Contracts - intended usage

Introduction

You interact with a æternity node through HTTP. To learn more about contracts and contract life cycles see the doc.

There are two basic types of API calls, off-chain operations and on-chain transactions.

For an up to date list of all HTTP API endpoints and their arguments see æternity node HTTP API

Sophia calldata creation

A number of functions described below create calldata for contract call or contract create transactions (code/encode-calldata, code/call, create/compute, call/compute). These support two ways of specifying the function and arguments to the call:

• Unchecked (legacy): Function name (except for create/compute) and arguments as a Sophia constant tuple. No checks are made to ensure that the given arguments match what the contracts expects.

• Checked: An argument call containing Sophia source code for a contract snippet containing (at least) a prototype for the function to be called and a special function __call() whose body is a single call to this function. This contract is type checked and the given arguments are checked to be compatible with the type that the called contract expects.

  For example, to call a function swap that expects a record argument you can give the following call:

  contract CallExample =
    record pt = {x : int, y : int}
    function swap : pt => pt
    function __call() = swap({x = 3, y = 4})

  The call contract can contain more definitions than are needed to type check the call. In particular, it can be the complete source code of the contract to be called, with an added __call function.

Off chain operations

An æternity node provides some utility functions to help you create contract transactions and test contracts.

Contract Compile

TODO => http compiler & other tools

Encode Call Data

TODO => http compiler & other tools

Call

TODO still relevant?

Dry-run

/debug/transactions/dry-run

The arguments to the /debug/transactions/dry-run endpoint are:

• txs - a list of unsigned transactions to execute.

• top - an optional blockhash at which to do the dry-run (if not specified top hash will be used).

• accounts - a list of "extra" accounts to be used in the dry-run.

Decode Call Data

TODO => http compiler & other tools

On chain transactions

An æternity node provides some APIs to format contract transactions and an API for submitting a signed transaction.

There are two contract transactions available: create and call.

You:

• Format the contract transaction using the corresponding API;

• (As for any other transaction) sign offline (i.e. outside of the æternity node) the transaction according to consensus;

• (As for any other transaction) submit the transaction to the æternity node using its API.

In order to affect the state of the chain you have to submit the signed transaction to a mining node.

Contract Create

/debug/contracts/create

Contract Call

/debug/contracts/call

Reading chain data

Contract Call Result

/transactions/{hash}/info