stateful-counter

Stateful Counter Example

We will create a simple stateful smart contract which will:

• Have a global variable counter
• Will increment counter each time we call the application.

Steps

• Create a file with Approval Program
• Create a file with Clear program
• Deploy New Application
• Opt-In to Application
• Call Application
• Update Application
• Delete Application

1. Create a file with Approval Program

We will create an approval program which has global counter and it is incremented by 1 each time we call the application. Put the code below in /assets/approval_program.teal:

#pragma version 4

int NoOp
txn OnCompletion
==

bnz application_call

int 1
return

application_call:

// read global state
byte "counter"
dup
app_global_get

// increment the value
int 1
+

// store to scratch space
dup
store 0

// update global state
app_global_put

// load return value as approval
load 0
return

This program has a single global key/value pair to store the number of times the program was called. The key is the string "counter" and the value will be defined as an integer when the application is created.

2. Create a file with Clear Program

Now, we will create clear program. This program does not evaluate any conditions and simply approves the call. Put the code below in /assets/clear_program.teal:

#pragma version 4

int 1
return

3. Deploy New Application

To deploy the contract use the following code in a new file named deploy.js in scripts folder of your project directory:

Create user accounts

const masterAccount = deployer.accountsByName.get("master-account");
const creatorAccount = deployer.accountsByName.get("alice");

const algoTxnParams = {
	type: types.TransactionType.TransferAlgo,
	sign: types.SignType.SecretKey,
	fromAccount: masterAccount,
	toAccountAddr: creatorAccount.addr,
	amountMicroAlgos: 200e6,
	payFlags: {},
};
// transfer some algos to creator account
await deployer.executeTx(algoTxnParams);

In the code above we declared user accounts and funded creatorAccount account. masterAccount is the default account used in algob private net.

Deploy stateful contract

Firstly we need to fund the contract. master account will fund it (as it has lot of algos):

// Create Application
// Note: An Account can have maximum of 10 Applications.
const sscInfo = await deployer.deployApp(
	creatorAccount,
	{
		appName: "CounterApp",
		metaType: types.MetaType.FILE
		approvalProgramFilename: "approval_program.teal", // approval program
		clearProgramFilename: "clear_program.teal", // clear program
		localInts: 1,
		localBytes: 1,
		globalInts: 1,
		globalBytes: 1,
	},
	{}
);

console.log(sscInfo);

Parameters passed are:

• Approval Program

• Clear Program

• SSC(stateful smart contract) arguments which includes sender and details for storage usage.

• Common transaction parameters (eg. totalFee)

• In above code we have deployed a new application.

• After deploying application you should see the following information on your terminal:

Created new app-id: 189
{
  creator: 'EDXG4GGBEHFLNX6A7FGT3F6Z3TQGIU6WVVJNOXGYLVNTLWDOCEJJ35LWJY',
  txID: 'BCP3ZKT26K2BEB475OMKQHOMBEFVWEHESRS3XMAWQEVASFP6JFUA',
  confirmedRound: 13899,
  appID: 189
}

4. Opt-In to Application

To Opt-In to an application use the following code in one of your scripts (in ./scripts):

await deployer.optInAccountToApp(account, applicationID, {}, {});

where Account is the account you want to opt-in and applicationID is application index.

5. Call Application

To call an application use the following code in one of your scripts (in ./scripts):

const tx = {
	type: types.TransactionType.CallApp,
	sign: types.SignType.SecretKey,
	fromAccount: creatorAccount,
	appID: applicationID,
	payFlags: {},
};

await deployer.executeTx(tx);

In tx there are following parameters:

• we set the type which is CallApp - Call to stateful smart contract
• set the sign to SecretKey (tx is signed by creatorAccount's sk)
• provide fromAccount details
• provide application index of SSC (retreived from checkpoint)
• provide payment flags, if any (eg. fee, firstValid, lastvalid etc)

Calling application each time will increase the stateful counter by 1. To view the global state of the application you can use the following code:

// Retreive Global State
let globalState = await readAppGlobalState(deployer, creatorAccount.addr, applicationID);
console.log(globalState);

Output:

[ { key: 'Y291bnRlcg==', value: { bytes: '', type: 2, uint: 2 } } ]
[ { key: 'Y291bnRlcg==', value: { bytes: '', type: 2, uint: 3 } } ]

here key 'Y291bnRlcg==' is base64 encoded form of counter.

6. Update Application

To update an application with (new_approval.teal, new_clear.teal), you can use:

const updatedRes = await deployer.updateApp(
	"CounterApp", // app name use for checkpoint
	creatorAccount,
	{}, // pay flags
	applicationID,
	{
		metaType: types.MetaType.FILE,
		approvalProgramFilename: "new_approval.teal",
		clearProgramFilename: "new_clear.teal",
	},
	{}
);
console.log("Application Updated: ", updatedRes);

7. Delete Application

To delete an existing application you can use:

const tx = {
	type: types.TransactionType.DeleteApp,
	sign: types.SignType.SecretKey,
	fromAccount: creatorAccount,
	appID: applicationID,
	payFlags: {},
	appArgs: [],
};

await deployer.executeTx(tx);

Note: Deleting non existing app will throw error.