Practicing WASM

This repository is for practice only!

Custom Node-RED node using WASM and LDK.

Structure

├── decode-invoice          // Node-RED custom node project
│   ├── invoiceAmount.html
│   ├── invoiceAmount.js
│   ├── package.json
│   └── package-lock.json
├── src                     // Rust source code
│   └── lib.rs
├── target                  // Compiled WASM first goes here
├── Cargo.toml              // Rust project config file
├── ldkwasm_test.js         // Javascript bindings for WASM
├── ldkwasm_test_bg.wasm    // WASM file that goes with bindings
└── README.md

Steps to reproduce

Add the wasm target to rustup:

$ rustup target add wasm32-unknown-unknown

Specify release target as WASM:

$ cargo build --release --target wasm32-unknown-unknown

Which creates a WASM binary at target/wasm32-unknown-unknown/release/ldkwasm_test.wasm.

Get wasm-bindgen-cli if you haven't already:

$ cargo install wasm-bindgen-cli

Next we must generate the JS bindings for this WASM, as follows:

$ wasm-bindgen target/wasm32-unknown-unknown/release/ldkwasm_test.wasm --target nodejs --out-dir . --no-typescript

The resulting files in project root ldkwasm_test_bg.wasm and ldkwasm_test.js are respectively the final WASM and bindings.

Using in Node-RED

The decode-invoice directory contains a basic custom Node-RED node.

It should be simple enough to read without documentation.

Load the wasm to use:

// Loads the bindings and wasm as a module
const hellowasm = require('./hellowasm);
const result = hellowasm.add(100, 23);
console.log(result);

Using in Node-RED custom node

From Node-RED home directory (usually ~/.node-red):

npm install [path-to-this-repo/decode-invoice]

Restart Node-RED and you will likely find this custom node!

It takes any BOLT11 invoice, and returns the amount in millisatoshis. (As a BigInt!)

Pitfalls