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2.0.0-rc.42 • Public • Published

Fadroma Agent: Scriptable User Agents for the Blockchain

The Fadroma Agent API is Fadroma's imperative API for interacting with smart contract platforms. It's designed for expressing smart contract operations in a concise and readable manner.

The API is specified by the @fadroma/agent package. In effect, it's a reduced and simplified vocabulary that covers the common ground between different implementations of smart contract-enabled chains.

Since different chains provide different client libraries and connection methods, the concrete implementations of the Fadroma Agent API are contained in separate packages:

@fadroma/connect reexports all available Fadroma Agent API implementations. It's recommended to use @fadroma/connect when depending on more than one of the above.

The overarching goal of Fadroma Agent is to enable developers to learn only a single client library for all supported blockchains and client platforms.

Connecting to a chain

Instances of the Chain class represents blockchains.

A chain may exists in one of several modes, represented by the chain.mode property and the ChainMode enum:

  • mainnet is a production chain storing real value;
  • testnet is a persistent remote chain used for testing;
  • devnet is a locally run chain node in a Docker container;
  • mocknet is a mock implementation of a chain.

The Chain.mainnet, Chain.testnet, Chain.devnet and Chain.mocknet static methods construct a chain in the given mode.

You can also check whether a chain is in a given mode using the chain.isMainnet, chain.isTestnet, chain.isDevnet and chain.isMocknet read-only boolean properties.

The chain.devMode property is true when the chain is a devnet or mocknet. Devnets and mocknets are under your control - i.e. you can delete them and start over. On the other hand, mainnet and testnet are global and persistent.

The chain.id property is a string that uniquely identifies a given blockchain. Examples are secret-4 (Secret Network mainnet), pulsar-3 (Secret Network testnet), or okp4-nemeton-1 (OKP4 testnet). Chains in different modes usually have distinct IDs.

The same chain may be accessible via different URLs. The chain.url property identifies the URL to which requests are sent.

Since the underlying API classes (e.g. CosmWasmClient or SecretNetworkClient) are initialized asynchronously, and JavaScript does not have async constructors, chains start out in an unitialized state, where the chain.api property is not populated. Awaiting the chain.ready one-shot promise returns the same chain object, but with the API client populated. Normally, this is done automatically when calling the chain's async methods; but if you want to access the API handle directly, you would need to await chain.ready. This is useful if you want to access a chain-specific feature that is not part of the Fadroma Agent API


const { api } = await chain.ready

Block height

The chain.height getter returns a Promise wrapping the current block height.

The chain.nextBlock getter returns a Promise which resolves when the block height increments, and contains the new block height.


// Get the current block height
const height = await chain.height

// Wait until the block height increments
await chain.nextBlock

Native tokens

The Chain.defaultDenom and chain.defaultDenom properties contain the default denomination of the chain's native token.

The chain.getBalance(denom, address) async method queries the balance of a given address in a given token.



Querying contracts

The chain.query(contract, message) async method calls a read-only query method of a smart contract.

The chain.getCodeId(address), chain.getHash(addressOrCodeId) and chain.getLabel(address) async methods query the corresponding metadata of a smart contract.

The chain.checkHash(address, codeHash) method warns if the code hash of a contract is not the expected one.



Authenticating an agent

To transact on a given chain, you need to authorize an Agent. This is done using the chain.authenticate(...) method, which synchonously returns a new Agent instance for the given chain.

Instantiating multiple agents allows the same program to interact with the chain from multiple distinct identities.

This method may be called with one of the following signatures:

  • chain.authenticate(options)
  • chain.authenticate(CustomAgentClass, options)
  • chain.authenticate(CustomAgentClass)

The returned Agent starts out uninitialized. Awaiting the agent.ready property makes sure the agent is initialized. Usually, agents are initialized the first time you call one of the async methods described below.

If you don't pass a mnemonic, a random mnemonic and address will be generated.



Agent identity

The agent.address property is the on-chain address that uniquely identifies the agent.

The agent.name property is a user-friendly name for an agent. On devnet, the name is also used to access the initial accounts that are created during devnet genesis.

