WASM Support

Jolt supports WebAssembly compatibility for the verification side of provable functions. This allows developers to run proof verification in WASM environments such as web browsers. Note that currently, only the verification process is supported in WASM; the proving process is not WASM-compatible at this time.

Creating a WASM-Compatible Project

To create a new project with WASM verification support, use the following command:

jolt new <PROJECT_NAME> --wasm

This creates a new project with the necessary structure and configuration for WASM-compatible verification.

Marking Functions for WASM Verification

For functions whose verification process should be WASM-compatible, extend the #[jolt::provable] macro with the wasm attribute:


#![allow(unused)]
fn main() {
#[jolt::provable(wasm)]
fn my_wasm_verifiable_function() {
    // function implementation
}
}

Building for WASM Verification

To compile your project for WASM verification, use the following command:

jolt build-wasm

This command performs several actions:

It extracts all functions marked with #[jolt::provable(wasm) from your guest/src/lib.rs file.
For each WASM-verifiable function, it preprocesses the function and saves the necessary verification data.
It creates an index.html file as an example of how to use your WASM-compiled verification functions in a web environment.
It uses wasm-pack to build your project, targeting web environments.

Important: The build process only compiles the verification functions for WASM. The proving process must still be performed outside of the WASM environment.

Adding Dependencies

When adding new dependencies for WASM-compatible projects, note that they must be added to both guest/Cargo.toml and the root Cargo.toml. The build-wasm process will automatically add necessary WASM-related dependencies to your project.

Switching Between WASM and Normal Compilation

The build process modifies the Cargo.toml files to enable WASM compilation. If you need to switch back to normal compilation, you may need to manually adjust these files. In the root Cargo.toml, you can remove the following lines:

[lib]
crate-type = ["cdylib"]
path = "guest/src/lib.rs"

Remember to restore these lines before attempting another WASM build.

Example Project Structure

After running jolt build-wasm, your project will include:

An index.html file in the root directory, providing a basic interface to verify proofs for each of your WASM-verifiable functions.
A pkg directory containing the WASM-compiled version of your project's verification functions.
Preprocessed data files for each WASM-verifiable function in the target/wasm32-unknown-unknown/release/ directory.

You can use this example as a starting point and customize it to fit your specific requirements.

Example: Modifying the Quickstart Project

You can use the example from the Quickstart chapter and modify the /src/main.rs file as follows:

use jolt::Serializable;
pub fn main() {
    let (prove_fib, _verify_fib) = guest::build_fib();

    let (_output, proof) = prove_fib(50);

    proof
        .save_to_file("proof.bin")
        .expect("Failed to save proof to file");
}

Remember to modify the Cargo.toml as described before for normal compilation, and then you can generate and save the proof with the following command:

cargo run -r

This will create a proof.bin file in the root directory. You can then verify this proof using the example index.html. Before doing this, change the crate type back to cdylib in the Cargo.toml and ensure that your /guest/src/lib.rs looks like this:


#![allow(unused)]
#![cfg_attr(feature = "guest", no_std)]
#![no_main]

fn main() {
#[jolt::provable(wasm)]
fn fib(n: u32) -> u128 {
    let mut a: u128 = 0;
    let mut b: u128 = 1;
    let mut sum: u128;
    for _ in 1..n {
        sum = a + b;
        a = b;
        b = sum;
    }

    b
}
}

Then run jolt build-wasm. After successful compilation, you can verify the proof using the index.html file. Start a local server from the project directory, for example with:

npx http-server .

Note: Make sure you have npx installed to use the http-server command.

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