Merge bitcoin/bitcoin#24454: tests: Fix calculation of external input weights

9f5ab67 tests: Use descriptor that requires both legacy and segwit (Andrew Chow)
8a04a38 tests: Calculate input weight more accurately (Andrew Chow)

Pull request description:

  The external input tests with specifying input weight would sometimes result in a test failure because it would add 2 to the calculated byte size in order to account for some of the variation in signature and script sizes. However 1 in 128 signatures are actually 1 byte smaller than we expect, so the difference between the actual signature size and our calculated size becomes 3 bytes which is outside of the tolerance of `assert_fee_amount` and would thus cause the test failure.

  To resolve this, the 2 byte buffer is reduced to 1 byte, so in the above scenario, the difference is 2 bytes which is within the tolerance of `assert_fee_amount`. Additionally, instead of putting a fixed size that we assume is the correct size for the length of the compact size length prefix of data, we actually get the length of the compact size uint.

  Lastly, the size calculation for a scriptWitness was simply incorrect and used fields that did not exist. This is fixed, and the test slightly modified so that it also produces a scriptWitness.

  Fixes #24151

ACKs for top commit:
  jonatack:
    re-ACK 9f5ab67
  glozow:
    code review ACK 9f5ab67

Tree-SHA512: b7c7ffe8fb0c07bc9e72fbff1f9ef57ee01a57c56bf54b8873345c8b9572c3ce9402b24dc211910b478114a9e6420faef5a4bf8866f38c299971354e54ec4745

Author: fanquake

test/functional/rpc_psbt.py

@@ -10,6 +10,10 @@
 
 from test_framework.descriptors import descsum_create
 from test_framework.key import ECKey
+from test_framework.messages import (
+    ser_compact_size,
+    WITNESS_SCALE_FACTOR,
+)
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_approx,
@@ -615,8 +619,8 @@ def test_psbt_input_keys(psbt_input, keys):
         self.nodes[1].createwallet("extfund")
         wallet = self.nodes[1].get_wallet_rpc("extfund")
 
-        # Make a weird but signable script. sh(pkh()) descriptor accomplishes this
-        desc = descsum_create("sh(pkh({}))".format(privkey))
+        # Make a weird but signable script. sh(wsh(pkh())) descriptor accomplishes this
+        desc = descsum_create("sh(wsh(pkh({})))".format(privkey))
         if self.options.descriptors:
             res = self.nodes[0].importdescriptors([{"desc": desc, "timestamp": "now"}])
         else:
@@ -634,7 +638,7 @@ def test_psbt_input_keys(psbt_input, keys):
         assert_raises_rpc_error(-4, "Insufficient funds", wallet.walletcreatefundedpsbt, [ext_utxo], {self.nodes[0].getnewaddress(): 15})
 
         # But funding should work when the solving data is provided
-        psbt = wallet.walletcreatefundedpsbt([ext_utxo], {self.nodes[0].getnewaddress(): 15}, 0, {"add_inputs": True, "solving_data": {"pubkeys": [addr_info['pubkey']], "scripts": [addr_info["embedded"]["scriptPubKey"]]}})
+        psbt = wallet.walletcreatefundedpsbt([ext_utxo], {self.nodes[0].getnewaddress(): 15}, 0, {"add_inputs": True, "solving_data": {"pubkeys": [addr_info['pubkey']], "scripts": [addr_info["embedded"]["scriptPubKey"], addr_info["embedded"]["embedded"]["scriptPubKey"]]}})
         signed = wallet.walletprocesspsbt(psbt['psbt'])
         assert not signed['complete']
         signed = self.nodes[0].walletprocesspsbt(signed['psbt'])
@@ -655,10 +659,11 @@ def test_psbt_input_keys(psbt_input, keys):
                 break
         psbt_in = dec["inputs"][input_idx]
         # Calculate the input weight
-        # (prevout + sequence + length of scriptSig + 2 bytes buffer) * 4 + len of scriptwitness
+        # (prevout + sequence + length of scriptSig + scriptsig + 1 byte buffer) * WITNESS_SCALE_FACTOR + num scriptWitness stack items + (length of stack item + stack item) * N stack items + 1 byte buffer
         len_scriptsig = len(psbt_in["final_scriptSig"]["hex"]) // 2 if "final_scriptSig" in psbt_in else 0
-        len_scriptwitness = len(psbt_in["final_scriptwitness"]["hex"]) // 2 if "final_scriptwitness" in psbt_in else 0
-        input_weight = ((41 + len_scriptsig + 2) * 4) + len_scriptwitness
+        len_scriptsig += len(ser_compact_size(len_scriptsig)) + 1
+        len_scriptwitness = (sum([(len(x) // 2) + len(ser_compact_size(len(x) // 2)) for x in psbt_in["final_scriptwitness"]]) + len(psbt_in["final_scriptwitness"]) + 1) if "final_scriptwitness" in psbt_in else 0
+        input_weight = ((40 + len_scriptsig) * WITNESS_SCALE_FACTOR) + len_scriptwitness
         low_input_weight = input_weight // 2
         high_input_weight = input_weight * 2
 

