open the file already on creation of the file attacher

otherwise it races against to_disk (the file will be gone / moved)

bndl/net/sendfile.py

@@ -9,17 +9,22 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
 '''
 Adapted from and generalized into a utility outside the web context:
 https://github.com/KeepSafe/aiohttp/blob/72e615b508dc2def975419da1bddc2e3a0970203/aiohttp/web_urldispatcher.py#L439
 '''
 
+from functools import partial
 import asyncio
 import contextlib
+import logging
 import os
 
 from bndl.net import aio
+from bndl.util.exceptions import catch
+
+
+logger = logging.getLogger(__name__)
 
 
 CHUNK_SIZE = 8 * 1024
@@ -34,32 +39,68 @@ def is_remote(data):
 
 
 def file_attachment(filename, offset, size, maybe_local=True):
-    assert hasattr(os, "sendfile")
+    attacher = FileAttacher(filename, offset, size, maybe_local)
+    return attacher.key, attacher
+
 
-    filename = filename.encode('utf-8')
+class FileAttacher(object):
+    def __init__(self, filename, offset, size, maybe_local=True):
+        assert hasattr(os, "sendfile")
+        self.key = filename.encode('utf-8')
+        self.offset = offset
+        self.size = size
+        self.maybe_local = maybe_local
+        self.fd = os.open(filename, os.O_RDONLY)
 
-    @contextlib.contextmanager
-    def _attacher(loop, writer):
-        socket = writer.get_extra_info('socket')
-        if maybe_local and socket.getpeername()[0] in ('::1', '127.0.0.1', socket.getsockname()[0]):
-            @asyncio.coroutine
-            def sender():
-                writer.write(_LOCAL)
-            yield 1, sender
+
+    def __call__(self, loop, writer):
+        self.loop = loop
+        self.writer = writer
+        return self
+
+
+    def __enter__(self):
+        socket = self.writer.get_extra_info('socket')
+        if self.maybe_local and \
+           socket.getpeername()[0] in ('::1', '127.0.0.1', socket.getsockname()[0]):
+            return 1, self.send_local
         else:
-            @asyncio.coroutine
-            def sender():
-                socket = writer.get_extra_info('socket')
-                with open(filename, 'rb') as file:
-                    if maybe_local:
-                        writer.write(_REMOTE)
-                    yield from aio.drain(writer)
-                    socket = socket.dup()
-                    socket.setblocking(False)
-                    yield from sendfile(socket.fileno(), file.fileno(), offset, size, loop)
-            yield size + int(maybe_local), sender
-
-    return filename, _attacher
+            return self.size + int(self.maybe_local), self.send_remote
+
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.close()
+
+
+    def close(self):
+        with catch():
+            os.close(self.fd)
+
+
+    def __del__(self):
+        self.close()
+
+
+    @asyncio.coroutine
+    def send_local(self):
+        self.writer.write(_LOCAL)
+
+
+    @asyncio.coroutine
+    def send_remote(self):
+        try:
+            socket = self.writer.get_extra_info('socket')
+            if self.maybe_local:
+                self.writer.write(_REMOTE)
+            yield from aio.drain(self.writer)
+            socket = socket.dup()
+            socket.setblocking(False)
+            yield from sendfile(socket.fileno(), self.fd,
+                                self.offset, self.size,
+                                self.loop)
+        except:
+            logger.exception('Unable to send file %r', self.key)
+
 
 
 def _sendfile_cb_system(loop, fut, out_fd, in_fd, offset, nbytes, registered):