Closely track mempool byte total. Add "getmempoolinfo" RPC.

Goal:  Gain live insight into the mempool.  Groundwork for future work
that caps mempool size.

src/rpcblockchain.cpp

@@ -531,3 +531,27 @@ Value getchaintips(const Array& params, bool fHelp)
 
     return res;
 }
+
+Value getmempoolinfo(const Array& params, bool fHelp)
+{
+    if (fHelp || params.size() != 0)
+        throw runtime_error(
+            "getmempoolinfo\n"
+            "\nReturns details on the active state of the TX memory pool.\n"
+            "\nResult:\n"
+            "{\n"
+            "  \"size\": xxxxx                (numeric) Current tx count\n"
+            "  \"bytes\": xxxxx               (numeric) Sum of all tx sizes\n"
+            "}\n"
+            "\nExamples:\n"
+            + HelpExampleCli("getmempoolinfo", "")
+            + HelpExampleRpc("getmempoolinfo", "")
+        );
+
+    Object ret;
+    ret.push_back(Pair("size", (int64_t) mempool.size()));
+    ret.push_back(Pair("bytes", (int64_t) mempool.GetTotalTxSize()));
+
+    return ret;
+}
+

src/rpcserver.cpp

@@ -256,6 +256,7 @@ static const CRPCCommand vRPCCommands[] =
     { "blockchain",         "getblockhash",           &getblockhash,           true,      false,      false },
     { "blockchain",         "getchaintips",           &getchaintips,           true,      false,      false },
     { "blockchain",         "getdifficulty",          &getdifficulty,          true,      false,      false },
+    { "blockchain",         "getmempoolinfo",         &getmempoolinfo,         true,      true,       false },
     { "blockchain",         "getrawmempool",          &getrawmempool,          true,      false,      false },
     { "blockchain",         "gettxout",               &gettxout,               true,      false,      false },
     { "blockchain",         "gettxoutsetinfo",        &gettxoutsetinfo,        true,      false,      false },

src/rpcserver.h

@@ -200,6 +200,7 @@ extern json_spirit::Value getblockcount(const json_spirit::Array& params, bool f
 extern json_spirit::Value getbestblockhash(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value getdifficulty(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value settxfee(const json_spirit::Array& params, bool fHelp);
+extern json_spirit::Value getmempoolinfo(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value getrawmempool(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value getblockhash(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value getblock(const json_spirit::Array& params, bool fHelp);

src/txmempool.cpp

@@ -402,6 +402,7 @@ bool CTxMemPool::addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry)
         for (unsigned int i = 0; i < tx.vin.size(); i++)
             mapNextTx[tx.vin[i].prevout] = CInPoint(&tx, i);
         nTransactionsUpdated++;
+        totalTxSize += entry.GetTxSize();
     }
     return true;
 }
@@ -426,6 +427,8 @@ void CTxMemPool::remove(const CTransaction &tx, std::list<CTransaction>& removed
             removed.push_front(tx);
             BOOST_FOREACH(const CTxIn& txin, tx.vin)
                 mapNextTx.erase(txin.prevout);
+
+            totalTxSize -= mapTx[hash].GetTxSize();
             mapTx.erase(hash);
             nTransactionsUpdated++;
         }
@@ -477,6 +480,7 @@ void CTxMemPool::clear()
     LOCK(cs);
     mapTx.clear();
     mapNextTx.clear();
+    totalTxSize = 0;
     ++nTransactionsUpdated;
 }
 
@@ -487,9 +491,12 @@ void CTxMemPool::check(CCoinsViewCache *pcoins) const
 
     LogPrint("mempool", "Checking mempool with %u transactions and %u inputs\n", (unsigned int)mapTx.size(), (unsigned int)mapNextTx.size());
 
+    uint64_t checkTotal = 0;
+
     LOCK(cs);
     for (std::map<uint256, CTxMemPoolEntry>::const_iterator it = mapTx.begin(); it != mapTx.end(); it++) {
         unsigned int i = 0;
+        checkTotal += it->second.GetTxSize();
         const CTransaction& tx = it->second.GetTx();
         BOOST_FOREACH(const CTxIn &txin, tx.vin) {
             // Check that every mempool transaction's inputs refer to available coins, or other mempool tx's.
@@ -518,6 +525,8 @@ void CTxMemPool::check(CCoinsViewCache *pcoins) const
         assert(tx.vin.size() > it->second.n);
         assert(it->first == it->second.ptx->vin[it->second.n].prevout);
     }
+
+    assert(totalTxSize == checkTotal);
 }
 
 void CTxMemPool::queryHashes(vector<uint256>& vtxid)

src/txmempool.h

@@ -68,6 +68,7 @@ private:
     CMinerPolicyEstimator* minerPolicyEstimator;
 
     CFeeRate minRelayFee; // Passed to constructor to avoid dependency on main
+    uint64_t totalTxSize; // sum of all mempool tx' byte sizes
 
 public:
     mutable CCriticalSection cs;
@@ -108,6 +109,11 @@ public:
         LOCK(cs);
         return mapTx.size();
     }
+    uint64_t GetTotalTxSize()
+    {
+        LOCK(cs);
+        return totalTxSize;
+    }
 
     bool exists(uint256 hash)
     {