Merge bitcoin/bitcoin#29122: test: adds outbound eviction functional tests, updates comment in ConsiderEviction

d53d84834747c37f4060a9ef379e0a6b50155246 test: adds outbound eviction tests for non outbound-full-relay peers (Sergi Delgado Segura)
a8d9a0edc7cef2c31a557ef53eb45520976b0d65 test: adds outbound eviction functional tests, updates comment in ConsiderEviction (Sergi Delgado Segura)

Pull request description:

  ## Motivation

  While checking the outbound eviction code I realized a case was not considered within the comments, which in turn made me realize we had no functional tests for the outbound eviction case (when I went to check/add the test case).

  This PR updates the aforementioned comment and adds functional tests to cover the outbound eviction logic, in addition to the existing unit tests found at `src/test/denialofservice_tests.cpp`.

ACKs for top commit:
  davidgumberg:
    reACK https://github.com/bitcoin/bitcoin/commit/d53d84834747c37f4060a9ef379e0a6b50155246
  tdb3:
    Re ACK for d53d84834747c37f4060a9ef379e0a6b50155246
  achow101:
    ACK d53d84834747c37f4060a9ef379e0a6b50155246
  cbergqvist:
    ACK d53d84834747c37f4060a9ef379e0a6b50155246

Tree-SHA512: 633b84bb1229fe21e2f650c1beada33ca7f190b64eafd64df2266516d21175e5d652e019ff7114f00cb8bd19f5817dc19e65adf75767a88e24dc0842ce40c63e

