Check if key images already in mempool

Partially solves issue:
https://github.com/moneroexamples/openmonero/issues/48

It checks if a tx that you are submitting contains key images
that are present in mempool, and print outs an appropiate
error message.

Ideally, differnt outputs should be used by the frontend in this case.
But for now, we have to just wait till our past txs get confirmed and disappear from the mempool.

src/CurrentBlockchainStatus.cpp

@@ -895,6 +895,56 @@ CurrentBlockchainStatus::find_tx_in_mempool(
     return false;
 }
 
+bool
+CurrentBlockchainStatus::find_key_images_in_mempool(std::vector<txin_v> const& vin)
+{
+    mempool_txs_t mempool_tx_cpy;
+
+    {
+        // make local copy of the mempool, so that we dont lock it for
+        // long, as this function can take longer to execute
+        std::lock_guard<std::mutex> lck (searching_threads_map_mtx);
+        mempool_tx_cpy = mempool_txs;
+    }
+
+    // perform exhostive search to check if any key image in vin vector
+    // is in the mempool. This is used to check if a tx generated by the frontend
+    // is using any key images that area already in the mempool.
+    for (auto const& kin: vin)
+    {
+        if(kin.type() != typeid(txin_to_key))
+            continue;
+
+        // get tx input key
+        const txin_to_key& tx_in_to_key
+                = boost::get<cryptonote::txin_to_key>(kin);
+
+        for (auto const& mtx: mempool_tx_cpy)
+        {
+            const transaction &m_tx = mtx.second;
+
+            vector<txin_to_key> input_key_imgs = xmreg::get_key_images(m_tx);
+
+            for (auto const& mki: input_key_imgs)
+            {
+                // if a matching key image found in the mempool
+                if (mki.k_image == tx_in_to_key.k_image)
+                    return true;
+            }
+        }
+    }
+
+    return false;
+}
+
+
+bool
+CurrentBlockchainStatus::find_key_images_in_mempool(transaction const& tx)
+{
+    return find_key_images_in_mempool(tx.vin);
+}
+
+
 bool
 CurrentBlockchainStatus::get_tx(crypto::hash const& tx_hash, transaction& tx)
 {

src/CurrentBlockchainStatus.h

@@ -198,6 +198,12 @@ struct CurrentBlockchainStatus
     find_tx_in_mempool(crypto::hash const& tx_hash,
                        transaction& tx);
 
+    static bool
+    find_key_images_in_mempool(std::vector<txin_v> const& vin);
+
+    static bool
+    find_key_images_in_mempool(transaction const& tx);
+
     static bool
     get_tx(crypto::hash const& tx_hash, transaction& tx);
 

src/YourMoneroRequests.cpp

@@ -821,17 +821,56 @@ YourMoneroRequests::submit_raw_tx(const shared_ptr< Session > session, const Byt
 
     string error_msg;
 
+    // before we submit the tx into the deamon, we are going to do a few checks.
+    // first, we parse the hexbuffer submmited by the frontend into binary buffer block
+    // second, we are going to check if we can construct valid transaction object
+    // fromt that binary buffer.
+    // third, we are going to check if any key image in this tx is in any of the txs
+    // in the mempool. This allows us to make a clear comment that the tx
+    // uses outputs just spend. This happens we a users submits few txs, one after another
+    // before previous txs get included in a block and are still present in the mempool.
+
+    std::string tx_blob;
+
+    if(!epee::string_tools::parse_hexstr_to_binbuff(raw_tx_blob, tx_blob))
+    {
+        j_response["status"] = "error";
+        j_response["error"]  = "Tx faild parse_hexstr_to_binbuff";
+        session_close(session, j_response.dump());
+        return;
+    }
+
+    transaction tx_to_be_submitted;
+
+    if (!parse_and_validate_tx_from_blob(tx_blob, tx_to_be_submitted))
+    {
+        j_response["status"] = "error";
+        j_response["error"]  = "Tx faild parse_and_validate_tx_from_blob";
+        session_close(session, j_response.dump());
+        return;
+    }
+
+    if (CurrentBlockchainStatus::find_key_images_in_mempool(tx_to_be_submitted))
+    {
+        j_response["status"] = "error";
+        j_response["error"]  = "Tx uses your outputs that area already in the mempool. "
+                               "Please wait till your previous tx(s) get mined";
+        session_close(session, j_response.dump());
+        return;
+    }
+
     if (!CurrentBlockchainStatus::commit_tx(
             raw_tx_blob, error_msg,
             CurrentBlockchainStatus::do_not_relay))
     {
         j_response["status"] = "error";
         j_response["error"]  = error_msg;
+        session_close(session, j_response.dump());
+        return;
     }
-    else
-    {
-        j_response["status"] = "success";
-    }
+
+    j_response["status"] = "success";
+
 
     string response_body = j_response.dump();