From 8c5b3646b5afe8a61f5c66478d8e11f0d2ce5108 Mon Sep 17 00:00:00 2001 From: Greg Sanders Date: Wed, 5 Oct 2022 14:50:30 -0400 Subject: Relax MIN_STANDARD_TX_NONWITNESS_SIZE to 65 non-witness bytes Since the original fix was set to be a "reasonable" transaction to reduce allocations and the true motivation later revealed, it makes sense to relax this check to something more principled. There are more exotic transaction patterns that could take advantage of a relaxed requirement, such as 1 input, 1 output OP_RETURN to burn a utxo to fees for CPFP purposes when change isn't practical. Two changes could be accomplished: 1) Anything not 64 bytes could be allowed 2) Anything above 64 bytes could be allowed In the Great Consensus Cleanup, suggestion (2) was the route taken. It would not allow an "empty" OP_RETURN but would reduce the required padding from 22 bytes to 5. The functional test is also modified to test the actual case we care about: 64 bytes --- test/functional/test_framework/script_util.py | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) (limited to 'test/functional/test_framework') diff --git a/test/functional/test_framework/script_util.py b/test/functional/test_framework/script_util.py index b114002145..39dcb418b7 100755 --- a/test/functional/test_framework/script_util.py +++ b/test/functional/test_framework/script_util.py @@ -13,12 +13,13 @@ from test_framework.script import ( OP_EQUAL, OP_EQUALVERIFY, OP_HASH160, + OP_RETURN, hash160, sha256, ) # To prevent a "tx-size-small" policy rule error, a transaction has to have a -# non-witness size of at least 82 bytes (MIN_STANDARD_TX_NONWITNESS_SIZE in +# non-witness size of at least 65 bytes (MIN_STANDARD_TX_NONWITNESS_SIZE in # src/policy/policy.h). Considering a Tx with the smallest possible single # input (blank, empty scriptSig), and with an output omitting the scriptPubKey, # we get to a minimum size of 60 bytes: @@ -28,15 +29,15 @@ from test_framework.script import ( # Output: 8 [Amount] + 1 [scriptPubKeyLen] = 9 bytes # # Hence, the scriptPubKey of the single output has to have a size of at -# least 22 bytes, which corresponds to the size of a P2WPKH scriptPubKey. -# The following script constant consists of a single push of 21 bytes of 'a': -# <21-bytes of 'a'> -# resulting in a 22-byte size. It should be used whenever (small) fake -# scriptPubKeys are needed, to guarantee that the minimum transaction size is -# met. -DUMMY_P2WPKH_SCRIPT = CScript([b'a' * 21]) -DUMMY_2_P2WPKH_SCRIPT = CScript([b'b' * 21]) - +# least 5 bytes. +MIN_STANDARD_TX_NONWITNESS_SIZE = 65 +MIN_PADDING = MIN_STANDARD_TX_NONWITNESS_SIZE - 10 - 41 - 9 +assert MIN_PADDING == 5 + +# This script cannot be spent, allowing dust output values under +# standardness checks +DUMMY_MIN_OP_RETURN_SCRIPT = CScript([OP_RETURN] + ([OP_0] * (MIN_PADDING - 1))) +assert len(DUMMY_MIN_OP_RETURN_SCRIPT) == MIN_PADDING def key_to_p2pk_script(key): key = check_key(key) -- cgit v1.2.3