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GNTL Blockchain Explorer

In this example, these limitations are addressed by development of an GNTL Onion Blockchain Explorer. The example not only shows how to use GNTL C++ libraries, but also demonstrates how to use:

  • crow - C++ micro web framework
  • mstch - C++ {{mustache}} templates
  • json - JSON for Modern C++
  • fmt - Small, safe and fast string formatting library

Blockchain Explorers

GNTL MainNet Primary:

GNTL MainNet Backup:

GNTL StageNet Primary:

  • https://explorerstg.gntl.uk - StageNet version of MainNet Explorer used for GNTL Codebase Development only. Has no influence to MainNet.

GNTL Onion Blockchain Explorer features

The key features of the GNTL Onion Blockchain Explorer are:

  • no cookies, no web analytics trackers, no images,
  • open sourced,
  • made fully in C++,
  • showing encrypted payments ID,
  • showing ring signatures,
  • showing transaction extra field,
  • showing public components of GNTL addresses,
  • decoding which outputs and mixins belong to the given GNTL address and viewkey,
  • can prove that you send GNTL to someone,
  • detailed information about ring members, such as, their age, timescale and their ring sizes,
  • showing number of amount output indices,
  • support GNTL testnet and stagnet networks,
  • tx checker and pusher for online pushing of transactions,
  • estimate possible spendings based on address and viewkey,
  • can provide total amount of all miner fees,
  • decoding encrypted payment id,
  • decoding outputs and proving txs sent to sub-address,
  • can list RandomARQ code for each block.

Compiling from source

Our build has been tested on Debian 11 and Ubuntu Server 20.04. Other versions of OS should work, but are out of scope in this guide

Compile the latest GNTL Release version

Download and compile the most recent GNTL into your home folder, following the steps in the repository:

https://github.com/The-GNTL-Project/gntl

Install prerequisite
sudo apt install -y libcurl4-openssl-dev
Compile the Explorer

Once the GNTL has been compiled, the explorer can be downloaded and compiled as follows:

cd ~
git clone https://github.com/The-GNTL-Project/explorer-gntl
cd explorer-gntl
make
Sync the GNTL Daemon

The Explorer uses the a local daemon, so you must sync it before use.

Run the Explorer
./build/gntlblocks

By default it will look for blockchain in its default location i.e., ~/.gntl/lmdb. You can use -b option if its in different location.

For example:

./gntlblocks -b /home/gntl/non-defult-gntl-location/lmdb/

Example output:

[gntl@us blockchain-explorer]$ ./gntlblocks
2016-May-28 10:04:49.160280 Blockchain initialized. last block: 1056761, d0.h0.m12.s47 time ago, current difficulty: 1517857750
(2016-05-28 02:04:49) [INFO    ] Crow/0.1 server is running, local port 8081

