Add initial signposting headers (#493)

* Add first draft of signposting headers.

* Fixed checkstyle issues.

src/main/java/nl/dtls/fairdatapoint/api/controller/metadata/GenericController.java

@@ -26,6 +26,7 @@
 import io.swagger.v3.oas.annotations.tags.Tag;
 import lombok.RequiredArgsConstructor;
 import nl.dtls.fairdatapoint.database.rdf.repository.RepositoryMode;
+import jakarta.servlet.http.HttpServletResponse;
 import nl.dtls.fairdatapoint.database.rdf.repository.exception.MetadataRepositoryException;
 import nl.dtls.fairdatapoint.database.rdf.repository.generic.GenericMetadataRepository;
 import nl.dtls.fairdatapoint.entity.exception.ForbiddenException;
@@ -46,7 +47,9 @@
 import org.eclipse.rdf4j.model.Model;
 import org.eclipse.rdf4j.model.Value;
 import org.eclipse.rdf4j.model.impl.LinkedHashModel;
+import org.eclipse.rdf4j.model.util.Models;
 import org.eclipse.rdf4j.model.vocabulary.DCTERMS;
+import org.eclipse.rdf4j.model.vocabulary.RDF;
 import org.eclipse.rdf4j.rio.RDFFormat;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
@@ -149,7 +152,8 @@ public Model getMetaDataExpanded(
     )
     public Model getMetaData(
             @PathVariable final Optional<String> oUrlPrefix,
-            @PathVariable final Optional<String> oRecordId
+            @PathVariable final Optional<String> oRecordId,
+            HttpServletResponse response
     ) throws MetadataServiceException {
         // 1. Init
         final Model resultRdf = new LinkedHashModel();
@@ -171,7 +175,9 @@ public Model getMetaData(
         metadataEnhancer.enhanceWithLinks(entityUri, entity, rd, persistentUrl, resultRdf);
         metadataEnhancer.enhanceWithResourceDefinition(entityUri, rd, resultRdf);
 
-        // 5. Create response
+        enhanceWithSignposting(response, entityUri, resultRdf);
+
+        // 6. Create response
         return resultRdf;
     }
 
@@ -416,4 +422,37 @@ private Optional<Model> retrieveChildModel(MetadataService childMetadataService,
     private String createLink(String entityUrl, String childPrefix, int page, int size, String rel) {
         return format("<%s/page/%s?page=%d&size=%d>; rel=\"%s\"", entityUrl, childPrefix, page, size, rel);
     }
+
+    private void enhanceWithSignposting(HttpServletResponse response, IRI entityUri, Model resultRdf) {
+        // author
+        Models.getProperty(resultRdf, entityUri, DCTERMS.PUBLISHER).ifPresent(pub -> {
+            addSignpostingHeader(response, pub, "author");
+        });
+
+        // cite-as
+        addSignpostingHeader(response, entityUri, "cite-as");
+
+        // describedby
+        // TODO
+
+        // type
+        Models.getProperties(resultRdf, entityUri, RDF.TYPE).forEach(type -> {
+            addSignpostingHeader(response, type, "type");
+        });
+
+        // license
+        Models.getPropertyIRI(resultRdf, entityUri, DCTERMS.LICENSE).ifPresent(license -> {
+            addSignpostingHeader(response, license, "license");
+        });
+
+        // item
+        // TODO
+
+        // collection
+        // TODO
+    }
+
+    private void addSignpostingHeader(HttpServletResponse response, Value link, String rel) {
+        response.addHeader(HttpHeaders.LINK, format("<%s>; rel=\"%s\"", link, rel));
+    }
 }

src/test/java/nl/dtls/fairdatapoint/acceptance/metadata/SingpostingTest.java

@@ -0,0 +1,60 @@
+/**
+ * The MIT License
+ * Copyright © 2017 DTL
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package nl.dtls.fairdatapoint.acceptance.metadata;
+
+import static java.lang.String.format;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.collection.IsIn.in;
+import static org.hamcrest.core.Is.is;
+import java.net.URI;
+import nl.dtls.fairdatapoint.WebIntegrationTest;
+import org.junit.jupiter.api.Test;
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.RequestEntity;
+
+public class SingpostingTest extends WebIntegrationTest {
+    private URI url(String id) {
+        return URI.create(format("/catalog/%s", id));
+    }
+
+    @Test
+    public void testCatalogSignpostingHeaders() {
+        // GIVEN:
+        var request = RequestEntity
+                .get(url("catalog-1"))
+                .header(HttpHeaders.ACCEPT, "text/turtle")
+                .build();
+        var responseType = new ParameterizedTypeReference<String>() {};
+
+        // WHEN:
+        var result = client.exchange(request, responseType);
+
+        // THEN:
+        var linkHeaderMatcher = is(in(result.getHeaders().get(HttpHeaders.LINK)));
+        assertThat("<http://example.com/publisher>; rel=\"author\"", linkHeaderMatcher);
+        assertThat("<http://localhost:8088/catalog/catalog-1>; rel=\"cite-as\"", linkHeaderMatcher);
+        assertThat("<http://www.w3.org/ns/dcat#Catalog>; rel=\"type\"", linkHeaderMatcher);
+        assertThat("<http://rdflicense.appspot.com/rdflicense/cc-by-nc-nd3.0>; rel=\"license\"", linkHeaderMatcher);
+    }
+}