6 files changed, 29 insertions, 14 deletions

diff --git a/qa/rpc-tests/p2p-segwit.py b/qa/rpc-tests/p2p-segwit.py
index 0f844883b1..dcf2b9a7de 100755
--- a/qa/rpc-tests/p2p-segwit.py
+++ b/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:
diff --git a/qa/rpc-tests/segwit.py b/qa/rpc-tests/segwit.py
index 36eb0dbdc8..50ace12aa7 100755
--- a/qa/rpc-tests/segwit.py
+++ b/qa/rpc-tests/segwit.py
@@ -250,9 +250,12 @@ 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.log.info("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"))
+        #assert_raises_jsonrpc(-8, "Support for 'segwit' rule requires explicit client support", self.nodes[0].getblocktemplate, {})
+        tmpl = self.nodes[0].getblocktemplate()
+        # TODO: add a transaction with witness to mempool, and verify it's not
+        # selected for mining.
 
         self.log.info("Verify behaviour of importaddress, addwitnessaddress and listunspent")
 
diff --git a/src/miner.cpp b/src/miner.cpp
index 67e7ff155b..ff28a5680e 100644
--- a/src/miner.cpp
+++ b/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();
 
diff --git a/src/miner.h b/src/miner.h
index c105d07c23..a159b05534 100644
--- a/src/miner.h
+++ b/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
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index abdfa651ab..4db8ffaa7d 100644
--- a/src/rpc/mining.cpp
+++ b/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())));
     }
 
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,
     }
 };