Merge bitcoin/bitcoin#14604: tests: Add test and refactor feature_block.py

5531119 Added new test for future blocks reacceptance (sanket1729)
511a5af Fixed inconsistencies between code and comments (sanket1729)

Pull request description:

  This Commit does 3 things:
  1) Adds a test case for checking reacceptance a previously rejected block which
  was too far in the future.
  ~~2) clean up uses of rehash or calc_sha256 where it was not needed~~
  3) While constructing block 44, this commit makes the code consistent with the expected figure in
  the comment just above it by adding a transaction to the block.
  4) Fix comment describing `sign_tx()` function

ACKs for top commit:
  duncandean:
    reACK 5531119
  brunoerg:
    reACK 5531119

Tree-SHA512: d40c72fcdbb0b2a0715adc58441eeea08147ee2ec5e371a4ccc824ebfdc6450698bd40aaeecb7ea7bfdb3cd1b264dd821b890276fff8b8d89b7225cdd9d6b546

Author: MarcoFalke

test/functional/feature_block.py

@@ -591,6 +591,8 @@ def run_test(self):
         b44.hashPrevBlock = self.tip.sha256
         b44.nBits = 0x207fffff
         b44.vtx.append(coinbase)
+        tx = self.create_and_sign_transaction(out[14], 1)
+        b44.vtx.append(tx)
         b44.hashMerkleRoot = b44.calc_merkle_root()
         b44.solve()
         self.tip = b44
@@ -678,7 +680,7 @@ def run_test(self):
         # Test block timestamps
         #  -> b31 (8) -> b33 (9) -> b35 (10) -> b39 (11) -> b42 (12) -> b43 (13) -> b53 (14) -> b55 (15)
         #                                                                                   \-> b54 (15)
-        #
+        #                                                                        -> b44 (14)\-> b48 ()
         self.move_tip(43)
         b53 = self.next_block(53, spend=out[14])
         self.send_blocks([b53], False)
@@ -698,6 +700,21 @@ def run_test(self):
         self.send_blocks([b55], True)
         self.save_spendable_output()
 
+        # The block which was previously rejected because of being "too far(3 hours)" must be accepted 2 hours later.
+        # The new block is only 1 hour into future now and we must reorg onto to the new longer chain.
+        # The new bestblock b48p is invalidated manually.
+        #  -> b31 (8) -> b33 (9) -> b35 (10) -> b39 (11) -> b42 (12) -> b43 (13) -> b53 (14) -> b55 (15)
+        #                                                                                   \-> b54 (15)
+        #                                                                        -> b44 (14)\-> b48 () -> b48p ()
+        self.log.info("Accept a previously rejected future block at a later time")
+        node.setmocktime(int(time.time()) + 2*60*60)
+        self.move_tip(48)
+        self.block_heights[b48.sha256] = self.block_heights[b44.sha256] + 1 # b48 is a parent of b44
+        b48p = self.next_block("48p")
+        self.send_blocks([b48, b48p], success=True) # Reorg to the longer chain
+        node.invalidateblock(b48p.hash) # mark b48p as invalid
+        node.setmocktime(0)
+
         # Test Merkle tree malleability
         #
         # -> b42 (12) -> b43 (13) -> b53 (14) -> b55 (15) -> b57p2 (16)
@@ -1308,7 +1325,7 @@ def create_tx(self, spend_tx, n, value, script=CScript([OP_TRUE, OP_DROP] * 15 +
         return create_tx_with_script(spend_tx, n, amount=value, script_pub_key=script)
 
     # sign a transaction, using the key we know about
-    # this signs input 0 in tx, which is assumed to be spending output n in spend_tx
+    # this signs input 0 in tx, which is assumed to be spending output 0 in spend_tx
     def sign_tx(self, tx, spend_tx):
         scriptPubKey = bytearray(spend_tx.vout[0].scriptPubKey)
         if (scriptPubKey[0] == OP_TRUE):  # an anyone-can-spend