Merge #19884: p2p: No delay in adding fixed seeds if -dnsseed=0 and peers.dat is empty

fe3e993968 [p2p] No delay in adding fixed seeds if -dnsseed=0 and peers.dat is empty. Add -fixedseeds arg. (Dhruv Mehta)

Pull request description:

  Closes #19795

  Before PR: If `peers.dat` is empty and `-dnsseed=0`, bitcoind will fallback on to fixed seeds but only after a 60 seconds delay.
  After PR: There's no 60 second delay.

  To reproduce:
  `rm ~/.bitcoin/peers.dat && src/bitcoind -dnsseed=0` without and with patch code

  Other changes in the PR:
  - `-fixedseeds` command line argument added: `-dnsseed=0 -fixedseeds=0 -addnode=X` provides a trusted peer only setup. `-dnsseed=0 -fixedseeds=0` allows for a `addnode` RPC to add a trusted peer without falling back to hardcoded seeds.

ACKs for top commit:
  LarryRuane:
    re-ACK fe3e993968
  laanwj:
    re-ACK fe3e993968

Tree-SHA512: 79449bf4e83a315be6dbac9bdd226de89d2a3f7f76d9c5640a2cb3572866e6b0e8ed67e65674c9824054cf13119dc01c7e1a33848daac6b6c34dbc158b6dba8f

test/functional/feature_config_args.py

@@ -5,6 +5,7 @@
 """Test various command line arguments and configuration file parameters."""
 
 import os
+import time
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework import util
@@ -147,11 +148,67 @@ class ConfArgsTest(BitcoinTestFramework):
             self.start_node(0, extra_args=['-nonetworkactive=1'])
         self.stop_node(0)
 
+    def test_seed_peers(self):
+        self.log.info('Test seed peers, this will take about 2 minutes')
+        default_data_dir = self.nodes[0].datadir
+
+        # No peers.dat exists and -dnsseed=1
+        # We expect the node will use DNS Seeds, but Regtest mode has 0 DNS seeds
+        # So after 60 seconds, the node should fallback to fixed seeds (this is a slow test)
+        assert not os.path.exists(os.path.join(default_data_dir, "peers.dat"))
+        start = time.time()
+        with self.nodes[0].assert_debug_log(expected_msgs=[
+                "Loaded 0 addresses from peers.dat",
+                "0 addresses found from DNS seeds",
+                "Adding fixed seeds as 60 seconds have passed and addrman is empty"], timeout=80):
+            self.start_node(0, extra_args=['-dnsseed=1'])
+        assert time.time() - start >= 60
+        self.stop_node(0)
+
+        # No peers.dat exists and -dnsseed=0
+        # We expect the node will fallback immediately to fixed seeds
+        assert not os.path.exists(os.path.join(default_data_dir, "peers.dat"))
+        start = time.time()
+        with self.nodes[0].assert_debug_log(expected_msgs=[
+                "Loaded 0 addresses from peers.dat",
+                "DNS seeding disabled",
+                "Adding fixed seeds as -dnsseed=0, -addnode is not provided and and all -seednode(s) attempted\n"]):
+            self.start_node(0, extra_args=['-dnsseed=0'])
+        assert time.time() - start < 60
+        self.stop_node(0)
+
+        # No peers.dat exists and dns seeds are disabled.
+        # We expect the node will not add fixed seeds when explicitly disabled.
+        assert not os.path.exists(os.path.join(default_data_dir, "peers.dat"))
+        start = time.time()
+        with self.nodes[0].assert_debug_log(expected_msgs=[
+                "Loaded 0 addresses from peers.dat",
+                "DNS seeding disabled",
+                "Fixed seeds are disabled"]):
+            self.start_node(0, extra_args=['-dnsseed=0', '-fixedseeds=0'])
+        assert time.time() - start < 60
+        self.stop_node(0)
+
+        # No peers.dat exists and -dnsseed=0, but a -addnode is provided
+        # We expect the node will allow 60 seconds prior to using fixed seeds
+        assert not os.path.exists(os.path.join(default_data_dir, "peers.dat"))
+        start = time.time()
+        with self.nodes[0].assert_debug_log(expected_msgs=[
+                "Loaded 0 addresses from peers.dat",
+                "DNS seeding disabled",
+                "Adding fixed seeds as 60 seconds have passed and addrman is empty"],
+                timeout=80):
+            self.start_node(0, extra_args=['-dnsseed=0', '-addnode=fakenodeaddr'])
+        assert time.time() - start >= 60
+        self.stop_node(0)
+
+
     def run_test(self):
         self.stop_node(0)
 
         self.test_log_buffer()
         self.test_args_log()
+        self.test_seed_peers()
         self.test_networkactive()
 
         self.test_config_file_parser()