Agents and block height

The agent.height and agent.nextBlock methods are equivalent to the same methods on the chain object, and are replicated on the Agent class purely for convenience.

const height = await agent.height

await agent.nextBlock

Native token transactions

The agent.getBalance(denom, address) async method works the same as chain.getBalance(...) but defaults to the agent's address.

The agent.balance readonly property is a shorthand for querying the current agent's balance in the chain's main native token.

The agent.send(address, amounts, options) async method sends one or more amounts of native tokens to the specified address.

The agent.sendMany([[address, coin], [address, coin]...]) async method sends native tokens to multiple addresses.


await agent.balance // In the default native token

await agent.getBalance() // In the default native token

await agent.getBalance('token') // In a non-default native token

await agent.send('recipient-address', 1000)

await agent.send('recipient-address', '1000')

await agent.send('recipient-address', [
  {denom:'token1', amount: '1000'}
  {denom:'token2', amount: '2000'}

Uploading and instantiating contracts

The agent.upload(...) uploads a contract binary to the chain.

The agent.instantiate(...) async method takes a code ID and returns a contract instance.

The agent.instantiateMany(...) async method instantiates multiple contracts within the same transaction.

On Secret Network, it's not possible to send multiple separate upload transactions within the same block. Therefore, when uploading multiple contracts, agent.nextBlock needs to be awaited between them. agent.uploadMany(...) does this automatically.


import { examples } from './fixtures/Fixtures.ts.md'
import { readFileSync } from 'node:fs'

// uploading from a Buffer
await agent.upload(readFileSync(examples['KV'].path), {
  // optional metadata
  codePath: examples['KV'].path

// Uploading from a filename
await agent.upload('example.wasm') // TODO

// Uploading an Uploadable object
await agent.upload({ artifact: './example.wasm', codeHash: 'expectedCodeHash' }) // TODO

const c1 = await agent.instantiate({
  codeId:   '1',
  codeHash: 'verify!',
  label:    'unique1',
  initMsg:  { arg: 'val' }

const [ c2, c3 ] = await agent.instantiateMany([
  { codeId: '2', label: 'unique2', initMsg: { arg: 'values' } },
  { codeId: '3', label: 'unique3', initMsg: { arg: 'values' } }

Executing transactions and performing queries

The agent.query(contract, message) async method calls a query method of a smart contract. This is equivalent to chain.query(...).

The agent.execute(contract, message) async method calls a transaction method of a smart contract, signing the transaction as the given agent.


const response = await agent.query(c1, { get: { key: '1' } })
assert.rejects(agent.query(c1, { invalid: "query" }))

const result = await agent.execute(c1, { set: { key: '1', value: '2' } })
assert.rejects(agent.execute(c1, { invalid: "tx" }))

Batching transactions

The agent.batch(...) method creates an instance of Batch.

Conceptually, you can view a batch as a kind of agent that does not execute transactions immediately - it collects them, and waits for the batch.broadcast() method. You can pass a batch anywhere you can pass an agent.

The main difference between a batch and and agent is that you cannot query from a batch. This is because a batch is an atomic action, and queries made inbetween individual transactions of a batch would return the state as it was before all the transactions. Therefore, to avoid confusion and outdated state, the query methods of the batch "agent" throw errors. If you need to perform queries, use a regular agent before or after the batch.

Instead of broadcasting, you can also export an unsigned batch, and pass it around manually as part of a multisig transaction.

To create and submit a batch in a single expression, you can use batch.wrap(async (batch) => { ... }):


const results = await agent.batch(async batch=>{
  await batch.execute(c1, { del: { key: '1' } })
  await batch.execute(c2, { set: { key: '3', value: '4' } })

Gas fees

Transacting creates load on the network, which incurs costs on node operators. Compensations for transactions are represented by the gas metric.

