@schleifner/assemblyscript-transform

Introduction

This repo is AssemblyScript transforms to enhance AssemblyScript features

Utf8 string literal

This is a transform of AssemblyScript to store const utf8 string literal.

The string literal in AssemblyScript is utf16 encoded into Wasm data section, this brings two problems:

• String storage has too much overhead for ascii strings
• Need to convert utf16 to utf8 string when calling native API which receives utf8/ascii strings.

To solve this problem, this repo provides a transform of AssemblyScript to define utf8 string literals

Principle

This transform scans function call pattern

utf8.build("string literal");

and replace it to

utf8.build_internal(memory.data<u8>([bytes in utf8]), length of bytes);

For example:

utf8.build("test3");

is transferred to

utf8.build_internal(memory.data<u8>([116, 101, 115, 116, 51]), 5);

Attentions:

• The AST transform is based on string pattern matcher, so alias is not supported. Please don't use name alias of import and indirect function call to utf8.build, for example import {utf8 as utf_8} or let foo = utf8.build; foo("abc").

• The parameter of utf8.build must be string literal

Usage

Install assemblyscript-transform

npm install @schleifner/assemblyscript-transform

In AssemblyScript code, src/index.ts

import {utf8} from "../node_modules/@schleifner/assemblyscript-transform/as/utf8ConstStr"
const str = utf8.build("test3");

Build with transform

asc -o out.wasm --transform ./node_modules/@schleifner/assemblyscript-transform/dist/transformBuildUtf8ConstStr.mjs ./src/index.ts