Post Asynchronous Requests

Asynchronous requests enable interactions between different contracts. Learn how to navigate the subtleties of posting asynchronous requests on the Tangle, and how to effectively manage tokens and delays in execution.

Overview of Asynchronous Function Calls

Posting Requests on the Tangle

Asynchronous function calls occur through requests posted on the Tangle. These calls can invoke any function that is not a View on any smart contract chain.

Function Descriptor Methods

To post a request, use the following methods from the function descriptor:

• post(): Posts to the current chain.
• postToChain(): Allows specifying the chain through the chain ID parameter.

Delayed Execution

You can set a delay in the execution using the delay() method, enhancing smart contracts with timed actions or time-lock functionalities.

Go

eor := ScFuncs.EndOfRound(ctx)
eor.Func.Delay(3600).Post()

Rust

let eor = ScFuncs::end_of_round(ctx);
eor.func.delay(3600).post();

Typescript

let eor = sc.ScFuncs.endOfRound(ctx);
eor.func.delay(3600).post();

Managing Tokens in Asynchronous Calls

Mandatory Token Transfer

Asynchronous requests require a minimum token transfer to cover the gas for function call execution. Unused tokens return to the caller's account on the chain.

Specifying Tokens

You can specify tokens:

• Explicitly, as in to synchronous calls.
• Automatically, letting WasmLib determine the minimum requisite amount.

Prohibited delay() with call()

Using delay() before a call() will cause a panic due to indeterminate user intentions at compile-time without substantial overhead.

Handling Return Values

If you need some return values, you will have to create a mechanism that can do so. For example, you can provide a callback chain/contract/function combination as part of the input parameters of the requested function so that upon completion, that function can asynchronously post the results to the indicated function. It will require a certain degree of cooperation between both smart contracts.

Future Prospects

Future developments aim to facilitate a generic mechanism for seamless return value communication in asynchronous function calls.