feat(nix): package the PipeWire capture helper - #448
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The third native component, and the last one #419 listed as deliberately left out. Without it pipeWireCursorRecordingSession reports "Linux cursor helper is not available" and the app degrades to no cursor data on Wayland -- the same quiet reduction the compositor addon produced before it was packaged, and the one the smoke test exists to catch. The crate is far easier to package than its sibling, and for a reason worth stating: it is a separate process spawned over stdio, not a napi addon dlopen'd into Electron, so Chromium's libffmpeg.so is not in its address space and the osff_ symbol prefixing that dominates compositor-view.nix has no counterpart here. ffmpeg links normally. PipeWire itself is not a build input at all -- the C shim resolves every entry point with dlsym against vendored headers, which is what lets the crate build on a machine with no libpipewire-0.3-dev. That last part has a corollary the Vulkan loader already taught us: an soname reached only by dlopen is invisible to the linker, so nothing puts libpipewire on the binary's RPATH and dlopen fails on any host without an ld.so.cache. Added by hand, with --force-rpath because build.rs passes --disable-new-dtags on purpose and patchelf would otherwise convert DT_RPATH to DT_RUNPATH and undo it. Three consumers now share one subtle ffmpeg override, so it moves to nix/ffmpeg-lgpl.nix rather than being copied a third time. package.nix keeps the headless variant for the CLI binary, which is a deliberate difference and is written down as such. flake.nix binds each component once instead of applying callPackage twice -- harmless today, since identical arguments give an identical store path, but it meant an override applied to the exposed attribute never reached the app, and with a second component the mistake would have been made twice. CI gains an assertion, because nothing exercises this helper: it needs a Wayland portal the runner does not have. What can be checked is that the wrapper's three --set paths exist and that the helper's libraries resolve, read out of the built wrapper rather than re-derived, so it tests the artefact and not the recipe. A wrapper pointing somewhere wrong is exactly how these components fail. Co-Authored-By: Claude <noreply@anthropic.com>
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📝 WalkthroughWalkthroughThe Nix packaging now provides an LGPL FFmpeg variant and a standalone PipeWire helper. OpenScreen receives both native components, and CI validates their paths and shared-library resolution. ChangesNative Linux components
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟡 Moderate · up to The PR adds the Wayland cursor helper and its PipeWire runtime path, but the current CI check can miss failures loading PipeWire dynamically. The validation should be strengthened before merge so the packaged helper cannot appear healthy while failing at runtime. Sequence Diagram(s)sequenceDiagram
participant flake.nix
participant nix/package.nix
participant pipewire-helper
participant nix-build workflow
flake.nix->>nix/package.nix: Pass compositor-view and pipewire-helper
nix/package.nix->>pipewire-helper: Expose OPENSCREEN_LINUX_CURSOR_HELPER_EXE
nix/package.nix-->>nix-build workflow: Produce wrapper artifact
nix-build workflow->>nix-build workflow: Validate native paths and run ldd
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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In @.github/workflows/nix-build.yml:
- Around line 162-189: The helper validation around
OPENSCREEN_LINUX_CURSOR_HELPER_EXE must enforce the runtime contract directly:
require HELPER to be executable with -x, inspect its DT_RPATH or DT_RUNPATH
using readelf -d, and verify at least one listed directory contains
libpipewire-0.3.so.0. Retain the existing unresolved-library check, but do not
rely on ldd alone to validate the manually added PipeWire RPATH.
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.github/workflows/nix-build.ymlflake.nixnix/compositor-view.nixnix/ffmpeg-lgpl.nixnix/package.nixnix/pipewire-helper.nix
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The review caught that the assertion validated everything except the thing this PR adds. ldd resolves DT_NEEDED entries; libpipewire is reached by dlopen and is therefore never a DT_NEEDED and never appears in that output. The check would have gone green with the hand-added RPATH missing entirely -- which is the whole of the packaging work, and the one failure mode it was written to catch. Read the RPATH out of the binary instead and require that one of its directories actually holds libpipewire-0.3.so.0, expanding $ORIGIN against the binary's own location since the ffmpeg entries use it. Whichever of DT_RPATH or DT_RUNPATH is present is read rather than asserted, so a silent conversion by patchelf reports itself instead of looking like an absent RPATH. ldd stays, demoted to what it is good for: unresolved DT_NEEDED entries are a different fault and this is where they would show. Also -x rather than -e for the two paths that get spawned. The app already sets that bar -- helperCandidates requires X_OK before accepting a candidate -- so a present-but-not-executable file passed here and was rejected at runtime. The compositor addon is require()'d, not spawned, so -r is its bar. Co-Authored-By: Claude <noreply@anthropic.com>
