Network upgrade activation mechanism

src/Makefile.am

@@ -138,6 +138,7 @@ BITCOIN_CORE_H = \
   compressor.h \
   consensus/consensus.h \
   consensus/params.h \
+  consensus/upgrades.h \
   consensus/validation.h \
   core_io.h \
   core_memusage.h \
@@ -354,6 +355,7 @@ libbitcoin_common_a_SOURCES = \
   chainparams.cpp \
   coins.cpp \
   compressor.cpp \
+  consensus/upgrades.cpp \
   core_read.cpp \
   core_write.cpp \
   hash.cpp \

src/chainparams.cpp

@@ -90,6 +90,9 @@ public:
         consensus.nPowMaxAdjustDown = 32; // 32% adjustment down
         consensus.nPowMaxAdjustUp = 16; // 16% adjustment up
         consensus.nPowTargetSpacing = 2.5 * 60;
+        consensus.vUpgrades[Consensus::BASE_SPROUT].nActivationHeight =
+            Consensus::NetworkUpgrade::ALWAYS_ACTIVE;
+
         /**
          * The message start string should be awesome! ⓩ❤
          */
@@ -241,6 +244,9 @@ public:
         consensus.nPowMaxAdjustDown = 32; // 32% adjustment down
         consensus.nPowMaxAdjustUp = 16; // 16% adjustment up
         consensus.nPowTargetSpacing = 2.5 * 60;
+        consensus.vUpgrades[Consensus::BASE_SPROUT].nActivationHeight =
+            Consensus::NetworkUpgrade::ALWAYS_ACTIVE;
+
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0x1a;
         pchMessageStart[2] = 0xf9;
@@ -341,6 +347,8 @@ public:
         consensus.nPowMaxAdjustDown = 0; // Turn off adjustment down
         consensus.nPowMaxAdjustUp = 0; // Turn off adjustment up
         consensus.nPowTargetSpacing = 2.5 * 60;
+        consensus.vUpgrades[Consensus::BASE_SPROUT].nActivationHeight =
+            Consensus::NetworkUpgrade::ALWAYS_ACTIVE;
 
         pchMessageStart[0] = 0xaa;
         pchMessageStart[1] = 0xe8;

src/consensus/params.h

@@ -9,6 +9,47 @@
 #include "uint256.h"
 
 namespace Consensus {
+
+/**
+ * Index into Params.vUpgrades and NetworkUpgradeInfo
+ *
+ * Being array indices, these MUST be numbered consecutively.
+ *
+ * The order of these indices MUST match the order of the upgrades on-chain, as
+ * several functions depends on the enum being sorted.
+ */
+enum UpgradeIndex {
+    // Sprout must be first
+    BASE_SPROUT,
+    // NOTE: Also add new upgrades to NetworkUpgradeInfo in upgrades.cpp
+    MAX_NETWORK_UPGRADES
+};
+
+struct NetworkUpgrade {
+    /**
+     * Height of the first block for which the new consensus rules will be active
+     */
+    int nActivationHeight;
+
+    /**
+     * Special value for nActivationHeight indicating that the upgrade is always active.
+     * This is useful for testing, as it means tests don't need to deal with the activation
+     * process (namely, faking a chain of somewhat-arbitrary length).
+     *
+     * New blockchains that want to enable upgrade rules from the beginning can also use
+     * this value. However, additional care must be taken to ensure the genesis block
+     * satisfies the enabled rules.
+     */
+    static constexpr int ALWAYS_ACTIVE = 0;
+
+    /**
+     * Special value for nActivationHeight indicating that the upgrade will never activate.
+     * This is useful when adding upgrade code that has a testnet activation height, but
+     * should remain disabled on mainnet.
+     */
+    static constexpr int NO_ACTIVATION_HEIGHT = -1;
+};
+
 /**
  * Parameters that influence chain consensus.
  */
@@ -39,6 +80,7 @@ struct Params {
     int nMajorityEnforceBlockUpgrade;
     int nMajorityRejectBlockOutdated;
     int nMajorityWindow;
+    NetworkUpgrade vUpgrades[MAX_NETWORK_UPGRADES];
     /** Proof of work parameters */
     uint256 powLimit;
     int64_t nPowAveragingWindow;

