WebPush support for urgency and coalescing

changelog.d/213.feature

@@ -0,0 +1 @@
+WebPush: add support for Urgency and Topic header

docs/applications.md

@@ -255,7 +255,24 @@ so it can be used to pass identifiers specific to your client
 
 ##### events_only
 
-As of the time of writing, all webpush-supporting browsers require you to set `userVisibleOnly: true` when calling (`pushManager.subscribe`)[https://developer.mozilla.org/en-US/docs/Web/API/PushManager/subscribe], to (prevent abusing webpush to track users)[https://goo.gl/yqv4Q4] without their knowledge. With this (mandatory) flag, the browser will show a "site has been updated in the background" notification if no notifications are visible after your service worker processes a `push` event. This can easily happen when sygnal sends a push message to clear the unread count, which is not specific to an event. With `events_only: true` in the pusher data, sygnal won't forward any push message without a event id. This prevents your service worker being forced to show a notification to push messages that clear the unread count.
+As of the time of writing, all webpush-supporting browsers require you to set 
+`userVisibleOnly: true` when calling (`pushManager.subscribe`)
+[https://developer.mozilla.org/en-US/docs/Web/API/PushManager/subscribe], to 
+(prevent abusing webpush to track users)[https://goo.gl/yqv4Q4] without their 
+knowledge. With this (mandatory) flag, the browser will show a "site has been 
+updated in the background" notification if no notifications are visible after
+your service worker processes a `push` event. This can easily happen when sygnal
+sends a push message to clear the unread count, which is not specific
+to an event. With `events_only: true` in the pusher data, sygnal won't forward
+any push message without a event id. This prevents your service worker being
+forced to show a notification to push messages that clear the unread count.
+
+##### only_last_per_room
+
+You can opt in to only receive the last notification per room by setting
+`only_last_per_room: true` in the push data. Note that if a first notification
+can be delivered before the second one is sent, you will still get both;
+it only has effect for when notifications are queued up on the gateway.
 
 ##### Multiple pushers on one origin
 

sygnal/webpushpushkin.py

@@ -15,6 +15,8 @@
 import json
 import logging
 import os.path
+from base64 import urlsafe_b64encode
+from hashlib import blake2s
 from io import BytesIO
 from typing import List, Optional, Pattern
 from urllib.parse import urlparse
@@ -102,7 +104,7 @@ def __init__(self, name, sygnal, config):
             contextFactory=tls_client_options_factory,
             proxy_url_str=proxy_url,
         )
-        self.http_agent_wrapper = HttpAgentWrapper(self.http_agent)
+        self.http_request_factory = HttpRequestFactory()
 
         self.allowed_endpoints = None  # type: Optional[List[Pattern]]
         allowed_endpoints = self.get_config("allowed_endpoints")
@@ -173,6 +175,17 @@ async def _dispatch_notification_unlimited(self, n, device, context):
         payload = WebpushPushkin._build_payload(n, device)
         data = json.dumps(payload)
 
+        # web push only supports normal and low priority, so assume normal if absent
+        low_priority = n.prio == "low"
+        # allow dropping earlier notifications in the same room if requested
+        topic = None
+        if n.room_id and device.data.get("only_last_per_room") is True:
+            # ask for a 22 byte hash, so the base64 of it is 32,
+            # the limit webpush allows for the topic
+            topic = urlsafe_b64encode(
+                blake2s(n.room_id.encode(), digest_size=22).digest()
+            )
+
         # note that webpush modifies vapid_claims, so make sure it's only used once
         vapid_claims = {
             "sub": "mailto:{}".format(self.vapid_contact_email),
@@ -186,15 +199,17 @@ async def _dispatch_notification_unlimited(self, n, device, context):
         try:
             with SEND_TIME_HISTOGRAM.time():
                 with ACTIVE_REQUESTS_GAUGE.track_inprogress():
-                    response_wrapper = webpush(
+                    request = webpush(
                         subscription_info=subscription_info,
                         data=data,
                         ttl=self.ttl,
                         vapid_private_key=self.vapid_private_key,
                         vapid_claims=vapid_claims,
-                        requests_session=self.http_agent_wrapper,
+                        requests_session=self.http_request_factory,
+                    )
+                    response = await request.execute(
+                        self.http_agent, low_priority, topic
                     )
-                    response = await response_wrapper.deferred
                     response_text = (await readBody(response)).decode()
         finally:
             self.connection_semaphore.release()
@@ -314,14 +329,11 @@ def _handle_response(self, response, response_text, pushkey, endpoint_domain):
         return False
 
 
-class HttpAgentWrapper:
+class HttpRequestFactory:
     """
     Provide a post method that matches the API expected from pywebpush.
     """
 
-    def __init__(self, http_agent):
-        self.http_agent = http_agent
-
     def post(self, endpoint, data, headers, timeout):
         """
         Convert the requests-like API to a Twisted API call.
@@ -336,25 +348,15 @@ def post(self, endpoint, data, headers, timeout):
             timeout (int)
                 Ignored for now
         """
-        body_producer = FileBodyProducer(BytesIO(data))
-        # Convert the headers to the camelcase version.
-        headers = {
-            b"User-Agent": ["sygnal"],
-            b"Content-Encoding": [headers["content-encoding"]],
-            b"Authorization": [headers["authorization"]],
-            b"TTL": [headers["ttl"]],
-        }
-        deferred = self.http_agent.request(
-            b"POST",
-            endpoint.encode(),
-            headers=Headers(headers),
-            bodyProducer=body_producer,
-        )
-        return HttpResponseWrapper(deferred)
+        return HttpDelayedRequest(endpoint, data, headers)
 
 
-class HttpResponseWrapper:
+class HttpDelayedRequest:
     """
+    Captures the values received from pywebpush for the endpoint request.
+    The request isn't immediately executed, to allow adding headers
+    not supported by pywebpush, like Topic and Urgency.
+
     Provide a response object that matches the API expected from pywebpush.
     pywebpush expects a synchronous API, while we use an asynchronous API.
 
@@ -363,8 +365,6 @@ class HttpResponseWrapper:
     in the background.
 
     Attributes:
-        deferred (Deferred):
-            The deferred to await the actual response after calling pywebpush.
         status_code (int):
             Defined to be 200 so the pywebpush check to see if is below 202
             passes.
@@ -375,5 +375,26 @@ class HttpResponseWrapper:
     status_code = 200
     text = None
 
-    def __init__(self, deferred):
-        self.deferred = deferred
+    def __init__(self, endpoint, data, vapid_headers):
+        self.endpoint = endpoint
+        self.data = data
+        self.vapid_headers = vapid_headers
+
+    def execute(self, http_agent, low_priority, topic):
+        body_producer = FileBodyProducer(BytesIO(self.data))
+        # Convert the headers to the camelcase version.
+        headers = {
+            b"User-Agent": ["sygnal"],
+            b"Content-Encoding": [self.vapid_headers["content-encoding"]],
+            b"Authorization": [self.vapid_headers["authorization"]],
+            b"TTL": [self.vapid_headers["ttl"]],
+            b"Urgency": ["low" if low_priority else "normal"],
+        }
+        if topic:
+            headers[b"Topic"] = [topic]
+        return http_agent.request(
+            b"POST",
+            self.endpoint.encode(),
+            headers=Headers(headers),
+            bodyProducer=body_producer,
+        )