Roc WASM Platform

roc wasm platform can be used by roc to build wasm modules.

It creates a wasm module, where the wasm runtime and the roc code can use any types as arguments, that can be decoded by json.

The encoding format will probably change in the future.

How to use it

With the current wasm standard, it is not possible to send custom types between the wasm runtime and the wasm module. Only numbers can be transferred directly.

To send other data, the wasm runtime has to convert it to raw bytes, allocate enough memory in wasm and call the wasm function with the pointer to that memory as argument.

The roc wasm platform reads the memory from the given pointer, decodes it (as json) and calls the roc function with the decoded data.

For the return value, the same happens the other way around.

For this to work, the wasm runtime and the roc app have to use the same type.

The wasm-module exports this two functions:

(TODO: Get the wasm signature)

allocUint8(length: u32) [*]u8;
run_roc(pointer: [*]u8, length: usize) [*]const u8

Issues

There are currently some issues with roc you have to know about:

Build from source

You have to build the roc binary from source. See roc-lang/roc#5573

One way to do it is by running from the roc source code with:

cargo run -- build /PATH/TO/YOUR/main.roc --target=wasm32

Zig Version

You can use zig 0.9.1 or zig 0.10.1. Both versions have issues.

0.9.1

There is a caching bug in zig 0.9.1. To work around it, you have to remove the zig cache before running roc build. Every time! See: ziglang/zig#12864

find  ~/.cache/roc/ -name zig-cache -exec rm -r {} \;

0.10.1

To use zig 0.10.1, there are two small required changes to the roc sourcecode:

https://github.com/roc-lang/roc/compare/main...ostcar:zig_0.10

To use zig 0.10.1 is possible, but there will be warnings like

wasm-ld: warning: Linking two modules of different data layouts: '/home/max/src/roc/target/debug/build/wasi_libc_sys-661fd49d43379bb3/out/wasi-libc.a(llrintl.o at 2476264)' is 'e-m:e-p:32:32-i64:64-n32:64-S128-ni:1:10:20' whereas 'ld-temp.o' is 'e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20'

It seems, that they can be ignored.