libtorrent-wasm

arvidn/libtorrent compiled to a single-threaded WebAssembly module that runs in a Web Worker. Networking is plumbed through the FKN WebVPN via the @webvpn/net and @webvpn/dgram polyfills, so a browser-hosted session can talk real TCP and uTP to internet peers.

Layout

libtorrent/    # git submodule, pinned at the merge base from upstream RC_2_0
patches/       # *.patch files applied to libtorrent/ at build time
src/           # the WASM port itself
  wrapper.cpp        - C++ entry points exposed to JS
  disk_io.{cpp,hpp}  - libtorrent disk_interface impl backed by a JS callback
  library_fkn.js     - emscripten js-library: socket syscalls + disk bridge
  index.ts           - public JS API (Session)
  opfs.ts            - StorageBackend impl backed by the OPFS
  types.ts           - shared TS types
src/app/       # browser harness with diagnostic pages
dist/          # emcc output (gitignored)
build/         # vite output + copied wasm artefacts (gitignored)

Building

The full build runs inside Docker so the host needs nothing but Docker + Node:

./build.sh     # one-shot: builds the image, copies dist/* out

For iterative C++ development:

npm install
npm run dev    # rebuilds dist/ + vite on change

After dist/libtorrent.{js,wasm} exists, the app harness can run:

cp dist/libtorrent.{js,wasm} src/app/
cd src/app
npm install
npm run dev    # vite dev server on :4560

Patches

patches/*.patch carry the WASM-specific edits on top of pinned upstream libtorrent: uTP LEDBAT bypass, WASI errno values, FIONREAD tolerance, etc. They're applied via git apply at build time (make apply-patches). To rebase against a newer upstream, bump the submodule and rerun make apply-patches; rejected hunks must be reconciled manually.