Go to your browser: http://127.0.0.1:8081

The explorer's command line options

gntlblocks, GNTL Onion Blockchain Explorer:
  -h [ --help ] [=arg(=1)] (=0)				produce help message
  -t [ --testnet ] [=arg(=1)] (=0)			use testnet blockchain
  -s [ --stagenet ] [=arg(=1)] (=0)			use stagenet blockchain
  --enable-pusher [=arg(=1)] (=1)			enable signed transaction pusher
  --enable-random-arq [=arg(=1)] (=1)			enable generation of random_arq code
  --enable-mixin-details [=arg(=1)] (=0)		enable mixin details for key images, e.g., timescale, mixin of mixins, in tx context
  --enable-key-image-checker [=arg(=1)] (=1)		enable key images file checker
  --enable-output-key-checker [=arg(=1)] (=1)		enable outputs key file checker
  --enable-json-api [=arg(=1)] (=1)			enable JSON REST api
  --enable-as-hex [=arg(=1)] (=0)			enable links to provide hex representation of an tx and block
  --enable-autorefresh-option [=arg(=1)] (=1)		enable users to have the index page on autorefresh
  --enable-emission-monitor [=arg(=1)] (=1)		enable GNTL Network total emission monitoring thread
  -p [ --port ] arg (=19990)				default explorer port
  -x [ --bindaddr ] arg (=0.0.0.0)			default bind address for the explorer (default=127.0.0.1)
  --testnet-url arg					you can specify testnet url, if you run it on mainnet or stagenet. link will show on front page to testnet explorer
  --stagenet-url arg					you can specify stagenet url, if you run it on mainnet or testnet. link will show on front page to stagenet explorer
  --mainnet-url arg					you can specify mainnet url, if you run it on testnet or stagenet. link will show on front page to mainnet explorer
  --no-blocks-on-index arg (=49)			number of last blocks to be shown on index page
  --mempool-info-timeout arg (=5000)			maximum time, in milliseconds, to wait for mempool data for the front page
  --mempool-refresh-time arg (=5)			time, in seconds, for each refresh of mempool state
  -c [ --concurrency ] arg (=0)				number of threads handling queries. 0 (default) is auto and depends on host CPU
  -b [ --bc-path ] arg					path to lmdb folder of the blockchain, e.g., ~/.gntl/lmdb
  --ssl-crt-file arg					path to crt file for ssl (https) functionality
  --ssl-key-file arg					path to key file for ssl (https) functionality
  -d [ --daemon-url ] arg (=http:://127.0.0.1:16662)	GNTL Network daemon url

Example usage, defined as bash aliases.

# for mainnet explorer
alias gntlblocksmainnet='~/blockchain-explorer/build/gntlblocks --testnet-url "http://139.162.32.245:8082"'

Enable GNTL emission

Obtaining current GNTL emission amount is not straight forward. Thus, by default it is disabled. To enable it use --enable-emission-monitor flag, e.g.,

gntlblocks --enable-emission-monitor

This flag will enable emission monitoring thread. When started, the thread will initially scan the entire blockchain, and calculate the cumulative emission based on each block. Since it is a separate thread, the explorer will work as usual during this time. Every 10000 blocks, the thread will save current emission in a file, by default, in ~/.gntl/lmdb/emission_amount.txt. For testnet or stagenet networks, it is ~/.gntl/testnet/lmdb/emission_amount.txt or ~/.gntl/stagenet/lmdb/emission_amount.txt. This file is used so that we don't need to rescan entire blockchain whenever the explorer is restarted. When the explorer restarts, the thread will first check if ~/.gntl/lmdb/emission_amount.txt is present, read its values, and continue from there if possible. Subsequently, only the initial use of the tread is time consuming. Once the thread scans the entire blockchain, it updates the emission amount using new blocks as they come. Since the explorer writes this file, there can be only one instance of it running for mainnet, testnet and stagenet. Thus, for example, you cant have two explorers for mainnet running at the same time, as they will be trying to write and read the same file at the same time, leading to unexpected results. Off course having one instance for mainnet and one instance for testnet is fine, as they write to different files.

When the emission monitor is enabled, information about current emission of coinbase and fees is displayed on the front page, e.g., :

GNTL emission (fees) is 14485540.430 (52545.373) as of 1313448 block

The values given, can be checked using GNTL daemon's print_coinbase_tx_sum command. For example, for the above example: print_coinbase_tx_sum 0 1313449.

To disable the monitor, simply restart the explorer without --enable-emission-monitor flag.

Enable SSL (https)

By default, the explorer does not use ssl. But it has such a functionality.

As an example, you can generate your own ssl certificates as follows:

cd /tmp # example folder
openssl genrsa -out server.key 1024
openssl req -new -key server.key -out server.csr
openssl x509 -req -days 3650 -in server.csr -signkey server.key -out server.crt

Having the crt and key files, run gntlblocks in the following way:

./gntlblocks --ssl-crt-file=/tmp/server.crt --ssl-key-file=/tmp/server.key

Note: Because we generated our own certificate, modern browsers will complain about it as they cant verify the signatures against any third party. So probably for any practical use need to have properly issued ssl certificates.

