compile API to WASM

[fr-an-k]

This compiles the library (libredwg.a) but a.wasm is 1kb.
How do I get a libredwg.wasm that contains the actual exports?

./autogen.sh
mkdir build
cd build
emconfigure ../configure --disable-bindings --disable-shared
make -j -s

Related to #876

[fr-an-k]

I think it should work like this, but it doesn't:
(dwg.h)

#include <emscripten/emscripten.h>

... (EXPORT is defined here)

// Redefine it to also export all function to emscripten
#define EXPORT EXPORT EMSCRIPTEN_KEEPALIVE
...

[fr-an-k]

starting with a clean clone and emscripten installation, I commented out m4_include([m4/ax_printf_size_t.m4]) in aclocal.m4 and ran sh ./autogen.sh but I still get this when running emconfigure ../configure --disable-bindings --disable-shared:

checking for printf() modifier to use with size_t... unknown
configure: error: cannot find a suitable modifier

[rurban]

As I said: #892 (comment)

[fr-an-k]

I finally managed running LibreDWG in the browser.
This issue should IMO only be closed when emscripten/WASM is added to the automatic builds, suitable for the browser and Node.js but I don't have time for that yet.

FYI anyone needing this:

The error above was probably caused by a wrong CC environment variable or installation or something.

mkdir .build-wasm
mkdir -p bindings/js
cd bindings/js
npm i -g yarn
yarn create vite
./autogen.sh
cd .build-wasm
emconfigure ../configure --disable-bindings --disable-shared
emmake make
emcc -gsource-map --bind -s LINKABLE=1 -s EXPORTED_FUNCTIONS='["_dwg_convert_read","_dwg_convert_write","_dwg_convert_free","_malloc","_free"]' -s EXPORTED_RUNTIME_METHODS='["cwrap", "ccall","stringToUTF8","UTF8ToString"]' -o ../bindings/js/src/libredwg.js -O2 -sMODULARIZE=1 -s EXPORT_ES6=1 -s ENVIRONMENT=web -Isrc -I../include src/*.o programs/dwgconvert.o -s ALLOW_MEMORY_GROWTH=1 -s INITIAL_MEMORY=3GB --no-entry

I wrote a separate JSON conversion program using dwg_decode/dwg_decode directly (as well as dwg_fixup_BLOCKS_entities for DWG downgrades), since dependency on filenames as per the original API is unnecessary and undesirable in my opinion, although emscripten does provide a limited virtual fs. It's possible to call those functions directly from JS, without create a separate library/program.

I used Node.js and emscripten from the emsdk repository and installed a bunch of other stuff, but I'm not sure what's necessary.

The source map doesn't work but I can see file names and line numbers when WASM crashes.

I probably won't have time for a long time to create an automatic WASM build, javascript bindings or NPM library.

I need to figure out how to set SIDE_MODULE=2/MAIN_MODULE=2 to avoid all functions being exposed, but the LibreDWG API is in there and could be used (I prefer working with JSON however).

Currently there is a bug in Chrome 133 for debug symbols, so you need to use 134 beta or another browser. You probably also need the DWARF browser extension.

It seems there is a bug in emscripten occurring within calloc within hash_new (hash.c); it's unclear what could be causing this but the source code (dlmalloc function) is available here: https://github.com/emscripten-core/emscripten/blob/main/system/lib/dlmalloc.c.
Setting initial memory to 3GB circumvents the issue in my case, but it depends on what you do.

-O2 or -O3 also seems necessary to avoid an error of too many local variables; there might be a big buffer in the stack somewhere.