Merge bitcoin/bitcoin#27596: assumeutxo (2)

edbed31066e3674ba52b8c093ab235625527f383 chainparams: add signet assumeutxo param at height 160_000 (Sjors Provoost)
b8cafe38713cbf10d15459042f7f911bcc1b1e4e chainparams: add testnet assumeutxo param at height 2_500_000 (Sjors Provoost)
99839bbfa7110c7abf22e587ae2f72c9c57d3c85 doc: add note about confusing HaveTxsDownloaded name (James O'Beirne)
7ee46a755f1d57ce9d51975d3b54dc9ac3d08d52 contrib: add script to demo/test assumeutxo (James O'Beirne)
42cae39356fd20d521aaf99aff1ed85856f3c9f3 test: add feature_assumeutxo functional test (James O'Beirne)
0f64bac6030334d798ae205cd7af4bf248feddd9 rpc: add getchainstates (James O'Beirne)
bb0585779472962f40d9cdd9c6532132850d371c refuse to activate a UTXO snapshot if mempool not empty (James O'Beirne)
ce585a9a158476b0ad3296477b922e79f308e795 rpc: add loadtxoutset (James O'Beirne)
62ac519e718eb7a31dca1102a96ba219fbc7f95d validation: do not activate snapshot if behind active chain (James O'Beirne)
9511fb3616b7bbe1d0d2f54a45ea0a650ba0367b validation: assumeutxo: swap m_mempool on snapshot activation (James O'Beirne)
7fcd21544a333ffdf1910b65c573579860be6a36 blockstorage: segment normal/assumedvalid blockfiles (James O'Beirne)
4c3b8ca35c2e4a441264749bb312df2bd054b5b8 validation: populate nChainTx value for assumedvalid chainstates (James O'Beirne)
49ef778158c43859946a592e11ec34fe1b93a5b6 test: adjust chainstate tests to use recognized snapshot base (James O'Beirne)
1019c399825b0d512c1fd751c376d46fed4992b9 validation: pruning for multiple chainstates (James O'Beirne)
373cf91531b84bfdd06fdf8abf4dca228029ce6b validation: indexing changes for assumeutxo (James O'Beirne)
1fffdd76a1bca908f55d73b64983655b14cf7432 net_processing: validationinterface: ignore some events for bg chain (James O'Beirne)
fbe0a7d7ca680358237b6c2369b3fd2b43221113 wallet: validationinterface: only handle active chain notifications (James O'Beirne)
f073917a9e7ba423643dcae0339776470b628f65 validationinterface: only send zmq notifications for active (James O'Beirne)
4d8f4dcb450d31e4847804e62bf91545b949fa14 validation: pass ChainstateRole for validationinterface calls (James O'Beirne)
1e59acdf17309f567c370885f0cf02605e2baa58 validation: only call UpdatedBlockTip for active chainstate (James O'Beirne)
c6af23c5179cc383f8e6c275373af8d11e6a989f validation: add ChainstateRole (James O'Beirne)
9f2318c76cc6986d48e13831cf5bd8dab194fdf4 validation: MaybeRebalanceCaches when chain leaves IBD (James O'Beirne)
434495a8c1496ca23fe35b84499f3daf668d76b8 chainparams: add blockhash to AssumeutxoData (James O'Beirne)
c711ca186f8d8a28810be0beedcb615ddcf93163 assumeutxo: remove snapshot during -reindex{-chainstate} (James O'Beirne)
c93ef43e4fd4fbc1263cdc9e98ae5856830fe89e bugfix: correct is_snapshot_cs in VerifyDB (James O'Beirne)
b73d3bbd23220857bf17cbb6401275bf58013b72 net_processing: Request assumeutxo background chain blocks (Suhas Daftuar)

Pull request description:

  - Background and FAQ: https://github.com/jamesob/assumeutxo-docs/tree/2019-04-proposal/proposal
  - Prior progress/project: https://github.com/bitcoin/bitcoin/projects/11
  - Replaces https://github.com/bitcoin/bitcoin/pull/15606, which was closed due to Github slowness. Original description and commentary can be found there.

