Merge bitcoin/bitcoin#22112: Force port 0 in I2P

4101ec9d2e doc: mention that we enforce port=0 in I2P (Vasil Dimov)
e0a2b390c1 addrman: reset I2P ports to 0 when loading from disk (Vasil Dimov)
41cda9d075 test: ensure I2P ports are handled as expected (Vasil Dimov)
4f432bd738 net: do not connect to I2P hosts on port!=0 (Vasil Dimov)
1f096f091e net: distinguish default port per network (Vasil Dimov)
aeac3bce3e net: change I2P seeds' ports to 0 (Vasil Dimov)
38f900290c net: change assumed I2P port to 0 (Vasil Dimov)

Pull request description:

  _This is an alternative to https://github.com/bitcoin/bitcoin/pull/21514, inspired by https://github.com/bitcoin/bitcoin/pull/21514#issuecomment-815049933. They are mutually exclusive. Just one of them should be merged._

  Change assumed ports for I2P to 0 (instead of the default 8333) as this is closer to what actually happens underneath with SAM 3.1 (https://github.com/bitcoin/bitcoin/pull/21514#issuecomment-812632520, https://github.com/bitcoin/bitcoin/pull/21514#issuecomment-816564719).

  Don't connect to I2P peers with advertised port != 0 (we don't specify a port to our SAM 3.1 proxy and it always connects to port = 0).

  Note, this change:
  * Keeps I2P addresses with port != 0 in addrman and relays them to others via P2P gossip. There may be non-bitcoin-core-22.0 peers using SAM 3.2 and for them such addresses may be useful.
  * Silently refuses to connect to I2P hosts with port != 0. This is ok for automatically chosen peers from addrman. Not so ok for peers provided via `-addnode` or `-connect` - a user who specifies `foo.b32.i2p:1234` (non zero port) may wonder why "nothing is happening".

  Fixes #21389

ACKs for top commit:
  laanwj:
    Code review ACK 4101ec9d2e
  jonatack:
    re-ACK 4101ec9d2e per `git range-diff efff9c3 0b0ee03 4101ec9`, built with DDEBUG_ADDRMAN, did fairly extensive testing on mainnet both with and without a peers.dat / -dnsseeds=0 to test boostrapping.

Tree-SHA512: 0e3c019e1dc05e54f559275859d3450e0c735596d179e30b66811aad9d5b5fabe3dcc44571e8f7b99f9fe16453eee393d6e153454dd873b9ff14907d4e6354fe

test/functional/p2p_i2p_ports.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+# Copyright (c) 2021-2021 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 ports handling for I2P hosts
+"""
+
+import re
+
+from test_framework.test_framework import BitcoinTestFramework
+
+
+class I2PPorts(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 1
+        # The test assumes that an I2P SAM proxy is not listening here.
+        self.extra_args = [["-i2psam=127.0.0.1:60000"]]
+
+    def run_test(self):
+        node = self.nodes[0]
+
+        self.log.info("Ensure we don't try to connect if port!=0")
+        addr = "zsxwyo6qcn3chqzwxnseusqgsnuw3maqnztkiypyfxtya4snkoka.b32.i2p:8333"
+        raised = False
+        try:
+            with node.assert_debug_log(expected_msgs=[f"Error connecting to {addr}"]):
+                node.addnode(node=addr, command="onetry")
+        except AssertionError as e:
+            raised = True
+            if not re.search(r"Expected messages .* does not partially match log", str(e)):
+                raise AssertionError(f"Assertion raised as expected, but with an unexpected message: {str(e)}")
+        if not raised:
+            raise AssertionError("Assertion should have been raised")
+
+        self.log.info("Ensure we try to connect if port=0 and get an error due to missing I2P proxy")
+        addr = "h3r6bkn46qxftwja53pxiykntegfyfjqtnzbm6iv6r5mungmqgmq.b32.i2p:0"
+        with node.assert_debug_log(expected_msgs=[f"Error connecting to {addr}"]):
+            node.addnode(node=addr, command="onetry")
+
+
+if __name__ == '__main__':
+    I2PPorts().main()

test/functional/test_runner.py

@@ -293,6 +293,7 @@ BASE_SCRIPTS = [
     'p2p_permissions.py',
     'feature_blocksdir.py',
     'wallet_startup.py',
+    'p2p_i2p_ports.py',
     'feature_config_args.py',
     'feature_settings.py',
     'rpc_getdescriptorinfo.py',