test/functional/wallet_send.py

@@ -10,6 +10,10 @@
 from test_framework.authproxy import JSONRPCException
 from test_framework.descriptors import descsum_create
 from test_framework.key import ECKey
+from test_framework.messages import (
+    ser_compact_size,
+    WITNESS_SCALE_FACTOR,
+)
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
@@ -488,8 +492,8 @@ def run_test(self):
         self.nodes[1].createwallet("extfund")
         ext_fund = self.nodes[1].get_wallet_rpc("extfund")
 
-        # Make a weird but signable script. sh(pkh()) descriptor accomplishes this
-        desc = descsum_create("sh(pkh({}))".format(privkey))
+        # Make a weird but signable script. sh(wsh(pkh())) descriptor accomplishes this
+        desc = descsum_create("sh(wsh(pkh({})))".format(privkey))
         if self.options.descriptors:
             res = ext_fund.importdescriptors([{"desc": desc, "timestamp": "now"}])
         else:
@@ -507,7 +511,7 @@ def run_test(self):
         self.test_send(from_wallet=ext_wallet, to_wallet=self.nodes[0], amount=15, inputs=[ext_utxo], add_inputs=True, psbt=True, include_watching=True, expect_error=(-4, "Insufficient funds"))
 
         # But funding should work when the solving data is provided
-        res = self.test_send(from_wallet=ext_wallet, to_wallet=self.nodes[0], amount=15, inputs=[ext_utxo], add_inputs=True, psbt=True, include_watching=True, solving_data={"pubkeys": [addr_info['pubkey']], "scripts": [addr_info["embedded"]["scriptPubKey"]]})
+        res = self.test_send(from_wallet=ext_wallet, to_wallet=self.nodes[0], amount=15, inputs=[ext_utxo], add_inputs=True, psbt=True, include_watching=True, solving_data={"pubkeys": [addr_info['pubkey']], "scripts": [addr_info["embedded"]["scriptPubKey"], addr_info["embedded"]["embedded"]["scriptPubKey"]]})
         signed = ext_wallet.walletprocesspsbt(res["psbt"])
         signed = ext_fund.walletprocesspsbt(res["psbt"])
         assert signed["complete"]
@@ -526,10 +530,11 @@ def run_test(self):
                 break
         psbt_in = dec["inputs"][input_idx]
         # Calculate the input weight
-        # (prevout + sequence + length of scriptSig + 2 bytes buffer) * 4 + len of scriptwitness
+        # (prevout + sequence + length of scriptSig + scriptsig + 1 byte buffer) * WITNESS_SCALE_FACTOR + num scriptWitness stack items + (length of stack item + stack item) * N stack items + 1 byte buffer
         len_scriptsig = len(psbt_in["final_scriptSig"]["hex"]) // 2 if "final_scriptSig" in psbt_in else 0
-        len_scriptwitness = len(psbt_in["final_scriptwitness"]["hex"]) // 2 if "final_scriptwitness" in psbt_in else 0
-        input_weight = ((41 + len_scriptsig + 2) * 4) + len_scriptwitness
+        len_scriptsig += len(ser_compact_size(len_scriptsig)) + 1
+        len_scriptwitness = (sum([(len(x) // 2) + len(ser_compact_size(len(x) // 2)) for x in psbt_in["final_scriptwitness"]]) + len(psbt_in["final_scriptwitness"]) + 1) if "final_scriptwitness" in psbt_in else 0
+        input_weight = ((40 + len_scriptsig) * WITNESS_SCALE_FACTOR) + len_scriptwitness
 
         # Input weight error conditions
         assert_raises_rpc_error(