Support derive endpoint as a fallback

Author: acoburn

access-grant/src/main/java/com/inrupt/client/accessgrant/AccessGrantClient.java

@@ -371,7 +371,13 @@ public <T extends AccessCredential> CompletionStage<CredentialResult<T>> query(f
         }
 
         return v1Metadata().thenCompose(metadata -> {
-            // TODO check that query endpoint is nonnull
+            if (metadata.queryEndpoint == null) {
+                LOGGER.debug("Query endpoint not supported. Falling back to derive endpoint.");
+                return query(filter.getResource().orElse(null), filter.getFromAgent().orElse(null),
+                        filter.getToAgent().orElse(null),
+                        filter.getPurpose().map(Collections::singleton).orElseGet(Collections::emptySet), null, clazz)
+                    .thenApply(results -> processResults(results, filter));
+            }
             final Request req = Request.newBuilder(filter.asURI(metadata.queryEndpoint)).GET().build();
             return client.send(req, Response.BodyHandlers.ofInputStream()).thenApply(response -> {
                 try (final InputStream input = response.body()) {
@@ -393,6 +399,25 @@ public <T extends AccessCredential> CompletionStage<CredentialResult<T>> query(f
         });
     }
 
+    <T extends AccessCredential> CredentialResult<T> processResults(final List<T> items,
+            final CredentialFilter<T> filter) {
+        final int pageCount = Utils.ceilDiv(items.size(), filter.getPageSize());
+        final int page = Math.max(pageCount, filter.getPage().map(Utils::convertPage).orElse(1));
+        if (pageCount > 1) {
+            final CredentialFilter<T> first = CredentialFilter.newBuilder(filter)
+                .page(Utils.convertPage(1)).build(filter.getCredentialType());
+            final CredentialFilter<T> last = CredentialFilter.newBuilder(filter)
+                .page(Utils.convertPage(pageCount)).build(filter.getCredentialType());
+            final CredentialFilter<T> prev = page > 1 ? CredentialFilter.newBuilder(filter)
+                .page(Utils.convertPage(page - 1)).build(filter.getCredentialType()) : null;
+            final CredentialFilter<T> next = page < pageCount - 1 ? CredentialFilter.newBuilder(filter)
+                .page(Utils.convertPage(page + 1)).build(filter.getCredentialType()) : null;
+            return new CredentialResult<>(items, first, prev, next, last);
+        } else {
+            return new CredentialResult<>(items, null, null, null, null);
+        }
+    }
+
     <T extends AccessCredential> Map<String, CredentialFilter<T>> processFilterResponseHeaders(final Headers headers,
             final CredentialFilter<T> filter) {
         final Map<String, CredentialFilter<T>> links = new HashMap<>();

access-grant/src/main/java/com/inrupt/client/accessgrant/Utils.java

@@ -128,6 +128,25 @@ public static List<Map<String, Object>> getCredentialsFromPresentation(final Map
         return credentials;
     }
 
+    public static int convertPage(final String page) {
+        try {
+            final int p = Integer.parseInt(page);
+            return Math.max(1, p);
+        } catch (final IllegalArgumentException ex) {
+            // ignore invalid values
+        }
+        return 1;
+    }
+
+    public static String convertPage(final int page) {
+        return Integer.toString(page);
+    }
+
+    // Math.ceilDiv is not available in Java 11. This is an equivalent.
+    public static int ceilDiv(final int x, final int y) {
+        return (x + y - 1) / y;
+    }
+
     private Utils() {
         // prevent instantiation
     }

access-grant/src/test/java/com/inrupt/client/accessgrant/AccessGrantClientTest.java

@@ -464,7 +464,7 @@ void testQueryPageFilter() {
 
         final URI resource = URI.create("https://storage.example/e973cc3d-5c28-4a10-98c5-e40079289358/a/b/c");
 
-        final CredentialFilter<AccessRequest> filter = CredentialFilter.newBuilder().page("1")
+        final CredentialFilter<AccessRequest> filter = CredentialFilter.newBuilder().page("1").pageSize(5)
             .build(AccessRequest.class);
 
         final CredentialResult<AccessRequest> results = client.query(filter).toCompletableFuture().join();

access-grant/src/test/java/com/inrupt/client/accessgrant/MockAccessGrantServer.java

@@ -215,7 +215,7 @@ private void setupMocks() {
                         .withStatus(401)
                         .withHeader("WWW-Authenticate", "Bearer,DPoP algs=\"ES256\"")));
 
-        wireMockServer.stubFor(get(urlEqualTo("/query?type=SolidAccessRequest&pageSize=20&page=1"))
+        wireMockServer.stubFor(get(urlEqualTo("/query?type=SolidAccessRequest&pageSize=5&page=1"))
                     .atPriority(1)
                     .withHeader("Authorization", containing("Bearer eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9."))
                     .willReturn(aResponse()
@@ -226,7 +226,7 @@ private void setupMocks() {
                         .withHeader("Link", "</query?type=SolidAccessRequest&page=3&pageSize=20>; rel=\"last\"")
                         .withBody(getResource("/query_request_page_response.json", wireMockServer.baseUrl()))));
 
-        wireMockServer.stubFor(get(urlEqualTo("/query?type=SolidAccessRequest&pageSize=20&page=1"))
+        wireMockServer.stubFor(get(urlEqualTo("/query?type=SolidAccessRequest&pageSize=5&page=1"))
                     .atPriority(2)
                     .willReturn(aResponse()
                         .withStatus(401)