Clarity SDK Quickstart

You can use the software developer kit (SDK) to develop, test, and deploy Clarity smart contracts. The SDK goes beyond the basic test environment to allow for development of Javascript or TypeScript clients that call upon Clarity contracts.

Clarity is in pre-release

Clarity, its accompanying toolset, and the SDK are in pre-release. If you encounter issues with or have feature requests regarding Clarity, please create an issue on the blockstack/blockstack-core repository. To read previous or join ongoing discussions about smart contracts in general and Clarity in particular, visit the Smart Contracts topic in the Blockstack Forum.

About this tutorial and the prerequisites you need

Note: This tutorial was written on macOS High Sierra 10.13.4. If you use a Windows or Linux system, you can still follow along. However, you will need to "translate" appropriately for your operating system.

For this tutorial, you will use npm to manage dependencies and scripts. Before you begin, verify you have installed npm using the which command to verify.

$ which npm
/usr/local/bin/npm

If you don’t find npm in your system, install it.

Task 1: Install the SDK command line

The SDK comes with a command line for setting up the SDK and creating new projects. Use npm to install the clarity SDK command:

npm install -g @blockstack/clarity-cli

Verify you have installed the command correctly:

$ clarity --help
The Clarity CLI is used to manage Clarity smart contracts from the command line.

VERSION
  @blockstack/clarity-cli/0.1.13-alpha.3 darwin-x64 node-v12.10.0

USAGE
  $ clarity [COMMAND]

COMMANDS
  help   display help for clarity
  new    Generate new project
  setup  Install blockstack-core and its dependencies

Task 2: Generate an initial Clarity project

In this task, you generate a project scaffold — an initial set of directories and files.

  1. Create a new Clarity project .

     clarity new hello-clarity-sdk
    

    The system responds by creating a scaffolding for your Clarity project and initializing the packaging:

     $ clarity new hello-clarity-sdk
       create .vscode/extensions.json
       create .vscode/launch.json
       create contracts/sample/hello-world.clar
       create test/mocha.opts
       create tsconfig.json
       create test/hello-world.ts
       create .gitignore
       create package.json
       ...
     added 126 packages from 632 contributors and audited 226 packages in 4.678s
     found 0 vulnerabilities
    
     Project created at /tmp/hello-clarity-sdk
    

    Depending on your connection speed, it may take time to construct the scaffolding.

  2. Change into your new project directory.

     cd hello-clarity-sdk
    

Task 3: Investigate the generated project

Your project should contain three directories:

Directory Description
contracts Contains .clar files (Clarity contract files) here.
test Contains files for testing your application.
node_modules Contains packages the project depends on. Added by npm.

The contracts directory contains a single file in sample/hello-world.clar file.

(define (say-hi)
   "hello world")

(define (echo-number (val int))
   val)

The contract exposes 2 rudimentary functions. The say-hi returns a hello world string. The increment-number: echos val.

The project also includes tests/hello-world.ts file. The the mocha.opts file supports the testing by the Mocha Javascript test framework.

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import { Client, Provider, ProviderRegistry, Result } from "@blockstack/clarity";
import { assert } from "chai";

describe("hello world contract test suite", () => {
  let helloWorldClient: Client;
  let provider: Provider;

  before(async () => {
    provider = await ProviderRegistry.createProvider();
    helloWorldClient = new Client("hello-world", "sample/hello-world", provider);
  });

  it("should have a valid syntax", async () => {
    await helloWorldClient.checkContract();
  });

  describe("deploying an instance of the contract", () => {
    before(async () => {
      await helloWorldClient.deployContract();
    });

    it("should return 'hello world'", async () => {
      const query = helloWorldClient.createQuery({ method: { name: "say-hi", args: [] } });
      const receipt = await helloWorldClient.submitQuery(query);
      const result = Result.unwrap(receipt);
      const parsedResult = Buffer.from(result.replace("0x", ""), "hex").toString();
      assert.equal(parsedResult, "hello world");
    });

    it("should echo number", async () => {
      const query = helloWorldClient.createQuery({
        method: { name: "echo-number", args: ["123"] }
      });
      const receipt = await helloWorldClient.submitQuery(query);
      const result = Result.unwrap(receipt);
      assert.equal(result, "123");
    });
  });

  after(async () => {
    await provider.close();
  });
});

The hello-world.ts test file is a client that runs the hello-world.clar contract. Tests are critical for smart contracts as they are intended to manipulate assets and their ownership. These manipulations are irreversible within a blockchain. As you create a contracts, you should not be surprise if you end up spending more time and having more code in your tests than in your contracts directory. The tests/hello-world.ts file in the scaffold has the following content:

The first part of the test (lines 1 -10) sets up the test environment. It defines a Clarity provider and launches it (line 9). The Client instance contains a contract name and the path to the sample code. This test also checks the client (line 14) and then launches it (line 19), this is equivalent to running clarity-cli check with the command line. The remaining test code exercises the contract. Try running this test.

npm run test

> hello-clarity-sdk@0.0.0 test /private/tmp/hello-clarity-sdk
> mocha



  hello world contract test suite
    ✓ should have a valid syntax
    deploying an instance of the contract
      ✓ should print hello world message
      ✓ should echo number


  3 passing (182ms)

In the next section, try your hand at expanding the hello-world.clar program.

Task 4: Try to expand the contract

In this task, you are challenged to expand the contents of the contracts/hello-world.clar file. Use your favorite editor and open the contracts/hello-world.clar file. If you use Visual Studio Code, you can install the Blockstack Clarity extension. The extension provides syntax coloration and some autocompletion.

Edit the contracts/hello-world.clar file.

;; Functions

(define (hello-world)
   "hello world")

(define (echo-number (val int))
   val)

Use the + function to create a increment-number-by-10 function.

;; Functions

(define (say-hi)
"hello world")

(define (increment-number (number int))
(+ 1 number))

(define (increment-number-by-10 (number int))
(+ 10 number))

Use the + and - function to create a decrement-number user-defined method.

    ;; Functions

   (define (say-hi)
   "hello world")

   (define (increment-number (number int))
   (+ 1 number))

   (define (increment-number-by-10 (number int))
   (+ 10 number))

   (define (decrement-number (number int))
   (- number 1))
    

Finally, try adding a counter variable and be sure to store it. Increment counter in your code and add a get-counter funtion to return the result. Here is a hint, you can add a var` to a contract by adding the following line (before the function):

;; Storage

(define-data-var internal-value int 0)
;; Storage

(define-data-var counter int 0)

;; Functions

(define (say-hi)
"hello world")

(define (increment-number (number int))
(+ 1 number))

(define (increment-number-by-10 (number int))
(+ 10 number))

(define (decrement-number (number int))
(- number 1))

(define (increment-counter)
  (set-var! counter (+ 1 counter)))

(define (get-counter)
  (counter))

To review other, longer sample programs visit the clarity-js-sdk repository.