fix: resume from reader cursor when no senders configured

In cases where a reader was configured with no senders (eg. only
configured with searches), then in case of reloads/restarts the resume
cursor was assumed `None`, and the default 'initial_position' of 'head'
is fallen back to. This would end up causing all matching searchg to
resend metric events immediately.

journalpump/journalpump.py

@@ -838,7 +838,11 @@ def configure_readers(self):
 
         for reader_name, reader_config in new_config.items():
             reader_state = state.get("readers", {}).get(reader_name, {})
-            resume_cursor = None
+
+            # Default to reader's cursor, in case we have no senders
+            resume_cursor = reader_state.get("cursor")
+
+            # Check sender cursors
             for sender_name, sender in reader_state.get("senders", {}).items():
                 sender_cursor = sender["sent"]["cursor"]
                 if sender_cursor is None:

test/test_journalpump.py

@@ -982,6 +982,52 @@ def test_log_level_filtering(self):
         assert len(sender_d_msgs) == expected_results
 
 
+def test_journalpump_resume_cursor(tmpdir) -> None:
+    journalpump_path = str(tmpdir.join("journalpump.json"))
+    statefile_path = str(tmpdir.join("journalpump_state.json"))
+
+    config = {
+        "json_state_file_path": statefile_path,
+        "readers": {
+            "without_senders": {"senders": {}},
+            "with_sender": {
+                "senders": {
+                    "fake_syslog": {
+                        "output_type": "rsyslog",
+                        "rsyslog_server": "127.0.0.1",
+                        "rsyslog_port": 514,
+                    },
+                }
+            },
+        },
+    }
+
+    state = {
+        "readers": {
+            "without_senders": {
+                "cursor": "reader_cursor",
+            },
+            "with_sender": {
+                "cursor": "reader_cursor",
+                "senders": {"fake_syslog": {"sent": {"cursor": "sender_cursor"}}},
+            },
+        },
+        "start_time": datetime.now().isoformat()
+    }
+
+    with open(journalpump_path, "w") as fp:
+        fp.write(json.dumps(config))
+
+    with open(statefile_path, "w") as fp:
+        fp.write(json.dumps(state))
+
+    pump = JournalPump(journalpump_path)
+
+    # Check that readers are initialized with the right cursors
+    assert pump.readers["without_senders"].cursor == "reader_cursor"
+    assert pump.readers["with_sender"].cursor == "sender_cursor"
+
+
 def test_journalpump_state_file(tmpdir):
     journalpump_path = str(tmpdir.join("journalpump.json"))
     statefile_path = str(tmpdir.join("journalpump_state.json"))