[tests] make pruning test faster

This commit makes the pruning.py much faster.

Key insights to do this:

- pruning.py doesn't care what kind of transactions make up the big
blocks that are pruned in the test. Instead of making blocks with
several large, expensive to construct and validate transactions,
instead make the large blocks contain a single coinbase transaction with
a huge OP_RETURN txout.
- avoid stop-starting nodes where possible.

This test could probably be made even faster by using the P2P interface
for submitting blocks instead of the submitblock RPC.

Author: jnewbery

test/functional/feature_pruning.py

@@ -8,11 +8,13 @@
 This test uses 4GB of disk space.
 This test takes 30 mins or more (up to 2 hours)
 """
+import os
 
+from test_framework.blocktools import create_coinbase
+from test_framework.messages import CBlock, ToHex
+from test_framework.script import CScript, OP_RETURN, OP_NOP
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal, assert_greater_than, assert_raises_rpc_error, connect_nodes, mine_large_block, sync_blocks, wait_until
-
-import os
+from test_framework.util import assert_equal, assert_greater_than, assert_raises_rpc_error, connect_nodes, disconnect_nodes, sync_blocks, wait_until
 
 MIN_BLOCKS_TO_KEEP = 288
 
@@ -21,6 +23,47 @@
 # compatible with pruning based on key creation time.
 TIMESTAMP_WINDOW = 2 * 60 * 60
 
+def mine_large_blocks(node, n):
+    # Make a large scriptPubKey for the coinbase transaction. This is OP_RETURN
+    # followed by 950k of OP_NOP. This would be non-standard in a non-coinbase
+    # transaction but is consensus valid.
+
+    # Get the block parameters for the first block
+    big_script = CScript([OP_RETURN] + [OP_NOP] * 950000)
+    best_block = node.getblock(node.getbestblockhash())
+    height = int(best_block["height"]) + 1
+    try:
+        # Static variable ensures that time is monotonicly increasing and is therefore
+        # different for each block created => blockhash is unique.
+        mine_large_blocks.nTime = min(mine_large_blocks.nTime, int(best_block["time"])) + 1
+    except AttributeError:
+        mine_large_blocks.nTime = int(best_block["time"]) + 1
+    previousblockhash = int(best_block["hash"], 16)
+
+    for _ in range(n):
+        # Build the coinbase transaction (with large scriptPubKey)
+        coinbase_tx = create_coinbase(height)
+        coinbase_tx.vin[0].nSequence = 2 ** 32 - 1
+        coinbase_tx.vout[0].scriptPubKey = big_script
+        coinbase_tx.rehash()
+
+        # Build the block
+        block = CBlock()
+        block.nVersion = best_block["version"]
+        block.hashPrevBlock = previousblockhash
+        block.nTime = mine_large_blocks.nTime
+        block.nBits = int('207fffff', 16)
+        block.nNonce = 0
+        block.vtx = [coinbase_tx]
+        block.hashMerkleRoot = block.calc_merkle_root()
+        block.solve()
+
+        # Submit to the node
+        node.submitblock(ToHex(block))
+
+        previousblockhash = block.sha256
+        height += 1
+        mine_large_blocks.nTime += 1
 
 def calc_usage(blockdir):
     return sum(os.path.getsize(blockdir + f) for f in os.listdir(blockdir) if os.path.isfile(os.path.join(blockdir, f))) / (1024. * 1024.)
@@ -29,11 +72,10 @@ class PruneTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 6
-        self.rpc_timeout = 900
 
         # Create nodes 0 and 1 to mine.
         # Create node 2 to test pruning.
-        self.full_node_default_args = ["-maxreceivebuffer=20000", "-checkblocks=5", "-limitdescendantcount=100", "-limitdescendantsize=5000", "-limitancestorcount=100", "-limitancestorsize=5000"]
+        self.full_node_default_args = ["-maxreceivebuffer=20000", "-checkblocks=5"]
         # Create nodes 3 and 4 to test manual pruning (they will be re-started with manual pruning later)
         # Create nodes 5 to test wallet in prune mode, but do not connect
         self.extra_args = [
@@ -73,8 +115,7 @@ def create_big_chain(self):
         self.nodes[0].generate(150)
 
         # Then mine enough full blocks to create more than 550MiB of data
-        for i in range(645):
-            mine_large_block(self.nodes[0], self.utxo_cache_0)
+        mine_large_blocks(self.nodes[0], 645)
 
         sync_blocks(self.nodes[0:5])
 
@@ -84,8 +125,7 @@ def test_height_min(self):
         self.log.info("Though we're already using more than 550MiB, current usage: %d" % calc_usage(self.prunedir))
         self.log.info("Mining 25 more blocks should cause the first block file to be pruned")
         # Pruning doesn't run until we're allocating another chunk, 20 full blocks past the height cutoff will ensure this
-        for i in range(25):
-            mine_large_block(self.nodes[0], self.utxo_cache_0)
+        mine_large_blocks(self.nodes[0], 25)
 
