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    @iov/core is the main entrypoint into the monorepo, exposing high-level functionality to easily build blockchain clients. It uses the keymanagement functionality of UserProfile, and the generic blockchain connection of BlockchainConnection, and pulls them together into one MultiChainSigner, which can query state and sign transactions on multiple blockchains. The examples below show a basic usage of the core library. You may also want to experiment with @iov/cli as a developer tool to familiarize yourself with this functionality.

    Full Api Docs

    Full API Docs from the latest release are hosted at:

    If you want to generate documentation for a development branch, please run yarn docs in the current directory and go to docs/index.html.


    Here are some example use cases. They all build on each other and assume all imports from above. I also use await syntax here, which works inside of async functions and experimentally in the @iov/cli REPL. (All imports are done for you in the REPL as well, so you can skip the import statements. They are provided for guidance when integrating into your own codebase).

    Before starting, either run from source in ../iov-cli via yarn build && ./bin/iov-cli or install from npm via npm install -g @iov/cli; iov-cli. Inside the cli the remaining code should work verbatim.

    Key Management

    Create a random mnemonic:

    import { Bip39, Random } from '@iov/crypto';
    // 16 bytes -> 12 word phrase
    const entropy16 = await Random.getBytes(16);
    const mnemonic12 = Bip39.encode(entropy16).toString();
    // 32 bytes -> 24 word phrase
    const entropy32 = await Random.getBytes(32);
    const mnemonic24 = Bip39.encode(entropy32).toString();

    Create a new profile with two wallets:

    import { Ed25519HdWallet, UserProfile } from '@iov/keycontrol';
    const profile = new UserProfile();
    const wallet1 = profile.addWallet(Ed25519HdWallet.fromMnemonic(mnemonic12));
    const wallet2 = profile.addWallet(Ed25519HdWallet.fromMnemonic(mnemonic24));

    Inspect the profile:

    // look at profile (value reads current state)
    // listen to the profile (stream of updates, good for reactive UI)
    const sub = profile.wallets.updates.subscribe({ next: wallets => console.log(wallets) });
    profile.setWalletLabel(, "12 words");
    profile.setWalletLabel(, "24 words");

    Create identies on the two wallets:

    import { ChainId } from '@iov/bcp';
    import { HdPaths } from '@iov/keycontrol';
    import { Encoding } from '@iov/encoding';
    const { fromHex, toHex } = Encoding;
    const chainId = 'bov-hugnet' as ChainId;
    // this creates two different public key identities, generated from the
    // first mnemonic using two different SLIP-0010 paths
    const id1a = await profile.createIdentity(, chainId, HdPaths.iov(0));
    const id1b = await profile.createIdentity(, chainId, HdPaths.iov(1));
    console.log(id1a.pubkey.algo, toHex(
    console.log(id1b.pubkey.algo, toHex(
    // this creates a different key from the second mnemonic,
    // this uses the same HD path as id1a, but different seed.
    const id2 = await profile.createIdentity(, chainId, HdPaths.iov(0));
    console.log(id2.pubkey.algo, toHex(;
    // we can also add labels to the individual identies
    profile.setIdentityLabel(id1a, 'main account');

    Save and reload keyring:

    const levelup = require('levelup');
    // this is for local leveldb in node
    const leveldown = require('leveldown');
    // use this for indexdb storage in browser
    // const browsedown = require('browsedown');
    const db = levelup(leveldown('./my_secret_keys'));
    // const db = levelup(browsedown('keystore'));
    const passphrase = "is seven words enough for the checker?"
    await profile.storeIn(db, passphrase);
    // this throws an error:
    // await UserProfile.loadFrom(db, "garbage");
    const loaded = await UserProfile.loadFrom(db, passphrase);
    // and we have the same data
    const ids = profile.getIdentities(loaded.wallets.value[0].id);

    Interacting with BCP Blockchain

    The main use of private keypairs is not just to generate and organize them, but to actually sign transactions (or encrypt/decrypt messages... not there yet). To demonstrate this part, we need a working blockchain. If you are ambitious, you can check out bcp-demo, and build the bov and tendermint binaries, construct your genesis file and run the client against your one-node "dev net"...

