"Aborted(`Module.asm` has been replaced by `wasmExports` ..." error in WASM bundle example

[liammcdermott]

Using rustc 1.74.0 (79e9716c9 2023-11-13), the latest release of pdfium-lib (6183), and an up-to-date clone of pdfium-render, this error is printed to the browser console (Firefox 120.0.1 and Chrome 120.0.6099.109):

Aborted(`Module.asm` has been replaced by `wasmExports` (the initial value can be provided on Module, but after startup the value is only looked for on a local variable of that name)) [pdfium.js:8:24592](http://localhost:4000/pdfium.js?v=chromium/6183)

Steps to reproduce

I followed the instructions at Bundling for WASM closely, but I'll recreate what I did here.

From within a clone of the pdfium-render repo:

$ mkdir release
$ cargo install wasm-pack && wasm-pack build examples/ --target no-modules
    Updating crates.io index
     Ignored package `wasm-pack v0.12.1` is already installed, use --force to override
[INFO]: 🎯  Checking for the Wasm target...
[INFO]: 🌀  Compiling to Wasm...
   Compiling pdfium-render v0.8.16 (/home/liam/code/pdfium-render)
   Compiling pdfium-render-wasm-example v1.0.0 (/home/liam/code/pdfium-render/examples)
    Finished release [optimized] target(s) in 7.32s
[INFO]: ⬇️  Installing wasm-bindgen...
[INFO]: Optimizing wasm binaries with `wasm-opt`...
[INFO]: Optional fields missing from Cargo.toml: 'description', 'repository', and 'license'. These are not necessary, but recommended
[INFO]: ✨   Done in 28.83s
[INFO]: 📦   Your wasm pkg is ready to publish at examples/pkg.
$ cp examples/pkg/{pdfium_render_wasm_example.js,pdfium_render_wasm_example_bg.wasm} release/
$ wget https://github.com/paulocoutinhox/pdfium-lib/releases/download/6183/wasm.tgz
[...]
$ mkdir pdfium-lib
$ mv wasm.tgz pdfium-lib/
$ cd pdfium-lib/
$ tar -xzf wasm.tgz 
$ cp release/node/{pdfium.js,pdfium.wasm} ../release/
$ cd ..
$ cp examples/index.html release/
$ cp test/form-test.pdf release/test.pdf
$ cp examples/serve.sh release/
$ cd release/
$ chmod +x serve.sh
$ ./serve.sh

Then visiting http://localhost:4000 yields this result:

[liammcdermott]

I'm assuming the issue is in pdfium-render, as running this:

cp ../pdfium-lib/release/node/index.html .

which swaps in pdfium-lib's example PDF viewer, works. I was able to upload a PDF into that sample app, and view it, as expected. That assumption may be wrong, of course!

[ajrcarey]

Hi @liammcdermott , thank you for reporting the issue and my apologies for the delay in replying - I've been away.

At first glance the problem is likely caused by a packaging change upstream in the WASM build of Pdfium. You may find that using an older version (from, say, a couple of months ago) may work perfectly. Upstream does from time to time change their packaging, e.g. #95.

I've set aside some time this week to look at this for you.

[ajrcarey]

Likely related to upstream emscripten change https://github.com/emscripten-core/emscripten/pull/19816

[ajrcarey]

Upstream emscripten change introduced into pdfium-lib as part of https://github.com/paulocoutinhox/pdfium-lib/pull/98

[ajrcarey]

Short-term work-around is to use https://github.com/paulocoutinhox/pdfium-lib/releases/tag/6008 instead of https://github.com/paulocoutinhox/pdfium-lib/releases/tag/6183

[ajrcarey]

Added fall-backs for Module['wasmExports'] for _malloc and _free in response to upstream packaging changes. Confirmed WASM example now runs correctly using pdfium-lib 6183.

You can test the changes by taking pdfium-render as a git dependency in your project's Cargo.toml.

[ajrcarey]

As there have been no further comments, and I believe the issue is resolved, I am closing the issue. Feel free to re-open if you believe the issue has not been resolved.

Confirmed no unexpected regression impact when using pdfium-lib pre-6183. Corrected a typo. Updated README. Scheduled for release in crate version 0.8.17.

[liammcdermott]

@ajrcarey Just wanted to drop a note to say thank you very much for fixing this so quickly!

I ended up finding a different way to solve my problem, and the way I would test is the same you already did, so I don't think I can add anything useful. Thanks again!