#+title: github continuous integration
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# +html_link_home: index.html
# +html_link_up: development-environment.html

* Motivation

    We want to use a custom (~docker~) container with ~github~ actions,  and prepare it using ~nix~.

    Several advantages:

    1. control over build software (e.g. gcc version).

    2. reproducibility -- nix-to-container pipeline guarantees perfect reproducibility

    3. flexibility -- container can include prepared software that isn't available on ubuntu

    4. size -- container with no excess baggage

* Contents

  repos under https://github.com/Rconybea

   | scheme   | builder   | src-repo              | action-repo            |
   |----------+-----------+-----------------------+------------------------|
   | scheme 1 | ubuntu    | [[https://github.com/Rconybea/hello-example][hello-example]]         | (same)                 |
   | scheme 2 | ubuntu    | [[https://github.com/Rconybea/docker-action-example][docker-action-example]] | (same)                 |
   | scheme 3 | container | [[https://github.com/Rconybea/docker-nix-hello][docker-nix-hello]]      | [[https://github.com/Rconybea/docker-action-example2][docker-action-example2]] |
   | scheme 4 | container | [[https://github.com/Rconybea/docker-cpp-builder][docker-cpp-builder]]    | [[https://github.com/rconybea/docker-action-example3][docker-action-example3]] |

* Progressive Implementation

  We'll present several progressive CI-with-github examples,
  that converge on goals above.

** Scheme 1 - github build using base o/s platform

*** Preliminaries

source for ~Scheme 1~ is on github here: [[https://github.com/Rconybea/hello-example]]

**** Directory structure

   #+begin_example
   hello-example
   +- .github
   |  \- workflow
   |     \- main.yml
   +- CMakeLists.txt
   \- hello.cpp
   #+end_example

**** Source

   #+begin_src c++
     // hello.cpp

     #include <iostream>

     using namespace std;

     int
     main(int argc, char * argv[]) {
         std::string subject = "World";

         if (argc > 1)
             subject = argv[1];

         cout << "Hello, " << subject << "!" << std::endl;
     } /*main*/

   #+end_src

**** Cmake build files
   #+begin_src cmake
     # CMakeLists.txt

     cmake_minimum_required(VERSION 3.10)

     project(hello-example VERSION 1.0)

     enable_language(CXX)

     # write compile_commands.json for LSP
     set(CMAKE_EXPORT_COMPILE_COMMANDS ON CACHE INTERNAL "")

     set(SELF_EXE hello-example)
     set(SELF_SOURCE_FILES hello.cpp)

     add_executable(${SELF_EXE} ${SELF_SOURCE_FILES})

     install(TARGETS ${SELF_EXE} DESTINATION bin)

     if(CMAKE_EXPORT_COMPILE_COMMANDS)
         # include otherwise-omitted system directories in compile_commands.json,
         # so LSP knows exactly what compiler is using
         set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
     endif()
   #+end_src

**** Build + Run
   #+begin_example
   $ cd hello-example
   $ mkdir build
   $ cmake ..
   -- Configuring done
   -- Generating done
   -- Build files have been written to: /home/roland/proj/hello-example/build
   $ make
   [ 50%] Building CXX object CMakeFiles/hello-example.dir/hello.cpp.o
   [100%] Linking CXX executable hello-example
   [100%] Built target hello-example
   $ ./hello-example
   Hello, World!
   #+end_example

**** Continuous Integration with Github

   We need to do two things:
   1. setup a github repo holding our sources:
      #+begin_src
      $ cd hello-world
      $ git remote -v
      origin  git@github.com:rconybea/hello-example.git (fetch)
      origin  git@github.com:rconybea/hello-example.git (push)
      #+end_src
   2. configure github actions for that repo
      We add one file, ~hello-world/.github/workflows/main.yml~

      #+begin_src yaml
      name: c++ build with cmake

      on:
        push:
          branches: ["main"]
        pull_request:
          branches: ["main"]

      env:
        BUILD_TYPE: Release

      jobs:
        build_job:
          runs-on: ubuntu-latest

          steps:
          - name: checkout self (hello-example)
            uses: actions/checkout@v3

          - name: configure self (hello-example)
            run: cmake -B ${{github.workspace}}/build -DCMAKE_INSTALL_PREFIX=${{github.workspace}}/local -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}}

          - name: build self (hello-example)
            run: cmake --build ${{github.workspace}}/build --verbose

          - name: test self (hello-example)
            working-directory: ${{github.workspace}}/build
            run: ./hello-example
      #+end_src

      github will automatically trigger a build whenever new sources are pushed.
      build will run the contents of ~steps~ in order.

** Scheme 2 - docker build using base o/s platform

   Instead of building on github-provided base ubuntu platform,
   use github-built docker container.

   Initially replacing c++ program with shell script,  we'll restore it later.

