Bundle;
 import org.hl7.fhir.r4.model.Composition;
+import org.hl7.fhir.r4.model.Enumerations;
+import org.hl7.fhir.r4.model.HumanName;
 import org.hl7.fhir.r4.model.IdType;
 import org.hl7.fhir.r4.model.InstantType;
 import org.hl7.fhir.r4.model.OperationOutcome;
+import org.hl7.fhir.r4.model.Parameters;
 import org.hl7.fhir.r4.model.Patient;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeEach;
@@ -195,6 +198,40 @@ public class WebTest {
 		assertThat(summaryPage.asNormalizedText(), containsString("\"diagnostics\": \"VALIDATION FAILURE\""));
 	}
 
+	@Test
+	public void testInvokeCustomOperation_Diff() throws IOException {
+		registerAndUpdatePatient();
+
+		HtmlPage searchResultPage = searchForPatients();
+		HtmlTable controlsTable = searchResultPage.getHtmlElementById("resultControlsTable");
+		List<HtmlTableRow> controlRows = controlsTable.getBodies().get(0).getRows();
+		HtmlTableCell controlsCell = controlRows.get(0).getCell(0);
+
+		HtmlPage diffPage = controlsCell
+			.getElementsByTagName("button")
+			.stream()
+			.filter(t -> t.asNormalizedText().equals("$diff"))
+			.findFirst()
+			.orElseThrow()
+			.click();
+
+		assertThat(diffPage.asNormalizedText(), containsString("\"resourceType\": \"Parameters\""));
+	}
+
+	private void registerAndUpdatePatient() {
+		Patient p = new Patient();
+		Patient p2 = new Patient();
+		HumanName humanName = new HumanName();
+		humanName.addGiven("Yui");
+		humanName.setFamily("Hirasawa");
+		p2.getName().add(humanName);
+		p.setId("Patient/A");
+		p.getMeta().setLastUpdatedElement(new InstantType("2022-01-01T12:12:12.000Z"));
+		p.setActive(true);
+		IIdType iid = ourPatientProvider.store(p);
+		ourFhirServer.getFhirClient().update().resource(p2).withId(iid).execute();
+	}
+
 	private HtmlPage searchForPatients() throws IOException {
 		// Load home page
 		HtmlPage page = myWebClient.getPage("http://localhost/");
@@ -238,6 +275,12 @@ public class WebTest {
 			throw new PreconditionFailedException("failure", oo);
 		}
 
+		@Operation(name = "diff", typeName = "Patient", idempotent = true)
+		public Parameters diff(@IdParam IIdType theId) {
+			Parameters parameters = new Parameters();
+			return parameters;
+		}
+
 	}
 
 	private static class MyServletContextHandler extends ServletContextHandler {

hapi-fhir-testpage-overlay/src/test/java/ca/uhn/fhir/jpa/test/WebTestFhirTesterConfig.java

@@ -31,6 +31,7 @@ public class WebTestFhirTesterConfig {
 			.withBaseUrl("http://localhost:8000")
 			.withName("Localhost Server")
 			.withSearchResultRowOperation("$summary", id -> "Patient".equals(id.getResourceType()))
+			.withSearchResultRowOperation("$diff", id -> id.isVersionIdPartValidLong() && id.getVersionIdPartAsLong() > 1)
 			.withSearchResultRowOperation("$validate", id -> true)
 			.enableDebugTemplates();
 		return retVal;