Merge #9955: Don't require segwit in getblocktemplate for segwit signalling or mining

c85ffe6 Test transaction selection when gbt called without segwit support (Suhas Daftuar)
abe7b3d Don't require segwit in getblocktemplate for segwit signalling or mining (Suhas Daftuar)

Tree-SHA512: 172496b6d7cdf1879de1266748f2b4ed9fd2ba9ff4a1fd964d74d73c674c16d74bf01a3ba42bf25f2d69f348217c0bbf3412ac64821f222efc9de25a287a5240

qa/rpc-tests/p2p-segwit.py

@@ -1698,9 +1698,11 @@ class SegWitTest(BitcoinTestFramework):
         for node in [self.nodes[0], self.nodes[2]]:
             gbt_results = node.getblocktemplate()
             block_version = gbt_results['version']
-            # If we're not indicating segwit support, we should not be signalling
-            # for segwit activation, nor should we get a witness commitment.
-            assert_equal(block_version & (1 << VB_WITNESS_BIT), 0)
+            # If we're not indicating segwit support, we will still be
+            # signalling for segwit activation.
+            assert_equal((block_version & (1 << VB_WITNESS_BIT) != 0), node == self.nodes[0])
+            # If we don't specify the segwit rule, then we won't get a default
+            # commitment.
             assert('default_witness_commitment' not in gbt_results)
 
         # Workaround:

qa/rpc-tests/segwit.py

@@ -8,9 +8,9 @@ from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
 from test_framework.mininode import sha256, ripemd160, CTransaction, CTxIn, COutPoint, CTxOut, COIN
 from test_framework.address import script_to_p2sh, key_to_p2pkh
-from test_framework.script import CScript, OP_HASH160, OP_CHECKSIG, OP_0, hash160, OP_EQUAL, OP_DUP, OP_EQUALVERIFY, OP_1, OP_2, OP_CHECKMULTISIG, hash160
+from test_framework.script import CScript, OP_HASH160, OP_CHECKSIG, OP_0, hash160, OP_EQUAL, OP_DUP, OP_EQUALVERIFY, OP_1, OP_2, OP_CHECKMULTISIG, hash160, OP_TRUE
 from io import BytesIO
-from test_framework.mininode import FromHex, ToHex
+from test_framework.mininode import ToHex, FromHex, COIN
 
 NODE_0 = 0
 NODE_1 = 1
@@ -250,9 +250,54 @@ class SegWitTest(BitcoinTestFramework):
         assert(tmpl['transactions'][0]['txid'] == txid)
         assert(tmpl['transactions'][0]['sigops'] == 8)
 
-        self.log.info("Non-segwit miners are not able to use GBT response after activation.")
-        send_to_witness(1, self.nodes[0], find_unspent(self.nodes[0], 50), self.pubkey[0], False, Decimal("49.998"))
-        assert_raises_jsonrpc(-8, "Support for 'segwit' rule requires explicit client support", self.nodes[0].getblocktemplate, {})
+        self.nodes[0].generate(1) # Mine a block to clear the gbt cache
+
+        self.log.info("Non-segwit miners are able to use GBT response after activation.")
+        # Create a 3-tx chain: tx1 (non-segwit input, paying to a segwit output) ->
+        #                      tx2 (segwit input, paying to a non-segwit output) ->
+        #                      tx3 (non-segwit input, paying to a non-segwit output).
+        # tx1 is allowed to appear in the block, but no others.
+        txid1 = send_to_witness(1, self.nodes[0], find_unspent(self.nodes[0], 50), self.pubkey[0], False, Decimal("49.996"))
+        hex_tx = self.nodes[0].gettransaction(txid)['hex']
+        tx = FromHex(CTransaction(), hex_tx)
+        assert(tx.wit.is_null()) # This should not be a segwit input
+        assert(txid1 in self.nodes[0].getrawmempool())
+
+        # Now create tx2, which will spend from txid1.
+        tx = CTransaction()
+        tx.vin.append(CTxIn(COutPoint(int(txid1, 16), 0), b''))
+        tx.vout.append(CTxOut(int(49.99*COIN), CScript([OP_TRUE])))
+        tx2_hex = self.nodes[0].signrawtransaction(ToHex(tx))['hex']
+        txid2 = self.nodes[0].sendrawtransaction(tx2_hex)
+        tx = FromHex(CTransaction(), tx2_hex)
+        assert(not tx.wit.is_null())
+
+        # Now create tx3, which will spend from txid2
+        tx = CTransaction()
+        tx.vin.append(CTxIn(COutPoint(int(txid2, 16), 0), b""))
+        tx.vout.append(CTxOut(int(49.95*COIN), CScript([OP_TRUE]))) # Huge fee
+        tx.calc_sha256()
+        txid3 = self.nodes[0].sendrawtransaction(ToHex(tx))
+        assert(tx.wit.is_null())
+        assert(txid3 in self.nodes[0].getrawmempool())
+
+        # Now try calling getblocktemplate() without segwit support.
+        template = self.nodes[0].getblocktemplate()
+
+        # Check that tx1 is the only transaction of the 3 in the template.
+        template_txids = [ t['txid'] for t in template['transactions'] ]
+        assert(txid2 not in template_txids and txid3 not in template_txids)
+        assert(txid1 in template_txids)
+
+        # Check that running with segwit support results in all 3 being included.
+        template = self.nodes[0].getblocktemplate({"rules": ["segwit"]})
+        template_txids = [ t['txid'] for t in template['transactions'] ]
+        assert(txid1 in template_txids)
+        assert(txid2 in template_txids)
+        assert(txid3 in template_txids)
+
+        # Mine a block to clear the gbt cache again.
+        self.nodes[0].generate(1)
 