src/consensus/upgrades.cpp

@@ -0,0 +1,94 @@
+// Copyright (c) 2018 The Zcash developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "consensus/upgrades.h"
+
+/**
+ * General information about each network upgrade.
+ * Ordered by Consensus::UpgradeIndex.
+ */
+const struct NUInfo NetworkUpgradeInfo[Consensus::MAX_NETWORK_UPGRADES] = {
+    {
+        /*.nBranchId =*/ 0,
+        /*.strName =*/ "Sprout",
+        /*.strInfo =*/ "The Zcash network at launch",
+    }
+};
+
+UpgradeState NetworkUpgradeState(
+    int nHeight,
+    const Consensus::Params& params,
+    Consensus::UpgradeIndex idx)
+{
+    assert(nHeight >= 0);
+    assert(idx >= Consensus::BASE_SPROUT && idx < Consensus::MAX_NETWORK_UPGRADES);
+    auto nActivationHeight = params.vUpgrades[idx].nActivationHeight;
+
+    if (nActivationHeight == Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT) {
+        return UPGRADE_DISABLED;
+    } else if (nHeight >= nActivationHeight) {
+        // From ZIP ???:
+        //
+        // ACTIVATION_HEIGHT
+        //     The block height at which the network upgrade rules will come into effect.
+        //
+        //     For removal of ambiguity, the block at height ACTIVATION_HEIGHT - 1 is
+        //     subject to the pre-upgrade consensus rules.
+        return UPGRADE_ACTIVE;
+    } else {
+        return UPGRADE_PENDING;
+    }
+}
+
+bool NetworkUpgradeActive(
+    int nHeight,
+    const Consensus::Params& params,
+    Consensus::UpgradeIndex idx)
+{
+    return NetworkUpgradeState(nHeight, params, idx) == UPGRADE_ACTIVE;
+}
+
+int CurrentEpoch(int nHeight, const Consensus::Params& params) {
+    for (auto idxInt = Consensus::MAX_NETWORK_UPGRADES - 1; idxInt >= Consensus::BASE_SPROUT; idxInt--) {
+        if (NetworkUpgradeActive(nHeight, params, Consensus::UpgradeIndex(idxInt))) {
+            return idxInt;
+        }
+    }
+}
+
+uint32_t CurrentEpochBranchId(int nHeight, const Consensus::Params& params) {
+    return NetworkUpgradeInfo[CurrentEpoch(nHeight, params)].nBranchId;
+}
+
+bool IsActivationHeight(
+    int nHeight,
+    const Consensus::Params& params,
+    Consensus::UpgradeIndex idx)
+{
+    assert(idx >= Consensus::BASE_SPROUT && idx < Consensus::MAX_NETWORK_UPGRADES);
+
+    // Don't count Sprout as an activation height
+    if (idx == Consensus::BASE_SPROUT) {
+        return false;
+    }
+
+    return nHeight >= 0 && nHeight == params.vUpgrades[idx].nActivationHeight;
+}
+
+bool IsActivationHeightForAnyUpgrade(
+    int nHeight,
+    const Consensus::Params& params)
+{
+    if (nHeight < 0) {
+        return false;
+    }
+
+    // Don't count Sprout as an activation height
+    for (int idx = Consensus::BASE_SPROUT + 1; idx < Consensus::MAX_NETWORK_UPGRADES; idx++) {
+        if (nHeight == params.vUpgrades[idx].nActivationHeight)
+            return true;
+    }
+
+    return false;
+}

src/consensus/upgrades.h

@@ -0,0 +1,77 @@
+// Copyright (c) 2018 The Zcash developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef ZCASH_CONSENSUS_UPGRADES_H
+#define ZCASH_CONSENSUS_UPGRADES_H
+
+#include "consensus/params.h"
+
+enum UpgradeState {
+    UPGRADE_DISABLED,
+    UPGRADE_PENDING,
+    UPGRADE_ACTIVE
+};
+
+struct NUInfo {
+    /** Branch ID (a random non-zero 32-bit value) */
+    uint32_t nBranchId;
+    /** User-facing name for the upgrade */
+    std::string strName;
+    /** User-facing information string about the upgrade */
+    std::string strInfo;
+};
+
+extern const struct NUInfo NetworkUpgradeInfo[];
+
+/**
+ * Checks the state of a given network upgrade based on block height.
+ * Caller must check that the height is >= 0 (and handle unknown heights).
+ */
+UpgradeState NetworkUpgradeState(
+    int nHeight,
+    const Consensus::Params& params,
+    Consensus::UpgradeIndex idx);
+
+/**
+ * Returns true if the given network upgrade is active as of the given block
+ * height. Caller must check that the height is >= 0 (and handle unknown
+ * heights).
+ */
+bool NetworkUpgradeActive(
+    int nHeight,
+    const Consensus::Params& params,
+    Consensus::UpgradeIndex idx);
+
+/**
+ * Returns the index of the most recent upgrade as of the given block height
+ * (corresponding to the current "epoch"). Consensus::BASE_SPROUT is the
+ * default value if no upgrades are active. Caller must check that the height
+ * is >= 0 (and handle unknown heights).
+ */
+int CurrentEpoch(int nHeight, const Consensus::Params& params);
+
+/**
+ * Returns the branch ID of the most recent upgrade as of the given block height
+ * (corresponding to the current "epoch"), or 0 if no upgrades are active.
+ * Caller must check that the height is >= 0 (and handle unknown heights).
+ */
+uint32_t CurrentEpochBranchId(int nHeight, const Consensus::Params& params);
+
+/**
+ * Returns true if the given block height is the activation height for the given
+ * upgrade.
+ */
+bool IsActivationHeight(
+    int nHeight,
+    const Consensus::Params& params,
+    Consensus::UpgradeIndex upgrade);
+
+/**
+ * Returns true if the given block height is the activation height for any upgrade.
+ */
+bool IsActivationHeightForAnyUpgrade(
+    int nHeight,
+    const Consensus::Params& params);
+
+#endif // ZCASH_CONSENSUS_UPGRADES_H