WebAssembly.instantiate(): Wasm code generation disallowed by embedder

Hey folks,

I'm trying to get a Wasm library to work in a Pages function, but I'm having the hardest time instantiating it.

At first I was fetching the .wasm binary to instantiate, but someone in #pages-help told me it had to be bundled within the _worker.js script. Okay, now it's a UInt8Array directly in the _worker.js script but I still get this error.

Is there more information on how the wasm binary should be bundled? Is it a specific format that will make the CF worker accept it?

zegevlier•2/1/24, 7:24 PM

It should be imported, like in this example: https://developers.cloudflare.com/workers/runtime-apis/webassembly/javascript/#use-from-javascript

zegevlier•2/1/24, 7:25 PM

Anything else will not work. You cannot create a WebAssembly object from anything that could chance at runtime

xeon06OP•2/1/24, 7:27 PM

How does that get bundled in the end? I am using Astro here so maybe that's my problem, Vite can't bundle my wasm as expected

xeon06OP•2/1/24, 7:27 PM

Is there any more info on the format that this is to be expected to be in for the upload? I could always create a vite plugin

xeon06OP•2/1/24, 7:27 PM

I imagine wrangler is doing the bundling directly in that instance?

xeon06OP•2/1/24, 7:28 PM

Ah yes scrolling up reveals that

Xxeon06 Is there any more info on the format that this is to be expected to be in for th...

zegevlier•2/1/24, 7:34 PM

I believe they would be uploaded seperately (so the .wasm binary file would be uploaded, along with the code), although I'm having a hard time finding documentation for it. I'm sure the requests are made somewhere in the wrangler source (https://github.com/cloudflare/workers-sdk), but I wouldn't be able to tell you where.

xeon06OP•2/1/24, 7:35 PM

All good I appreciate it. Push comes to shove I can always try bundling a minimal example with wrangler and see what comes out. Thanks!

xeon06OP•2/1/24, 8:34 PM

It turns out the Astro adapter has already done the work of the vite plugin for this and it works great if you configure it properly

I am curious about the impact of this external wasm file on bundle size though. The wrangler deploy --dry run option doesn't seem to take it into consideration, although it does show it in an "additional modules" table?

xeon06OP•2/1/24, 8:34 PM

xeon06OP•2/1/24, 8:36 PM

Ah I tried taking it out of the bundle and it does count the file in the table in that total

zegevlier•2/2/24, 9:13 AM

Yea, it's definitely something to consider when using wasm. If the entire worker goes over 1mb you'll have longer cold start times

xeon06OP•2/2/24, 3:48 PM

Ah, I had read that the bigger the size the slower the cold start but is there like a different code path taken > 1 mb?

zegevlier•2/3/24, 10:18 AM

Yea. Above 1mb they are not stored at every datacenter around the world, lower they are (on paid plan at least)

WebAssembly.instantiate(): Wasm code generation disallowed by embedder

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