1 files changed, 14 insertions, 4 deletions

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())));
     }