constructor

Constructor

The constructor package is used for coordinating the construction and broadcast of transactions on any blockchain that implements the Mesh API. It was designed to power automated Construction API testing in the mesh-cli (check:construction) but could be useful for anyone building a Mesh API wallet.

Framework

When first learning about a new topic, it is often useful to understand the hierarchy of concerns. In the constructor, this "hierarchy" is as follows:

Workflows -> Jobs
  Scenarios
    Actions

Workflows contain collections of Scenarios to execute. Scenarios are executed atomically in database transactions (rolled back if execution fails) and culminate in an optional broadcast. This means that a single Workflow could contain multiple broadcasts (which can be useful for orchestrating staking-related transactions that affect a single account).

To perform a Workflow, we create a Job. This Job has a unique identifier and stores state for all Scenarios in the Workflow. State is shared across an entire Job so Actions in a Scenario can access the output of Actions in other Scenarios. The syntax for accessing this shared state can be found here.

Actions are discrete operations that can be performed in the context of a Scenario. A full list of all Actions that can be performed can be found here.

If you have suggestions for more actions, please open an issue in mesh-sdk-go!

Broadcast Invocation

If you'd like to broadcast a transaction at the end of a Scenario, you must populate the following fields:

• <scenario>.network
• <scenario>.operations
• <scenario>.confirmation_depth (allows for stake-related transactions to complete before marking as a success)

Optionally, you can populate the following field:

• <scenario>.preprocess_metadata

Once a transaction is confirmed on-chain (after the provided <scenario>.confirmation_depth, it is stored by the tester at <scenario>.transaction for access by other Scenarios in the same Job.

Dry Runs

In UTXO-based blockchains, it may be necessary to amend the operations stored in <scenario>.operations based on the suggested_fee returned in /construction/metadata. The constructor supports running a "dry run" of a transaction broadcast if you set the follow field:

• <scenario>.dry_run = true

The suggested fee will then be stored as <scenario>.suggested_fee for use by other Scenarios in the same Job. You can find an example of this in the Ethereum configuration.

If this field is not populated or set to false, the transaction will be constructed, signed, and broadcast.

Using with mesh-cli

If you use the constructor for automated Construction API testing (without prefunded accounts), you MUST implement 2 required Workflows:

• create_account
• request_funds

If you don't implement these 2 Workflows, processing could stall.

Please note that create_account can contain a transaction broadcast if on-chain origination is required for new accounts on your blockchain.

If you plan to run the constructor in CI, you may wish to provide prefunded accounts when running the tester (otherwise you would need to manually fund generated accounts).

Optionally, you can also provide a return_funds workflow that will be invoked when exiting check:construction. This can be useful in CI when you want to return all funds to a single accout or faucet (instead of black-holing them in all the addresses created during testing).

Writing Workflows

It is possible to write Workflows from scratch using JSON, however, it is highly recommended to use the Mesh Constructor DSL. You can see an example of how these two approaches compare below:

Without DSL

[
  {
    "name": "request_funds",
    "concurrency": 1,
    "scenarios": [
      {
        "name": "find_account",
        "actions": [
          {
            "input": "{\"symbol\":\"tBTC\", \"decimals\":8}",
            "type": "set_variable",
            "output_path": "currency"
          },
          {
            "input": "{\"minimum_balance\":{\"value\": \"0\", \"currency\": {{currency}}}, \"create_limit\":1}",
            "type": "find_balance",
            "output_path": "random_account"
          }
        ]
      },
      {
        "name": "request",
        "actions": [
          {
            "type": "load_env",
            "output_path": "min_balance",
            "input": "MIN_BALANCE"
          },
          {
            "type": "math",
            "ouput_path": "adjusted_min",
            "input": "{\"operation\":\"addition\", \"left_value\": {{min_balance}}, \"right_value\": \"600\"}"
          },
          {
            "input": "{\"account_identifier\": {{random_account.account_identifier}}, \"minimum_balance\":{\"value\": {{adjusted_min}}, \"currency\": {{currency}}}}",
            "type": "find_balance",
            "output_path": "loaded_account"
          }
        ]
      }
    ]
  },
  {
    "name": "create_account",
    "concurrency": 1,
    "scenarios": [
      {
        "name": "create_account",
        "actions": [
          {
            "input": "{\"network\":\"Testnet3\", \"blockchain\":\"Bitcoin\"}",
            "type": "set_variable",
            "output_path": "network"
          },
          {
            "input": "{\"curve_type\": \"secp256k1\"}",
            "type": "generate_key",
            "output_path": "key"
          },
          {
            "input": "{\"network_identifier\": {{network}}, \"public_key\": {{key.public_key}}}",
            "type": "derive",
            "output_path": "account"
          },
          {
            "input": "{\"account_identifier\": {{account.account_identifier}}, \"keypair\": {{key}}}",
            "type": "save_account"
          }
        ]
      }
    ]
  }
]

With DSL

request_funds(1){
  find_account{
    currency = {
      "symbol":"tBTC",
      "decimals":8
    };
    random_account = find_balance({
      "minimum_balance":{
        "value": "0",
        "currency": {{currency}}
      },
      "create_limit":1
    });
  },
  request{
    min_balance = load_env("MIN_BALANCE");
    adjusted_min = {{min_balance}} + 600;
    loaded_account = find_balance({
      "account_identifier": {{random_account.account_identifier}},
      "minimum_balance":{
        "value": {{adjusted_min}},
        "currency": {{currency}}
      }
    });
  }
}

create_account(1){
  create_account{
    network = {"network":"Testnet3", "blockchain":"Bitcoin"};
    key = generate_key({"curve_type":"secp256k1"});
    account = derive({
      "network_identifier": {{network}},
      "public_key": {{key.public_key}}
    });
    save_account({
      "account_identifier": {{account.account_identifier}},
      "keypair": {{key}}
    });
  }
}

Future Work

• Create a wallet package that uses Workflows as core logic
  • Requests made to the wallet could be injected into the Workflow state before starting execution to enable user-provided parameters
• Support the creation of modular functions that can be reused across Workflows
  • The functions would likely maintain their own state and just require some collection of inputs to be defined when they start execution and allow for mapping results back to the Workflow state when finished.
• Develop a testing suite that allows Workflow writers to test their scripts
  • Often times, the development cycle for working with Workflows is to write and then test on a live network. It should be possible to mock Actions and ensure a set of Operations are created.