Don't require segwit in getblocktemplate for segwit signalling or mining

Segwit's version bit will be signalled for all invocations of CreateNewBlock,
and not specifying segwit only will cause CreateNewBlock to skip transactions
with witness from being selected.

Github-Pull: #9955
Rebased-From: abe7b3d3abe10e3554b770f40824174b3b217490

6 files changed, 28 insertions, 25 deletions

diff --git a/qa/rpc-tests/p2p-segwit.py b/qa/rpc-tests/p2p-segwit.py
index 2f339bb54f..479f1c6796 100755
--- a/qa/rpc-tests/p2p-segwit.py
+++ b/qa/rpc-tests/p2p-segwit.py
@@ -1701,9 +1701,11 @@ 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:
diff --git a/qa/rpc-tests/segwit.py b/qa/rpc-tests/segwit.py
index d6831e00e3..5dfc7a2f06 100755
--- a/qa/rpc-tests/segwit.py
+++ b/qa/rpc-tests/segwit.py
@@ -251,20 +251,11 @@ class SegWitTest(BitcoinTestFramework):
         assert(tmpl['transactions'][0]['txid'] == txid)
         assert(tmpl['transactions'][0]['sigops'] == 8)
 
-        print("Verify non-segwit miners get a valid GBT response after the fork")
-        send_to_witness(1, self.nodes[0], find_unspent(self.nodes[0], 50), self.pubkey[0], False, Decimal("49.998"))
-        try:
-            tmpl = self.nodes[0].getblocktemplate({})
-            assert(len(tmpl['transactions']) == 1)  # Doesn't include witness tx
-            assert(tmpl['sizelimit'] == 1000000)
-            assert('weightlimit' not in tmpl)
-            assert(tmpl['sigoplimit'] == 20000)
-            assert(tmpl['transactions'][0]['hash'] == txid)
-            assert(tmpl['transactions'][0]['sigops'] == 2)
-            assert(('!segwit' in tmpl['rules']) or ('segwit' not in tmpl['rules']))
-        except JSONRPCException:
-            # This is an acceptable outcome
-            pass
+        print("Non-segwit miners are able to use GBT response after activation.")
+        txid = send_to_witness(1, self.nodes[0], find_unspent(self.nodes[0], 50), self.pubkey[0], False, Decimal("49.998"))
+        tmpl = self.nodes[0].getblocktemplate()
+        # TODO: add a transaction with witness to mempool, and verify it's not
+        # selected for mining.
 
         print("Verify behaviour of importaddress, addwitnessaddress and listunspent")
 
diff --git a/src/miner.cpp b/src/miner.cpp
index d01edd93b5..7b3d94d0e4 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -127,7 +127,7 @@ void BlockAssembler::resetBlock()
     blockFinished = false;
 }
 
-std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn)
+std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn, bool fMineWitnessTx)
 {
     resetBlock();
 
@@ -165,7 +165,7 @@ 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;
 
     addPriorityTxs();
     addPackageTxs();
diff --git a/src/miner.h b/src/miner.h
index 3ba92b16b8..29013c3bcc 100644
--- a/src/miner.h
+++ b/src/miner.h
@@ -165,7 +165,7 @@ private:
 public:
     BlockAssembler(const CChainParams& chainparams);
     /** 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
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 77cd282a3d..38d7b1eb1e 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -519,12 +519,22 @@ 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;
@@ -533,10 +543,11 @@ 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");
 
@@ -686,8 +697,7 @@ 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())));
     }
 
diff --git a/src/versionbits.cpp b/src/versionbits.cpp
index d73f340510..8a7cce7485 100644
--- a/src/versionbits.cpp
+++ b/src/versionbits.cpp
@@ -17,7 +17,7 @@ const struct BIP9DeploymentInfo VersionBitsDeploymentInfo[Consensus::MAX_VERSION
     },
     {
         /*.name =*/ "segwit",
-        /*.gbt_force =*/ false,
+        /*.gbt_force =*/ true,
     }
 };