The last native component. Without it resolveWhisperServer finds nothing, `openscreen captions` fails and the AI edition's transcription pump never starts. The model is deliberately not packaged. modelManager.ts downloads a GGML file from HuggingFace into userData on first use, checksums it and replaces a stale copy; that is a runtime cache the user owns, and baking a multi-gigabyte blob into the store would be wrong even if the sandbox allowed the download. The awkward part is that the CMakeLists pulls whisper.cpp, cpp-httplib and nlohmann/json with FetchContent at configure time, over a network the build does not have. Patching the CMakeLists was the wrong answer: those pins are deliberate and documented there -- one of them exists because a build once picked up OpenSSL from the host and shipped a binary that died in the Windows loader -- and a nix-only fork of them would drift from what every other platform builds. CMake already provides the override for this, so the three trees are fetched here and handed over through FETCHCONTENT_SOURCE_DIR_<name>, with FETCHCONTENT_FULLY_DISCONNECTED so a missed one fails loudly rather than reaching for the network. fetchurl on pinned tags rather than fetchFromGitHub, which is a trade and not a preference. fetchFromGitHub hashes the unpacked tree and is immune to GitHub re-compressing an archive, but its hash cannot be computed or checked without nix, and there is no nix on the machine this was written on. A tarball hash can be verified by anyone with curl and sha256sum. If a tag is ever re-compressed the build fails closed and the fix is one line. Vulkan is on, matching what scripts/build-whisper-stt.sh selects for Linux. The alternative is a CPU-only binary, which works and is the same class of silent reduction this packaging exists to remove. Nothing is dlopen'd by soname here -- ggml links libvulkan normally -- so unlike the other two derivations no RPATH surgery is needed. OSC_NATIVE_CPU stays off per the CMakeLists' own warning: it compiles for whichever machine ran the build, and a nix package is precisely a thing built once and run elsewhere. Co-Authored-By: Claude <noreply@anthropic.com>
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What this does
Packages
electron/native/pipewire-capture— Wayland screen capture through xdg-desktop-portal, plus the cursor sampling the compositor cannot provide. It is the third native component and the last one #419 listed as deliberately left out.Without it,
pipeWireCursorRecordingSessionreports "Linux cursor helper is not available" and the app degrades to no cursor data on Wayland — the same quiet reduction the compositor addon produced before it was packaged.Why it is much smaller than its sibling
Worth stating, because the difference is load-bearing: the helper is a separate process spawned over stdio, not a napi addon dlopen'd into Electron. Chromium's
libffmpeg.sois not in its address space, so the flat-namespace collision that forces theosff_symbol prefixing incompositor-view.nixcannot happen. ffmpeg links normally, and the derivation is a fraction of the size.PipeWire is not a build input at all —
csrc/pw_shim.cresolves every entry point withdlsymagainst vendored headers, which is what lets the crate build withoutlibpipewire-0.3-dev.That has a corollary the Vulkan loader already taught us in #419: an soname reached only by
dlopenis invisible to the linker. Nothing puts libpipewire on the binary's RPATH, sodlopen("libpipewire-0.3.so.0")fails on any host without anld.so.cache— every NixOS host. Added by hand, with--force-rpathbecausebuild.rspasses--disable-new-dtagsdeliberately (it wants DT_RPATH so entries apply to the transitive ffmpeg libs) and patchelf would otherwise write DT_RUNPATH and undo that choice.Two things tidied while here
nix/ffmpeg-lgpl.nix. Three consumers now want the same subtlewithOpenh264 = true; withGPL = false;pair, so it moves to one file instead of being copied a third time.package.nixkeeps the headless variant for the CLI binary — a deliberate difference, now written down as such rather than looking like drift.flake.nixbinds each component once. It appliedcallPackage ./nix/compositor-view.nixtwice: once for the exposed attribute, once inline aspackage.nix's argument. Harmless in store terms — identical arguments give an identical path — but it meant an override applied topackages.compositor-viewnever reached the app. With a second component the mistake would have been made twice.What CI can and cannot check
Nothing exercises this helper: it needs a Wayland portal the runner does not have, so there is no equivalent of the record/export assertion that vouches for the compositor addon.
What can be checked is the failure mode that actually bites — a
--setpointing somewhere wrong. A new step reads the three paths out of the built wrapper rather than re-deriving them, asserts each exists, and runslddon the helper to confirm the hand-added RPATH resolves:That tests the artefact, not the recipe.
Verified
electron/native/pipewire-capture/Cargo.lock, socargoLock.lockFileneeds nooutputHashes.build.rsasserts on are git-tracked, so they survive thegitTrackedsource filter.flake.nixpasses;flake.nixis the only caller of any of these files.meta.mainProgramis set, whichlib.getExeinpackage.nixrequires.runblocks passbash -n. The new step's wrapper-parsing was tested against a syntheticmakeWrapperscript, including the variable-absent case.Not verified: none of this has been built. No nix on the machine it was written on, and
nix-build.ymldoes not run on pull requests, so the first real signal is the post-merge run. The things I would watch, in order: whetherfs.gitTracked/fs.toSourcescoped to a subdirectory behaves as written, whetherrustPlatform.bindgenHooksatisfiesbuild.rs's bindgen pass over the ffmpeg headers, and whetherpatchelf --force-rpath --add-rpathcomposes with the linker's existing DT_RPATH rather than replacing it.🤖 Generated with Claude Code
Summary by CodeRabbit
New Features
Bug Fixes