Merge #16756: test: Connection eviction logic tests

45eff751c6d07007dabc365dc4c0e6c63e3fe5cf Add functional test for P2P eviction logic of inbound peers (Martin Zumsande)

Pull request description:

  This adds a functional test for the eviction logic for inbound peers, which is triggered when the number of maximum connections is exceeded.

  The functional test covers eviction protection for peers that  have sent us blocks or txns recently, or that have faster pings. I couldn't find a way to test the logic of `CConnman::AttemptToEvictConnection` that is based on netgroup (see #14210 for related discussion)

  Fixes #16660 (at least partially).

  [Edit: Earlier, this PR also contained a unit test, which was removed after the discussion]

ACKs for top commit:
  jonatack:
    ACK 45eff751c6d07007dabc365dc4c0e6c63e3fe5cf
  naumenkogs:
    Tested ACK 45eff75
  fjahr:
    re-ACK 45eff751c6d07007dabc365dc4c0e6c63e3fe5cf
  andrewtoth:
    re-ACK 45eff751c6d07007dabc365dc4c0e6c63e3fe5cf

Tree-SHA512: 177208ab6f30dc62da1cc5f51e654f7c9770d8c6b42aca6ae7ecb30e29d3096e04d75739578e7d149a0f29dd92652b4a707e93c0f1be8aa7ed315e6ec3ab07a4

2 files changed, 130 insertions, 0 deletions

diff --git a/test/functional/p2p_eviction.py b/test/functional/p2p_eviction.py
new file mode 100755
index 0000000000..b2b3a89aab
--- /dev/null
+++ b/test/functional/p2p_eviction.py
@@ -0,0 +1,129 @@
+#!/usr/bin/env python3
+# Copyright (c) 2019 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 node eviction logic
+
+When the number of peers has reached the limit of maximum connections,
+the next connecting inbound peer will trigger the eviction mechanism.
+We cannot currently test the parts of the eviction logic that are based on
+address/netgroup since in the current framework, all peers are connecting from
+the same local address. See Issue #14210 for more info.
+Therefore, this test is limited to the remaining protection criteria.
+"""
+
+import time
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.mininode import P2PInterface, P2PDataStore
+from test_framework.util import assert_equal, wait_until
+from test_framework.blocktools import create_block, create_coinbase
+from test_framework.messages import CTransaction, FromHex, msg_pong, msg_tx
+
+
+class SlowP2PDataStore(P2PDataStore):
+    def on_ping(self, message):
+        time.sleep(0.1)
+        self.send_message(msg_pong(message.nonce))
+
+class SlowP2PInterface(P2PInterface):
+    def on_ping(self, message):
+        time.sleep(0.1)
+        self.send_message(msg_pong(message.nonce))
+
+class P2PEvict(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 1
+        # The choice of maxconnections=32 results in a maximum of 21 inbound connections
+        # (32 - 10 outbound - 1 feeler). 20 inbound peers are protected from eviction:
+        # 4 by netgroup, 4 that sent us blocks, 4 that sent us transactions and 8 via lowest ping time
+        self.extra_args = [['-maxconnections=32']]
+
+    def run_test(self):
+        protected_peers = set()  # peers that we expect to be protected from eviction
+        current_peer = -1
+        node = self.nodes[0]
+        node.generatetoaddress(101, node.get_deterministic_priv_key().address)
+
+        self.log.info("Create 4 peers and protect them from eviction by sending us a block")
+        for _ in range(4):
+            block_peer = node.add_p2p_connection(SlowP2PDataStore())
+            current_peer += 1
+            block_peer.sync_with_ping()
+            best_block = node.getbestblockhash()
+            tip = int(best_block, 16)
+            best_block_time = node.getblock(best_block)['time']
+            block = create_block(tip, create_coinbase(node.getblockcount() + 1), best_block_time + 1)
+            block.solve()
+            block_peer.send_blocks_and_test([block], node, success=True)
+            protected_peers.add(current_peer)
+
+        self.log.info("Create 5 slow-pinging peers, making them eviction candidates")
+        for _ in range(5):
+            node.add_p2p_connection(SlowP2PInterface())
+            current_peer += 1
+
+        self.log.info("Create 4 peers and protect them from eviction by sending us a tx")
+        for i in range(4):
+            txpeer = node.add_p2p_connection(SlowP2PInterface())
+            current_peer += 1
+            txpeer.sync_with_ping()
+
+            prevtx = node.getblock(node.getblockhash(i + 1), 2)['tx'][0]
+            rawtx = node.createrawtransaction(
+                inputs=[{'txid': prevtx['txid'], 'vout': 0}],
+                outputs=[{node.get_deterministic_priv_key().address: 50 - 0.00125}],
+            )
+            sigtx = node.signrawtransactionwithkey(
+                hexstring=rawtx,
+                privkeys=[node.get_deterministic_priv_key().key],
+                prevtxs=[{
+                    'txid': prevtx['txid'],
+                    'vout': 0,
+                    'scriptPubKey': prevtx['vout'][0]['scriptPubKey']['hex'],
+                }],
+            )['hex']
+            txpeer.send_message(msg_tx(FromHex(CTransaction(), sigtx)))
+            protected_peers.add(current_peer)
+
+        self.log.info("Create 8 peers and protect them from eviction by having faster pings")
+        for _ in range(8):
+            fastpeer = node.add_p2p_connection(P2PInterface())
+            current_peer += 1
+            wait_until(lambda: "ping" in fastpeer.last_message, timeout=10)
+
+        # Make sure by asking the node what the actual min pings are
+        peerinfo = node.getpeerinfo()
+        pings = {}
+        for i in range(len(peerinfo)):
+            pings[i] = peerinfo[i]['minping'] if 'minping' in peerinfo[i] else 1000000
+        sorted_pings = sorted(pings.items(), key=lambda x: x[1])
+
+        # Usually the 8 fast peers are protected. In rare case of unreliable pings,
+        # one of the slower peers might have a faster min ping though.
+        for i in range(8):
+            protected_peers.add(sorted_pings[i][0])
+
+        self.log.info("Create peer that triggers the eviction mechanism")
+        node.add_p2p_connection(SlowP2PInterface())
+
+        # One of the non-protected peers must be evicted. We can't be sure which one because
+        # 4 peers are protected via netgroup, which is identical for all peers,
+        # and the eviction mechanism doesn't preserve the order of identical elements.
+        evicted_peers = []
+        for i in range(len(node.p2ps)):
+            if not node.p2ps[i].is_connected:
+                evicted_peers.append(i)
+
+        self.log.info("Test that one peer was evicted")
+        self.log.debug("{} evicted peer: {}".format(len(evicted_peers), set(evicted_peers)))
+        assert_equal(len(evicted_peers), 1)
+
+        self.log.info("Test that no peer expected to be protected was evicted")
+        self.log.debug("{} protected peers: {}".format(len(protected_peers), protected_peers))
+        assert evicted_peers[0] not in protected_peers
+
+if __name__ == '__main__':
+    P2PEvict().main()
diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index c0bc471d5a..8b11dc8376 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -190,6 +190,7 @@ BASE_SCRIPTS = [
     'rpc_preciousblock.py',
     'wallet_importprunedfunds.py',
     'p2p_leak_tx.py',
+    'p2p_eviction.py',
     'rpc_signmessage.py',
     'rpc_generateblock.py',
     'wallet_balance.py',