         # Wait for blk00000.dat to be pruned
         wait_until(lambda: not os.path.isfile(os.path.join(self.prunedir, "blk00000.dat")), timeout=30)
@@ -102,22 +142,13 @@ def create_chain_with_staleblocks(self):
         for j in range(12):
             # Disconnect node 0 so it can mine a longer reorg chain without knowing about node 1's soon-to-be-stale chain
             # Node 2 stays connected, so it hears about the stale blocks and then reorg's when node0 reconnects
-            # Stopping node 0 also clears its mempool, so it doesn't have node1's transactions to accidentally mine
-            self.stop_node(0)
-            self.start_node(0, extra_args=self.full_node_default_args)
+            disconnect_nodes(self.nodes[0], 1)
+            disconnect_nodes(self.nodes[0], 2)
             # Mine 24 blocks in node 1
-            for i in range(24):
-                if j == 0:
-                    mine_large_block(self.nodes[1], self.utxo_cache_1)
-                else:
-                    # Add node1's wallet transactions back to the mempool, to
-                    # avoid the mined blocks from being too small.
-                    self.nodes[1].resendwallettransactions()
-                    self.nodes[1].generate(1) #tx's already in mempool from previous disconnects
+            mine_large_blocks(self.nodes[1], 24)
 
             # Reorg back with 25 block chain from node 0
-            for i in range(25):
-                mine_large_block(self.nodes[0], self.utxo_cache_0)
+            mine_large_blocks(self.nodes[0], 25)
 
             # Create connections in the order so both nodes can see the reorg at the same time
             connect_nodes(self.nodes[0], 1)
@@ -129,10 +160,6 @@ def create_chain_with_staleblocks(self):
     def reorg_test(self):
         # Node 1 will mine a 300 block chain starting 287 blocks back from Node 0 and Node 2's tip
         # This will cause Node 2 to do a reorg requiring 288 blocks of undo data to the reorg_test chain
-        # Reboot node 1 to clear its mempool (hopefully make the invalidate faster)
-        # Lower the block max size so we don't keep mining all our big mempool transactions (from disconnected blocks)
-        self.stop_node(1)
-        self.start_node(1, extra_args=["-maxreceivebuffer=20000","-blockmaxweight=20000", "-checkblocks=5"])
 
         height = self.nodes[1].getblockcount()
         self.log.info("Current block height: %d" % height)
@@ -153,9 +180,9 @@ def reorg_test(self):
         assert self.nodes[1].getblockcount() == self.forkheight - 1
         self.log.info("New best height: %d" % self.nodes[1].getblockcount())
 
-        # Reboot node1 to clear those giant tx's from mempool
-        self.stop_node(1)
-        self.start_node(1, extra_args=["-maxreceivebuffer=20000","-blockmaxweight=20000", "-checkblocks=5"])
+        # Disconnect node1 and generate the new chain
+        disconnect_nodes(self.nodes[0], 1)
+        disconnect_nodes(self.nodes[1], 2)
 
         self.log.info("Generating new longer chain of 300 more blocks")
         self.nodes[1].generate(300)
@@ -167,17 +194,10 @@ def reorg_test(self):
 
         self.log.info("Verify height on node 2: %d" % self.nodes[2].getblockcount())
         self.log.info("Usage possibly still high because of stale blocks in block files: %d" % calc_usage(self.prunedir))
-        self.log.info("Mine 220 more large blocks so we have requisite history")
 
-        # Get node0's wallet transactions back in its mempool, to avoid the
-        # mined blocks from being too small.
-        self.nodes[0].resendwallettransactions()
+        self.log.info("Mine 220 more large blocks so we have requisite history")
 
-        for i in range(22):
-            # This can be slow, so do this in multiple RPC calls to avoid
-            # RPC timeouts.
-            self.nodes[0].generate(10) #node 0 has many large tx's in its mempool from the disconnects
-        sync_blocks(self.nodes[0:3], timeout=300)
+        mine_large_blocks(self.nodes[0], 220)
 
         usage = calc_usage(self.prunedir)
         self.log.info("Usage should be below target: %d" % usage)
@@ -331,16 +351,9 @@ def wallet_test(self):
         self.log.info("Success")
 
     def run_test(self):
-        self.log.info("Warning! This test requires 4GB of disk space and takes over 30 mins (up to 2 hours)")
-        self.log.info("Mining a big blockchain of 995 blocks")
-
-        # Determine default relay fee
-        self.relayfee = self.nodes[0].getnetworkinfo()["relayfee"]
-
-        # Cache for utxos, as the listunspent may take a long time later in the test
-        self.utxo_cache_0 = []
-        self.utxo_cache_1 = []
+        self.log.info("Warning! This test requires 4GB of disk space")
 
+        self.log.info("Mining a big blockchain of 995 blocks")
         self.create_big_chain()
         # Chain diagram key:
         # *   blocks on main chain