2 files changed, 254 insertions, 0 deletions

diff --git a/test/functional/p2p_outbound_eviction.py b/test/functional/p2p_outbound_eviction.py
new file mode 100755
index 0000000000..8d89688999
--- /dev/null
+++ b/test/functional/p2p_outbound_eviction.py
@@ -0,0 +1,253 @@
+#!/usr/bin/env python3
+# Copyright (c) 2019-2021 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 node outbound peer eviction logic
+
+A subset of our outbound peers are subject to eviction logic if they cannot keep up
+with our vision of the best chain. This criteria applies only to non-protected peers,
+and can be triggered by either not learning about any blocks from an outbound peer after
+a certain deadline, or by them not being able to catch up fast enough (under the same deadline).
+
+This tests the different eviction paths based on the peer's behavior and on whether they are protected
+or not.
+"""
+import time
+
+from test_framework.messages import (
+    from_hex,
+    msg_headers,
+    CBlockHeader,
+)
+from test_framework.p2p import P2PInterface
+from test_framework.test_framework import BitcoinTestFramework
+
+# Timeouts (in seconds)
+CHAIN_SYNC_TIMEOUT = 20 * 60
+HEADERS_RESPONSE_TIME = 2 * 60
+
+
+class P2POutEvict(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 1
+
+    def test_outbound_eviction_unprotected(self):
+        # This tests the eviction logic for **unprotected** outbound peers (that is, PeerManagerImpl::ConsiderEviction)
+        node = self.nodes[0]
+        cur_mock_time = node.mocktime
+
+        # Get our tip header and its parent
+        tip_header = from_hex(CBlockHeader(), node.getblockheader(node.getbestblockhash(), False))
+        prev_header = from_hex(CBlockHeader(), node.getblockheader(f"{tip_header.hashPrevBlock:064x}", False))
+
+        self.log.info("Create an outbound connection and don't send any headers")
+        # Test disconnect due to no block being announced in 22+ minutes (headers are not even exchanged)
+        peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="outbound-full-relay")
+        # Wait for over 20 min to trigger the first eviction timeout. This sets the last call past 2 min in the future.
+        cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+        node.setmocktime(cur_mock_time)
+        peer.sync_with_ping()
+        # Wait for over 2 more min to trigger the disconnection
+        peer.wait_for_getheaders(block_hash=tip_header.hashPrevBlock)
+        cur_mock_time += (HEADERS_RESPONSE_TIME + 1)
+        node.setmocktime(cur_mock_time)
+        self.log.info("Test that the peer gets evicted")
+        peer.wait_for_disconnect()
+
+        self.log.info("Create an outbound connection and send header but never catch up")
+        # Mimic a node that just falls behind for long enough
+        # This should also apply for a node doing IBD that does not catch up in time
+        # Connect a peer and make it send us headers ending in our tip's parent
+        peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="outbound-full-relay")
+        peer.send_and_ping(msg_headers([prev_header]))
+
+        # Trigger the timeouts
+        cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+        node.setmocktime(cur_mock_time)
+        peer.sync_with_ping()
+        peer.wait_for_getheaders(block_hash=tip_header.hashPrevBlock)
+        cur_mock_time += (HEADERS_RESPONSE_TIME + 1)
+        node.setmocktime(cur_mock_time)
+        self.log.info("Test that the peer gets evicted")
+        peer.wait_for_disconnect()
+
+        self.log.info("Create an outbound connection and keep lagging behind, but not too much")
+        # Test that if the peer never catches up with our current tip, but it does with the
+        # expected work that we set when setting the timer (that is, our tip at the time)
+        # we do not disconnect the peer
+        peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="outbound-full-relay")
+
+        self.log.info("Mine a block so our peer starts lagging")
+        prev_prev_hash = tip_header.hashPrevBlock
+        best_block_hash = self.generateblock(node, output="raw(42)", transactions=[])["hash"]
+        peer.sync_with_ping()
+
+        self.log.info("Keep catching up with the old tip and check that we are not evicted")
+        for i in range(10):
+            # Generate an additional block so the peers is 2 blocks behind
+            prev_header = from_hex(CBlockHeader(), node.getblockheader(best_block_hash, False))
+            best_block_hash = self.generateblock(node, output="raw(42)", transactions=[])["hash"]
+            peer.sync_with_ping()
+
+            # Advance time but not enough to evict the peer
+            cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+            node.setmocktime(cur_mock_time)
+            peer.sync_with_ping()
+
+            # Wait until we get out last call (by receiving a getheaders)
+            peer.wait_for_getheaders(block_hash=prev_prev_hash)
+
+            # Send a header with the previous tip (so we go back to 1 block behind)
+            peer.send_and_ping(msg_headers([prev_header]))
+            prev_prev_hash = tip_header.hash
+
+        self.log.info("Create an outbound connection and take some time to catch up, but do it in time")
+        # Check that if the peer manages to catch up within time, the timeouts are removed (and the peer is not disconnected)
+        # We are reusing the peer from the previous case which already sent us a valid (but old) block and whose timer is ticking
+
+        # Send an updated headers message matching our tip
+        peer.send_and_ping(msg_headers([from_hex(CBlockHeader(), node.getblockheader(best_block_hash, False))]))
+
+        # Wait for long enough for the timeouts to have triggered and check that we are still connected
+        cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+        node.setmocktime(cur_mock_time)
+        peer.sync_with_ping()
+        cur_mock_time += (HEADERS_RESPONSE_TIME + 1)
+        node.setmocktime(cur_mock_time)
+        self.log.info("Test that the peer does not get evicted")
+        peer.sync_with_ping()
+
+        node.disconnect_p2ps()
+
+    def test_outbound_eviction_protected(self):
+        # This tests the eviction logic for **protected** outbound peers (that is, PeerManagerImpl::ConsiderEviction)
+        # Outbound connections are flagged as protected as long as they have sent us a connecting block with at least as
+        # much work as our current tip and we have enough empty protected_peers slots.
+        node = self.nodes[0]
+        cur_mock_time = node.mocktime
+        tip_header = from_hex(CBlockHeader(), node.getblockheader(node.getbestblockhash(), False))
+
