Access blockchain information using C++

How to develop on top of Monero? One way is to use json-rpc calls from any language capable of this, for example, as shown in python. Another way is to use pubilc api of existing Monero services such as moneroblocks. Some Monero functions are even avaliable in JavaScript if you look at the source code of mymonero.com. This allows to develop some web applications with only HTML and JavaScript, such as, XMR test.

The other way, presented here, is to directly tap into Monero C++ libraries. However, there are no tutorials or any information how to do it.

For this reason this example was created, i.e., to show how to access Monero C++ libraries and do something with them.

Small disclaimer: I don't know if this is the correct way of doing this, but it seems to be working. If something is done in a stupid or wrong way, or my explanations in the comments are incorrect, please let me know.

Aim: check which transaction's outputs belong to a given address

There's been a lot of talk in Monero about viewkeys. But how do you actually use them? Well, they can be used to to check which transaction's outputs in a given block belong to a given address. Without the private viewkey associated with the given Monero address, it is not possible to check how much Monero there are in that address. The same, if we know that a given transaction was sent to a specific address, it is not possible to check in a blockchain which outputs of that transaction actually were meant to belong to that address without the private viewkey of that address. The viewkey allows to filter out outputs not bind to the address.

Checking if any of a transaction's outputs belong to a given address with the private viewkey of that address is already possible using XMR test website. This is very good, since it allows us to verify the results obtained using this example with those provided by that website.

Prerequisites

Everthing here was done and tested on Ubuntu 14.04 x86_64 and Ubuntu 15.10 x86_64.

Monero node that I run is using lmdb database for blockchain. Thus I use this database in this example.

Dependencies

# refresh ubuntu's repository sudo apt-get update #install git sudo apt-get install git # install dependencies sudo apt-get install build-essential cmake libboost1.55-all-dev miniupnpc libunbound-dev graphviz doxygen libdb5.1++-dev

Monero compilation

# download the latest bitmonero source code from github git clone https://github.com/monero-project/bitmonero.git # go into bitmonero folder cd bitmonero/ make # or make -j number_of_threads, e.g., make -j 2

Monero static libraries

When the compilation finishes, a number of static Monero libraries should be generated. We will need them to link against.

Since they are spread out over different subfolders of the ./build/ folder, it is easier to just copy them into one folder. I assume that /opt/bitmonero-dev/libs is the folder where they are going to be copied to.

# create the folder sudo mkdir -p /opt/bitmonero-dev/libs # find the static libraries files (i.e., those with extension of *.a) # and copy them to /opt/bitmonero-dev/libs # assuming you are still in bitmonero/ folder which you downloaded from # github sudo find ./build/ -name ' *.a ' -exec cp {} /opt/bitmonero-dev/libs \;

Monero headers

Now we need to get Monero headers, as this is our interface to the Monero libraries. Folder /opt/bitmonero-dev/headers is assumed to hold the headers.

# create the folder sudo mkdir -p /opt/bitmonero-dev/headers # find the header files (i.e., those with extension of *.h) # and copy them to /opt/bitmonero-dev/headers. # but this time the structure of directories is important # so rsync is used to find and copy the headers files sudo rsync -zarv --include= " */ " --include= " *.h " --exclude= " * " --prune-empty-dirs ./ /opt/bitmonero-dev/headers

cmake config files

CMakeLists.txt files and the structure of this project can be checked at github. I wont be discussing them here. I tried to put comments in CMakeLists.txt to clarify what is there.

The location of the Monero's headers and static libraries must be correctly indicated in CMakeLists.txt . So if you place them in different folders that in this example, please change the root CMakeLists.txt file accordingly.

C++ code

The two most interesting C++ files in this example are MicroCore.cpp and main.cpp . Therefore, I will present only these to files here. Full source code is at github. The surfce code can also slighly vary with the code here, as it can be updated more frequently than the code presented here. So for the latest version of this example, please check the github repository directly.

MicroCore class is a micro version of cryptonode::core class. The cryptonote::core class is the main class with the access to the blockchain that the Monero daemon is using. In the cryptonode::core class, the most important method (at least for this example), is the init method. The main goal of the init method is to create an instance of Blockchain class. The Blockchain is the high level interface to blockchain database. The low level one is through BlockchainLMDB in our case, which can also be accessed through the Blockchain object.

The original cryptonote::core class does a lot of things, which we don't need here, such as reading program options. Thus its micro version was prepared for this example.

