SSE: add support for retry and comments

src/microdot/sse.py

@@ -17,7 +17,8 @@ class SSE:
         self.event = asyncio.Event()
         self.queue = []
 
-    async def send(self, data, event=None, event_id=None):
+    async def send(self, data, event=None, event_id=None, retry=None,
+                   comment=False):
         """Send an event to the client.
 
         :param data: the data to send. It can be given as a string, bytes, dict
@@ -27,6 +28,12 @@ class SSE:
                       given, it must be a string.
         :param event_id: an optional event id, to send along with the data. If
                       given, it must be a string.
+        :param retry: an optional reconnection time (in seconds) that the
+                      client should use when the connection is lost.
+        :param comment: when set to ``True``, the data is sent as a comment
+                        line, and all other parameters are ignored. This is
+                        useful as a heartbeat mechanism that keeps the
+                        connection alive.
         """
         if isinstance(data, (dict, list)):
             data = json.dumps(data)
@@ -34,11 +41,17 @@ class SSE:
             data = data.encode()
         elif not isinstance(data, bytes):
             data = str(data).encode()
-        data = b'data: ' + data + b'\n\n'
+        if comment:
-        if event_id:
+            data = b': ' + data + b'\n\n'
-            data = b'id: ' + event_id.encode() + b'\n' + data
+        else:
-        if event:
+            data = b'data: ' + data + b'\n\n'
-            data = b'event: ' + event.encode() + b'\n' + data
+            if event_id:
+                data = b'id: ' + event_id.encode() + b'\n' + data
+            if event:
+                data = b'event: ' + event.encode() + b'\n' + data
+            if retry:
+                data = b'retry: ' + str(int(retry * 1000)).encode() + b'\n' + \
+                    data
         self.queue.append(data)
         self.event.set()
 

src/microdot/test_client.py

@@ -78,6 +78,7 @@ class TestResponse:
                     data = None
                     event = None
                     event_id = None
+                    retry = None
                     for line in sse_event.split(b'\n'):
                         if line.startswith(b'data:'):
                             data = line[5:].strip()
@@ -85,6 +86,8 @@ class TestResponse:
                             event = line[6:].strip().decode()
                         elif line.startswith(b'id:'):
                             event_id = line[3:].strip().decode()
+                        elif line.startswith(b'retry:'):
+                            retry = int(line[7:].strip()) / 1000
                     if data:
                         data_json = None
                         try:
@@ -92,8 +95,9 @@ class TestResponse:
                         except ValueError:
                             pass
                         self.events.append({
-                            "data": data, "data_json": data_json,
+                            'data': data, 'data_json': data_json,
-                            "event": event, "event_id": event_id})
+                            'event': event, 'event_id': event_id,
+                            'retry': retry})
 
     @classmethod
     async def create(cls, res):

tests/test_sse.py

@@ -25,7 +25,9 @@ class TestWebSocket(unittest.TestCase):
             await sse.send('bar', event='test')
             await sse.send('bar', event='test', event_id='id42')
             await sse.send('bar', event_id='id42')
+            await sse.send('bar', retry=2.5)
             await sse.send({'foo': 'bar'})
+            await sse.send('ping', comment=True)
             await sse.send([42, 'foo', 'bar'])
             await sse.send(ValueError('foo'))
             await sse.send(b'foo')
@@ -38,35 +40,40 @@ class TestWebSocket(unittest.TestCase):
                                          'event: test\ndata: bar\n\n'
                                          'event: test\nid: id42\ndata: bar\n\n'
                                          'id: id42\ndata: bar\n\n'
+                                         'retry: 2500\ndata: bar\n\n'
                                          'data: {"foo": "bar"}\n\n'
+                                         ': ping\n\n'
                                          'data: [42, "foo", "bar"]\n\n'
                                          'data: foo\n\n'
                                          'data: foo\n\n'))
-        self.assertEqual(len(response.events), 8)
+        self.assertEqual(len(response.events), 9)
         self.assertEqual(response.events[0], {
             'data': b'foo', 'data_json': None, 'event': None,
-            'event_id': None})
+            'event_id': None, "retry": None})
         self.assertEqual(response.events[1], {
             'data': b'bar', 'data_json': None, 'event': 'test',
-            'event_id': None})
+            'event_id': None, "retry": None})
         self.assertEqual(response.events[2], {
             'data': b'bar', 'data_json': None, 'event': 'test',
-            'event_id': 'id42'})
+            'event_id': 'id42', "retry": None})
         self.assertEqual(response.events[3], {
             'data': b'bar', 'data_json': None, 'event': None,
-            'event_id': 'id42'})
+            'event_id': 'id42', "retry": None})
         self.assertEqual(response.events[4], {
-            'data': b'{"foo": "bar"}', 'data_json': {'foo': 'bar'},
+            'data': b'bar', 'data_json': None, 'event': None, 'event_id': None,
-            'event': None, 'event_id': None})
+            'retry': 2.5})
         self.assertEqual(response.events[5], {
-            'data': b'[42, "foo", "bar"]', 'data_json': [42, 'foo', 'bar'],
+            'data': b'{"foo": "bar"}', 'data_json': {'foo': 'bar'},
-            'event': None, 'event_id': None})
+            'event': None, 'event_id': None, "retry": None})
         self.assertEqual(response.events[6], {
-            'data': b'foo', 'data_json': None, 'event': None,
+            'data': b'[42, "foo", "bar"]', 'data_json': [42, 'foo', 'bar'],
-            'event_id': None})
+            'event': None, 'event_id': None, "retry": None})
         self.assertEqual(response.events[7], {
             'data': b'foo', 'data_json': None, 'event': None,
-            'event_id': None})
+            'event_id': None, "retry": None})
+        self.assertEqual(response.events[8], {
+            'data': b'foo', 'data_json': None, 'event': None,
+            'event_id': None, "retry": None})
 
     def test_sse_exception(self):
         app = Microdot()