Patch safekeeper control file on HTTP request (#6455)

Closes #6397

test_runner/fixtures/neon_fixtures.py

@@ -3443,6 +3443,24 @@ class SafekeeperHttpClient(requests.Session):
         assert isinstance(res_json, dict)
         return res_json
 
+    def patch_control_file(
+        self,
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+        patch: Dict[str, Any],
+    ) -> Dict[str, Any]:
+        res = self.patch(
+            f"http://localhost:{self.port}/v1/tenant/{tenant_id}/timeline/{timeline_id}/control_file",
+            json={
+                "updates": patch,
+                "apply_fields": list(patch.keys()),
+            },
+        )
+        res.raise_for_status()
+        res_json = res.json()
+        assert isinstance(res_json, dict)
+        return res_json
+
     def pull_timeline(self, body: Dict[str, Any]) -> Dict[str, Any]:
         res = self.post(f"http://localhost:{self.port}/v1/pull_timeline", json=body)
         res.raise_for_status()

test_runner/regress/test_wal_acceptor.py

@@ -1946,3 +1946,51 @@ def test_timeline_copy(neon_env_builder: NeonEnvBuilder, insert_rows: int):
             assert orig_digest == new_digest
 
     # TODO: test timelines can start after copy
+
+
+def test_patch_control_file(neon_env_builder: NeonEnvBuilder):
+    neon_env_builder.num_safekeepers = 1
+    env = neon_env_builder.init_start()
+
+    tenant_id = env.initial_tenant
+    timeline_id = env.initial_timeline
+
+    endpoint = env.endpoints.create_start("main")
+    # initialize safekeeper
+    endpoint.safe_psql("create table t(key int, value text)")
+
+    # update control file
+    res = (
+        env.safekeepers[0]
+        .http_client()
+        .patch_control_file(
+            tenant_id,
+            timeline_id,
+            {
+                "timeline_start_lsn": "0/1",
+            },
+        )
+    )
+
+    timeline_start_lsn_before = res["old_control_file"]["timeline_start_lsn"]
+    timeline_start_lsn_after = res["new_control_file"]["timeline_start_lsn"]
+
+    log.info(f"patch_control_file response: {res}")
+    log.info(
+        f"updated control file timeline_start_lsn, before {timeline_start_lsn_before}, after {timeline_start_lsn_after}"
+    )
+
+    assert timeline_start_lsn_after == "0/1"
+    env.safekeepers[0].stop().start()
+
+    # wait/check that safekeeper is alive
+    endpoint.safe_psql("insert into t values (1, 'payload')")
+
+    # check that timeline_start_lsn is updated
+    res = (
+        env.safekeepers[0]
+        .http_client()
+        .debug_dump({"dump_control_file": "true", "timeline_id": str(timeline_id)})
+    )
+    log.info(f"dump_control_file response: {res}")
+    assert res["timelines"][0]["control_file"]["timeline_start_lsn"] == "0/1"