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Clarity SDK

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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.

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About this tutorial and the prerequisites you need

{% include note.html content="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-public (say-hi)
   "hello world")

(define-public (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.

{% highlight cl linenos %} 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(); }); }); {% endhighlight %}

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-public (hello-world)
   "hello world")

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

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

ANSWER

;; Functions
(define-public (say-hi)
"hello world")
(define-public (increment-number (number int))
(+ 1 number))
(define-public (increment-number-by-10 (number int))
(+ 10 number))

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

ANSWER

    ;; Functions
(define-public (say-hi)
"hello world")
(define-public (increment-number (number int))
(+ 1 number))
(define-public (increment-number-by-10 (number int))
(+ 10 number))
(define-public (decrement-number (number int))
(- number 1))

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

;; Storage

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

ANSWER

;; Storage
(define-data-var counter int 0)
;; Functions
(define-public (say-hi)
"hello world")
(define-public (increment-number (number int))
(+ 1 number))
(define-public (increment-number-by-10 (number int))
(+ 10 number))
(define-public (decrement-number (number int))
(- number 1))
(define-public (increment-counter)
(set-var! counter (+ 1 counter)))
(define-public (get-counter)
(counter))

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