Merge bitcoin/bitcoin#31223: net, init: derive default onion port if a user specified a -port

1dd3af8fbc Add release note for #31223 (Martin Zumsande)
997757dd2b test: add functional test for -port behavior (Martin Zumsande)
0e2b12b92a net, init: derive default onion port if a user specified a -port (Martin Zumsande)

Pull request description:

  This resolves #31133 (setups with multiple local nodes each using a different `-port` no longer working with v28.0, see the issue description for more details) by deriving the default onion listening port to be the value specified by `-port` incremented by 1 (idea by vasild / laanwj).
  Note that with this fix, the chosen `-port` values of two local nodes cannot be adjacent, otherwise there will be port collisions again.

  From the discussion in the linked issue, this was the most popular option, followed by doing nothing and telling affected users to change their setups to use `-bind` instead of `-port`. But more opinions are certainly welcome!

  I think that if we decide to do something about the problem described in the issue, we should do so soon (in 28.1.), so I opened this PR.
  Fixes #31133

ACKs for top commit:
  achow101:
    ACK 1dd3af8fbc
  laanwj:
    Tested ACK 1dd3af8fbc
  tdb3:
    Code review ACK 1dd3af8fbc

Tree-SHA512: 37fda2b23bbedcab5df3a401cf5afce66ae5318fb78f9660f83e3fd075b528e8156d7a0903f9a12ffe97ab5d83860587116b74af28670a1f4c2f0d1be4999f40

test/functional/feature_port.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+# Copyright (c) 2024-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""
+Test the -port option and its interactions with
+-bind.
+"""
+
+from test_framework.test_framework import (
+    BitcoinTestFramework,
+)
+from test_framework.util import (
+    p2p_port,
+)
+
+
+class PortTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        # Avoid any -bind= on the command line.
+        self.bind_to_localhost_only = False
+        self.num_nodes = 1
+
+    def run_test(self):
+        node = self.nodes[0]
+        node.has_explicit_bind = True
+        port1 = p2p_port(self.num_nodes)
+        port2 = p2p_port(self.num_nodes + 5)
+
+        self.log.info("When starting with -port, bitcoind binds to it and uses port + 1 for an onion bind")
+        with node.assert_debug_log(expected_msgs=[f'Bound to 0.0.0.0:{port1}', f'Bound to 127.0.0.1:{port1 + 1}']):
+            self.restart_node(0, extra_args=["-listen", f"-port={port1}"])
+
+        self.log.info("When specifying -port multiple times, only the last one is taken")
+        with node.assert_debug_log(expected_msgs=[f'Bound to 0.0.0.0:{port2}', f'Bound to 127.0.0.1:{port2 + 1}'], unexpected_msgs=[f'Bound to 0.0.0.0:{port1}']):
+            self.restart_node(0, extra_args=["-listen", f"-port={port1}", f"-port={port2}"])
+
+        self.log.info("When specifying ports with both -port and -bind, the one from -port is ignored")
+        with node.assert_debug_log(expected_msgs=[f'Bound to 0.0.0.0:{port2}'], unexpected_msgs=[f'Bound to 0.0.0.0:{port1}']):
+            self.restart_node(0, extra_args=["-listen", f"-port={port1}", f"-bind=0.0.0.0:{port2}"])
+
+        self.log.info("When -bind specifies no port, the values from -port and -bind are combined")
+        with self.nodes[0].assert_debug_log(expected_msgs=[f'Bound to 0.0.0.0:{port1}']):
+            self.restart_node(0, extra_args=["-listen", f"-port={port1}", "-bind=0.0.0.0"])
+
+        self.log.info("When an onion bind specifies no port, the value from -port, incremented by 1, is taken")
+        with self.nodes[0].assert_debug_log(expected_msgs=[f'Bound to 127.0.0.1:{port1 + 1}']):
+            self.restart_node(0, extra_args=["-listen", f"-port={port1}", "-bind=127.0.0.1=onion"])
+
+        self.log.info("Invalid values for -port raise errors")
+        self.stop_node(0)
+        node.extra_args = ["-listen", "-port=65536"]
+        node.assert_start_raises_init_error(expected_msg="Error: Invalid port specified in -port: '65536'")
+        node.extra_args = ["-listen", "-port=0"]
+        node.assert_start_raises_init_error(expected_msg="Error: Invalid port specified in -port: '0'")
+
+
+if __name__ == '__main__':
+    PortTest(__file__).main()

test/functional/test_framework/test_node.py

@@ -221,10 +221,9 @@ class TestNode():
             extra_args = self.extra_args
 
         # If listening and no -bind is given, then bitcoind would bind P2P ports on
-        # 0.0.0.0:P and 127.0.0.1:18445 (for incoming Tor connections), where P is
+        # 0.0.0.0:P and 127.0.0.1:P+1 (for incoming Tor connections), where P is
         # a unique port chosen by the test framework and configured as port=P in
-        # bitcoin.conf. To avoid collisions on 127.0.0.1:18445, change it to
-        # 127.0.0.1:tor_port().
+        # bitcoin.conf. To avoid collisions, change it to 127.0.0.1:tor_port().
         will_listen = all(e != "-nolisten" and e != "-listen=0" for e in extra_args)
         has_explicit_bind = self.has_explicit_bind or any(e.startswith("-bind=") for e in extra_args)
         if will_listen and not has_explicit_bind:

test/functional/test_runner.py

@@ -341,6 +341,7 @@ BASE_SCRIPTS = [
     'feature_minchainwork.py',
     'rpc_estimatefee.py',
     'rpc_getblockstats.py',
+    'feature_port.py',
     'feature_bind_port_externalip.py',
     'wallet_create_tx.py --legacy-wallet',
     'wallet_send.py --legacy-wallet',