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Defining the ABI

docs/developers/backend/abi.md

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Defining the ABI

The Application Binary Interface (ABI) of a Linera application defines how to interact with this application from other parts of the system. It includes the data structures, data types, and functions exposed by on-chain contracts and services.

ABIs are usually defined in src/lib.rs and compiled across all architectures (Wasm and native).

For a reference guide, check out the documentation of the crate.

Defining a marker struct

The library part of your application (generally in src/lib.rs) must define a public empty struct that implements the Abi trait.

rust
struct CounterAbi;

The Abi trait combines the ContractAbi and ServiceAbi traits to include the types that your application exports.

rust,ignore
{{#include ../../../linera-base/src/abi.rs:abi}}

Next, we're going to implement each of the two traits.

Contract ABI

The ContractAbi trait defines the data types that your application uses in a contract. Each type represents a specific part of the contract's behavior:

rust,ignore
{{#include ../../../linera-base/src/abi.rs:contract_abi}}

All these types must implement the Serialize, DeserializeOwned, Send, Sync, Debug traits, and have a 'static lifetime.

In our example, we would like to change our Operation to u64, like so:

rust,ignore
{{#include ../../../examples/counter/src/lib.rs:contract_abi}}

Service ABI

The ServiceAbi is in principle very similar to the ContractAbi, just for the service component of your application.

The ServiceAbi trait defines the types used by the service part of your application:

rust,ignore
{{#include ../../../linera-base/src/abi.rs:service_abi}}

For our Counter example, we'll be using GraphQL to query our application so our ServiceAbi should reflect that:

rust,ignore
use async_graphql::{Request, Response};

{{#include ../../../examples/counter/src/lib.rs:service_abi}}

References