*** Preliminaries

    source for ~Scheme 2~ is on github here: https://github.comt/Rconybea/docker-action-example

    Build docker container (using resources from ubuntu base platform).
    Container:
    - invokes a shell script to say hello
    - can be used as a github action

**** Directory Structure

     #+begin_example
     docker-action-example
     +- .github
     |  \- workflows
     |     \- main.yml
     +- action.yml
     \- entrypoint.sh
     #+end_example

**** Source

     ~entrypoint.sh~:
     #+begin_src sh
       #!/usr/bin/env bash
       echo "Hello $1"
       time=$(date)
       echo "time=$time" >> $GITHUB_OUTPUT
     #+end_src

**** Docker Container

     ~DockerFile~:
     #+begin_example
     # base container image
     FROM ubuntu:22.04

     # copy files from repo to container filesystem
     COPY entrypoint.sh /entrypoint.sh

     # default startup executable
     ENTRYPOINT ["/entrypoint.sh"]
     #+end_example

**** Use Container as github action

     toplevel ~action.yml~ describes a custom github action
     that operates by invoking docker image
     (automagically built from enclosed ~DockerFile~)

     ~action.yml~:

     #+begin_src yaml
     name: 'Hello World'

     description: 'Greet someone + record the time'

     inputs:
       who-to-greet:
         description: 'Who to greet'
         required: true
         default: "World"

     outputs:
       time:
         description: "time when greeting made"

     runs:
       using: 'docker'
       image: 'DockerFile'
       args:
         - ${{ inputs.who-to-greet }}

     #+end_src

**** Continuous Integration with Github

     Configure github actions for repo https://github.com/Rconybea/docker-action-example;

     File ~.github/workflows/main.yml~
     #+begin_src yaml
       on: [push]

       jobs:
         hello_world_job:
           runs-on: ubuntu-latest
           name: a job to say hello, perhaps fiercely
           steps:
             - name: hello world action step
               id: hello
               uses: rconybea/docker-action-example@v1
               with:
                 who-to-greet: 'Iffy!  What are you doing??'
                 # do something with output
                 - name: get output time
                   run: echo "The time was ${{ steps.hello.outputs.time }}"
     #+end_src

     In ~main.yml~ here:
     - ~rconybea/docker-action-example~ is our github repo,
     - ~v1~ is target github tag

** Scheme 3 - custom docker container via nix (no c++)

*** Preliminaries

Source for ~Scheme 3~ uses two repos:

- Custom container build here: [[https://github.com/Rconybea/docker-nix-hello]]
- Workflow using container here: [[https://github.com/Rconybea/docker-action-example2]]
- See also: https://blog.bitsrc.io/using-github-container-registry-in-practice-295677c6f65e]]

**** Directory structure

     #+begin_example
     docker-nix-hello
     +- flake.nix
     \- flake.lock    # automatically created by nix
     #+end_example

     #+begin_example
     docker-action-example2
     \- .github
        \- workflows
           \- main.yml
     #+end_example

**** Source
Prepare minimal custom docker container using a nix flake.

~flake.nix~:
     #+begin_src nix
     {
       description = "hello world";

       # dependencies
       inputs = rec {
         nixpkgs.url = "github:nixos/nixpkgs/23.05";
       };

       outputs = { self, nixpkgs } :
         let
           system = "x86_64-linux";
           pkgs = import nixpkgs { inherit system; };

           hello_deriv = pkgs.writeShellScriptBin "entrypoint.sh" ''
             echo "Hello $1"
             time=$(date)
             echo "time=$time" >> $GITHUB_OUTPUT
           '';

           docker_hello_deriv =
             pkgs.dockerTools.buildLayeredImage {
               name = "docker-nix-hello";
               tag = "v1";
               contents = [ self.packages.${system}.hello
                            self.packages.${system}.bash
                            # for /bin/tail,  assumed by github actions when invoking a docker container
                            self.packages.${system}.coreutils ];

               config = {
                 Cmd = [ "/bin/entrypoint.sh" ];
                 WorkingDir = "/";
               };
             };

         in rec {
           packages.${system} = {
             default = docker_hello_deriv;

             docker_hello = docker_hello_deriv;
             hello = hello_deriv;

             bash = pkgs.bash;
             # for example,  github actions creates container with --entrypoint "tail",
             # so container must provide executable with that name in $PATH
             #
             coreutils = pkgs.coreutils;
           };
         };
     }
     #+end_src

**** Build Container + Upload to github

     Container will be ~docker-nix-hello~.

     Steps:
     1. get github personal access token,
        so docker can send images to ~ghcr.io~.
        on [[https://github.com/Rconybea]]:
        - visit profile (upper rhs of ~github~ webpage)
        - developer settings (bottom of sidebar)
        - personal access token
        - tokens (classic)
        - generate personal access token with scopes:
          ~read:packages~ ~write:packages~ ~delete:packages~
     2. have docker login to github
        #+begin_src sh
          export CR_PAT=${token}
          echo $CR_PAT | docker login ghcr.io -u rconybea --password-stdin
        #+end_src
     3. nix builds custom image (using ~docker-nix-hello/flake.nix~)
        #+begin_src sh
          cd ~/proj/docker-nix-hello
          nix build
        #+end_src
     4. load image into docker
        #+begin_src sh
          docker load <~/proj/docker-nix-hello/result
        #+end_src
     5. tag image the way github expects: ~ghcr.io/${username}/${imagename}:${tag}~
        #+begin_src sh
          docker image tag docker-nix-hello:v1 ghcr.io/rconybea/docker-nix-hello:v1
        #+end_src
     6. push to github container registry
        (will show up at https://github.com/Rconybea?tab=packages)
        #+begin_src sh
          docker image push ghcr.io/rconybea/docker-nix-hello:v1
        #+end_src
     7. make package public from package's settings link

