track double spending in the txpool

Transactions in the txpool are marked when another transaction
is seen double spending one or more of its inputs.
This is then exposed wherever appropriate.

Note that being marked with this "double spend seen" flag does
NOT mean this transaction IS a double spend and will never be
mined: it just means that the network has seen at least another
transaction spending at least one of the same inputs, so care
should be taken to wait for a few confirmations before acting
upon that transaction (ie, mostly of use for merchants wanting
to accept unconfirmed transactions).

src/rpc/core_rpc_server.cpp

@@ -478,15 +478,17 @@ namespace cryptonote
     // try the pool for any missing txes
     size_t found_in_pool = 0;
     std::unordered_set<crypto::hash> pool_tx_hashes;
+    std::unordered_map<crypto::hash, bool> double_spend_seen;
     if (!missed_txs.empty())
     {
-      std::list<transaction> pool_txs;
-      bool r = m_core.get_pool_transactions(pool_txs);
+      std::vector<tx_info> pool_tx_info;
+      std::vector<spent_key_image_info> pool_key_image_info;
+      bool r = m_core.get_pool_transactions_and_spent_keys_info(pool_tx_info, pool_key_image_info);
       if(r)
       {
         // sort to match original request
         std::list<transaction> sorted_txs;
-        std::list<cryptonote::transaction>::const_iterator i;
+        std::vector<tx_info>::const_iterator i;
         for (const crypto::hash &h: vh)
         {
           if (std::find(missed_txs.begin(), missed_txs.end(), h) == missed_txs.end())
@@ -500,11 +502,26 @@ namespace cryptonote
             sorted_txs.push_back(std::move(txs.front()));
             txs.pop_front();
           }
-          else if ((i = std::find_if(pool_txs.begin(), pool_txs.end(), [h](cryptonote::transaction &tx) { return h == cryptonote::get_transaction_hash(tx); })) != pool_txs.end())
+          else if ((i = std::find_if(pool_tx_info.begin(), pool_tx_info.end(), [h](const tx_info &txi) { return epee::string_tools::pod_to_hex(h) == txi.id_hash; })) != pool_tx_info.end())
           {
-            sorted_txs.push_back(*i);
+            cryptonote::transaction tx;
+            if (!cryptonote::parse_and_validate_tx_from_blob(i->tx_blob, tx))
+            {
+              res.status = "Failed to parse and validate tx from blob";
+              return true;
+            }
+            sorted_txs.push_back(tx);
             missed_txs.remove(h);
             pool_tx_hashes.insert(h);
+            const std::string hash_string = epee::string_tools::pod_to_hex(h);
+            for (const auto &ti: pool_tx_info)
+            {
+              if (ti.id_hash == hash_string)
+              {
+                double_spend_seen.insert(std::make_pair(h, ti.double_spend_seen));
+                break;
+              }
+            }
             ++found_in_pool;
           }
         }
@@ -530,11 +547,21 @@ namespace cryptonote
       if (e.in_pool)
       {
         e.block_height = e.block_timestamp = std::numeric_limits<uint64_t>::max();
+        if (double_spend_seen.find(tx_hash) != double_spend_seen.end())
+        {
+          e.double_spend_seen = double_spend_seen[tx_hash];
+        }
+        else
+        {
+          MERROR("Failed to determine double spend status for " << tx_hash);
+          e.double_spend_seen = false;
+        }
       }
       else
       {
         e.block_height = m_core.get_blockchain_storage().get_db().get_tx_block_height(tx_hash);
         e.block_timestamp = m_core.get_blockchain_storage().get_db().get_block_timestamp(e.block_height);
+        e.double_spend_seen = false;
       }
 
       // fill up old style responses too, in case an old wallet asks

src/rpc/core_rpc_server_commands_defs.h

@@ -566,6 +566,7 @@ namespace cryptonote
       std::string as_hex;
       std::string as_json;
       bool in_pool;
+      bool double_spend_seen;
       uint64_t block_height;
       uint64_t block_timestamp;
       std::vector<uint64_t> output_indices;
@@ -575,6 +576,7 @@ namespace cryptonote
         KV_SERIALIZE(as_hex)
         KV_SERIALIZE(as_json)
         KV_SERIALIZE(in_pool)
+        KV_SERIALIZE(double_spend_seen)
         KV_SERIALIZE(block_height)
         KV_SERIALIZE(block_timestamp)
         KV_SERIALIZE(output_indices)
@@ -1357,6 +1359,8 @@ namespace cryptonote
     bool relayed;
     uint64_t last_relayed_time;
     bool do_not_relay;
+    bool double_spend_seen;
+    std::string tx_blob;
 
     BEGIN_KV_SERIALIZE_MAP()
       KV_SERIALIZE(id_hash)
@@ -1372,6 +1376,8 @@ namespace cryptonote
       KV_SERIALIZE(relayed)
       KV_SERIALIZE(last_relayed_time)
       KV_SERIALIZE(do_not_relay)
+      KV_SERIALIZE(double_spend_seen)
+      KV_SERIALIZE(tx_blob)
     END_KV_SERIALIZE_MAP()
   };
 
@@ -1480,6 +1486,7 @@ namespace cryptonote
     uint32_t num_not_relayed;
     uint64_t histo_98pc;
     std::vector<txpool_histo> histo;
+    uint32_t num_double_spends;
 
     BEGIN_KV_SERIALIZE_MAP()
       KV_SERIALIZE(bytes_total)
@@ -1494,6 +1501,7 @@ namespace cryptonote
       KV_SERIALIZE(num_not_relayed)
       KV_SERIALIZE(histo_98pc)
       KV_SERIALIZE_CONTAINER_POD_AS_BLOB(histo)
+      KV_SERIALIZE(num_double_spends)
     END_KV_SERIALIZE_MAP()
   };
 

src/rpc/message_data_structs.h

@@ -95,6 +95,7 @@ namespace rpc
     uint64_t last_relayed_time;
     bool relayed;
     bool do_not_relay;
+    bool double_spend_seen;
   };
 
   typedef std::unordered_map<crypto::key_image, std::vector<crypto::hash> > key_images_with_tx_hashes;