  ---

  This changeset finishes the first phase of the assumeutxo project. It makes UTXO snapshots loadable via RPC (`loadtxoutset`) and adds `assumeutxo` parameters to chainparams. It contains all the remaining changes necessary to both use an assumedvalid snapshot chainstate and do a full validation sync in the background.

  This may look like a lot to review, but note that
  - ~200 lines are a (non-essential) demo shell script
  - Many lines are functional test, documentation, and relatively dilute RPC code.

  So it shouldn't be as burdensome to review as the linecount might suggest.

  - **P2P**: minor changes are made to `init.cpp` and `net_processing.cpp` to make simultaneous IBD across multiple chainstates work.
  - **Pruning**: implement correct pruning behavior when using a background chainstate
  - **Blockfile separation**: to prevent "fragmentation" in blockfile storage, have background chainstates use separate blockfiles from active snapshot chainstates to avoid interleaving heights and impairing pruning.
  - **Indexing**: some `CValidationInterface` events are given with an additional parameter, ChainstateRole, and all indexers ignore events from ChainstateRole::ASSUMEDVALID so that indexation only happens sequentially.
  - Have `-reindex` properly wipe snapshot chainstates.
  - **RPC**: introduce RPC commands `loadtxoutset` and (hidden) `getchainstates`.
  - **Release docs & first assumeutxo commitment**: add notes and a particular assumeutxo hash value for first AU-enabled release.
    - This will complete the project and allow use of UTXO snapshots for faster node bootstrap.

  The next phase, if it were to be pursued, would be coming up with a way to distribute the UTXO snapshots over the P2P network.

  ---

  ### UTXO snapshots

  Create your own with `./contrib/devtools/utxo_snapshot.sh`, e.g.
  ```shell
  ./contrib/devtools/utxo_snapshot.sh 788000 utxo.dat ./src/bitcoin-cli -datadir=$(pwd)/testdata`)
  ```
  or use the pre-generated ones listed below.

  - Testnet: **2'500'000** (Sjors):
    - torrent: `magnet:?xt=urn:btih:511e09f4bf853aefab00de5c070b1e031f0ecbe9&dn=utxo-testnet-2500000.dat&tr=udp%3A%2F%2Ftracker.bitcoin.sprovoost.nl%3A6969`
    - sha256: `79db4b025448cc0ac388d8589a28eab02de53055d181e34eb47391717aa16388`
  - Signet: **160'000** (Sjors):
    - torrent: `magnet:?xt=urn:btih:9da986cb27b3980ea7fd06b21e199b148d486880&dn=utxo-signet-160000.dat&tr=udp%3A%2F%2Ftracker.bitcoin.sprovoost.nl%3A6969`
    - sha256: `eeeca845385ba91e84ef58c09d38f98f246a24feadaad57fe1e5874f3f92ef8c`
  - Mainnet: **800'000** (Sjors):
    - Note: this needs the following commit cherry-picked in: https://github.com/Sjors/bitcoin/commit/24deb2022b822f22fba9fcbee201e37a83225eb2
    - torrent: `magnet:?xt=urn:btih:50ee955bef37f5ec3e5b0df4cf0288af3d715a2e&dn=utxo-800000.dat&tr=udp%3A%2F%2Ftracker.bitcoin.sprovoost.nl%3A6969`

  ### Testing

  #### For fun (~5min)

  If you want to do a quick test, you can run `./contrib/devtools/test_utxo_snapshots.sh` and follow the instructions. This is mostly obviated by the functional tests, though.