**** Workflow Using Custom Container

     in ~docker-action-example2/.github/workflows/main.yml~:
     #+begin_src yaml
       on: [push]

       jobs:
         hello_world_job:
           name: a job to say hello,  using separate docker container
           runs-on: ubuntu-latest
           container:
             image: ghcr.io/rconybea/docker-nix-hello:v1
             steps:
               - name: hello world action step
                 id: hello
                 run: /bin/entrypoint.sh 'Xioni!'
                 - name: get output time
                   run: echo "The time was ${{ steps.hello.outputs.time }}"
     #+end_src

** Scheme 4 - custom docker container via nix (with gcc)

Source for ~Scheme 4~ in two repos:

- Custom container build here: [[https://github.com/Rconybea/docker-cpp-builder]]
- Workflow using container here: [[https://github.com/Rconybea/docker-action-example3]]

**** Directory structure

#+begin_example
docker-cpp-builder
+- flake.nix
\- flake.lock    # automatically created by nix
#+end_example

#+begin_example
docker-action-example3
+- .github
|  \- workflows
|     \- main.yml
+- Makefile
+- hello.cpp
#+end_example

**** Source
Prepare custom docker container to deliver build stack (=gcc=, =cmake=, ...)

~flake.nix~:
#+begin_src nix
{
  description = "docker c++ builder (using nix)";

  # dependencies
  inputs = rec {
    nixpkgs.url = "github:nixos/nixpkgs/23.05";
  };

  outputs = { self, nixpkgs } :
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs { inherit system; };

      docker_builder_deriv =
        pkgs.dockerTools.buildLayeredImage {
          name = "docker-cpp-builder";
          tag = "v3";
          contents = [ self.packages.${system}.git
                       self.packages.${system}.cacert
                       self.packages.${system}.gnumake
                       self.packages.${system}.gcc
                       self.packages.${system}.binutils
                       self.packages.${system}.bash
                       # for /bin/tail,  assumed by github actions when invoking a docker contianer
                       self.packages.${system}.coreutils ];
        };

    in rec {
      packages.${system} = {
        default = docker_builder_deriv;

        docker_builder = docker_builder_deriv;

        git = pkgs.git;
        cacert = pkgs.cacert;
        gnumake = pkgs.gnumake;
        gcc = pkgs.gcc;
        binutils = pkgs.binutils;
        bash = pkgs.bash;
        coreutils = pkgs.coreutils;
      };
    };
}

#+end_src

**** Build Container + Upload to github

Instructions are the same as for Scheme 3,  but using =~/proj/docker-cpp-builder= instead of =~/proj/docker-nix-hello=

#+begin_src sh
  cd ~/proj/docker-cpp-builder
  git tag v1
  nix build
  docker load <~/proj/docker-cpp-builder/result
  docker image tag docker-cpp-builder:v1 ghcr.io/rconybea/rconybea/docker-cpp-builder:v1
  docker image push ghcr.io/rconybea/docker-cpp-builder:v1
#+end_src

After uploading package (docker image) for gcc builder  appears here: [[https://github.com/Rconybea?tab=packages]]:

**** Workflow using Custom Container

in ~docker-action-example3/.github/workflows/main.yml~:
#+begin_src yaml
  on: [push]

  env:
    # personal accesss token (using automatically-supplied GIT_TOKEN) with read access to public repos
    GIT_USER: rconybea

  jobs:
    build_job:
      name: compile hello world, using prepared docker container
      runs-on: ubuntu-latest
      container:
        image: ghcr.io/rconybea/docker-cpp-builder:v3
      steps:
        - name: checkout
          run:
            # not using usual checkout action: bc complications from within container
            GIT_SSL_NO_VERIFY=true git clone https://${{env.GIT_USER}}:${{env.GIT_TOKEN}}@github.com/rconybea/docker-action-example3.git

        - name: compile
          run:
            # make,g++ will run in container..
            make -C docker-action-example3

        - name: hello
          run:
            ./docker-action-example3/hello Roland
            #${{github.workspace}}/hello Roland

#+end_src

Note: in non-container build we can checkout code with something like:
#+begin_src yaml
  steps:
  - name: checkout
  - uses: rconybea/my-repo@my-git-tag
#+end_src

Unfortunately that doesn't work out-of-the-box when we use a container for build,
because of a permissioning problem.   Spent some time on various internet-advised workarounds,
before settling on the solution above:  including =git= in custom docker image,  and checking source
out from inside the container.

We need to set ~GIT_SSL_NO_VERIFY~ to prevent an obscure error (passed along from SSL) mentioning an `unrecognized scheme`.
Presumably there's a problem authenticating github.com's certificate