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Contract

Loading contract code

note

This is different then deploying contracts on the network. Think of loading a contract as preparing its content to act as a blueprint for when we chose to make it live (hence its associated online type name, LiveContract).

A contract can be loaded from 2 sources: either referencing a local file or by giving the contract's code directly. To load a contract one of the following methods can be used:

  • Contract.newFrom - given either the path of the .sol file or the actual code of it, retrieves a single Contract instance. If there are multiple contracts defined, by default, the first one is retrieved. This can be overwritten to retrieve either the n-th index contract (by default index=0) or a contract by name.
  • Contract.allFrom - same as Contract.name in all regards except for the fact that it does not take in an index nor a contract name and retrieves an array of all the available contracts. When building a Contract instance, there's also a ignoreWarnings property which is, by default, set to false that allows to bypass solidity's warnings when building the contract's code.

A thing to keep in mind here is the fact that, once a Contract instance has been constructed, this is also a guarantee that the provided code was accepted by the solidity compiler. This is the reason why Contracts have byteCode property defined on it.

Deploying contracts

Once an ApiSession and a Contract is available, deploying the code on the network is as simple as doing an session.upload(contract) method call. This returns a Promise<LiveContract> so you might want await-ing for the result.

Transaction meta-arguments

Going into more depth with this method, if one wants to tweak the Hedera File Service - Create File Transaction step with extra-arguments, just pass in a second param to the upload call which is a object of the form {_file: {...}} containing any required options. For example, to attach a "Hello Strato" memo to the uploaded contract code, the resulting call would end up being: session.upload(contract, {_file: {fileMemo: "Hello Strato"}}).

To pass Create Smart Contract Transaction parameters, have the second object parameter contain a property called _contract with the same rationale in mind: set values that you wish to send to the ContractCreateTransaction constructor. For instance, if you would like to set a gas contract-creation limit to 100,000tℏ, your end upload call would be: session.upload(contract, {_contract: {gas: 100_000}}). By the way, the default gas set for contract-creation transaction can be tweaked by the HEDERAS_DEFAULT_CONTRACT_TRANSACTION_GAS environment variable and is currently set to 169_000.

You can, of course, pass in both _file and _contract options. Merging the above 2 examples, session.upload(contract, {_contract: {gas: 100_000}, _file: {fileMemo: "Hello Strato"}}) would end up uploading a Contract.byteCode to Hedera and have a memo attached to the resulting file called "Hello Strato". It would then set a gas limit of 100,000tℏ to create the contract. A working example of this, could look as follows:

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Constructor parameters

Passing in constructor parameters is easy, just add them when ApiSession.upload-ing like so: session.upload(contract, arg1, arg2, ... argn). If you're going to have meta-arguments (see above) as well as constructor-args passed in, add the meta-args object first and then add whatever constructor arguments are desired.

Example:

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This uploads a contract with a gas create-contract transaction set to 100,000tℏ and calling the contract's constructor passing in the string Strato is amazing!.

Interacting with deployed contracts

Calling methods

As you've probably seen so many times now, following a successful deployment, await-ing a ApiSession.upload call returns a LiveContract instance which has the solidity's contract functions dynamically attached to it and available for calling. This means that if a contract A has a method foo on it, the resulting LiveContract will also have a function foo defined on it.

So if, for example, we were to upload solidity-by-example's First App Contract via a session.upload call, that will eventually resolve to a LiveContract instance which would have a get, an inc and a dec defined on it as one might expect.

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Of course, function arguments are also supported so if we have such a live-contract function (solidity-by-example's State Variable code, for instance), you can call into these methods, passing in the expected values as expected.

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note

When dealing with big numbers, the library uses the same one used by the Hedera SDK: bignumber.js. This is intentional since one of the core design principles of Strato's API is to try to mimic as close as possible Hedera's own SDK return types.

I say as close as possible to allow for specially thought-of exceptions backed-up by common sense reasoning where the benefit in doing things in another way would be greater then following 1-to-1 with Hedera's SDK.

One such exception has to do with returning bytes from a method. While Hedera would just return a hex-encoded string of those bytes, as of v0.7.5, Strato returns a managed bytes collection (eg Uint8Array) of bytes.

Dealing with events

Contract events are propagated upwards from LiveContract through the EventEmitter-inspired methods. As such one can listen to an event by simply calling a .onEvent("event_name", () => { ... }) on the live-contract instance. Our test cases include solidity-by-example's Events code to make sure this works. Have a look for yourself, if interested, or check it out right now:

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Logs can also be emitted from within contract constructors provided that either the HEDERAS_DEFAULT_EMIT_CONSTRUCTOR_LOGS parameter is set to true or that emitConstructorLogs meta-arg is set to true in the _contract object when upload-ing the contract.

To get access to the constructor logs, you would need to destructure the live-contract upload result like so:

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As you can see from running the above snippet, the resulting logs are an array of objects which adhere to the following schema:

{
name: string,
payload: any
}

name is the name of the event while payload is a JS object with keys named after the arguments of the event and values being the actual data passed when emit-ing that particular event.

Transaction meta-arguments

Similar to when uploading a Smart Contract, calling any of its methods follows the same meta-arguments passing logic: if the first argument is a JS object which has certain properties of interest, those properties are unpacked and used inside the transaction. One such property is the maxQueryPayment which makes for a good example: lets say that we would like to set a maximum query payment of 0.001ℏ for calling the solidity-by-example's State Variable > get method. In this case, you would simply do a liveContract.get({maxQueryPayment: 100000}) and it would suffice.

Of course, similar to the "upload contract operation" detailed above, any argument following the the meta-arguments object would be passed to the method itself. In this regards, using the same State Variable contract, doing a liveContract.set({maxTransactionFee: 100000}, 42) would call the set method passing in integer 42 as parameter and setting the maxTransactionFee for the transaction to 100,000tℏ which is 0.001ℏ.

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Retrieving deployed contracts

Uploading a Contract is not the only way to get a hold on a deployed, LiveContract instance. ApiSession also exposes a getLiveContract method which takes in a ContractId as it's id object param and the contract's ABI as its abi parameter to lock onto a deployed version of that code on the network.

Want to find out more? Have a look at our test-case for an example on how one might go about doing just that or check it out yourself with a pre-uploaded testnet SimpleStorage contract just for the sake of example:

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note

The abi type required for the getLiveContract property can be a ethers Interface object or anything that can be parsed into one. For our above example we used a more human readable approach.

Deleting a live contract

To delete a deployed contract owned by the account associated with the current ApiSession, just do a LiveContract.deleteEntity({ transferAccountId?: AccountId, transferContractId?: ContractId }) where you can optionally pass in a transferAccountId or a transferContractId to transfer the hbar present on the deleted account to either an AccountId or a ContractId. If nothing is specified, the owner of the current ApiSession will get the remainder of the tokens.

Updating a live contract

Updating a deployed contract is not currently possible but will be supported in a future release.