Outline for my blog post about getting started with wasm

outline.md

• Why?
  • Use existing code and libraries, especially for encryption or hashing
  • Sharing code for algorithms or compute intensive operations
  • Don’t intend expose much (anything?) to the wasm instance
  • There some gotchas like 64bit integers
• Browser only, no toolchain
  • I have toolchain fatigue and it turns out the latest browsers are kinda great
  • import and export, async and await, wasm, etc all work
  • I like to use a tiny file server to serve a directory on a port on localhost
    • serve
• clang is all you need
  • Don’t use anything else. Seriously don’t.
  • Basic C example
  • wasm2wat
  • Exports and imports
  • Optmizations
  • Module and Instance
  • Memory
  • Always async. Two way to expose the API:
    • load then get exports
    • export only async functions which await on a Promise or the instance as their first item of business
• WASI for stdlib
  • We need malloc and free if we are going to do anything interesting
  • Setup a sysroot
  • Example using malloc to send a string from js into C, manipulate it, and read it back out in js
  • Imports show up as needed
  • The start function
• Heap
  • I’ve made a utility class to wrap all my memory related stuffs so I can free all memory left at the end or in the event of an error
  • This isn’t a library yet because I’m not done figuring out exactly what I need and like
• Something useful: argon2
  • There was a hashing competitor and argon2 won
  • This can be useful to derive a key from a password to use for encryption or to implement something like SRPX
  • Which files do we need?
  • How do we disable threads?
  • clang
  • Imports required by WASI
• Other ideas: libsodium
  • Can work the same way with just clang
  • Give it a try or try using a c library or project that you can about in the browser
• i64 and i32
  • Link to data types in wasm
  • Cannot call a function which expects a 64bit int
  • Numbers are not safe in JS
  • BigInt isn’t in every browser and cannot be polyfilled transparently
    • JSBI (I don’t like this, but it’s what we got)
  • Converting to and from little endien 8 bytes
  • Can write a proxy function which takes a void pointer and just cast and realize and forward
  • This is very useful if you are using an existing library which uses a lot of unsigned long longs cough libsodium cough