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

9f5ab670e7c8165f161ec44dbd95778c5515ece0 tests: Use descriptor that requires both legacy and segwit (Andrew Chow)
8a04a386f75d099f4b9864b0cdf7f26442b5801f 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 9f5ab670e7c8165f161ec44dbd95778c5515ece0
  glozow:
    code review ACK 9f5ab670e7c8165f161ec44dbd95778c5515ece0

Tree-SHA512: b7c7ffe8fb0c07bc9e72fbff1f9ef57ee01a57c56bf54b8873345c8b9572c3ce9402b24dc211910b478114a9e6420faef5a4bf8866f38c299971354e54ec4745

2 files changed, 22 insertions, 12 deletions

diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index b037807b53..444e56610e 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -10,6 +10,10 @@ from itertools import product
 
 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 @@ class PSBTTest(BitcoinTestFramework):
         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 @@ class PSBTTest(BitcoinTestFramework):
         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 @@ class PSBTTest(BitcoinTestFramework):
                 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
 
diff --git a/test/functional/wallet_send.py b/test/functional/wallet_send.py
index 86e36be8f7..07baa0595e 100755
--- a/test/functional/wallet_send.py
+++ b/test/functional/wallet_send.py
@@ -10,6 +10,10 @@ from itertools import product
 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 @@ class WalletSendTest(BitcoinTestFramework):
         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 @@ class WalletSendTest(BitcoinTestFramework):
         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 @@ class WalletSendTest(BitcoinTestFramework):
                 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(