versionbits: add expiry support to versionbit deployments

Github-Pull: #238
Rebased-From: 7de9918

Author: dathonohm

src/consensus/params.h

@@ -52,6 +52,9 @@ struct BIP9Deployment {
      *  boundary.
      */
     int min_activation_height{0};
+    /** For temporary softforks: number of blocks the deployment remains active after activation.
+     *  std::numeric_limits<int>::max() means permanent (never expires). */
+    int active_duration{std::numeric_limits<int>::max()};
 
     /** Constant for nTimeout very far in the future. */
     static constexpr int64_t NO_TIMEOUT = std::numeric_limits<int64_t>::max();

src/deploymentstatus.h

@@ -20,7 +20,15 @@ inline bool DeploymentActiveAfter(const CBlockIndex* pindexPrev, const Consensus
 inline bool DeploymentActiveAfter(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos dep, VersionBitsCache& versionbitscache)
 {
     assert(Consensus::ValidDeployment(dep));
-    return ThresholdState::ACTIVE == versionbitscache.State(pindexPrev, params, dep);
+    if (ThresholdState::ACTIVE != versionbitscache.State(pindexPrev, params, dep)) return false;
+
+    const auto& deployment = params.vDeployments[dep];
+    // Permanent deployment (never expires)
+    if (deployment.active_duration == std::numeric_limits<int>::max()) return true;
+
+    const int activation_height = versionbitscache.StateSinceHeight(pindexPrev, params, dep);
+    const int height = pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1;
+    return height < activation_height + deployment.active_duration;
 }
 
 /** Determine if a deployment is active for this block */

src/rpc/blockchain.cpp

@@ -1729,7 +1729,13 @@ static void SoftForkDescPushBack(const CBlockIndex* blockindex, UniValue& softfo
     UniValue rv(UniValue::VOBJ);
     rv.pushKV("type", "bip9");
     if (ThresholdState::ACTIVE == next_state) {
-        rv.pushKV("height", chainman.m_versionbitscache.StateSinceHeight(blockindex, chainman.GetConsensus(), id));
+        const int activation_height = chainman.m_versionbitscache.StateSinceHeight(blockindex, chainman.GetConsensus(), id);
+        rv.pushKV("height", activation_height);
+        // Add height_end for temporary softforks
+        const auto& deployment = chainman.GetConsensus().vDeployments[id];
+        if (deployment.active_duration < std::numeric_limits<int>::max()) {
+            rv.pushKV("height_end", activation_height + deployment.active_duration - 1);
+        }
     }
     rv.pushKV("active", ThresholdState::ACTIVE == next_state);
     rv.pushKV("bip9", std::move(bip9));
@@ -1826,7 +1832,8 @@ RPCHelpMan getblockchaininfo()
 namespace {
 const std::vector<RPCResult> RPCHelpForDeployment{
     {RPCResult::Type::STR, "type", "one of \"buried\", \"bip9\""},
-    {RPCResult::Type::NUM, "height", /*optional=*/true, "height of the first block which the rules are or will be enforced (only for \"buried\" type, or \"bip9\" type with \"active\" status)"},
+    {RPCResult::Type::NUM, "height", /*optional=*/true, "height of the first block which enforces the rules (only for \"buried\" type, or \"bip9\" type with \"active\" status)"},
+    {RPCResult::Type::NUM, "height_end", /*optional=*/true, "height of the last block which enforces the rules (only for \"bip9\" type with \"active\" status and temporary deployments)"},
     {RPCResult::Type::BOOL, "active", "true if the rules are enforced for the mempool and the next block"},
     {RPCResult::Type::OBJ, "bip9", /*optional=*/true, "status of bip9 softforks (only for \"bip9\" type)",
     {