[qa] p2p segwit tests

mininode now supports witness transactions/blocks, blocktools
has a helper for adding witness commitments to blocks, and script
has a function to calculate hashes for signature under sigversion
1, used by segwit.

Py3 conversion by Marco Falke

Test to make sure upgraded nodes don't ask for non-wit blocks by
Gregory Sanders.

qa/rpc-tests/test_framework/blocktools.py

@@ -5,7 +5,7 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 from .mininode import *
-from .script import CScript, OP_TRUE, OP_CHECKSIG
+from .script import CScript, OP_TRUE, OP_CHECKSIG, OP_RETURN
 
 # Create a block (with regtest difficulty)
 def create_block(hashprev, coinbase, nTime=None):
@@ -22,6 +22,29 @@ def create_block(hashprev, coinbase, nTime=None):
     block.calc_sha256()
     return block
 
+# From BIP141
+WITNESS_COMMITMENT_HEADER = b"\xaa\x21\xa9\xed"
+
+# According to BIP141, blocks with witness rules active must commit to the
+# hash of all in-block transactions including witness.
+def add_witness_commitment(block, nonce=0):
+    # First calculate the merkle root of the block's
+    # transactions, with witnesses.
+    witness_nonce = nonce
+    witness_root = block.calc_witness_merkle_root()
+    witness_commitment = uint256_from_str(hash256(ser_uint256(witness_root)+ser_uint256(witness_nonce)))
+    # witness_nonce should go to coinbase witness.
+    block.vtx[0].wit.vtxinwit = [CTxinWitness()]
+    block.vtx[0].wit.vtxinwit[0].scriptWitness.stack = [ser_uint256(witness_nonce)]
+
+    # witness commitment is the last OP_RETURN output in coinbase
+    output_data = WITNESS_COMMITMENT_HEADER + ser_uint256(witness_commitment)
+    block.vtx[0].vout.append(CTxOut(0, CScript([OP_RETURN, output_data])))
+    block.vtx[0].rehash()
+    block.hashMerkleRoot = block.calc_merkle_root()
+    block.rehash()
+
+
 def serialize_script_num(value):
     r = bytearray(0)
     if value == 0: