Merge #750: [0.18] feature_blocksign.py: Allot for possibility of non…

…-empty block 0.5RTT

128d7e0 feature_blocksign.py: Allot for possibility of non-empty block 0.5RTT (Gregory Sanders)

Pull request description:

  Backport of #747

Tree-SHA512: 9d5aaeb47bc595975fd45269aa2d2d99f943a4dc53739791e558a3eb682c08c60cc7bf761c6c4e230d919c8e4da3926738b8c8655ec4bc02a3f7ce9c65d3361e

test/functional/feature_blocksign.py

@@ -114,16 +114,19 @@ def mine_block(self, make_transactions):
         # miner makes a block
         block = miner.getnewblockhex()
 
-        # other signing nodes get fed compact blocks
+        # All nodes get compact blocks, first node may get complete
+        # block in 0.5 RTT even with transactions thanks to p2p connection
+        # with non-signing node being miner
         for i in range(self.num_keys):
             if i == mineridx:
                 continue
             sketch = miner.getcompactsketch(block)
             compact_response = self.nodes[i].consumecompactsketch(sketch)
-            if make_transactions:
+            if "block_tx_req" in compact_response:
                 block_txn =  self.nodes[i].consumegetblocktxn(block, compact_response["block_tx_req"])
                 final_block = self.nodes[i].finalizecompactblock(sketch, block_txn, compact_response["found_transactions"])
             else:
+                assert (mineridx == 4 and i == 0) or not make_transactions
                 # If there's only coinbase, it should succeed immediately
                 final_block = compact_response["blockhex"]
             # Block should be complete, sans signatures