JSON API

The explorer has JSON api. For the API, it uses conventions defined by JSend. By default the api is disabled. To enable it, use --enable-json-api flag, e.g.,

./gntlblocks --enable-json-api

api/transaction/<tx_hash>

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/transaction/6093260dbe79fd6277694d14789dc8718f1bd54457df8bab338c2efa3bb0f03d"

Partial results shown:

{
  "data": {
    "block_height": 1268252,
    "coinbase": false,
    "confirmations": 1,
    "current_height": 1268253,
    "extra": "01be23e277aed6b5f41f66b05244bf994c13108347366ec678ae16657f0fc3a22b",
    "inputs": [
      {
        "amount": 0,
        "key_image": "67838fd0ffd79f13e735830d3ec60412aed59e53e1f997feb6f73d088b949611",
        "mixins": [
          {
            "block_no": 1238623,
            "public_key": "0a5b853c55303c10e1326acfb085b9e246e088b1ccac7e37f7a810d46a28a914"
          },
          {
            "block_no": 1246942,
            "public_key": "527cf86f5abbfb006c970f7c6eb40493786d4751306f8985c6a43f98a88c0dff"
          }
        ]
      }
    ],
    "mixin": 9,
    "outputs": [
      {
        "amount": 0,
        "public_key": "525779873776e4a42f517fd79b72e7c31c3ba03e730fc32287f6414fb702c1d7"
      },
      {
        "amount": 0,
        "public_key": "e25f00fceb77af841d780b68647618812695b4ca6ebe338faba6e077f758ac30"
      }
    ],
    "payment_id": "",
    "payment_id8": "",
    "rct_type": 1,
    "timestamp": 1489753456,
    "timestamp_utc": "2017-03-17 12:24:16",
    "tx_fee": 12517785574,
    "tx_hash": "6093260dbe79fd6277694d14789dc8718f1bd54457df8bab338c2efa3bb0f03d",
    "tx_size": 13323,
    "tx_version": 2,
    "gntl_inputs": 0,
    "gntl_outputs": 0
  },
  "status": "success"
}

api/transactions

Transactions in last 25 blocks

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/transactions"

Partial results shown:

{
  "data": {
    "blocks": [
      {
        "age": "33:16:49:53",
        "height": 1268252,
        "size": 105390000000000000,
        "timestamp": 1489753456,
        "timestamp_utc": "2017-03-17 12:24:16",
        "txs": [
          {
            "coinbase": true,
            "mixin": 0,
            "outputs": 8491554678365,
            "rct_type": 0,
            "tx_fee": 0,
            "tx_hash": "7c4286f64544568265bb5418df84ae69afaa3567749210e46f8340c247f4803f",
            "tx_size": 151000000000000,
            "tx_version": 2
          },
          {
            "coinbase": false,
            "mixin": 5,
            "outputs": 0,
            "rct_type": 2,
            "tx_fee": 17882516700,
            "tx_hash": "2bfbccb918ee5f050808dd040ce03943b7315b81788e9cdee59cf86b557ba48c",
            "tx_size": 19586000000000000,
            "tx_version": 2
          }
        ]
      }
    ],
    "limit": 25,
    "page": 0
  },
  "status": "success"
}

api/transactions?page=<page_no>&limit=<tx_per_page>

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/transactions?page=2&limit=10"

Result analogical to the one above.

api/block/<block_number|block_hash>

curl  -w "\n" -X GET "http://139.162.32.245:8081/api/block/1293257"

Partial results shown:

{
  "data": {
    "block_height": 1293257,
    "block_reward": 0,
    "current_height": 1293264,
    "hash": "9ef6bb8f9b8bd253fc6390e5c2cdc45c8ee99fad16447437108bf301fe6bd6e1",
    "size": 141244,
    "timestamp": 1492761974,
    "timestamp_utc": "2017-04-21 08:06:14",
    "txs": [
      {
        "coinbase": true,
        "extra": "018ae9560eb85d5ebd22d3beaed55c21d469eab430c5e3cac61b3fe2f5ad156770020800000001a9030800",
        "mixin": 0,
        "payment_id": "",
        "payment_id8": "",
        "rct_type": 0,
        "tx_fee": 0,
        "tx_hash": "3ff71b65bec34c9261e01a856e6a03594cf0472acf6b77db3f17ebd18eaa30bf",
        "tx_size": 95,
        "tx_version": 2,
        "gntl_inputs": 0,
        "gntl_outputs": 8025365394426
      }
    ]
  },
  "status": "success"
}

api/mempool

Return all txs in the mempool.

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/mempool"

Partial results shown:

{
  "data": {
    "limit": 100000000,
    "page": 0,
    "total_page_no": 0,
    "txs": [
      {
        "coinbase": false,
        "extra": "022100325f677d96f94155a4840a84d8e0c905f7a4697a25744633bcb438feb1e51fb2012eda81bf552c53c2168f4130dbe0265c3a7898f3a7eee7c1fed955a778167b5d",
        "mixin": 3,
        "payment_id": "325f677d96f94155a4840a84d8e0c905f7a4697a25744633bcb438feb1e51fb2",
        "payment_id8": "",
        "rct_type": 2,
        "timestamp": 1494470894,
        "timestamp_utc": "2017-05-11 02:48:14",
        "tx_fee": 15894840000,
        "tx_hash": "9f3374f8ac67febaab153eab297937a3d0d2c706601e496bf5028146da0c9aef",
        "tx_size": 13291,
        "tx_version": 2,
        "gntl_inputs": 0,
        "gntl_outputs": 0
      }
    ],
    "txs_no": 7
  },
  "status": "success"
}

Limit of 100000000 is just default value above to ensure that all mempool txs are fetched if no specific limit given.

api/mempool?limit=<no_of_top_txs>

Return number of newest mempool txs, e.g., only 10.

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/mempool?limit=10"

Result analogical to the one above.

api/search/<block_number|tx_hash|block_hash>

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/search/1293669"

Partial results shown:

{
  "data": {
    "block_height": 1293669,
    "current_height": 1293670,
    "hash": "5d55b8fabf85b0b4c959d66ad509eb92ddfe5c2b0e84e1760abcb090195c1913",
    "size": 118026,
    "timestamp": 1492815321,
    "timestamp_utc": "2017-04-21 22:55:21",
    "title": "block",
    "txs": [
      {
        "coinbase": true,
        "extra": "01cb7fda09033a5fa06dc601b9295ef3790397cf3c645e958e34cf7ab699d2f5230208000000027f030200",
        "mixin": 0,
        "payment_id": "",
        "payment_id8": "",
        "rct_type": 0,
        "tx_fee": 0,
        "tx_hash": "479ba432f5c88736b438dd4446a11a13046a752d469f7828151f5c5b86be4e9a",
        "tx_size": 95,
        "tx_version": 2,
        "gntl_inputs": 0,
        "gntl_outputs": 7992697599717
      }
    ]
  },
  "status": "success"
}

api/outputs?txhash=<tx_hash>&address=&viewkey=&txprove=<0|1>

For txprove=0 we check which outputs belong to given address and corresponding viewkey. For txprove=1 we use to prove to the recipient that we sent them founds. For this, we use recipient's address and our tx private key as a viewkey value, i.e., viewkey=<tx_private_key>

Checking outputs:

# we use here official GNTL project's donation address as an example
curl  -w "\n" -X GET "http://127.0.0.1:8081/api/outputs?txhash=17049bc5f2d9fbca1ce8dae443bbbbed2fc02f1ee003ffdd0571996905faa831&address=44AFFq5kSiGBoZ4NMDwYtN18obc8AemS33DBLWs3H7otXft3XjrpDtQGv7SqSsaBYBb98uNbr2VBBEt7f2wfn3RVGQBEP3A&viewkey=f359631075708155cc3d92a32b75a7d02a5dcf27756707b47a2b31b21c389501&txprove=0"
{
  "data": {
    "address": "42f18fc61586554095b0799b5c4b6f00cdeb26a93b20540d366932c6001617b75db35109fbba7d5f275fef4b9c49e0cc1c84b219ec6ff652fda54f89f7f63c88",
    "outputs": [
      {
        "amount": 34980000000000,
        "match": true,
        "output_idx": 0,
        "output_pubkey": "35d7200229e725c2bce0da3a2f20ef0720d242ecf88bfcb71eff2025c2501fdb"
      },
      {
        "amount": 0,
        "match": false,
        "output_idx": 1,
        "output_pubkey": "44efccab9f9b42e83c12da7988785d6c4eb3ec6e7aa2ae1234e2f0f7cb9ed6dd"
      }
    ],
    "tx_hash": "17049bc5f2d9fbca1ce8dae443bbbbed2fc02f1ee003ffdd0571996905faa831",
    "tx_prove": false,
    "viewkey": "f359631075708155cc3d92a32b75a7d02a5dcf27756707b47a2b31b21c389501"
  },
  "status": "success"
}

Proving transfer:

We use recipient's address (i.e. not our address from which we sent gntl to recipient). For the viewkey, we use tx_private_key (although the GET variable is still called viewkey) that we obtained by sending this txs.

# this is for testnet transaction
curl  -w "\n" -X GET "http://127.0.0.1:8082/api/outputs?txhash=94782a8c0aa8d8768afa0c040ef0544b63eb5148ca971a024ac402cad313d3b3&address=9wUf8UcPUtb2huK7RphBw5PFCyKosKxqtGxbcKBDnzTCPrdNfJjLjtuht87zhTgsffCB21qmjxjj18Pw7cBnRctcKHrUB7N&viewkey=e94b5bfc599d2f741d6f07e3ab2a83f915e96fb374dfb2cd3dbe730e34ecb40b&txprove=1"
{
  "data": {
    "address": "71bef5945b70bc0a31dbbe6cd0bd5884fe694bbfd18fff5f68f709438554fb88a51b1291e378e2f46a0155108782c242cc1be78af229242c36d4f4d1c4f72da2",
    "outputs": [
      {
        "amount": 1000000000,
        "match": true,
        "output_idx": 0,
        "output_pubkey": "c1bf4dd020b5f0ab70bd672d2f9e800ea7b8ab108b080825c1d6cfc0b7f7ee00"
      },
      {
        "amount": 0,
        "match": false,
        "output_idx": 1,
        "output_pubkey": "8c61fae6ada2a103565dfdd307c7145b2479ddb1dab1eaadfa6c34db65d189d5"
      }
    ],
    "tx_hash": "94782a8c0aa8d8768afa0c040ef0544b63eb5148ca971a024ac402cad313d3b3",
    "tx_prove": true,
    "viewkey": "e94b5bfc599d2f741d6f07e3ab2a83f915e96fb374dfb2cd3dbe730e34ecb40b"
  },
  "status": "success"
}

Result analogical to the one above.

api/networkinfo

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/networkinfo"
{
  "data": {
    "alt_blocks_count": 0,
    "block_size_limit": 600000,
    "cumulative_difficulty": 2091549555696348,
    "difficulty": 7941560081,
    "fee_per_kb": 303970000,
    "grey_peerlist_size": 4991,
    "hash_rate": 66179667,
    "height": 1310423,
    "incoming_connections_count": 0,
    "outgoing_connections_count": 5,
    "start_time": 1494822692,
    "status": "OK",
    "target": 120,
    "target_height": 0,
    "testnet": false,
    "top_block_hash": "76f9e85d62415312758bc09e0b9b48fd2b005231ad1eee435a8081e551203f82",
    "tx_count": 1219048,
    "tx_pool_size": 2,
    "white_peerlist_size": 1000
  },
  "status": "success"
}

api/outputsblocks

Search for our outputs in last few blocks (up to 5 blocks), using provided address and viewkey.