  #### For real (longer)

  If you'd like to experience a real usage of assumeutxo, you can do that too.
  I've cut a new snapshot at height 788'000 (http://img.jameso.be/utxo-788000.dat - but you can do it yourself with `./contrib/devtools/utxo_snapshot.sh` if you want). Download that, and then create a datadir for testing:
  ```sh
  $ cd ~/src/bitcoin  # or whatever

  # get the snapshot
  $ curl http://img.jameso.be/utxo-788000.dat > utxo-788000.dat

  # you'll want to do this if you like copy/pasting
  $ export AU_DATADIR=/home/${USER}/au-test # or wherever

  $ mkdir ${AU_DATADIR}
  $ vim ${AU_DATADIR}/bitcoin.conf

  dbcache=8000  # or, you know, something high
  blockfilterindex=1
  coinstatsindex=1
  prune=3000
  logthreadnames=1
  ```
  Obtain this branch, build it, and then start bitcoind:
  ```sh
  $ git remote add jamesob https://github.com/jamesob/bitcoin
  $ git fetch jamesob assumeutxo
  $ git checkout jamesob/assumeutxo

  $ ./configure $conf_args && make  # (whatever you like to do here)

  # start 'er up and watch the logs
  $ ./src/bitcoind -datadir=${AU_DATADIR}
  ```
  Then, in some other window, load the snapshot
  ```sh
  $ ./src/bitcoin-cli -datadir=${AU_DATADIR} loadtxoutset $(pwd)/utxo-788000.dat
  ```

  You'll see some log messages about headers retrieval and waiting to see the snapshot in the headers chain. Once you get the full headers chain, you'll spend a decent amount of time (~10min) loading the snapshot, checking it, and flushing it to disk. After all that happens, you should be syncing to tip in pretty short order, and you'll see the occasional `[background validation]` log message go by.

  In yet another window, you can check out chainstate status with
  ```sh
  $ ./src/bitcoin-cli -datadir=${AU_DATADIR} getchainstates
  ```
  as well as usual favorites like `getblockchaininfo`.

ACKs for top commit:
  achow101:
    ACK edbed31066e3674ba52b8c093ab235625527f383

Tree-SHA512: 6086fb9a38dc7df85fedc76b30084dd8154617a2a91e89a84fb41326d34ef8e7d7ea593107afba01369093bf8cc91770621d98f0ea42a5b3b99db868d2f14dc2

