Polkadot Substrate C++ API

Install Prerequisites

Boost

sudo apt-get install libboost-all-dev

Build tools

sudo apt-get -y install build-essential cmake

curl headers

sudo apt-get install libcurl4-openssl-dev

doxygen

sudo apt-get install doxygen python-pydot python-pydot-ng graphviz

Other dependencies: websocketpp, sr25519-crust...

make deps

Installation

This is work in progress, so installation is only possible from the source code. Here are instructions how to compile the library and run examples:

Checkout and build

git clone https://github.com/usetech-llc/polkadot_api_cpp
cd polkadot_api_cpp
cmake .
make
sudo make install

Build "clip" example client

make clip

Run connect basic example

Connect example will establish WebSocket connection to the polkadot node and read and output basic information.

bin/clip connect

Read Address Balance Example

Balance example will establish WebSocket connection and read and output address balance in DOTs.

bin/clip balance <your polkadot address>

Transfer DOTs Example

trasnfer <from address> <to address> <amount> <private key file>

Running Unit Tests

make test

How to Use

Files to include

#include <polkadotcpp/polkadot.h>

Files to link

/usr/lib/polkadotcpp/libpolkacpp.a

Library Initialization

Parity node URL is the only required parameter, though URL must include port. Example:

auto api = polkadot::api::getInstance()->app();

Eastablishing and maintaining connection

This call will establish connection and start message thread. It will also ping the node several times per minute with "health" request to keep the connection alive.

api->connect("wss://poc3-rpc.polkadot.io:443/");

Reading data from polkadot node

The data is returned as C structures. This example shows how to read (and output) system info:

auto systemInfo = api->getSystemInfo();

cout << "  Chain ID       : " << systemInfo->chainId << endl
     << "  Chain Name     : " << systemInfo->chainName << endl
     << "  Token Decimals : " << systemInfo->tokenDecimals << endl
     << "  Token Symbol   : " << systemInfo->tokenSymbol << endl;

Subscribing for updates

Subscribing is done by calling a matching subscribe method with parameters (if needed) and a callback (or a lambda function). This example subscribes for balance updates and prints new balance when it arrives:

api->subscribeBalance(address, [&](uint128 balance) {
    cout << endl << "  Balance: " << (uint64_t)balance << endl << endl;
});

In order to stop subscription, call matching unsubsribe method:

api->unsubscribeBalance();

Sending transactions (signed Extrinsics)

This example sends some DOTs between addresses and waits for execution. Transaction is signed with private key.

api->signAndSendTransfer(senderAddr, senderPrivateKeyStr, recipientAddr, amount, [&](string result) {
    if (result == "ready")
        cout << endl << endl << "   ---=== Transaction was registered in network ===--- " << endl << endl << endl;
    if (result == "finalized") {
        cout << endl << endl << "   ---=== Transaction was mined! ===--- " << endl << endl << endl;
        done = true;
    }
});

Finishing work

When connection is not needed anymore, call

api->disconnect();

More Information

The complete documentation of API interface can be found at this starting point: https://htmlpreview.github.io/?https://github.com/usetech-llc/polkadot_api_cpp/blob/master/doc/html/classIApplication.html

For more examples see:

• examples folder,
• test folder with unit and E2E tests,
• polkadot_ui repository, which implements a GTK 3.0 UI and uses this API.