You can specify default gas limits for each method by defining the fees: Record<string, IFee> property of your client class:

const fee1 = new Fee('100000', 'uscrt')
client.fees['my_method'] = fee1

assert.deepEqual(client.getFee('my_method'), fee1)
assert.deepEqual(client.getFee({'my_method':{'parameter':'value'}}), fee1)

You can also specify one fee for all transactions, using client.withFee({ gas, amount: [...] }). This method works by returning a copy of client with fees overridden by the provided value.

const fee2 = new Fee('200000', 'uscrt')

assert.deepEqual(await client.withFee(fee2).getFee('my_method'), fee2)


Contract clients

The Client class represents a handle to a smart contract deployed to a given chain.

To provide a robust SDK to users of your project, simply publish a NPM package containing subclasses of Client that correspond to your contracts and invoke their methods.

To operate a smart contract through a Client, you need an agent, an address, and a codeHash:


import { Client } from '@fadroma/agent'

class MyClient extends Client {

  myMethod = (param) => this.execute({
    my_method: { param }

  myQuery = (param) => this.query({
    my_query: { param }


let address  = Symbol('some-addr')
let codeHash = Symbol('some-hash')
let client: Client = new MyClient({ agent, address, codeHash })

assert.equal(client.agent,    agent)
assert.equal(client.address,  address)
assert.equal(client.codeHash, codeHash)
client = agent.getClient(MyClient, address, codeHash)
await client.execute({ my_method: {} })
await client.query({ my_query: {} })

Client agent

By default, the Client's agent property is equal to the agent which deployed the contract. This property determines the address from which subsequent transactions with that Client will be sent.

In case you want to deploy the contract as one identity, then interact with it from another one as part of the same procedure, you can set agent to another instance of Agent:

assert.equal(client.agent, agent)
client.agent = await chain.authenticate()
assert.notEqual(client.agent, agent)

Similarly to withFee, the as method returns a new instance of your client class, bound to a different agent, thus allowing you to execute transactions as a different identity.

const agent1 = await chain.authenticate(/*...*/)
const agent2 = await chain.authenticate(/*...*/)

client = agent1.getClient(Client, "...")

// executed by agent1:
client.execute({ my_method: {} })

// executed by agent2
client.withAgent(agent2).execute({ my_method: {} })

Client metadata

The original Contract object from which the contract was deployed can be found on the optional meta property of the Client.

import { Contract } from '@hackbg/fadroma'
assert.ok(client.meta instanceof Contract)

Fetching metadata:

import { fetchLabel } from '@fadroma/agent'

await fetchCodeId(client, agent)
await fetchLabel(client, agent)

The code ID is a unique identifier for compiled code uploaded to a chain.

The code hash also uniquely identifies for the code that underpins a contract. However, unlike the code ID, which is opaque, the code hash corresponds to the actual content of the code. Uploading the same code multiple times will give you different code IDs, but the same code hash.

Contract deployments

These classes are used for describing systems consisting of multiple smart contracts, such as when deploying them from source. By defining such a system as one or more subclasses of Deployment, Fadroma enables declarative, idempotent, and reproducible smart contract deployments.

The Deployment class represents a set of interrelated contracts. To define your deployment, extend the Deployment class, and use the this.template({...}) and this.contract({...}) methods to specify what contracts to deploy:

// in your project's api.ts:

import { Deployment } from '@fadroma/agent'

export class DeploymentA extends Deployment {

  kv1 = this.contract({
    name: 'kv1',
    crate: 'examples/kv',
    initMsg: {}

  kv2 = this.contract({
    name: 'kv2',
    crate: 'examples/kv',
    initMsg: {}



To prepare a deployment for deploying, use getDeployment. This will provide a populated instance of your deployment class.

import { getDeployment } from '@hackbg/fadroma'
deployment = getDeployment(DeploymentA, /* ...constructor args */)

Deploying everything

Then, call its deploy method:

await deployment.deploy()

For each contract defined in the deployment, this will do the following:

  • If it's not compiled yet, this will build it.
  • If it's not uploaded yet, it will upload it.
  • If it's not instantiated yet, it will instantiate it.

Expecting contracts to be deployed

Having deployed a contract, you want to obtain a Client instance that points to it, so you can call the contract's methods.

