Respond with 409 when creating duplicate asset blobs

dandiapi/api/tests/test_upload.py

@@ -524,16 +524,10 @@ def test_upload_validate_wrong_etag(api_client, user, upload):
 def test_upload_validate_existing_assetblob(api_client, user, upload, asset_blob_factory):
     api_client.force_authenticate(user=user)
 
-    asset_blob = asset_blob_factory(etag=upload.etag, size=upload.size)
+    asset_blob_factory(etag=upload.etag, size=upload.size)
 
     resp = api_client.post(f'/api/uploads/{upload.upload_id}/validate/')
-    assert resp.status_code == 200
-    assert resp.data == {
-        'blob_id': str(asset_blob.blob_id),
-        'etag': asset_blob.etag,
-        'sha256': asset_blob.sha256,
-        'size': asset_blob.size,
-    }
+    assert resp.status_code == 409
 
     assert AssetBlob.objects.all().count() == 1
     assert not Upload.objects.all().exists()
@@ -549,16 +543,10 @@ def test_upload_validate_embargo_existing_assetblob(
     embargoed_upload = embargoed_upload_factory(dandiset=dandiset)
 
     # The upload should recognize this preexisting AssetBlob and use it instead
-    asset_blob = asset_blob_factory(etag=embargoed_upload.etag, size=embargoed_upload.size)
+    asset_blob_factory(etag=embargoed_upload.etag, size=embargoed_upload.size)
 
     resp = api_client.post(f'/api/uploads/{embargoed_upload.upload_id}/validate/')
-    assert resp.status_code == 200
-    assert resp.data == {
-        'blob_id': str(asset_blob.blob_id),
-        'etag': asset_blob.etag,
-        'sha256': asset_blob.sha256,
-        'size': asset_blob.size,
-    }
+    assert resp.status_code == 409
 
     assert AssetBlob.objects.all().count() == 1
 
@@ -574,17 +562,9 @@ def test_upload_validate_embargo_existing_embargoed_assetblob(
 
     # The upload should recognize this preexisting embargoed AssetBlob and use it instead
     # This only works because the embargoed asset blob belongs to the same dandiset
-    embargoed_asset_blob = embargoed_asset_blob_factory(
-        etag=embargoed_upload.etag, size=embargoed_upload.size
-    )
+    embargoed_asset_blob_factory(etag=embargoed_upload.etag, size=embargoed_upload.size)
 
     resp = api_client.post(f'/api/uploads/{embargoed_upload.upload_id}/validate/')
-    assert resp.status_code == 200
-    assert resp.data == {
-        'blob_id': str(embargoed_asset_blob.blob_id),
-        'etag': embargoed_asset_blob.etag,
-        'sha256': embargoed_asset_blob.sha256,
-        'size': embargoed_asset_blob.size,
-    }
+    assert resp.status_code == 409
 
     assert AssetBlob.objects.all().count() == 1

dandiapi/api/views/upload.py

@@ -240,23 +240,26 @@ def upload_validate_view(request: Request, upload_id: str) -> HttpResponseBase:
             f'ETag {upload.etag} does not match actual ETag {upload.actual_etag()}.'
         )
 
-    # Use a transaction here so we can use select_for_update to lock the DB rows to avoid
-    # a race condition where two clients are uploading the same blob at the same time.
-    # This also ensures that the minting of the new AssetBlob and deletion of the Upload
-    # is an atomic operation.
     with transaction.atomic():
-        try:
-            # Perhaps another upload completed before this one and has already created an AssetBlob.
-            asset_blob = AssetBlob.objects.select_for_update(no_key=True).get(
-                etag=upload.etag, size=upload.size
-            )
-        except AssetBlob.DoesNotExist:
-            asset_blob = upload.to_asset_blob()
-            asset_blob.save()
+        # Avoid a race condition where two clients are uploading the same blob at the same time.
+        asset_blob, created = AssetBlob.objects.get_or_create(
+            etag=upload.etag,
+            size=upload.size,
+            defaults={
+                'embargoed': upload.embargoed,
+                'blob_id': upload.upload_id,
+                'blob': upload.blob,
+            },
+        )
 
         # Clean up the upload
         upload.delete()
 
+    if not created:
+        return Response(
+            'An identical blob has already been uploaded.', status=status.HTTP_409_CONFLICT
+        )
+
     # Start calculating the sha256 in the background
     calculate_sha256.delay(asset_blob.blob_id)