4 files changed, 257 insertions, 2 deletions

diff --git a/test/functional/feature_assumeutxo.py b/test/functional/feature_assumeutxo.py
new file mode 100755
index 0000000000..be1aa18993
--- /dev/null
+++ b/test/functional/feature_assumeutxo.py
@@ -0,0 +1,246 @@
+#!/usr/bin/env python3
+# Copyright (c) 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 for assumeutxo, a means of quickly bootstrapping a node using
+a serialized version of the UTXO set at a certain height, which corresponds
+to a hash that has been compiled into bitcoind.
+
+The assumeutxo value generated and used here is committed to in
+`CRegTestParams::m_assumeutxo_data` in `src/chainparams.cpp`.
+
+## Possible test improvements
+
+- TODO: test submitting a transaction and verifying it appears in mempool
+- TODO: test what happens with -reindex and -reindex-chainstate before the
+      snapshot is validated, and make sure it's deleted successfully.
+
+Interesting test cases could be loading an assumeutxo snapshot file with:
+
+- TODO: An invalid hash
+- TODO: Valid hash but invalid snapshot file (bad coin height or truncated file or
+      bad other serialization)
+- TODO: Valid snapshot file, but referencing an unknown block
+- TODO: Valid snapshot file, but referencing a snapshot block that turns out to be
+      invalid, or has an invalid parent
+- TODO: Valid snapshot file and snapshot block, but the block is not on the
+      most-work chain
+
+Interesting starting states could be loading a snapshot when the current chain tip is:
+
+- TODO: An ancestor of snapshot block
+- TODO: Not an ancestor of the snapshot block but has less work
+- TODO: The snapshot block
+- TODO: A descendant of the snapshot block
+- TODO: Not an ancestor or a descendant of the snapshot block and has more work
+
+"""
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal, wait_until_helper
+
+START_HEIGHT = 199
+SNAPSHOT_BASE_HEIGHT = 299
+FINAL_HEIGHT = 399
+COMPLETE_IDX = {'synced': True, 'best_block_height': FINAL_HEIGHT}
+
+
+class AssumeutxoTest(BitcoinTestFramework):
+
+    def set_test_params(self):
+        """Use the pregenerated, deterministic chain up to height 199."""
+        self.num_nodes = 3
+        self.rpc_timeout = 120
+        self.extra_args = [
+            [],
+            ["-fastprune", "-prune=1", "-blockfilterindex=1", "-coinstatsindex=1"],
+            ["-txindex=1", "-blockfilterindex=1", "-coinstatsindex=1"],
+        ]
+
+    def setup_network(self):
+        """Start with the nodes disconnected so that one can generate a snapshot
+        including blocks the other hasn't yet seen."""
+        self.add_nodes(3)
+        self.start_nodes(extra_args=self.extra_args)
+
+    def run_test(self):
+        """
+        Bring up two (disconnected) nodes, mine some new blocks on the first,
+        and generate a UTXO snapshot.
+
+        Load the snapshot into the second, ensure it syncs to tip and completes
+        background validation when connected to the first.
+        """
+        n0 = self.nodes[0]
+        n1 = self.nodes[1]
+        n2 = self.nodes[2]
+
+        # Mock time for a deterministic chain
+        for n in self.nodes:
+            n.setmocktime(n.getblockheader(n.getbestblockhash())['time'])
+
+        self.sync_blocks()
+
+        def no_sync():
+            pass
+
+        # Generate a series of blocks that `n0` will have in the snapshot,
+        # but that n1 doesn't yet see. In order for the snapshot to activate,
+        # though, we have to ferry over the new headers to n1 so that it
+        # isn't waiting forever to see the header of the snapshot's base block
+        # while disconnected from n0.
+        for i in range(100):
+            self.generate(n0, nblocks=1, sync_fun=no_sync)
+            newblock = n0.getblock(n0.getbestblockhash(), 0)
+
+            # make n1 aware of the new header, but don't give it the block.
+            n1.submitheader(newblock)
+            n2.submitheader(newblock)
+
+        # Ensure everyone is seeing the same headers.
+        for n in self.nodes:
+            assert_equal(n.getblockchaininfo()["headers"], SNAPSHOT_BASE_HEIGHT)
