circom-helper/README.md

A convenient way for developers to compile, cache, and execute circom circuits, as well as to generate proofs.

# `circom-helper`

`circom-helper` allows developers to test circom circuits quickly and easily.

It uses circom version 2, which has better performance than the previous
version. Note that circuits written for the previous version of circom must be
slightly modified to be compatible with circom 2.

To use the old version of circom, install `circom-helper` 0.1.0 or 0.2.0 via
NPM.

It compiles circuits and exposes a JSON-RPC API which allows developers to
generate witnesses and access signal values without writing command-line glue
scripts.

## Installation

`npm i circom-helper`

To build from source:

```
git clone git@github.com:weijiekoh/circom-helper.git && \
cd circom-helper && \
npm i && \
npm run build
```

### Install OS dependencies

On Debian, Ubuntu, or derivatives:

```
sudo apt-get install libgmp-dev nlohmann-json3-dev nasm g++
```

On openSUSE or derivatives:

```
sudo zypper install gmp-devel nlohmann_json-devel nasm g++
```

## User guide

1. Create a config file. Use `config.example.json` as a reference. 

    - The `circuitDirs` field should be an array of directories which contain
      the `circom` files you wish to compile. Note that there should not be any
      filename collisions, even across directories.
    - The `circom` field should be a path to the `circom` binary, relative to
      the config file's path.
    - The `snarkjs` field should be a path to the `build/cli.cjs` in a
      `snarkjs` `node_modules` package.

2. Create a `compiled/` and `temp/` directory for compiled circuits and
   tempoary files.

3. Run the server:

        npm run serve

4. Run the internal test suite for the server:

        npm run test-server

5. Run a test suite for the example circuit under `example/`:

        npm run test-snarks

### JSON-RPC API

**`gen_witness`**

Generates a witness given a circuit name and public inputs.

Inputs:

- `circuit`: the name of the circuit. For example, if `test.circom` is in one
  of the `circuitDirs`, and you want to generate a witness for inputs to this
  circuit, set this value as `test`.
- `inputs`: the public inputs to the circuit (as a JS object). For example: `{
  left: '1', right: '2' }`. The number values should be strings as the JS safe
  integer limit is lower than the group order for BN254 and other elliptic
  curves used for ZK proofs.

Returns:

- `witness`: an array of strings (e.g. `[1, 3, 1, 2]`).

To find the index of any signal (e.g. `main.out`), use `get_signal_index`. With
this index, you can then look up this array and get the value of the signal.

**`get_signal_index`**

Inputs:

- `circuit`: the name of the circuit.
- `name`: the signal name (e.g. `main.out`).

Returns:

- `index`: a numeric value as a string.