Encode and Decode

To interact with the FuelVM, types must be encoded and decoded per the argument encoding specification. The SDK provides the Interface class to encode and decode data.

The relevant methods of Interface are:

• encodeType
• decodeType

The Interface class requires you to pass the ABI on initialization. Both methods accept a concreteTypeId, which must exist in the ABI's concreteTypes array. After that, a suitable coder will be assigned to encode/decode that type.

Imagine we are working with the following script that returns the sum of two u32 integers:

<<< @/../../docs/sway/script-sum/src/main.sw#encode-and-decode-1{rust:line-numbers}

When you build this script, using:

forc build

It will produce the following ABI:

<<< @./snippets/encode-and-decode.jsonc#encode-and-decode-2{json:line-numbers}

Now, let's prepare some data to pass to the main function to retrieve the combined integer. The function expects and returns a u32 integer. So here, we will encode the u32 to pass it to the function and receive the same u32 back, as bytes, that we'll use for decoding. We can do both of these with the Interface.

First, let's prepare the transaction:

<<< @./snippets/encode-and-decode.ts#encode-and-decode-3{ts:line-numbers}

Now, we can encode the script data to use in the transaction:

<<< @./snippets/encode-and-decode.ts#encode-and-decode-4{ts:line-numbers}

Finally, we can decode the result:

<<< @./snippets/encode-and-decode.ts#encode-and-decode-5{ts:line-numbers}

A similar approach can be taken with Predicates; however, you must set the encoded values to the predicateData property.

Contracts require more care. Although you can utilize the scriptData property, the arguments must be encoded as part of the contract call script. Therefore, it is recommended to use a FunctionInvocationScope when working with contracts which will be instantiated for you when submitting a contract function, and therefore handles all the encoding.

Full Example

Here is the full example of the encoding and decoding methods:

<<< @./snippets/encode-and-decode.ts#full{ts:line-numbers}