streams: Add endpoint "GET /streams/{stream_id}" to get stream by id.

Fixes #22082.

templates/zerver/api/changelog.md

@@ -20,6 +20,11 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 6.0
 
+**Feature level 132**
+
+* [`GET /streams/{stream_id}`](/api/get-stream-by-id):
+  Added new endpoint to get a stream by ID.
+
 **Feature level 131**
 
 * [`GET /user_groups`](/api/get-user-groups),[`POST

templates/zerver/help/include/rest-endpoints.md

@@ -31,6 +31,7 @@
 * [Get all subscribers](/api/get-subscribers)
 * [Update subscription settings](/api/update-subscription-settings)
 * [Get all streams](/api/get-streams)
+* [Get a stream by ID](/api/get-stream-by-id)
 * [Get stream ID](/api/get-stream-id)
 * [Create a stream](/api/create-stream)
 * [Update a stream](/api/update-stream)

version.py

@@ -33,7 +33,7 @@ DESKTOP_WARNING_VERSION = "5.4.3"
 # Changes should be accompanied by documentation explaining what the
 # new level means in templates/zerver/api/changelog.md, as well as
 # "**Changes**" entries in the endpoint's documentation in `zulip.yaml`.
-API_FEATURE_LEVEL = 131
+API_FEATURE_LEVEL = 132
 
 # Bump the minor PROVISION_VERSION to indicate that folks should provision
 # only when going from an old version of the code to a newer version. Bump

zerver/openapi/zulip.yaml

@@ -13428,6 +13428,67 @@ paths:
                       `include_all_active` parameter (i.e. because they are not an organization
                       administrator):
   /streams/{stream_id}:
+    get:
+      operationId: get-stream-by-id
+      summary: Get a stream by ID
+      tags: ["streams"]
+      description: |
+        Fetch details for the stream with the ID `stream_id`.
+
+        `GET {{ api_url }}/v1/streams/{stream_id}`
+
+        **Changes**: New in Zulip 6.0 (feature level 132).
+      parameters:
+        - $ref: "#/components/parameters/StreamIdInPath"
+      responses:
+        "200":
+          description: Success.
+          content:
+            application/json:
+              schema:
+                allOf:
+                  - $ref: "#/components/schemas/JsonSuccessBase"
+                  - $ref: "#/components/schemas/SuccessDescription"
+                  - additionalProperties: false
+                    properties:
+                      result: {}
+                      msg: {}
+                      stream:
+                        $ref: "#/components/schemas/BasicStream"
+                    example:
+                      {
+                        "msg": "",
+                        "result": "success",
+                        "stream":
+                          {
+                            "description": "A Scandinavian country",
+                            "first_message_id": 1,
+                            "history_public_to_subscribers": True,
+                            "invite_only": False,
+                            "is_announcement_only": False,
+                            "is_web_public": False,
+                            "message_retention_days": null,
+                            "name": "Denmark",
+                            "rendered_description": "<p>A Scandinavian country</p>",
+                            "stream_id": 7,
+                            "stream_post_policy": 1,
+                          },
+                      }
+        "400":
+          description: Bad request.
+          content:
+            application/json:
+              schema:
+                allOf:
+                  - $ref: "#/components/schemas/CodedError"
+                  - example:
+                      {
+                        "code": "BAD_REQUEST",
+                        "msg": "Invalid stream id",
+                        "result": "error",
+                      }
+                    description: |
+                      An example JSON response for when the stream ID is not valid.
     delete:
       operationId: archive-stream
       summary: Archive a stream

zerver/tests/test_decorators.py

@@ -1983,7 +1983,7 @@ class RestAPITest(ZulipTestCase):
 
         result = self.client_options("/json/streams/15")
         self.assertEqual(result.status_code, 204)
-        self.assertEqual(str(result["Allow"]), "DELETE, PATCH")
+        self.assertEqual(str(result["Allow"]), "DELETE, GET, HEAD, PATCH")
 
     def test_http_accept_redirect(self) -> None:
         result = self.client_get("/json/users", HTTP_ACCEPT="text/html")

zerver/tests/test_subs.py

@@ -5457,6 +5457,40 @@ class GetStreamsTest(ZulipTestCase):
         ]
         self.assertEqual(sorted(s["name"] for s in json["streams"]), sorted(all_streams))
 
+    def test_get_single_stream_api(self) -> None:
+        self.login("hamlet")
+        realm = get_realm("zulip")
+        denmark_stream = get_stream("Denmark", realm)
+        result = self.client_get(f"/json/streams/{denmark_stream.id}")
+        self.assert_json_success(result)
+        json = result.json()
+        self.assertEqual(json["stream"]["name"], "Denmark")
+        self.assertEqual(json["stream"]["stream_id"], denmark_stream.id)
+
+        result = self.client_get("/json/streams/9999")
+        self.assert_json_error(result, "Invalid stream id")
+
+        private_stream = self.make_stream("private_stream", invite_only=True)
+        self.subscribe(self.example_user("cordelia"), "private_stream")
+
+        # Non-admins cannot access unsubscribed private streams.
+        result = self.client_get(f"/json/streams/{private_stream.id}")
+        self.assert_json_error(result, "Invalid stream id")
+
+        self.login("iago")
+        result = self.client_get(f"/json/streams/{private_stream.id}")
+        self.assert_json_success(result)
+        json = result.json()
+        self.assertEqual(json["stream"]["name"], "private_stream")
+        self.assertEqual(json["stream"]["stream_id"], private_stream.id)
+
+        self.login("cordelia")
+        result = self.client_get(f"/json/streams/{private_stream.id}")
+        self.assert_json_success(result)
+        json = result.json()
+        self.assertEqual(json["stream"]["name"], "private_stream")
+        self.assertEqual(json["stream"]["stream_id"], private_stream.id)
+
 
 class StreamIdTest(ZulipTestCase):
     def test_get_stream_id(self) -> None:

zerver/views/streams.py

@@ -754,6 +754,16 @@ def get_streams_backend(
     return json_success(request, data={"streams": streams})
 
 
+@has_request_variables
+def get_stream_backend(
+    request: HttpRequest,
+    user_profile: UserProfile,
+    stream_id: int,
+) -> HttpResponse:
+    (stream, sub) = access_stream_by_id(user_profile, stream_id, allow_realm_admin=True)
+    return json_success(request, data={"stream": stream.to_dict()})
+
+
 @has_request_variables
 def get_topics_backend(
     request: HttpRequest,

zproject/urls.py

@@ -145,6 +145,7 @@ from zerver.views.streams import (
     create_default_stream_group,
     deactivate_stream_backend,
     delete_in_topic,
+    get_stream_backend,
     get_streams_backend,
     get_subscribers_backend,
     get_topics_backend,
@@ -443,7 +444,10 @@ v1_api_and_json_patterns = [
     # GET returns "stream info" (undefined currently?), HEAD returns whether stream exists (200 or 404)
     rest_path("streams/<int:stream_id>/members", GET=get_subscribers_backend),
     rest_path(
-        "streams/<int:stream_id>", PATCH=update_stream_backend, DELETE=deactivate_stream_backend
+        "streams/<int:stream_id>",
+        GET=get_stream_backend,
+        PATCH=update_stream_backend,
+        DELETE=deactivate_stream_backend,
     ),
     # Delete topic in stream
     rest_path("streams/<int:stream_id>/delete_topic", POST=delete_in_topic),