webassembly-rs

A Rust library providing complete WebAssembly opcode constants, parsing, and encoding.

100% Spec Test Coverage: This library successfully parses all 4,441+ valid WebAssembly test cases from the official WebAssembly spec test suite.

Features

• ✅ Complete opcode coverage - All 300+ WebAssembly opcodes (Core Spec 3.0)
• ✅ Full parser and encoder - Parse .wasm files and encode back to bytes
• ✅ 100% spec test validation - Verified against 5,444 official spec tests
• ✅ Round-trip verified - parse → encode → parse produces valid wasm
• ✅ #![no_std] compatible - Works in embedded environments
• ✅ Zero dependencies - Only requires alloc

Usage

Add to your Cargo.toml:

[dependencies]
webassembly = "0.9"

Quick Start

use webassembly::{parse, encode};

// Parse a WebAssembly binary
let wasm_bytes = std::fs::read("example.wasm").expect("Failed to read wasm");
let program = parse(&wasm_bytes).expect("Failed to parse wasm");

// Access parsed sections
for section in &program.sections {
    println!("Found section: {:?}", section);
}

// Encode back to WebAssembly binary
let encoded = encode(&program);
std::fs::write("output.wasm", encoded).expect("Failed to write wasm");

Testing

The library is validated against the complete official WebAssembly spec test suite (5,444 tests):

# Run unit tests (LEB128, section parsing, round-trips)
cargo test

# Run spec test suite (5,444 WebAssembly binaries)
cargo test -- --ignored

# Or use make
make test-all

Test Results

Spec Test Coverage

This library achieves 100% coverage of valid WebAssembly from the official spec:

• All 4,441 valid WebAssembly test binaries parse successfully
• All 608 assert_malformed tests are correctly rejected
• Full round-trip validation (parse → encode → re-parse)

API Overview

Core Types

• Program - A parsed WebAssembly module containing sections
• Section - WebAssembly sections (Type, Import, Function, Memory, Export, Code, Data, etc.)
• Instruction - All WebAssembly opcodes with their operands
• ValType - Value types (I32, I64, F32, F64, etc.)

Opcode Constants

Complete opcode constants matching the WebAssembly spec:

use webassembly::op::*;

// Control flow
assert_eq!(UNREACHABLE, 0x00);
assert_eq!(NOP, 0x01);
assert_eq!(CALL, 0x10);

// Memory
assert_eq!(I32_LOAD, 0x28);
assert_eq!(I32_STORE, 0x36);

// SIMD (300+ SIMD opcodes included)
assert_eq!(I8X16_ADD, 0xFD);  // Prefixed opcodes

LEB128 Encoding

Utilities for WebAssembly's variable-length integer encoding:

use webassembly::leb;

let encoded = leb::encode_u32(1234);
let (value, bytes_read) = leb::decode_u32(&encoded).unwrap();

Features

#![no_std] Support

This library works without the standard library:

#![no_std]
extern crate alloc;
use webassembly::{parse, encode};

Spec Test Validation

The library includes comprehensive integration tests that parse the official WebAssembly spec test suite. To run:

# Requires spec tests submodule
git submodule update --init tests/spec-tests
cargo test -- --ignored

Related Projects

• watson - A more featureful WebAssembly library for Rust
• WebAssembly Spec - Official WebAssembly specification

License

This project is licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in webassembly by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.