From 0ecbffa8858b7d3992bea09b175cccf91a1942c5 Mon Sep 17 00:00:00 2001
From: Ruben Verborgh <ruben@verborgh.org>
Date: Wed, 2 Dec 2020 21:39:38 +0100
Subject: [PATCH] fix: Do not generate empty INSERT graph.

Fixes https://github.com/solid/community-server/issues/383
---
 src/storage/accessors/SparqlDataAccessor.ts   |  4 +++-
 .../accessors/SparqlDataAccessor.test.ts      | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/storage/accessors/SparqlDataAccessor.ts b/src/storage/accessors/SparqlDataAccessor.ts
index 56970bfb1..c67e1a3a3 100644
--- a/src/storage/accessors/SparqlDataAccessor.ts
+++ b/src/storage/accessors/SparqlDataAccessor.ts
@@ -238,7 +238,9 @@ export class SparqlDataAccessor implements DataAccessor {
     if (triples) {
       // This needs to be first so it happens before the insert
       updates.unshift(this.sparqlUpdateDeleteAll(name));
-      insert.push(this.sparqlUpdateGraph(name, triples));
+      if (triples.length > 0) {
+        insert.push(this.sparqlUpdateGraph(name, triples));
+      }
     }
 
     return {
diff --git a/test/unit/storage/accessors/SparqlDataAccessor.test.ts b/test/unit/storage/accessors/SparqlDataAccessor.test.ts
index f42f7de37..8c7e7e029 100644
--- a/test/unit/storage/accessors/SparqlDataAccessor.test.ts
+++ b/test/unit/storage/accessors/SparqlDataAccessor.test.ts
@@ -190,6 +190,25 @@ describe('A SparqlDataAccessor', (): void => {
     ]));
   });
 
+  it('overwrites the data and metadata when writing an empty resource.', async(): Promise<void> => {
+    metadata = new RepresentationMetadata('http://test.com/container/resource',
+      { [RDF.type]: [ toNamedNode(LDP.Resource) ]});
+    const empty = guardedStreamFrom([]);
+    await expect(accessor.writeDocument({ path: 'http://test.com/container/resource' }, empty, metadata))
+      .resolves.toBeUndefined();
+
+    expect(fetchUpdate).toHaveBeenCalledTimes(1);
+    expect(fetchUpdate.mock.calls[0][0]).toBe(endpoint);
+    expect(simplifyQuery(fetchUpdate.mock.calls[0][1])).toBe(simplifyQuery([
+      'DELETE WHERE { GRAPH <http://test.com/container/resource> { ?s ?p ?o. } };',
+      'DELETE WHERE { GRAPH <meta:http://test.com/container/resource> { ?s ?p ?o. } };',
+      'INSERT DATA {',
+      '  GRAPH <meta:http://test.com/container/resource> { <http://test.com/container/resource> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/ns/ldp#Resource>. }',
+      '  GRAPH <http://test.com/container/> { <http://test.com/container/> <http://www.w3.org/ns/ldp#contains> <http://test.com/container/resource>. }',
+      '}',
+    ]));
+  });
+
   it('removes all references when deleting a resource.', async(): Promise<void> => {
     metadata = new RepresentationMetadata('http://test.com/container/',
       { [RDF.type]: [ toNamedNode(LDP.Resource), toNamedNode(LDP.Container) ]});