+
+        self.log.info("-- Testing assumeutxo + some indexes + pruning")
+
+        assert_equal(n0.getblockcount(), SNAPSHOT_BASE_HEIGHT)
+        assert_equal(n1.getblockcount(), START_HEIGHT)
+
+        self.log.info(f"Creating a UTXO snapshot at height {SNAPSHOT_BASE_HEIGHT}")
+        dump_output = n0.dumptxoutset('utxos.dat')
+
+        assert_equal(
+            dump_output['txoutset_hash'],
+            'ef45ccdca5898b6c2145e4581d2b88c56564dd389e4bd75a1aaf6961d3edd3c0')
+        assert_equal(dump_output['nchaintx'], 300)
+        assert_equal(n0.getblockchaininfo()["blocks"], SNAPSHOT_BASE_HEIGHT)
+
+        # Mine more blocks on top of the snapshot that n1 hasn't yet seen. This
+        # will allow us to test n1's sync-to-tip on top of a snapshot.
+        self.generate(n0, nblocks=100, sync_fun=no_sync)
+
+        assert_equal(n0.getblockcount(), FINAL_HEIGHT)
+        assert_equal(n1.getblockcount(), START_HEIGHT)
+
+        assert_equal(n0.getblockchaininfo()["blocks"], FINAL_HEIGHT)
+
+        self.log.info(f"Loading snapshot into second node from {dump_output['path']}")
+        loaded = n1.loadtxoutset(dump_output['path'])
+        assert_equal(loaded['coins_loaded'], SNAPSHOT_BASE_HEIGHT)
+        assert_equal(loaded['base_height'], SNAPSHOT_BASE_HEIGHT)
+
+        monitor = n1.getchainstates()
+        assert_equal(monitor['normal']['blocks'], START_HEIGHT)
+        assert_equal(monitor['snapshot']['blocks'], SNAPSHOT_BASE_HEIGHT)
+        assert_equal(monitor['snapshot']['snapshot_blockhash'], dump_output['base_hash'])
+
+        assert_equal(n1.getblockchaininfo()["blocks"], SNAPSHOT_BASE_HEIGHT)
+
+        PAUSE_HEIGHT = FINAL_HEIGHT - 40
+
+        self.log.info("Restarting node to stop at height %d", PAUSE_HEIGHT)
+        self.restart_node(1, extra_args=[
+            f"-stopatheight={PAUSE_HEIGHT}", *self.extra_args[1]])
+
+        # Finally connect the nodes and let them sync.
+        self.connect_nodes(0, 1)
+
+        n1.wait_until_stopped(timeout=5)
+
+        self.log.info("Checking that blocks are segmented on disk")
+        assert self.has_blockfile(n1, "00000"), "normal blockfile missing"
+        assert self.has_blockfile(n1, "00001"), "assumed blockfile missing"
+        assert not self.has_blockfile(n1, "00002"), "too many blockfiles"
+
+        self.log.info("Restarted node before snapshot validation completed, reloading...")
+        self.restart_node(1, extra_args=self.extra_args[1])
+        self.connect_nodes(0, 1)
+
+        self.log.info(f"Ensuring snapshot chain syncs to tip. ({FINAL_HEIGHT})")
+        wait_until_helper(lambda: n1.getchainstates()['snapshot']['blocks'] == FINAL_HEIGHT)
+        self.sync_blocks(nodes=(n0, n1))
+
+        self.log.info("Ensuring background validation completes")
+        # N.B.: the `snapshot` key disappears once the background validation is complete.
+        wait_until_helper(lambda: not n1.getchainstates().get('snapshot'))
+
+        # Ensure indexes have synced.
+        completed_idx_state = {
+            'basic block filter index': COMPLETE_IDX,
+            'coinstatsindex': COMPLETE_IDX,
+        }
+        self.wait_until(lambda: n1.getindexinfo() == completed_idx_state)
+
+
+        for i in (0, 1):
+            n = self.nodes[i]
+            self.log.info(f"Restarting node {i} to ensure (Check|Load)BlockIndex passes")
+            self.restart_node(i, extra_args=self.extra_args[i])
+
+            assert_equal(n.getblockchaininfo()["blocks"], FINAL_HEIGHT)
+
+            assert_equal(n.getchainstates()['normal']['blocks'], FINAL_HEIGHT)
+            assert_equal(n.getchainstates().get('snapshot'), None)
+
+            if i != 0:
+                # Ensure indexes have synced for the assumeutxo node
+                self.wait_until(lambda: n.getindexinfo() == completed_idx_state)
+
+
+        # Node 2: all indexes + reindex
+        # -----------------------------
+
+        self.log.info("-- Testing all indexes + reindex")
+        assert_equal(n2.getblockcount(), START_HEIGHT)
+
+        self.log.info(f"Loading snapshot into third node from {dump_output['path']}")
