net: only add all addresses if listening on any

If `-bind=` is provided then we would bind only to a particular address
and should not add all the other addresses of the machine to the list of
local addresses.

Fixes bitcoin#20184 (case 4.)

src/init.cpp

@@ -1918,8 +1918,6 @@ bool AppInitMain(const util::Ref& context, NodeContext& node, interfaces::BlockA
     }
     LogPrintf("nBestHeight = %d\n", chain_active_height);
 
-    Discover();
-
     // Map ports with UPnP
     if (args.GetBoolArg("-upnp", DEFAULT_UPNP)) {
         StartMapPort();
@@ -1988,6 +1986,12 @@ bool AppInitMain(const util::Ref& context, NodeContext& node, interfaces::BlockA
         connOptions.vWhiteBinds.push_back(whitebind);
     }
 
+    if (connOptions.vBinds.empty() && connOptions.vWhiteBinds.empty()) {
+        // Only add all IP addresses on the machine if we would be listening on
+        // any address (0.0.0.0, aka *). See CConnman::InitBinds().
+        Discover();
+    }
+
     for (const auto& net : args.GetArgs("-whitelist")) {
         NetWhitelistPermissions subnet;
         bilingual_str error;

src/net.h

@@ -603,7 +603,15 @@ class CConnman
     friend struct CConnmanTest;
     friend struct ConnmanTestMsg;
 };
+
+/**
+ * Lookup IP addresses from all interfaces on the machine and add them to the
+ * list of local addresses for self-advertise.
+ * The loopback interface is skipped and only the first address from each
+ * interface is used.
+ */
 void Discover();
+
 void StartMapPort();
 void InterruptMapPort();
 void StopMapPort();

test/functional/feature_bind_port_discover.py

@@ -0,0 +1,75 @@
+#!/usr/bin/env python3
+# Copyright (c) 2020 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 that -discover does not add all intefaces' addresses if we listen just on some
+"""
+
+from test_framework.test_framework import BitcoinTestFramework, SkipTest
+from test_framework.util import assert_equal
+
+# We need to bind to a routable address for this test to exercise the relevant code
+# and also must have another routable address on another interface which must not
+# be named "lo" or "lo0".
+# To set a routable address on the machine use:
+# Linux:
+# ifconfig lo:0 1.1.1.1/32 up && ifconfig lo:1 2.2.2.2/32 up  # to set up
+# ifconfig lo:0 down && ifconfig lo:1 down  # to remove it, after the test
+# FreeBSD:
+# ifconfig em0 1.1.1.1/32 alias && ifconfig wlan0 2.2.2.2/32 alias  # to set up
+# ifconfig em0 1.1.1.1 -alias && ifconfig wlan0 2.2.2.2 -alias  # to remove it, after the test
+ADDR1 = '1.1.1.1'
+ADDR2 = '2.2.2.2'
+
+BIND_PORT = 20001;
+
+class BindPortDiscoverTest(BitcoinTestFramework):
+    def set_test_params(self):
+        # Avoid any -bind= on the command line. Force the framework to avoid adding -bind=127.0.0.1.
+        self.setup_clean_chain = True
+        self.bind_to_localhost_only = False
+        self.num_nodes = 2
+
+    def add_options(self, parser):
+        parser.add_argument(
+            "--ihave1111and2222", action='store_true', dest="ihave1111and2222",
+            help="Run the test, assuming {} and {} are configured on the machine".format(ADDR1, ADDR2),
+            default=False)
+
+    def setup_nodes(self):
+        if not self.options.ihave1111and2222:
+            raise SkipTest(
+                "To run this test make sure that {} and {} (a routable addresses) are assigned "
+                "to the interfaces on this machine and rerun with --ihave1111and2222".format(ADDR))
+        self.add_nodes(self.num_nodes, extra_args=[
+            ['-discover', '-port={}'.format(BIND_PORT)], # bind on any
+            ['-discover', '-bind={}:{}'.format(ADDR1, BIND_PORT)],
+        ])
+        self.start_nodes()
+
+    def run_test(self):
+        # Check that if no -bind= is given, then all addresses are added to localaddresses.
+        found_addr1 = False
+        found_addr2 = False
+        for local in self.nodes[0].getnetworkinfo()['localaddresses']:
+            if local['address'] == ADDR1:
+                found_addr1 = True
+                assert_equal(local['port'], BIND_PORT)
+            if local['address'] == ADDR2:
+                found_addr2 = True
+                assert_equal(local['port'], BIND_PORT)
+        assert(found_addr1)
+        assert(found_addr2)
+
+        # Check that if -bind= is given, just that address is added to localaddresses.
+        found_addr1 = False
+        for local in self.nodes[1].getnetworkinfo()['localaddresses']:
+            if local['address'] == ADDR1:
+                found_addr1 = True
+                assert_equal(local['port'], BIND_PORT)
+            assert(local['address'] != ADDR2)
+        assert(found_addr1)
+
+if __name__ == '__main__':
+    BindPortDiscoverTest().main()

test/functional/test_runner.py

@@ -240,6 +240,7 @@
     'feature_filelock.py',
     'feature_loadblock.py',
     'p2p_dos_header_tree.py',
+    'feature_bind_port_discover.py',
     'p2p_unrequested_blocks.py',
     'p2p_blockfilters.py',
     'feature_includeconf.py',