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diff --git a/src/_posts/2021-02-13-building-gomobile-using-nix.md b/src/_posts/2021-02-13-building-gomobile-using-nix.md deleted file mode 100644 index 3326266..0000000 --- a/src/_posts/2021-02-13-building-gomobile-using-nix.md +++ /dev/null @@ -1,232 +0,0 @@ ---- -title: >- - Building gomobile Using Nix -description: >- - Harder than I thought it would be! -series: nebula -tags: tech ---- - -When I last left off with the nebula project I wanted to [nix][nix]-ify the -build process for Cryptic's [mobile_nebula][mobile_nebula] fork. While I've made -progress on the overall build, one particular bit of it really held me up, so -I'm writing about that part here. I'll finish the full build at a later time. - -## gomobile - -[gomobile][gomobile] is a toolkit for the go programming language to allow for -running go code on Android and iOS devices. `mobile_nebula` uses `gomobile` to -build a simple wrapper around the nebula client that the mobile app can then -hook into. - -This means that in order to nix-ify the entire `mobile_nebula` project I first -need to nix-ify `gomobile`, and since there isn't (at time of writing) an -existing package for `gomobile` in the nixpkgs repo, I had to roll my own. - -I started with a simple `buildGoModule` nix expression: - -``` -pkgs.buildGoModule { - pname = "gomobile"; - version = "unstable-2020-12-17"; - src = pkgs.fetchFromGitHub { - owner = "golang"; - repo = "mobile"; - rev = "e6ae53a27f4fd7cfa2943f2ae47b96cba8eb01c9"; - sha256 = "03dzis3xkj0abcm4k95w2zd4l9ygn0rhkj56bzxbcpwa7idqhd62"; - }; - vendorSha256 = "1n1338vqkc1n8cy94501n7jn3qbr28q9d9zxnq2b4rxsqjfc9l94"; -} -``` - -The basic idea here is that `buildGoModule` will acquire a specific revision of -the `gomobile` source code from github, then attempt to build it. However, -`gomobile` is a special beast in that it requires a number of C/C++ libraries in -order to be built. I discovered this upon running this expression, when I -received this error: - -``` -./work.h:12:10: fatal error: GLES3/gl3.h: No such file or directory - 12 | #include <GLES3/gl3.h> // install on Ubuntu with: sudo apt-get install libegl1-mesa-dev libgles2-mesa-dev libx11-dev -``` - -This stumped me for a bit, as I couldn't figure out a) the "right" place to -source the `GLES3` header file from, and b) how to properly hook that into the -`buildGoModule` expression. My initial attempts involved trying to include -versions of the header file from my `androidsdk` nix package which I had already -gotten (mostly) working, but the version which ships there appears to expect to -be using clang. `cgo` (go's compiler which is used for C/C++ interop) only -supports gcc, so that strategy failed. - -I didn't like having to import the header file from `androidsdk` anyway, as it -meant that my `gomobile` would only work within the context of the -`mobile_nebula` project, rather than being a standalone utility. - -## nix-index - -At this point I flailed around some more trying to figure out where to get this -header file from. Eventually I stumbled on the [nix-index][nix-index] project, -which implements something similar to the `locate` utility on linux: you give it -a file pattern, and it searches your active nix channels for any packages which -provide a file matching that pattern. - -Since nix is amazing it's not actually necessary to install `nix-index`, I -simply start up a shell with the package available using `nix-shell -p -nix-index`. On first run I needed to populate the index by running the -`nix-index` command, which took some time, but after that finding packages which -provide the file I need is as easy as: - -``` -> nix-shell -p nix-index -[nix-shell:/tmp]$ nix-locate GLES3/gl3.h -(zulip.out) 82,674 r /nix/store/wbfw7w2ixdp317wip77d4ji834v1k1b9-libglvnd-1.3.2-dev/include/GLES3/gl3.h -libglvnd.dev 82,674 r /nix/store/pghxzmnmxdcarg5bj3js9csz0h85g08m-libglvnd-1.3.2-dev/include/GLES3/gl3.h -emscripten.out 82,666 r /nix/store/x3c4y2h5rn1jawybk48r6glzs1jl029s-emscripten-2.0.1/share/emscripten/system/include/GLES3/gl3.h -``` - -So my mystery file is provided by a few packages, but `libglvnd.dev` stood out -to me as it's also the pacman package which provides the same file in my real -operating system: - -``` -> yay -Qo /usr/include/GLES3/gl3.h -/usr/include/GLES3/gl3.h is owned by libglvnd 1.3.2-1 -``` - -This gave me some confidence that this was the right track. - -## cgo - -My next fight was with `cgo` itself. Go's build process provides a few different -entry points for C/C++ compiler/linker flags, including both environment -variables and command-line arguments. But I wasn't using `go build` directly, -instead I was working through nix's `buildGoModule` wrapper. This added a huge -layer of confusion as all of nixpkgs is pretty terribly documented, so you -really have to just divine behavior from the [source][buildGoModule-source] -(good luck). - -After lots of debugging (hint: `NIX_DEBUG=1`) I determined that all which is -actually needed is to set the `CGO_CFLAGS` variable within the `buildGoModule` -arguments. This would translate to the `CGO_CFLAGS` environment variable being -set during all internal commands, and whatever `go build` commands get used -would pick up my compiler flags from that. - -My new nix expression looked like this: - -``` -pkgs.buildGoModule { - pname = "gomobile"; - version = "unstable-2020-12-17"; - src = pkgs.fetchFromGitHub { - owner = "golang"; - repo = "mobile"; - rev = "e6ae53a27f4fd7cfa2943f2ae47b96cba8eb01c9"; - sha256 = "03dzis3xkj0abcm4k95w2zd4l9ygn0rhkj56bzxbcpwa7idqhd62"; - }; - vendorSha256 = "1n1338vqkc1n8cy94501n7jn3qbr28q9d9zxnq2b4rxsqjfc9l94"; - - CGO_CFLAGS = [ - "-I ${pkgs.libglvnd.dev}/include" - ]; -} -``` - -Running this produced a new error. Progress! The new error was: - -``` -/nix/store/p792j5f44l3f0xi7ai5jllwnxqwnka88-binutils-2.31.1/bin/ld: cannot find -lGLESv2 -collect2: error: ld returned 1 exit status -``` - -So pretty similar to the previous issue, but this time the linker wasn't finding -a library file rather than the compiler not finding a header file. Once again I -used `nix-index`'s `nix-locate` command to find that this library file is -provided by the `libglvnd` package (as opposed to `libglvnd.dev`, which provided -the header file). - -Adding `libglvnd` to the `CGO_CFLAGS` did not work, as it turns out that flags -for the linker `cgo` uses get passed in via `CGO_LDFLAGS` (makes sense). After -adding this new variable I got yet another error; this time `X11/Xlib.h` was not -able to be found. I repeated the process of `nix-locate`/add to `CGO_*FLAGS` a -few more times until all dependencies were accounted for. The new nix expression -looked like this: - -``` -pkgs.buildGoModule { - pname = "gomobile"; - version = "unstable-2020-12-17"; - src = pkgs.fetchFromGitHub { - owner = "golang"; - repo = "mobile"; - rev = "e6ae53a27f4fd7cfa2943f2ae47b96cba8eb01c9"; - sha256 = "03dzis3xkj0abcm4k95w2zd4l9ygn0rhkj56bzxbcpwa7idqhd62"; - }; - vendorSha256 = "1n1338vqkc1n8cy94501n7jn3qbr28q9d9zxnq2b4rxsqjfc9l94"; - - CGO_CFLAGS = [ - "-I ${pkgs.libglvnd.dev}/include" - "-I ${pkgs.xlibs.libX11.dev}/include" - "-I ${pkgs.xlibs.xorgproto}/include" - "-I ${pkgs.openal}/include" - ]; - - CGO_LDFLAGS = [ - "-L ${pkgs.libglvnd}/lib" - "-L ${pkgs.xlibs.libX11}/lib" - "-L ${pkgs.openal}/lib" - ]; -} -``` - -## Tests - -The `CGO_*FLAGS` variables took care of all compiler/linker errors, but there -was one issue left: `buildGoModule` apparently runs the project's tests after -the build phase. `gomobile`'s tests were actually mostly passing, but some -failed due to trying to copy files around, which nix was having none of. After -some more [buildGoModule source][buildGoModule-source] divination I found that -if I passed an empty `checkPhase` argument it would skip the check phase, and -therefore skip running these tests. - -## Fin! - -The final nix expression looks like so: - -``` -pkgs.buildGoModule { - pname = "gomobile"; - version = "unstable-2020-12-17"; - src = pkgs.fetchFromGitHub { - owner = "golang"; - repo = "mobile"; - rev = "e6ae53a27f4fd7cfa2943f2ae47b96cba8eb01c9"; - sha256 = "03dzis3xkj0abcm4k95w2zd4l9ygn0rhkj56bzxbcpwa7idqhd62"; - }; - vendorSha256 = "1n1338vqkc1n8cy94501n7jn3qbr28q9d9zxnq2b4rxsqjfc9l94"; - - CGO_CFLAGS = [ - "-I ${pkgs.libglvnd.dev}/include" - "-I ${pkgs.xlibs.libX11.dev}/include" - "-I ${pkgs.xlibs.xorgproto}/include" - "-I ${pkgs.openal}/include" - ]; - - CGO_LDFLAGS = [ - "-L ${pkgs.libglvnd}/lib" - "-L ${pkgs.xlibs.libX11}/lib" - "-L ${pkgs.openal}/lib" - ]; - - checkPhase = ""; -} -``` - -Once I complete the nix-ification of `mobile_nebula` I'll submit a PR to the -nixpkgs upstream with this, so that others can have `gomobile` available as -well! - -[nix]: https://nixos.org/manual/nix/stable/ -[mobile_nebula]: https://github.com/cryptic-io/mobile_nebula -[gomobile]: https://github.com/golang/mobile -[nix-index]: https://github.com/bennofs/nix-index -[buildGoModule-source]: https://github.com/NixOS/nixpkgs/blob/26117ed4b78020252e49fe75f562378063471f71/pkgs/development/go-modules/generic/default.nix |