# testnet address
curl  -w "\n" -X GET http://127.0.0.1:8081/api/outputsblocks?address=9sDyNU82ih1gdhDgrqHbEcfSDFASjFgxL9B9v5f1AytFUrYsVEj7bD9Pyx5Sw2qLk8HgGdFM8qj5DNecqGhm24Ce6QwEGDi&viewkey=807079280293998634d66e745562edaaca45c0a75c8290603578b54e9397e90a&limit=5&mempool=1

Example result:

{
{
  "data": {
    "address": "0182d5be0f708cecf2b6f9889738bde5c930fad846d5b530e021afd1ae7e24a687ad50af3a5d38896655669079ad0163b4a369f6c852cc816dace5fc7792b72f",
    "height": 960526,
    "limit": "5",
    "mempool": true,
    "outputs": [
      {
        "amount": 33000000000000,
        "block_no": 0,
        "in_mempool": true,
        "output_idx": 1,
        "output_pubkey": "2417b24fc99b2cbd9459278b532b37f15eab6b09bbfc44f9d17e15cd25d5b44f",
        "payment_id": "",
        "tx_hash": "9233708004c51d15f44e86ac1a3b99582ed2bede4aaac6e2dd71424a9147b06f"
      },
      {
        "amount": 2000000000000,
        "block_no": 960525,
        "in_mempool": false,
        "output_idx": 0,
        "output_pubkey": "9984101f5471dda461f091962f1f970b122d4469077aed6b978a910dc3ed4576",
        "payment_id": "0000000000000055",
        "tx_hash": "37825d0feb2e96cd10fa9ec0b990ac2e97d2648c0f23e4f7d68d2298996acefd"
      },
      {
        "amount": 96947454120000,
        "block_no": 960525,
        "in_mempool": false,
        "output_idx": 1,
        "output_pubkey": "e4bded8e2a9ec4d41682a34d0a37596ec62742b28e74b897fcc00a47fcaa8629",
        "payment_id": "0000000000000000000000000000000000000000000000000000000000001234",
        "tx_hash": "4fad5f2bdb6dbd7efc2ce7efa3dd20edbd2a91640ce35e54c6887f0ee5a1a679"
      }
    ],
    "viewkey": "807079280293998634d66e745562edaaca45c0a75c8290603578b54e9397e90a"
  },
  "status": "success"
}

api/emission

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/emission"
{
  "data": {
    "blk_no": 1313969,
    "coinbase": 14489473877253413000,
    "fee": 52601974988641130
  },
  "status": "success"
}

Emission only works when the emission monitoring thread is enabled.

api/version

curl  -w "\n" -X GET "http://127.0.0.1:8081/api/version"
{
  "data": {
    "api": 65536,
    "blockchain_height": 1357031,
    "git_branch_name": "update_to_current_gntl",
    "last_git_commit_date": "2021-03-02",
    "last_git_commit_hash": "",
    "gntl_version_full": "1.0.1"
  },
  "status": "success"
}

api number is store as uint32_t. In this case 65536 represents major version 1 and minor version 0. In JavaScript to get these numbers, one can do as follows:

var api_major = response.data.api >> 16;
var api_minor = response.data.api & 0xffff;

api/rawblock/<block_number|block_hash>

Return raw json block data, as represented in GNTL.

curl  -w "\n" -X GET "http://139.162.32.245:8081/api/rawblock/1293257"

Example result not shown.

api/rawtransaction/<tx_hash>

Return raw json tx data, as represented in GNTL.

curl  -w "\n" -X GET "http://139.162.32.245:8081/api/rawtransaction/6093260dbe79fd6277694d14789dc8718f1bd54457df8bab338c2efa3bb0f03d"

Example result not shown.

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