[PROJ] proj-wasm 0.1.0-alpha9

[Will Cohen]

Hello all,

An update on the grid fetching and worker questions from the January
proj.js thread. The latest release of proj-wasm (0.1.0-alpha9,
https://www.npmjs.com/package/proj-wasm) addresses them as follows:

Grid fetching now works in browsers and Node.js without curl in the build.
PROJ runs entirely inside workers, and grids come through PROJ's network
callback API backed by synchronous HTTP requests, which workers permit. In
Node.js, a small fetch worker bridges those synchronous callbacks to Node's
async http.

The WASM build is now fully single-threaded, with no pthreads. (Pthreads
ends up requiring SharedArrayBuffer and COOP/COEP headers, which limits the
usability of the WASM build to certain environments only.) Instead,
parallelism now comes from a pluggable pool of workers, each running its
own module instance, with PROJ contexts pinned to workers. The demo runs
this pool with network grids enabled: https://willcohen.github.io/clj-proj/

This is a slightly different path from Javier's
https://github.com/jjimenezshaw/wasm-proj, which is exercising the
ENABLE_EMSCRIPTEN_FETCH option from https://github.com/OSGeo/PROJ/pull/4627.
I still like the idea of trying to use that -- it definitely seems cleaner
and less like reinventing the wheel -- but I still want PROJ to be able to
nab grids without requiring that webpages be served with a particular set
of headers.

I've also since moved this worker plumbing into reusable libraries (
https://github.com/willcohen/clj-native and
https://github.com/willcohen/worker-router), and proj-wasm can adopt an
external pool the caller supplies. This is how backproj (live demo at
https://willcohen.github.io/backproj/), which uses proj-wasm to
back-project custom CRSes onto MapLibre, coordinates wasmts geometry
operations (JTS compiled to wasm) and proj-wasm projection operations in
one worker pool.

Now that these are settled and the mechanisms to build and hook into PROJ
on wasm are abstracted out, I plan to reuse them for a similar wasm build
of GDAL, hopefully without re-embedding PROJ inside it.

With PROJ, JTS (via wasmts), and eventually GDAL, I'm hoping that most GIS
functionality can happen client side in the browser!

Will
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