         self.log.info("Verify behaviour of importaddress, addwitnessaddress and listunspent")
 

src/miner.cpp

@@ -137,7 +137,7 @@ void BlockAssembler::resetBlock()
     nFees = 0;
 }
 
-std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn)
+std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn, bool fMineWitnessTx)
 {
     resetBlock();
 
@@ -175,7 +175,7 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& sc
     // -promiscuousmempoolflags is used.
     // TODO: replace this with a call to main to assess validity of a mempool
     // transaction (which in most cases can be a no-op).
-    fIncludeWitness = IsWitnessEnabled(pindexPrev, chainparams.GetConsensus());
+    fIncludeWitness = IsWitnessEnabled(pindexPrev, chainparams.GetConsensus()) && fMineWitnessTx;
 
     addPackageTxs();
 

src/miner.h

@@ -170,7 +170,7 @@ public:
     BlockAssembler(const CChainParams& params, const Options& options);
 
     /** Construct a new block template with coinbase to scriptPubKeyIn */
-    std::unique_ptr<CBlockTemplate> CreateNewBlock(const CScript& scriptPubKeyIn);
+    std::unique_ptr<CBlockTemplate> CreateNewBlock(const CScript& scriptPubKeyIn, bool fMineWitnessTx=true);
 
 private:
     // utility functions

src/rpc/mining.cpp

@@ -514,12 +514,22 @@ UniValue getblocktemplate(const JSONRPCRequest& request)
         // TODO: Maybe recheck connections/IBD and (if something wrong) send an expires-immediately template to stop miners?
     }
 
+    const struct BIP9DeploymentInfo& segwit_info = VersionBitsDeploymentInfo[Consensus::DEPLOYMENT_SEGWIT];
+    // If the caller is indicating segwit support, then allow CreateNewBlock()
+    // to select witness transactions, after segwit activates (otherwise
+    // don't).
+    bool fSupportsSegwit = setClientRules.find(segwit_info.name) != setClientRules.end();
+
     // Update block
     static CBlockIndex* pindexPrev;
     static int64_t nStart;
     static std::unique_ptr<CBlockTemplate> pblocktemplate;
+    // Cache whether the last invocation was with segwit support, to avoid returning
+    // a segwit-block to a non-segwit caller.
+    static bool fLastTemplateSupportsSegwit = true;
     if (pindexPrev != chainActive.Tip() ||
-        (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLast && GetTime() - nStart > 5))
+        (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLast && GetTime() - nStart > 5) ||
+        fLastTemplateSupportsSegwit != fSupportsSegwit)
     {
         // Clear pindexPrev so future calls make a new block, despite any failures from here on
         pindexPrev = nullptr;
@@ -528,10 +538,11 @@ UniValue getblocktemplate(const JSONRPCRequest& request)
         nTransactionsUpdatedLast = mempool.GetTransactionsUpdated();
         CBlockIndex* pindexPrevNew = chainActive.Tip();
         nStart = GetTime();
+        fLastTemplateSupportsSegwit = fSupportsSegwit;
 
         // Create new block
         CScript scriptDummy = CScript() << OP_TRUE;
-        pblocktemplate = BlockAssembler(Params()).CreateNewBlock(scriptDummy);
+        pblocktemplate = BlockAssembler(Params()).CreateNewBlock(scriptDummy, fSupportsSegwit);
         if (!pblocktemplate)
             throw JSONRPCError(RPC_OUT_OF_MEMORY, "Out of memory");
 
@@ -681,8 +692,7 @@ UniValue getblocktemplate(const JSONRPCRequest& request)
     result.push_back(Pair("bits", strprintf("%08x", pblock->nBits)));
     result.push_back(Pair("height", (int64_t)(pindexPrev->nHeight+1)));
 
-    const struct BIP9DeploymentInfo& segwit_info = VersionBitsDeploymentInfo[Consensus::DEPLOYMENT_SEGWIT];
-    if (!pblocktemplate->vchCoinbaseCommitment.empty() && setClientRules.find(segwit_info.name) != setClientRules.end()) {
+    if (!pblocktemplate->vchCoinbaseCommitment.empty() && fSupportsSegwit) {
         result.push_back(Pair("default_witness_commitment", HexStr(pblocktemplate->vchCoinbaseCommitment.begin(), pblocktemplate->vchCoinbaseCommitment.end())));
     }
 

src/versionbits.cpp

@@ -17,7 +17,7 @@ const struct BIP9DeploymentInfo VersionBitsDeploymentInfo[Consensus::MAX_VERSION
     },
     {
         /*.name =*/ "segwit",
-        /*.gbt_force =*/ false,
+        /*.gbt_force =*/ true,
     }
 };