+        self.log.info("Create an outbound connection to a peer that shares our tip so it gets granted protection")
+        peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="outbound-full-relay")
+        peer.send_and_ping(msg_headers([tip_header]))
+
+        self.log.info("Mine a new block and sync with our peer")
+        self.generateblock(node, output="raw(42)", transactions=[])
+        peer.sync_with_ping()
+
+        self.log.info("Let enough time pass for the timeouts to go off")
+        # Trigger the timeouts and check how we are still connected
+        cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+        node.setmocktime(cur_mock_time)
+        peer.sync_with_ping()
+        peer.wait_for_getheaders(block_hash=tip_header.hashPrevBlock)
+        cur_mock_time += (HEADERS_RESPONSE_TIME + 1)
+        node.setmocktime(cur_mock_time)
+        self.log.info("Test that the node does not get evicted")
+        peer.sync_with_ping()
+
+        node.disconnect_p2ps()
+
+    def test_outbound_eviction_mixed(self):
+        # This tests the outbound eviction logic for a mix of protected and unprotected peers.
+        node = self.nodes[0]
+        cur_mock_time = node.mocktime
+
+        self.log.info("Create a mix of protected and unprotected outbound connections to check against eviction")
+
+        # Let's try this logic having multiple peers, some protected and some unprotected
+        # We protect up to 4 peers as long as they have provided a block with the same amount of work as our tip
+        self.log.info("The first 4 peers are protected by sending us a valid block with enough work")
+        tip_header = from_hex(CBlockHeader(), node.getblockheader(node.getbestblockhash(), False))
+        headers_message = msg_headers([tip_header])
+        protected_peers = []
+        for i in range(4):
+            peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=i, connection_type="outbound-full-relay")
+            peer.send_and_ping(headers_message)
+            protected_peers.append(peer)
+
+        # We can create 4 additional outbound connections to peers that are unprotected. 2 of them will be well behaved,
+        # whereas the other 2 will misbehave (1 sending no headers, 1 sending old ones)
+        self.log.info("The remaining 4 peers will be mixed between honest (2) and misbehaving peers (2)")
+        prev_header = from_hex(CBlockHeader(), node.getblockheader(f"{tip_header.hashPrevBlock:064x}", False))
+        headers_message = msg_headers([prev_header])
+        honest_unprotected_peers = []
+        for i in range(2):
+            peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=4+i, connection_type="outbound-full-relay")
+            peer.send_and_ping(headers_message)
+            honest_unprotected_peers.append(peer)
+
+        misbehaving_unprotected_peers = []
+        for i in range(2):
+            peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=6+i, connection_type="outbound-full-relay")
+            if i%2==0:
+                peer.send_and_ping(headers_message)
+            misbehaving_unprotected_peers.append(peer)
+
+        self.log.info("Mine a new block and keep the unprotected honest peer on sync, all the rest off-sync")
+        # Mine a block so all peers become outdated
+        target_hash = prev_header.rehash()
+        tip_hash = self.generateblock(node, output="raw(42)", transactions=[])["hash"]
+        tip_header = from_hex(CBlockHeader(), node.getblockheader(tip_hash, False))
+        tip_headers_message = msg_headers([tip_header])
+
+        # Let the timeouts hit and check back
+        cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+        node.setmocktime(cur_mock_time)
+        for peer in protected_peers + misbehaving_unprotected_peers:
+            peer.sync_with_ping()
+            peer.wait_for_getheaders(block_hash=target_hash)
+        for peer in honest_unprotected_peers:
+            peer.send_and_ping(tip_headers_message)
+            peer.wait_for_getheaders(block_hash=target_hash)
+
+        cur_mock_time += (HEADERS_RESPONSE_TIME + 1)
+        node.setmocktime(cur_mock_time)
+        self.log.info("Check how none of the honest nor protected peers was evicted but all the misbehaving unprotected were")
+        for peer in protected_peers + honest_unprotected_peers:
+            peer.sync_with_ping()
+        for peer in misbehaving_unprotected_peers:
+            peer.wait_for_disconnect()
+
+        node.disconnect_p2ps()
+
+    def test_outbound_eviction_blocks_relay_only(self):
+        # The logic for outbound eviction protection only applies to outbound-full-relay peers
+        # This tests that other types of peers (blocks-relay-only for instance) are not granted protection
+        node = self.nodes[0]
+        cur_mock_time = node.mocktime
+        tip_header = from_hex(CBlockHeader(), node.getblockheader(node.getbestblockhash(), False))
+
+        self.log.info("Create an blocks-only outbound connection to a peer that shares our tip. This would usually grant protection")
+        peer = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="block-relay-only")
+        peer.send_and_ping(msg_headers([tip_header]))
+
+        self.log.info("Mine a new block and sync with our peer")
+        self.generateblock(node, output="raw(42)", transactions=[])
+        peer.sync_with_ping()
+
+        self.log.info("Let enough time pass for the timeouts to go off")
+        # Trigger the timeouts and check how the peer gets evicted, since protection is only given to outbound-full-relay peers
+        cur_mock_time += (CHAIN_SYNC_TIMEOUT + 1)
+        node.setmocktime(cur_mock_time)
+        peer.sync_with_ping()
+        peer.wait_for_getheaders(block_hash=tip_header.hash)
+        cur_mock_time += (HEADERS_RESPONSE_TIME + 1)
+        node.setmocktime(cur_mock_time)
+        self.log.info("Test that the peer gets evicted")
+        peer.wait_for_disconnect()
+
+        node.disconnect_p2ps()
+
+
+    def run_test(self):
+        self.nodes[0].setmocktime(int(time.time()))
+        self.test_outbound_eviction_unprotected()
+        self.test_outbound_eviction_protected()
+        self.test_outbound_eviction_mixed()
+        self.test_outbound_eviction_blocks_relay_only()
+
+
+if __name__ == '__main__':
+    P2POutEvict().main()
diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index 5ccb9d9496..690ab64c83 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -285,6 +285,7 @@ BASE_SCRIPTS = [
     'p2p_leak_tx.py --v1transport',
     'p2p_leak_tx.py --v2transport',
     'p2p_eviction.py',
+    'p2p_outbound_eviction.py',
     'p2p_ibd_stalling.py --v1transport',
     'p2p_ibd_stalling.py --v2transport',
     'p2p_net_deadlock.py --v1transport',