views: detect if input stream was already read

* In the case of having an external library which has already
  read the `request.stream` files REST fails with a server error
  since it will not be able to read the uploaded file (closes #197).

  This has happened with Sentry's `raven-python` library which
  reads the stream when the mimetype is `application/json` causing
  JSON files uploads to not work and throwing a misleading error.
  More here
  https://github.com/getsentry/raven-python/blob/719be9afae528962e683d086f9c2ceeda07f881b/raven/contrib/flask.py#L198

invenio_files_rest/views.py

@@ -267,6 +267,16 @@ def inner(self, bucket, key, upload_id, *args, **kwargs):
     return decorate
 
 
+def ensure_input_stream_is_not_exhausted(f):
+    """Make sure that the input stream has not been read already."""
+    @wraps(f)
+    def decorate(*args, **kwargs):
+        if request.content_length and request.stream.is_exhausted:
+            abort(500)
+        return f(*args, **kwargs)
+    return decorate
+
+
 #
 # Permission checking
 #
@@ -797,6 +807,7 @@ def get(self, bucket=None, key=None, version_id=None, upload_id=None,
     @use_kwargs(post_args)
     @pass_bucket
     @need_bucket_permission('bucket-update')
+    @ensure_input_stream_is_not_exhausted
     def post(self, bucket=None, key=None, uploads=missing, upload_id=None):
         """Upload a new object or start/complete a multipart upload.
 
@@ -815,6 +826,7 @@ def post(self, bucket=None, key=None, uploads=missing, upload_id=None):
     @use_kwargs(put_args)
     @pass_bucket
     @need_bucket_permission('bucket-update')
+    @ensure_input_stream_is_not_exhausted
     def put(self, bucket=None, key=None, upload_id=None):
         """Update a new object or upload a part of a multipart upload.
 

tests/test_views_multipart.py

@@ -543,3 +543,33 @@ def test_get_listuploads(client, db, bucket, multipart, multipart_url,
             bucket_id=str(bucket.id),
         ) + '?uploads')
         assert res.status_code == expected
+
+
+def test_already_exhausted_input_stream(app, client, db, bucket, admin_user):
+    """Test server error when file stream is already read."""
+    key = 'test.json'
+    data = b'{"json": "file"}'
+    object_url = url_for(
+        'invenio_files_rest.object_api', bucket_id=bucket.id, key=key)
+    # Add a new before request hook which reads the incoming request payload.
+    # This simulates what happens when Sentry's raven-python library when it
+    # reads the JSON payloads, breaking the upload of JSON files
+    # (`application/json`).
+
+    def consume_request_input_stream(*args):
+        """Reads input stream object."""
+        from flask import request
+        request.data
+
+    app.before_request(consume_request_input_stream)
+    login_user(client, admin_user)
+    resp = client.put(
+        object_url,
+        input_stream=BytesIO(data),
+    )
+    assert resp.status_code == 500
+    resp = client.post(
+        object_url,
+        input_stream=BytesIO(data),
+    )
+    assert resp.status_code == 500