Fix url_verification error with the Flask adapter (#543)

Author: seratch

examples/app_authorize.py

@@ -39,4 +39,4 @@ def event_test(body, say, logger):
 # pip install slack_bolt
 # export SLACK_SIGNING_SECRET=***
 # export MY_TOKEN=xoxb-***
-# python app.py
+# python app_authorize.py

examples/async_app.py

@@ -32,4 +32,4 @@ async def command(ack, body):
 # pip install slack_bolt
 # export SLACK_SIGNING_SECRET=***
 # export SLACK_BOT_TOKEN=xoxb-***
-# python app.py
+# python async_app.py

slack_bolt/adapter/flask/handler.py

@@ -17,6 +17,9 @@ def to_bolt_request(req: Request) -> BoltRequest:
 def to_flask_response(bolt_resp: BoltResponse) -> Response:
     resp: Response = make_response(bolt_resp.body, bolt_resp.status)
     for k, values in bolt_resp.headers.items():
+        if k.lower() == "content-type" and resp.headers.get("content-type") is not None:
+            # Remove the one set by Flask
+            resp.headers.pop("content-type")
         for v in values:
             resp.headers.add_header(k, v)
     return resp

tests/adapter_tests/flask/test_flask.py

@@ -99,6 +99,7 @@ def endpoint():
                 headers=self.build_headers(timestamp, body),
             )
             assert rv.status_code == 200
+            assert rv.headers.get("content-type") == "text/plain;charset=utf-8"
             assert_auth_test_count(self, 1)
 
     def test_shortcuts(self):
@@ -142,6 +143,7 @@ def endpoint():
                 headers=self.build_headers(timestamp, body),
             )
             assert rv.status_code == 200
+            assert rv.headers.get("content-type") == "text/plain;charset=utf-8"
             assert_auth_test_count(self, 1)
 
     def test_commands(self):
@@ -185,6 +187,7 @@ def endpoint():
                 headers=self.build_headers(timestamp, body),
             )
             assert rv.status_code == 200
+            assert rv.headers.get("content-type") == "text/plain;charset=utf-8"
             assert_auth_test_count(self, 1)
 
     def test_oauth(self):
@@ -205,4 +208,35 @@ def endpoint():
 
         with flask_app.test_client() as client:
             rv = client.get("/slack/install")
+            assert rv.headers.get("content-type") == "text/html; charset=utf-8"
             assert rv.status_code == 200
+
+    def test_url_verification(self):
+        app = App(
+            client=self.web_client,
+            signing_secret=self.signing_secret,
+        )
+
+        input = {
+            "token": "Jhj5dZrVaK7ZwHHjRyZWjbDl",
+            "challenge": "3eZbrw1aBm2rZgRNFdxV2595E9CY3gmdALWMmHkvFXO7tYXAYM8P",
+            "type": "url_verification",
+        }
+
+        timestamp, body = str(int(time())), f"payload={quote(json.dumps(input))}"
+
+        flask_app = Flask(__name__)
+
+        @flask_app.route("/slack/events", methods=["POST"])
+        def endpoint():
+            return SlackRequestHandler(app).handle(request)
+
+        with flask_app.test_client() as client:
+            rv = client.post(
+                "/slack/events",
+                data=body,
+                headers=self.build_headers(timestamp, body),
+            )
+            assert rv.status_code == 200
+            assert rv.headers.get("content-type") == "application/json;charset=utf-8"
+            assert_auth_test_count(self, 1)