Hello World Session Code

This session code accepts a message string and stores it in the calling account under the special_value NamedKey.

Usage: This session code expects a runtime argument named message of the type String.

Tests: There are two tests available to test the Hello World session code. The should_store_hello_world test verifies the successful path, where a string hello world is saved under the special_value NamedKey. The should_error_on_missing_runtime_arg test verifies that an error is displayed when the runtime argument is missing. The tests start by initializing the Casper crates and creating a genesis account. Then the contract Wasm is loaded to the session_code object. The deploy_item object is created using the details like payment method, session code arguments, and the account address. The deploy_item object is passed to the execute_request. Finally, the execution engine is invoked to process the execute_request.

Build and Test the Session Code

Set up the Rust toolchain

You need the Rust toolchain to develop smart contracts.

make prepare

Compile session code

Compile the session code to WebAssembly (Wasm)

make build-contract

Test

Run the tests suite.

make test

Deploy the Hello World Session Code

You can deploy the Hello World session code on a local network using NCTL. For more information on how to run an NCTL network, see Setting up an NCTL network.

This command provides a view into the faucet account details. The faucet is the special pre-funded Account created on the NCTL network.

nctl-view-faucet-account

Sample faucet account details

2022-06-21T10:06:56.354497 [INFO] [226848] NCTL :: faucet a/c secret key    : /home/ubuntu/casper-node/utils/nctl/assets/net-1/faucet/secret_key.pem
2022-06-21T10:06:56.356638 [INFO] [226848] NCTL :: faucet a/c key           : 0146e3d5235a9c895d22eba969f390d0217aedbe0b8abcda0ea7ed0c27b3cd9d36
2022-06-21T10:06:56.358489 [INFO] [226848] NCTL :: faucet a/c hash          : ba94ea5ab81adceb47ca4a0502f926633b5643d90beae3bdf3f55117ceaf2297
2022-06-21T10:06:56.360308 [INFO] [226848] NCTL :: faucet a/c purse         : uref-bc30bba7e0701b726e89c08154b6037a8bc4b0bb8635595fb254f6081f0da0b1-007
2022-06-21T10:06:56.362112 [INFO] [226848] NCTL :: faucet a/c purse balance : 1000000000000000000000000000000000
2022-06-21T10:06:56.363781 [INFO] [226848] NCTL :: faucet on-chain account  : see below

{
  "api_version": "1.0.0",
  "block_header": null,
  "merkle_proof": "[2160 hex chars]",
  "stored_value": {
    "Account": {
      "account_hash": "account-hash-ba94ea5ab81adceb47ca4a0502f926633b5643d90beae3bdf3f55117ceaf2297",
      "action_thresholds": {
        "deployment": 1,
        "key_management": 1
      },
      "associated_keys": [
        {
          "account_hash": "account-hash-ba94ea5ab81adceb47ca4a0502f926633b5643d90beae3bdf3f55117ceaf2297",
          "weight": 1
        }
      ],
      "main_purse": "uref-bc30bba7e0701b726e89c08154b6037a8bc4b0bb8635595fb254f6081f0da0b1-007",
      "named_keys": []
    }
  }
}

The following command will help you deploy the session code on the NCTL network. In the following command, the KEY PATH is the path of the faucet account secret key.

casper-client put-deploy \
    --node-address http://localhost:11101 \
    --chain-name casper-net-1 \
    --secret-key [KEY PATH]/secret_key.pem \
    --payment-amount 5000000000000 \
    --session-path [CONTRACT PATH]/contract.wasm \
    --session-arg "message:string='hello world'"

After the deploy is successful, you can view the new NamedKey special_value in the faucet account details.

Sample faucet account details after successful deploy

2022-06-21T10:11:49.190801 [INFO] [226848] NCTL :: faucet a/c secret key    : /home/ubuntu/casper-node/utils/nctl/assets/net-1/faucet/secret_key.pem
2022-06-21T10:11:49.192818 [INFO] [226848] NCTL :: faucet a/c key           : 0146e3d5235a9c895d22eba969f390d0217aedbe0b8abcda0ea7ed0c27b3cd9d36
2022-06-21T10:11:49.194613 [INFO] [226848] NCTL :: faucet a/c hash          : ba94ea5ab81adceb47ca4a0502f926633b5643d90beae3bdf3f55117ceaf2297
2022-06-21T10:11:49.196407 [INFO] [226848] NCTL :: faucet a/c purse         : uref-bc30bba7e0701b726e89c08154b6037a8bc4b0bb8635595fb254f6081f0da0b1-007
2022-06-21T10:11:49.198393 [INFO] [226848] NCTL :: faucet a/c purse balance : 999999999999999999999900000000000
2022-06-21T10:11:49.200185 [INFO] [226848] NCTL :: faucet on-chain account  : see below
{
  "api_version": "1.0.0",
  "block_header": null,
  "merkle_proof": "[2330 hex chars]",
  "stored_value": {
    "Account": {
      "account_hash": "account-hash-ba94ea5ab81adceb47ca4a0502f926633b5643d90beae3bdf3f55117ceaf2297",
      "action_thresholds": {
        "deployment": 1,
        "key_management": 1
      },
      "associated_keys": [
        {
          "account_hash": "account-hash-ba94ea5ab81adceb47ca4a0502f926633b5643d90beae3bdf3f55117ceaf2297",
          "weight": 1
        }
      ],
      "main_purse": "uref-bc30bba7e0701b726e89c08154b6037a8bc4b0bb8635595fb254f6081f0da0b1-007",
      "named_keys": [
        {
          "key": "uref-07ea6a04bc49f73d20b78f81d994cd324b60ea62046cc73e7a2030f4c25c2759-007",
          "name": "special_value"
        }
      ]
    }
  }
}

:::note

Make a note of the NamedKey URef hash in the faucet account details.

:::

View the value stored in the NamedKey

You can view the value stored in the NamedKey by using the URef hash assigned to the NamedKey. To do this, we will first find the state root hash of the network using the following command:

casper-client get-state-root-hash --node-address http://localhost:11101

Sample output with state root hash

{
  "id": -7547762796950564402,
  "jsonrpc": "2.0",
  "result": {
    "api_version": "1.0.0",
    "state_root_hash": "6097c728c1af6179a491b5c3d143c49b032c9d6bb69be553729cb9f1489c3833"
  }
}

Then use the URef hash and the state root hash to view the value stored in the NamedKey.

casper-client query-state \
> --node-address http://localhost:11101 \
> --key [NamedKey Uref Hash] \
> --state-root-hash [STATE ROOT HASH]

Sample output displaying the NamedKey value

{
  "id": 5590727100213957592,
  "jsonrpc": "2.0",
  "result": {
    "api_version": "1.0.0",
    "block_header": null,
    "merkle_proof": "[3958 hex chars]",
    "stored_value": {
      "CLValue": {
        "bytes": "0b00000068656c6c6f20776f726c64",
        "cl_type": "String",
        "parsed": "hello world"
      }
    }
  }
}