Using the contract.expect() method you can get an instance of the Client specified in the contract options, provided the contract is already deployed (i.e. its address is known).

assert(deployment.kv1.expect() instanceof Client)
assert(deployment.kv2.expect() instanceof Client)

This is the recommended method for passing handles to contracts to your UI code after deploying or connecting to a stored deployment (see below).

If the address of the request contract is not available, this will throw an error.

Deploying individual contracts with dependencies

By awaiting a Contract's deployed property, you say: "give me a handle to this contract; if it's not deployed, deploy it, and all of its dependencies (as specified by the initMsg method)".

assert(await deployment.kv1.deployed instanceof Client)
assert(await deployment.kv2.deployed instanceof Client)

Since this does not call the deployment's deploy method, it only deploys the requested contract and its dependencies but not any other contracts defined in the deployment.

Deploying with custom logic

The deployment.deploy method simply instantiates all contracts in order. You are free to override it and deploy the defined contracts according to some custom logic:

class DeploymentB extends Deployment {
  kv1 = this.contract({ crate: 'examples/kv', name: 'kv1', initMsg: {} })
  kv2 = this.contract({ crate: 'examples/kv', name: 'kv2', initMsg: {} })

  deploy = async (deployBoth: boolean = false) => {
    await this.kv1.deployed
    if (deployBoth) await this.kv2.deployed
    return this

Contract instances

The Contract class describes an individual smart contract instance and uniquely identifies it within the Deployment.

import { Contract } from '@fadroma/agent'

new Contract({
  repository: 'REPO',
  revision:   'REF',
  workspace:  'WORKSPACE'
  crate:      'CRATE',
  artifact:   'ARTIFACT',
  chain:      { /* ... */ },
  agent:      { /* ... */ },
  deployment: { /* ... */ },
  codeId:     0,
  codeHash:   'CODEHASH'
  client:     Client,
  name:       'NAME',
  initMsg:    async () => ({})

Naming and labels

The chain requires labels to be unique. Labels generated by Fadroma are of the format ${deployment.name}/${contract.name}.

Lazy init

The initMsg property of Contract can be a function returning the actual message. This function is only called during instantiation, and can be used to generate init messages on the fly, such as when passing the address of one contract to another.

Deploying contract instances

To instantiate a Contract, its agent property must be set to a valid Agent. When obtaining instances from a Deployment, their agent property is provided from deployment.agent.

import { Agent } from '@fadroma/agent'
assert(deployment.a.agent instanceof Agent)
assert.equal(deployment.a.agent, deployment.agent)

You can instantiate a Contract by awaiting the deployed property or the return value of the deploy() method. Since distributed ledgers are append-only, deployment is an idempotent operation, so the deploy will run only once and subsequent calls will return the same Contract with the same address.

await deployment.a.deploy()
await deployment.a.deployed

If contract.codeId is not set but either source code or a WASM binary is present, this will try to upload and build the code first.

await deployment.a.uploaded
await deployment.a.upload()

await deployment.a.built
await deployment.a.build()

Contract templates

The Template class represents a smart contract's source, compilation, binary, and upload. It can have a codeHash and codeId but not an address.

Instantiating a template refers to calling the template.instance method (or its plural, template.instances), which returns Contract, which represents a particular smart contract instance, which can have an address.

Deploying multiple contracts from a template

The deployment.template method adds a Template to the Deployment.


You can pass either an array or an object to template.instances.


Building from source code

To build, the compiler property must be set to a valid Compiler. When obtaining instances from a Deployment, the compiler property is provided automatically from deployment.compiler.


You can build a Template (or its subclass, Contract) by awaiting the built property or the return value of the build() method.


Uploading binaries

To upload, the uploader property must be set to a valid Uploader. When obtaining instances from a Deployment, the uploader property is provided automatically from deployment.uploader.


You can upload a Template (or its subclass, Contract) by awaiting the uploaded property or the return value of the upload() method.

If a WASM binary is not present (template.artifact is empty), but a source and a compiler are present, this will also try to build the contract.





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