    But, if you just want to see how the client works, let's run against iov's testnet and use the faucet to get some tokens. As of February 27, 2019, the current testnet is located at

    To connect, you need to know the address of the rpc server (above). It is also helpful to know the chainId of the chain. You can find that quite easily by looking at the genesis file under .result.genesis.chain_id. In our case this is bov-hugnet.

    Executing the commands

    Discover the address for your identity. This is chain-dependent, so we need to use the chain-dependent TxCodec to generate it. In our case, bnsCodec:

    import { bnsCodec } from '@iov/bns';
    const addr = bnsCodec.identityToAddress(id1a);

    If you are running your own "dev-net" give that address plenty of tokens in the genesis file, by running bov init IOV $ADDR.

    Now, connect to the network:

    import { bnsConnector, MultiChainSigner } from '@iov/core';
    const signer = new MultiChainSigner(profile);
    await signer.addChain(bnsConnector('wss://'));
    console.log(signer.chainIds()[0]); // is this what you got yourself?

    List the tokens on the network:

    const connection = signer.connection(chainId);
    const tokens = await connection.getAllTokens();

    Query the testnet for some existing genesis accounts:

    // this is pulled from the genesis account
    import { Address } from "@iov/bcp"
    const bert = "tiov1u29wnfhtjn7g3de7kl9adwrmlyltn0hsjckecc" as Address;
    const acct = await connection.getAccount({ address: bert });

    If you are running the testnet faucet, just ask for some free money.

    import { TokenTicker } from "@iov/bcp";
    import { IovFaucet } from "@iov/faucets";
    const faucet = new IovFaucet("");
    await, "ALT" as TokenTicker);

    Then query your account:

    const mine = await connection.getAccount({ address: addr });
    console.log(mine); // should show non-empty array for balance
    const addr2 = bnsCodec.identityToAddress(id2);
    let yours = await connection.getAccount({ address: addr2 });
    console.log(yours); // should be undefined

    Send a transaction to second id:

    import { SendTransaction, TokenTicker } from "@iov/bcp"
    const sendTx: SendTransaction = {
      kind: "bcp/send",
      creator: id1a, // this account must have money
      recipient: addr2,
      memo: "My first transaction",
      amount: { // 10.11 ALT (9 sig figs in tx codec)
        quantity: '10110000000',
        fractionalDigits: 9,
        tokenTicker: "ALT" as TokenTicker,
    // we must have the private key for the transaction creator (id1a)
    await signer.signAndPost(sendTx);
    // and we have a balance on the recipient now
    yours = await connection.getAccount({ address: addr2 });
    console.log(yours); // should show non-empty array for balance

    Now, query the transaction history:

    const history = await connection.searchTx({ sentFromOrTo: addr2 });
    const first = history[0].transaction as SendTransaction;
    // address of recipient
    // public key of sender
    // address of sender
    const sender = bnsCodec.identityToAddress(first);

    Reactive Clients

    If you query, the data can get stale, and you may be tempted to start polling the blockchain. Don't! Instead we offer event streams for anyone wishing to generate a reactive application. You can simply log these values, or feed them into a reducer to capture their value.

    // these are helpers for consuming streams
    // lastValue will always store the last value,
    // asArray will append to an array with list of all tx that were streamed
    import { asArray, lastValue } from '@iov/stream';
    const liveHeight = lastValue(client.watchBlockHeaders().map(header => header.height));
    // if you wait a few seconds, you should see the block-height increase
    // you can also watch an account balance
    const liveBalance = lastValue(client.watchAccount({address: addr}));
    // or a list of all transactions that touch this account
    const liveTx = asArray(client.liveTx({address: addr}));

    Now, go ahead, send some tokens to this account in another window, and read the value of the account and tx again, watch them grow.


    This package is part of the IOV-Core repository, licensed under the Apache License 2.0 (see NOTICE and LICENSE).




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