don't hang when asked to send a zero-length file

closes #98

src/wormhole/cli/cmd_send.py

@@ -290,8 +290,10 @@ class Sender:
 
         with self._timing.add("tx file"):
             with progress:
-                yield fs.beginFileTransfer(self._fd_to_send, record_pipe,
+                if filesize:
-                                           transform=_count_and_hash)
+                    # don't send zero-length files
+                    yield fs.beginFileTransfer(self._fd_to_send, record_pipe,
+                                               transform=_count_and_hash)
 
         expected_hash = hasher.digest()
         expected_hex = bytes_to_hexstr(expected_hash)

src/wormhole/test/test_scripts.py

@@ -239,7 +239,7 @@ class PregeneratedCode(ServerBase, ScriptsBase, unittest.TestCase):
     def _do_test(self, as_subprocess=False,
                  mode="text", addslash=False, override_filename=False,
                  fake_tor=False):
-        assert mode in ("text", "file", "directory", "slow-text")
+        assert mode in ("text", "file", "empty-file", "directory", "slow-text")
         if fake_tor:
             assert not as_subprocess
         send_cfg = config("send")
@@ -260,10 +260,12 @@ class PregeneratedCode(ServerBase, ScriptsBase, unittest.TestCase):
         receive_dir = self.mktemp()
         os.mkdir(receive_dir)
 
-        if mode == "text" or mode == "slow-text":
+        if mode in ("text", "slow-text"):
             send_cfg.text = message
 
-        elif mode == "file":
+        elif mode in ("file", "empty-file"):
+            if mode == "empty-file":
+                message = ""
             send_filename = "testfile"
             with open(os.path.join(send_dir, send_filename), "w") as f:
                 f.write(message)
@@ -503,6 +505,8 @@ class PregeneratedCode(ServerBase, ScriptsBase, unittest.TestCase):
         return self._do_test(mode="file", override_filename=True)
     def test_file_tor(self):
         return self._do_test(mode="file", fake_tor=True)
+    def test_empty_file(self):
+        return self._do_test(mode="empty-file")
 
     def test_directory(self):
         return self._do_test(mode="directory")

src/wormhole/transit.py

@@ -374,7 +374,8 @@ class Connection(protocol.Protocol, policies.TimeoutMixin):
         least that number of bytes have been written. This function will then
         return a Deferred (that fires with the number of bytes actually
         received). If the connection is lost while this Deferred is
-        outstanding, it will errback.
+        outstanding, it will errback. If 'expected' is 0, the Deferred will
+        fire right away.
 
         If 'expected' is None, then this function returns None instead of a
         Deferred, and you must call disconnectConsumer() when you are done."""
@@ -402,6 +403,9 @@ class Connection(protocol.Protocol, policies.TimeoutMixin):
         if expected is not None:
             d = defer.Deferred()
         self._consumer_deferred = d
+        if expected == 0:
+            # write empty record to kick consumer into shutdown
+            self._writeToConsumer(b"")
         # drain any pending records
         while self._consumer and self._inbound_records:
             r = self._inbound_records.popleft()
@@ -428,6 +432,7 @@ class Connection(protocol.Protocol, policies.TimeoutMixin):
     # optional callable which will be called on each write (with the number
     # of bytes written). Returns a Deferred that fires (with the number of
     # bytes written) when the count is reached or the RecordPipe is closed.
+
     def writeToFile(self, f, expected, progress=None, hasher=None):
         fc = FileConsumer(f, progress, hasher)
         return self.connectConsumer(fc, expected)