Crate wasm_encoder

source ·
Expand description

A WebAssembly encoder.

The main builder is the Module. You can build a section with a section-specific builder, like TypeSection or ImportSection, and then add it to the module with Module::section. When you are finished building the module, call either Module::as_slice or Module::finish to get the encoded bytes. The former gives a shared reference to the underlying bytes as a slice, while the latter gives you ownership of them as a vector.

Example

If we wanted to build this module:

(module
  (type (func (param i32 i32) (result i32)))
  (func (type 0)
    local.get 0
    local.get 1
    i32.add)
  (export "f" (func 0)))

then we would do this:

use wasm_encoder::{
    CodeSection, ExportKind, ExportSection, Function, FunctionSection, Instruction,
    Module, TypeSection, ValType,
};

let mut module = Module::new();

// Encode the type section.
let mut types = TypeSection::new();
let params = vec![ValType::I32, ValType::I32];
let results = vec![ValType::I32];
types.function(params, results);
module.section(&types);

// Encode the function section.
let mut functions = FunctionSection::new();
let type_index = 0;
functions.function(type_index);
module.section(&functions);

// Encode the export section.
let mut exports = ExportSection::new();
exports.export("f", ExportKind::Func, 0);
module.section(&exports);

// Encode the code section.
let mut codes = CodeSection::new();
let locals = vec![];
let mut f = Function::new(locals);
f.instruction(&Instruction::LocalGet(0));
f.instruction(&Instruction::LocalGet(1));
f.instruction(&Instruction::I32Add);
f.instruction(&Instruction::End);
codes.function(&f);
module.section(&codes);

// Extract the encoded Wasm bytes for this module.
let wasm_bytes = module.finish();

// We generated a valid Wasm module!
assert!(wasmparser::validate(&wasm_bytes).is_ok());

Structs

Enums

Traits

  • AsComponentExternName
    Helper trait to convert into a ComponentExternName either from that type or from a string.
  • ComponentSection
    A WebAssembly component section.
  • Encode
    Implemented by types that can be encoded into a byte sink.
  • Section
    A WebAssembly module section.

Type Definitions

  • Lane
    Describe an unchecked SIMD lane index.