Merge #16464: [qa] Ensure we don't generate a too-big block in p2sh sigops test

bf3be5297a746982cf8e83f45d342121e5665f80 [qa] Ensure we don't generate a too-big block in p2sh sigops test (Suhas Daftuar)

Pull request description:

  There's a bug in the loop that is calculating the block size in the p2sh sigops test -- we start with the size of the block when it has no transactions, and then increment by the size of each transaction we add, without regard to the changing size of the encoding for the number of transactions in the block.

  This might be fine if the block construction were deterministic, but the first transaction in the block has an ECDSA signature which can be variable length, so we see intermittent failures of this test when the initial transaction has a 70-byte signature and the block ends up being one byte too big.

  Fix this by double-checking the block size after construction.

ACKs for top commit:
  jonasschnelli:
    utACK bf3be5297a746982cf8e83f45d342121e5665f80
  jnewbery:
    tested ACK bf3be5297a746982cf8e83f45d342121e5665f80

Tree-SHA512: f86385b96f7a6feafa4183727f5f2c9aae8ad70060b574aad13b150f174a17ce9a0040bc51ae7a04bd08f2a5298b983a84b0aed5e86a8440189ebc63b99e64dc

1 files changed, 8 insertions, 0 deletions

diff --git a/test/functional/feature_block.py b/test/functional/feature_block.py
index b5eac88ba7..fdb608d457 100755
--- a/test/functional/feature_block.py
+++ b/test/functional/feature_block.py
@@ -486,6 +486,14 @@ class FullBlockTest(BitcoinTestFramework):
             tx_last = tx_new
             b39_outputs += 1
 
+        # The accounting in the loop above can be off, because it misses the
+        # compact size encoding of the number of transactions in the block.
+        # Make sure we didn't accidentally make too big a block. Note that the
+        # size of the block has non-determinism due to the ECDSA signature in
+        # the first transaction.
+        while (len(b39.serialize()) >= MAX_BLOCK_BASE_SIZE):
+            del b39.vtx[-1]
+
         b39 = self.update_block(39, [])
         self.send_blocks([b39], True)
         self.save_spendable_output()