Auto merge of #1946 - str4d:blockchain-stats-num-commitments, r=ebfull

Add total number of commitments to getblockchaininfo

src/gtest/test_merkletree.cpp

@@ -79,6 +79,9 @@ void test_tree(
     // The tree doesn't have a 'last' element added since it's blank.
     ASSERT_THROW(tree.last(), std::runtime_error);
 
+    // The tree is empty.
+    ASSERT_TRUE(tree.size() == 0);
+
     // We need to witness at every single point in the tree, so
     // that the consistency of the tree and the merkle paths can
     // be checked.
@@ -93,6 +96,9 @@ void test_tree(
         // Now append a commitment to the tree
         tree.append(test_commitment);
 
+        // Size incremented by one.
+        ASSERT_TRUE(tree.size() == i+1);
+
         // Last element added to the tree was `test_commitment`
         ASSERT_TRUE(tree.last() == test_commitment);
 

src/rpcblockchain.cpp

@@ -533,6 +533,7 @@ Value getblockchaininfo(const Array& params, bool fHelp)
             "  \"difficulty\": xxxxxx,     (numeric) the current difficulty\n"
             "  \"verificationprogress\": xxxx, (numeric) estimate of verification progress [0..1]\n"
             "  \"chainwork\": \"xxxx\"     (string) total amount of work in active chain, in hexadecimal\n"
+            "  \"commitments\": xxxxxx,    (numeric) the current number of note commitments in the commitment tree\n"
             "  \"softforks\": [            (array) status of softforks in progress\n"
             "     {\n"
             "        \"id\": \"xxxx\",        (string) name of softfork\n"
@@ -564,6 +565,10 @@ Value getblockchaininfo(const Array& params, bool fHelp)
     obj.push_back(Pair("chainwork",             chainActive.Tip()->nChainWork.GetHex()));
     obj.push_back(Pair("pruned",                fPruneMode));
 
+    ZCIncrementalMerkleTree tree;
+    pcoinsTip->GetAnchorAt(pcoinsTip->GetBestAnchor(), tree);
+    obj.push_back(Pair("commitments",           tree.size()));
+
     const Consensus::Params& consensusParams = Params().GetConsensus();
     CBlockIndex* tip = chainActive.Tip();
     Array softforks;

src/zcash/IncrementalMerkleTree.cpp

@@ -81,6 +81,25 @@ Hash IncrementalMerkleTree<Depth, Hash>::last() const {
     }
 }
 
+template<size_t Depth, typename Hash>
+size_t IncrementalMerkleTree<Depth, Hash>::size() const {
+    size_t ret = 0;
+    if (left) {
+        ret++;
+    }
+    if (right) {
+        ret++;
+    }
+    // Treat occupation of parents array as a binary number
+    // (right-shifted by 1)
+    for (size_t i = 0; i < parents.size(); i++) {
+        if (parents[i]) {
+            ret += (1 << (i+1));
+        }
+    }
+    return ret;
+}
+
 template<size_t Depth, typename Hash>
 void IncrementalMerkleTree<Depth, Hash>::append(Hash obj) {
     if (is_complete(Depth)) {

src/zcash/IncrementalMerkleTree.hpp

@@ -75,6 +75,8 @@ public:
                parents.size() * 32; // parents
     }
 
+    size_t size() const;
+
     void append(Hash obj);
     Hash root() const {
         return root(Depth, std::deque<Hash>());