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| -rw-r--r-- | src/_posts/2021-01-30-building-mobile-nebula.md | 1 | ||||
| -rw-r--r-- | src/_posts/2021-02-13-building-gomobile-using-nix.md | 232 |
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diff --git a/src/_posts/2021-01-30-building-mobile-nebula.md b/src/_posts/2021-01-30-building-mobile-nebula.md index 1329800..0645e70 100644 --- a/src/_posts/2021-01-30-building-mobile-nebula.md +++ b/src/_posts/2021-01-30-building-mobile-nebula.md @@ -3,6 +3,7 @@ title: >- Building Mobile Nebula description: >- Getting my hands dirty with Android development. +series: nebula tags: tech --- diff --git a/src/_posts/2021-02-13-building-gomobile-using-nix.md b/src/_posts/2021-02-13-building-gomobile-using-nix.md new file mode 100644 index 0000000..3326266 --- /dev/null +++ b/src/_posts/2021-02-13-building-gomobile-using-nix.md @@ -0,0 +1,232 @@ +--- +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 |