test: coverage for 16-20 segwit multisig scripts

This exercises the bug fixed by previous commits, where
we were unable to generate and sign for segwit redeem scripts
(in this case multisig redeem scripts) longer than 520 bytes.

and also, this adds coverage for legacy 15-15 multisig script
generation and signing.

Author: furszy

test/functional/rpc_createmultisig.py

@@ -56,12 +56,13 @@ def run_test(self):
         self.generate(self.wallet, 149)
 
         wallet_multi = self.create_wallet(node1, 'wmulti') if self._requires_wallet else None
-        self.create_keys(5)
-        for nkeys in [3, 5]:
-            for nsigs in [2, 3]:
-                for output_type in ["bech32", "p2sh-segwit", "legacy"]:
-                    self.do_multisig(nkeys, nsigs, output_type, wallet_multi)
+        self.create_keys(21)  # max number of allowed keys + 1
+        m_of_n = [(2, 3), (3, 3), (2, 5), (3, 5), (10, 15), (15, 15)]
+        for (sigs, keys) in m_of_n:
+            for output_type in ["bech32", "p2sh-segwit", "legacy"]:
+                self.do_multisig(keys, sigs, output_type, wallet_multi)
 
+        self.test_multisig_script_limit()
         self.test_mixing_uncompressed_and_compressed_keys(node0, wallet_multi)
         self.test_sortedmulti_descriptors_bip67()
 
@@ -83,6 +84,21 @@ def check_addmultisigaddress_errors(self):
         pubs = [self.nodes[1].getaddressinfo(addr)["pubkey"] for addr in addresses]
         assert_raises_rpc_error(-5, "Bech32m multisig addresses cannot be created with legacy wallets", self.nodes[0].addmultisigaddress, 2, pubs, "", "bech32m")
 
+    def test_multisig_script_limit(self):
+        node1 = self.nodes[1]
+        pubkeys = self.pub[0:20]
+
+        self.log.info('Test legacy redeem script max size limit')
+        assert_raises_rpc_error(-8, "redeemScript exceeds size limit: 684 > 520", node1.createmultisig, 16, pubkeys, 'legacy')
+
+        self.log.info('Test valid 16-20 multisig p2sh-legacy and bech32 (no wallet)')
+        self.do_multisig(nkeys=20, nsigs=16, output_type="p2sh-segwit", wallet_multi=None)
+        self.do_multisig(nkeys=20, nsigs=16, output_type="bech32", wallet_multi=None)
+
+        self.log.info('Test invalid 16-21 multisig p2sh-legacy and bech32 (no wallet)')
+        assert_raises_rpc_error(-8, "Number of keys involved in the multisignature address creation > 20", node1.createmultisig, 16, self.pub, 'p2sh-segwit')
+        assert_raises_rpc_error(-8, "Number of keys involved in the multisignature address creation > 20", node1.createmultisig, 16, self.pub, 'bech32')
+
     def do_multisig(self, nkeys, nsigs, output_type, wallet_multi):
         node0, node1, node2 = self.nodes
         pub_keys = self.pub[0: nkeys]
@@ -117,13 +133,13 @@ def do_multisig(self, nkeys, nsigs, output_type, wallet_multi):
             assert mredeemw == mredeem
 
         spk = address_to_scriptpubkey(madd)
-        value = decimal.Decimal("0.00001300")
+        value = decimal.Decimal("0.00004000")
         tx = self.wallet.send_to(from_node=self.nodes[0], scriptPubKey=spk, amount=int(value * COIN))
         prevtxs = [{"txid": tx["txid"], "vout": tx["sent_vout"], "scriptPubKey": spk.hex(), "redeemScript": mredeem, "amount": value}]
 
         self.generate(node0, 1)
 
-        outval = value - decimal.Decimal("0.00001000")
+        outval = value - decimal.Decimal("0.00002000")  # deduce fee (must be higher than the min relay fee)
         # send coins to node2 when wallet is enabled
         node2_balance = node2.getbalances()['mine']['trusted'] if self.is_wallet_compiled() else 0
         out_addr = node2.getnewaddress() if self.is_wallet_compiled() else getnewdestination('bech32')[2]
@@ -157,6 +173,7 @@ def do_multisig(self, nkeys, nsigs, output_type, wallet_multi):
 
         rawtx2 = node2.signrawtransactionwithkey(rawtx, priv_keys[0:nsigs - 1], prevtxs)
         rawtx3 = node2.signrawtransactionwithkey(rawtx2["hex"], [priv_keys[-1]], prevtxs)
+        assert rawtx3['complete']
 
         tx = node0.sendrawtransaction(rawtx3["hex"], 0)
         blk = self.generate(node0, 1)[0]