fix: Support empty PATCH requests

package.json

@@ -122,7 +122,7 @@
     "rdf-terms": "^1.5.1",
     "redis": "^3.0.2",
     "redlock": "^4.2.0",
-    "sparqlalgebrajs": "^2.5.1",
+    "sparqlalgebrajs": "^3.0.0",
     "sparqljs": "^3.1.2",
     "streamify-array": "^1.0.1",
     "url-join": "^4.0.1",

src/ldp/permissions/SparqlPatchPermissionsExtractor.ts

@@ -44,7 +44,7 @@ export class SparqlPatchPermissionsExtractor extends PermissionsExtractor {
   }
 
   private isSupported(op: Algebra.Operation): boolean {
-    if (op.type === Algebra.types.DELETE_INSERT) {
+    if (this.isDeleteInsert(op) || this.isNop(op)) {
       return true;
     }
     if (op.type === Algebra.types.COMPOSITE_UPDATE) {
@@ -57,7 +57,14 @@ export class SparqlPatchPermissionsExtractor extends PermissionsExtractor {
     return op.type === Algebra.types.DELETE_INSERT;
   }
 
+  private isNop(op: Algebra.Operation): op is Algebra.Nop {
+    return op.type === Algebra.types.NOP;
+  }
+
   private needsAppend(update: Algebra.Operation): boolean {
+    if (this.isNop(update)) {
+      return false;
+    }
     if (this.isDeleteInsert(update)) {
       return Boolean(update.insert && update.insert.length > 0);
     }
@@ -66,6 +73,9 @@ export class SparqlPatchPermissionsExtractor extends PermissionsExtractor {
   }
 
   private needsWrite(update: Algebra.Operation): boolean {
+    if (this.isNop(update)) {
+      return false;
+    }
     if (this.isDeleteInsert(update)) {
       return Boolean(update.delete && update.delete.length > 0);
     }

src/storage/patch/SparqlUpdatePatchHandler.ts

@@ -47,6 +47,12 @@ export class SparqlUpdatePatchHandler extends PatchHandler {
     // Verify the patch
     const { source, identifier, patch } = input;
     const op = (patch as SparqlUpdatePatch).algebra;
+
+    // In case of a NOP we can skip everything
+    if (op.type === Algebra.types.NOP) {
+      return [];
+    }
+
     this.validateUpdate(op);
 
     return this.applyPatch(source, identifier, op);

test/unit/ldp/permissions/SparqlPatchPermissionsExtractor.test.ts

@@ -32,6 +32,19 @@ describe('A SparqlPatchPermissionsExtractor', (): void => {
     await expect(result).rejects.toThrow('Can only determine permissions of a PATCH with DELETE/INSERT operations.');
   });
 
+  it('requires nothing for NOP operations.', async(): Promise<void> => {
+    const operation = {
+      method: 'PATCH',
+      body: { algebra: factory.createNop() },
+    } as unknown as Operation;
+    await expect(extractor.handle(operation)).resolves.toEqual({
+      read: false,
+      append: false,
+      write: false,
+      control: false,
+    });
+  });
+
   it('requires append for INSERT operations.', async(): Promise<void> => {
     const operation = {
       method: 'PATCH',

test/unit/storage/patch/SparqlUpdatePatchHandler.test.ts

@@ -93,6 +93,13 @@ describe('A SparqlUpdatePatchHandler', (): void => {
     await expect(handler.canHandle(input)).rejects.toThrow(NotImplementedHttpError);
   });
 
+  it('handles NOP operations by not doing anything.', async(): Promise<void> => {
+    await handle('');
+    expect(source.getRepresentation).toHaveBeenCalledTimes(0);
+    expect(converter.handleSafe).toHaveBeenCalledTimes(0);
+    expect(source.setRepresentation).toHaveBeenCalledTimes(0);
+  });
+
   it('handles INSERT DATA updates.', async(): Promise<void> => {
     await handle(fullfilledDataInsert);
     expect(await basicChecks(startQuads.concat(