+        loaded = n2.loadtxoutset(dump_output['path'])
+        assert_equal(loaded['coins_loaded'], SNAPSHOT_BASE_HEIGHT)
+        assert_equal(loaded['base_height'], SNAPSHOT_BASE_HEIGHT)
+
+        monitor = n2.getchainstates()
+        assert_equal(monitor['normal']['blocks'], START_HEIGHT)
+        assert_equal(monitor['snapshot']['blocks'], SNAPSHOT_BASE_HEIGHT)
+        assert_equal(monitor['snapshot']['snapshot_blockhash'], dump_output['base_hash'])
+
+        self.connect_nodes(0, 2)
+        wait_until_helper(lambda: n2.getchainstates()['snapshot']['blocks'] == FINAL_HEIGHT)
+        self.sync_blocks()
+
+        self.log.info("Ensuring background validation completes")
+        wait_until_helper(lambda: not n2.getchainstates().get('snapshot'))
+
+        completed_idx_state = {
+            'basic block filter index': COMPLETE_IDX,
+            'coinstatsindex': COMPLETE_IDX,
+            'txindex': COMPLETE_IDX,
+        }
+        self.wait_until(lambda: n2.getindexinfo() == completed_idx_state)
+
+        for i in (0, 2):
+            n = self.nodes[i]
+            self.log.info(f"Restarting node {i} to ensure (Check|Load)BlockIndex passes")
+            self.restart_node(i, extra_args=self.extra_args[i])
+
+            assert_equal(n.getblockchaininfo()["blocks"], FINAL_HEIGHT)
+
+            assert_equal(n.getchainstates()['normal']['blocks'], FINAL_HEIGHT)
+            assert_equal(n.getchainstates().get('snapshot'), None)
+
+            if i != 0:
+                # Ensure indexes have synced for the assumeutxo node
+                self.wait_until(lambda: n.getindexinfo() == completed_idx_state)
+
+        self.log.info("Test -reindex-chainstate of an assumeutxo-synced node")
+        self.restart_node(2, extra_args=[
+            '-reindex-chainstate=1', *self.extra_args[2]])
+        assert_equal(n2.getblockchaininfo()["blocks"], FINAL_HEIGHT)
+        wait_until_helper(lambda: n2.getblockcount() == FINAL_HEIGHT)
+
+        self.log.info("Test -reindex of an assumeutxo-synced node")
+        self.restart_node(2, extra_args=['-reindex=1', *self.extra_args[2]])
+        self.connect_nodes(0, 2)
+        wait_until_helper(lambda: n2.getblockcount() == FINAL_HEIGHT)
+
+
+if __name__ == '__main__':
+    AssumeutxoTest().main()
diff --git a/test/functional/test_framework/test_framework.py b/test/functional/test_framework/test_framework.py
index 73e7516ea7..73635b4397 100755
--- a/test/functional/test_framework/test_framework.py
+++ b/test/functional/test_framework/test_framework.py
@@ -979,3 +979,7 @@ class BitcoinTestFramework(metaclass=BitcoinTestMetaClass):
     def is_bdb_compiled(self):
         """Checks whether the wallet module was compiled with BDB support."""
         return self.config["components"].getboolean("USE_BDB")
+
+    def has_blockfile(self, node, filenum: str):
+        blocksdir = os.path.join(node.datadir, self.chain, 'blocks', '')
+        return os.path.isfile(os.path.join(blocksdir, f"blk{filenum}.dat"))
diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index 32aee3aa80..9a0b5c6f0a 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -324,6 +324,7 @@ BASE_SCRIPTS = [
     'wallet_coinbase_category.py --descriptors',
     'feature_filelock.py',
     'feature_loadblock.py',
+    'feature_assumeutxo.py',
     'p2p_dos_header_tree.py',
     'p2p_add_connections.py',
     'feature_bind_port_discover.py',
diff --git a/test/lint/lint-shell.py b/test/lint/lint-shell.py
index 1646bf0d3e..db84ca3d39 100755
--- a/test/lint/lint-shell.py
+++ b/test/lint/lint-shell.py
@@ -67,9 +67,13 @@ def main():
         '*.sh',
     ]
     files = get_files(files_cmd)
-    # remove everything that doesn't match this regex
     reg = re.compile(r'src/[leveldb,secp256k1,minisketch]')
-    files[:] = [file for file in files if not reg.match(file)]
+
+    def should_exclude(fname: str) -> bool:
+        return bool(reg.match(fname)) or 'test_utxo_snapshots.sh' in fname
+
+    # remove everything that doesn't match this regex
+    files[:] = [file for file in files if not should_exclude(file)]
 
     # build the `shellcheck` command
     shellcheck_cmd = [