# include " MicroCore.h " namespace xmreg { /** * The constructor is interesting, as * m_mempool and m_blockchain_storage depend * on each other. * * So basically m_mempool is initialized with * reference to Blockchain (i.e., Blockchain&) * and m_blockchain_storage is initialized with * reference to m_mempool (i.e., tx_memory_pool&) * * The same is done in cryptonode::core. */ MicroCore::MicroCore (): m_mempool (m_blockchain_storage), m_blockchain_storage (m_mempool) {} /** * Initialized the MicroCore object. * * Create BlockchainLMDB on the heap. * Open database files located in blockchain_path. * Initialize m_blockchain_storage with the BlockchainLMDB object. */ bool MicroCore::init ( const string& blockchain_path) { int db_flags = 0 ; // MDB_RDONLY will result in // m_blockchain_storage.deinit() producing // error messages. //db_flags |= MDB_RDONLY ; db_flags |= MDB_NOSYNC; BlockchainDB* db = nullptr ; db = new BlockchainLMDB (); try { // try opening lmdb database files db-> open (blockchain_path, db_flags); } catch ( const std::exception& e) { cerr << " Error opening database: " << e. what (); return false ; } // check if the blockchain database // is successful opened if (!db-> is_open ()) { return false ; } // initialize Blockchain object to manage // the database. return m_blockchain_storage. init (db, false ); } /** * Get m_blockchain_storage. * Initialize m_blockchain_storage with the BlockchainLMDB object. */ Blockchain& MicroCore::get_core () { return m_blockchain_storage; } /** * De-initialized Blockchain. * * Its needed to mainly deallocate * new BlockchainDB object * created in the MicroCore::init(). * * It also tries to synchronize the blockchain. * And this is the reason when, if MDB_RDONLY * is set, we are getting error messages. Because * blockchain is readonly and we try to synchronize it. */ MicroCore::~MicroCore () { m_blockchain_storage. deinit (); } }

This is the main file of the example. For the program to work, four input values are required:

address - Monero adress.

- Monero adress. viewkey - private view key associated with the address provided.

- private view key associated with the address provided. txhash - transaction id (i.e., hash) which outputs we want to check.

- transaction id (i.e., hash) which outputs we want to check. bc-path - a path to lmdb folder with the blockchain.

To run the program, at least correct bc-path is required. All other options have default values which work.

