Merge bitcoin/bitcoin#30362: test: p2p: check that connecting to ourself leads to disconnect

5d2fb14baf test: p2p: check that connecting to ourself leads to disconnect (Sebastian Falbesoner)

Pull request description:

  This small PR adds test coverage for the scenario of connecting to ourself, leading to an immediate disconnect:
  2f6dca4d1c/src/net_processing.cpp (L3729-L3735)

  This logic has been first introduced by Satoshi in October 2009, together with a couple of other changes and a version bump to "v0.1.6 BETA" (see commit cc0b4c3b62).

ACKs for top commit:
  kevkevinpal:
    tACK [5d2fb14](5d2fb14baf)
  maflcko:
    ACK 5d2fb14baf
  fjahr:
    tACK 5d2fb14baf
  tdb3:
    ACK 5d2fb14baf

Tree-SHA512: 30fb8c82cef94701affeca386ecd59daa32231635fa770fe225feb69fdab2ffedbfa157edd563f65099ec209f2dafffc1154f7f9292c2ea68bbd114750904875

test/functional/p2p_handshake.py

@@ -17,6 +17,7 @@ from test_framework.messages import (
     NODE_WITNESS,
 )
 from test_framework.p2p import P2PInterface
+from test_framework.util import p2p_port
 
 
 # Desirable service flags for outbound non-pruned and pruned peers. Note that
@@ -88,6 +89,12 @@ class P2PHandshakeTest(BitcoinTestFramework):
         with node.assert_debug_log([f"feeler connection completed"]):
             self.add_outbound_connection(node, "feeler", NODE_NONE, wait_for_disconnect=True)
 
+        self.log.info("Check that connecting to ourself leads to immediate disconnect")
+        with node.assert_debug_log(["connected to self", "disconnecting"]):
+            node_listen_addr = f"127.0.0.1:{p2p_port(0)}"
+            node.addconnection(node_listen_addr, "outbound-full-relay", self.options.v2transport)
+        self.wait_until(lambda: len(node.getpeerinfo()) == 0)
+
 
 if __name__ == '__main__':
     P2PHandshakeTest().main()