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Generating Candid files for Rust canisters

Beginner
Rust
Tutorial

Overview​

In versions of the Rusk CDK v0.11.0 and higher, the Candid export workflow has been changed. You can call the ic_cdk::export_candid!() macro to enable the Candid export behavior, then use the candid-extractor to extract the Candid from the canister's Wasm.

Preparation​

  • Step 1: Upgrade ic-cdk dependency to v0.11.0 or higher:​

Cargo.toml
[dependencies]
ic-cdk = "0.11.0"
cargo install candid-extractor

With cargo-binstall you can install the prebuilt binary without waiting for compilation:

cargo binstall candid-extractor

Workflow​

  • Step 1. Call the export_candid macro at the end of your lib.rs file:​

lib.rs
#[query]
fn hello(name: String) -> String {
    format!("Hello, {}!", name)
}

#[update]
fn world(name: String) -> String {
    format!("World, {}!", name)
}

// Enable Candid export
ic_cdk::export_candid!();

  • Step 2: Compile the Canister Wasm module.​

cargo build --release --target wasm32-unknown-unknown --package <CANISTER>

The Wasm module will be at:

target/wasm32-unknown-unknown/release/<CANISTER>.wasm

  • Step 3: Extract candid from the Wasm module and save to a file:​

candid-extractor target/wasm32-unknown-unknown/release/<CANISTER>.wasm > <CANISTER>.did