# include < iostream > # include < string > # include " src/MicroCore.h " # include " src/CmdLineOptions.h " # include " src/tools.h " using namespace std ; using boost::filesystem::path; using boost::filesystem::is_directory; // without this it wont work. I'm not sure what it does. // it has something to do with locking the blockchain and tx pool // during certain operations to avoid deadlocks. unsigned int epee::g_test_dbg_lock_sleep = 0 ; int main ( int ac, const char * av[]) { // get command line options xmreg::CmdLineOptions opts {ac, av}; auto help_opt = opts. get_option < bool >( " help " ); // if help was chosen, display help text and finish if (*help_opt) { return 0 ; } // get other options auto address_opt = opts. get_option <string>( " address " ); auto viewkey_opt = opts. get_option <string>( " viewkey " ); auto tx_hash_opt = opts. get_option <string>( " txhash " ); auto bc_path_opt = opts. get_option <string>( " bc-path " ); // default path to monero folder // on linux this is /home/<username>/.bitmonero string default_monero_dir = tools::get_default_data_dir (); // the default folder of the lmdb blockchain database // is therefore as follows string default_lmdb_dir = default_monero_dir + " /lmdb " ; // get the program command line options, or // some default values for quick check string address_str = address_opt ? *address_opt : " 48daf1rG3hE1Txapcsxh6WXNe9MLNKtu7W7tKTivtSoVLHErYzvdcpea2nSTgGkz66RFP4GKVAsTV14v6G3oddBTHfxP6tU " ; string viewkey_str = viewkey_opt ? *viewkey_opt : " 1ddabaa51cea5f6d9068728dc08c7ffaefe39a7a4b5f39fa8a976ecbe2cb520a " ; string tx_hash_str = tx_hash_opt ? *tx_hash_opt : " 66040ad29f0d780b4d47641a67f410c28cce575b5324c43b784bb376f4e30577 " ; path blockchain_path = bc_path_opt ? path (*bc_path_opt) : path (default_lmdb_dir); if (! is_directory (blockchain_path)) { cerr << " Given path \" " << blockchain_path << " \" " << " is not a folder or does not exist " << " " << endl; return 1 ; } blockchain_path = xmreg::remove_trailing_path_separator (blockchain_path); cout << " Blockchain path: " << blockchain_path << endl; // enable basic monero log output uint32_t log_level = 0 ; epee::log_space::get_set_log_detalisation_level ( true , log_level); epee::log_space::log_singletone::add_logger (LOGGER_CONSOLE, NULL , NULL ); // create instance of our MicroCore xmreg::MicroCore mcore; // initialize the core using the blockchain path if (!mcore. init (blockchain_path. string ())) { cerr << " Error accessing blockchain. " << endl; return 1 ; } // get the highlevel cryptonote::Blockchain object to interact // with the blockchain lmdb database cryptonote::Blockchain& core_storage = mcore. get_core (); // get the current blockchain height. Just to check // if it reads ok. uint64_t height = core_storage. get_current_blockchain_height (); cout << " Current blockchain height: " << height << endl; // parse string representing given monero address cryptonote::account_public_address address; if (! xmreg::parse_str_address (address_str, address)) { cerr << " Cant parse string address: " << address_str << endl; return 1 ; } // parse string representing of givenr private viewkey crypto::secret_key prv_view_key; if (! xmreg::parse_str_secret_key (viewkey_str, prv_view_key)) { cerr << " Cant parse view key: " << viewkey_str << endl; return 1 ; } // we also need tx public key, but we have tx hash only. // to get the key, first, we obtained transaction object tx // and then we get its public key from tx's extras. cryptonote::transaction tx; if (! xmreg::get_tx_pub_key_from_str_hash (core_storage, tx_hash_str, tx)) { cerr << " Cant find transaction with hash: " << tx_hash_str << endl; return 1 ; } crypto::public_key pub_tx_key = cryptonote::get_tx_pub_key_from_extra (tx); if (pub_tx_key == cryptonote::null_pkey) { cerr << " Cant get public key of tx with hash: " << tx_hash_str << endl; return 1 ; } // public transaction key is combined with our viewkey // to create, so called, derived key. crypto::key_derivation derivation; if (! generate_key_derivation (pub_tx_key, prv_view_key, derivation)) { cerr << " Cant get dervied key for: " << "

" << " pub_tx_key: " << prv_view_key << " and " << " prv_view_key " << prv_view_key << endl; return 1 ; } // lets check our keys cout << "

" << " address : < " << xmreg::print_address (address) << " >

" << " private view key : " << prv_view_key << "

" << " tx hash : < " << tx_hash_str << " >

" << " public tx key : " << pub_tx_key << "

" << " dervied key : " << derivation << "

" << endl; // each tx that we (or the address we are checking) received // contains a number of outputs. // some of them are ours, some not. so we need to go through // all of them in a given tx block, to check which outputs are ours. // get the total number of outputs in a transaction. size_t output_no = tx. vout . size (); // sum amount of xmr sent to us // in the given transaction uint64_t money_transfered { 0 }; // loop through outputs in the given tx // to check which outputs our ours. we compare outputs' // public keys with the public key that would had been // generated for us if we had gotten the outputs. // not sure this is the case though, but that's my understanding. for ( size_t i = 0 ; i < output_no; ++i) { // get the tx output public key // that normally would be generated for us, // if someone had sent us some xmr. crypto::public_key pubkey; crypto::derive_public_key (derivation, i, address. m_spend_public_key , pubkey); // get tx output public key const cryptonote::txout_to_key tx_out_to_key = boost::get<cryptonote::txout_to_key>(tx. vout [i]. target ); cout << " Output no: " << i << " , " << tx_out_to_key. key ; // check if the output's public key is ours if (tx_out_to_key. key == pubkey) { // if so, than add the xmr amount to the money_transfered money_transfered += tx. vout [i]. amount ; cout << " , mine key: " << cryptonote::print_money (tx. vout [i]. amount ) << endl; } else { cout << " , not mine key " << endl; } } cout << "

Total xmr received: " << cryptonote::print_money (money_transfered) << endl; cout << "

End of program. " << endl; return 0 ; }

Output example 1

Executing the program as follows:

./xmreg01 --address 48daf1rG3hE1Txapcsxh6WXNe9MLNKtu7W7tKTivtSoVLHErYzvdcpea2nSTgGkz66RFP4GKVAsTV14v6G3oddBTHfxP6tU --viewkey 1ddabaa51cea5f6d9068728dc08c7ffaefe39a7a4b5f39fa8a976ecbe2cb520a --txhash 66040ad29f0d780b4d47641a67f410c28cce575b5324c43b784bb376f4e30577

Results in the following output:

address : < 48daf1rG3hE1Txapcsxh6WXNe9MLNKtu7W7tKTivtSoVLHErYzvdcpea2nSTgGkz66RFP4GKVAsTV14v6G3oddBTHfxP6tU > private view key : < 1ddabaa51cea5f6d9068728dc08c7ffaefe39a7a4b5f39fa8a976ecbe2cb520a > tx hash : < 66040ad29f0d780b4d47641a67f410c28cce575b5324c43b784bb376f4e 30577> public tx key : < 0851f2ec7477b82618e028238164a9080325fe299dcf5f70f868729b50d 00284> dervied key : < 8017f9944635b7b2e4dc2ddb9b81787e49b384dcb2abd474355fe62bee79fdd 7> Output no: 0, < c65ee61d95480988c1fd70f6078afafd4d90ef730fc3c4df59951d64136e911f > , not mine key Output no: 1, < 67a5fd7e06640942f0d869e494fc9d297d5087609013cd3531d0da55de19045b > , not mine key Output no: 2, < a9e0f19422e68ed328315e92373388a3ebb418204a36d639bd1f2e870f4bc 919> , mine key: 0.800000000000 Output no: 3, < 849b56538f199f0a7522fcd0b132e53eec4a822e9b70b0e7e6c9e2632f1328db > , mine key: 4.000000000000 Output no: 4, < aba2e362f8ae0d79a4f33f9e4e27eecf79ad9c53eae86c27aa0281fb29aa6fdc > , not mine key Output no: 5, < 2602e4ac211216571ab1afe631aae1f905f252a1150cb8c4e5f34b820d0d6b4a > , not mine key Total xmr received: 4.800000000000

These results agree with those obtained using XMR test.

Output example 2

Executing the program as follows:

./xmreg01 --address 41vEA7Ye8Bpeda6g59v5t46koWrVn2PNgEKgzquJjmiKCFTsh9gajr8J3pad49rqu581TAtFGCH9CYTCkYrCpuWUG9GkgeB --viewkey fed77158ec692fe9eb951f6aeb22c3bda16fe8926c1aac13a5651a9c27f34309 --txhash ba807a90792f9202638e7288eff05949ccffbc54fd6a108571b65b963fee573a

Results in the following output:

address : < 41vEA7Ye8Bpeda6g59v5t46koWrVn2PNgEKgzquJjmiKCFTsh9gajr8J3pad49rqu581TAtFGCH9CYTCkYrCpuWUG9GkgeB > private view key : < fed77158ec692fe9eb951f6aeb22c3bda16fe8926c1aac13a5651a9c27f 34309> tx hash : < ba807a90792f9202638e7288eff05949ccffbc54fd6a108571b65b963fee573a > public tx key : < 70dd2b3a54dc153ab367d7bab9287db1e153053e02a5a273084da00344e11e 59> dervied key : < dad78e5ec247b91101cad60b98c09866cbcc46a3039c49a0de13be6e0645d8da > Output no: 0, < 460de8a6a3afea230c1a68db55054a67d2b33d80482cc5df645fed631d3b9c6e > , not mine key Output no: 1, < 54681e67463b5baf79a145ec90969ac0c1d358595e5a32c1e37e085290ee0dfe > , mine key: 0.080000000000 Output no: 2, < eb02627448c4cb2f21b3277f2a4359984cd89d0636a327ca068fe76f8d970bad > , mine key: 0.100000000000 Output no: 3, < 584df4be03187e5545c6255cd61fee33afbdfa0b70fba2d9678cd43fd23f4df 7> , not mine key Output no: 4, < 673f519e5a7e874485a5b239c54fc289941c7c15ad200f02d46ad98adfbd 8049> , mine key: 9.000000000000 Output no: 5, < e1956d1077a9e5310c22a6a103e32f25def9aab4a7214894ed30a76d18cde 271> , not mine key Total xmr received: 9.180000000000

These results agree also with those obtained using XMR test.

Output example 3

Executing the program as follows:

./xmreg01 --address 48daf1rG3hE1Txapcsxh6WXNe9MLNKtu7W7tKTivtSoVLHErYzvdcpea2nSTgGkz66RFP4GKVAsTV14v6G3oddBTHfxP6tU --viewkey 1ddabaa51cea5f6d9068728dc08c7ffaefe39a7a4b5f39fa8a976ecbe2cb520a --txhash b82fe6d1f40e71a89a0c6d517ee1e84e4403870cba4589d0e6ca341ef966e143

Results in the following output:

address : < 48daf1rG3hE1Txapcsxh6WXNe9MLNKtu7W7tKTivtSoVLHErYzvdcpea2nSTgGkz66RFP4GKVAsTV14v6G3oddBTHfxP6tU > private view key : < 1ddabaa51cea5f6d9068728dc08c7ffaefe39a7a4b5f39fa8a976ecbe2cb520a > tx hash : < b82fe6d1f40e71a89a0c6d517ee1e84e4403870cba4589d0e6ca341ef966e 143> public tx key : < 99b7c2876e2058718c496f36656e459352d055101cb87827f60e75d60f 632727> dervied key : < cdac177a666eba391d5edc4f835e1e0d3e8f8735e322a0476b91e4d6e3a3a7f 2> Output no: 0, < 2f1cf7db49a058592b58bdbb5a2121fb067f0be4fcd167936a242ad76fd7b32c > , mine key: 0.020000000000 Output no: 1, < 0c37db67fd9cab5c3ce939df0a64905278ceb4520dde102c87f0bf66b1465aaa > , mine key: 0.100000000000 Output no: 2, < dbf1aac53547cc8ad8b288bdd83ae642aec2216fc647980e64e0a776a42b 4267> , mine key: 9.000000000000 Total xmr received: 9.120000000000

These results also agree with those obtained using XMR test.

Output example 4

Executing the program as follows:

./xmreg01 --address 41vEA7Ye8Bpeda6g59v5t46koWrVn2PNgEKgzquJjmiKCFTsh9gajr8J3pad49rqu581TAtFGCH9CYTCkYrCpuWUG9GkgeB --viewkey fed77158ec692fe9eb951f6aeb22c3bda16fe8926c1aac13a5651a9c27f34309 --txhash 60b6c42f1a3bea6ecf2adb8a4f98753be5a0a3e032a98beb7bdc44a325cea7e6

Results in the following output:

address : < 41vEA7Ye8Bpeda6g59v5t46koWrVn2PNgEKgzquJjmiKCFTsh9gajr8J3pad49rqu581TAtFGCH9CYTCkYrCpuWUG9GkgeB > private view key : < fed77158ec692fe9eb951f6aeb22c3bda16fe8926c1aac13a5651a9c27f 34309> tx hash : < 60b6c42f1a3bea6ecf2adb8a4f98753be5a0a3e032a98beb7bdc44a325cea7e 6> public tx key : < c6e755802545f5444f095ab31be3c2aaca4500d0b016d34cc0953b37cb198a1d > dervied key : < a6e57d6eed1c17cdb1da1b43ee0a4f49c2bfd2138d8da237f354f324712a67ba > Output no: 0, < d58986ca9258cd4e4f7b0ef9baf3f61a49869364f5a9ec4a3d9186382a6b 5110> , mine key: 0.020000000000 Output no: 1, < 50fc47f931dfa393e369ab84a967c82dd866fd02205d656866dde9c2650329ca > , not mine key Output no: 2, < 55ea815f82a1552af2cf003b70f023bcde201ce3ad1ae8453ce9291b788d1cac > , mine key: 0.100000000000 Output no: 3, < e0d26e4d31022197d0831d3ba08b6b43e57672ccb9229880b29404468fd5984a > , not mine key Output no: 4, < 1ba3063bd57752537ca7ccd47ff2c0a72b7dcd8d8510fc222737636f208174cc > , mine key: 9.000000000000 Total xmr received: 9.120000000000

These results agree also with those obtained using XMR test.

Compile this example

The dependencies are same as those for Monero, so I assume Monero compiles correctly. If so then to download and compile this example, the following steps can be executed:

# download the source code git clone https://github.com/moneroexamples/access-blockchain-in-cpp.git # enter the downloaded sourced code folder cd access-blockchain-in-cpp # create the makefile cmake . # compile make

After this, xmreg01 executable file should be present in access-blockchain-in-cpp folder. How to use it, can be seen in the above example outputs.

How can you help?

Constructive criticism, code and website edits are always good. They can be made through github.

Some Monero are also welcome: