So You Want To Build A Golang App

Well, maybe you don’t and you want to know why the hell I would. I’ve been building PowerShell tools for about 10 years and I’m pretty good at it. PowerShell is even available on Linux now. So, why Go? It’s freaking everywhere. Here are some of the FOSS tools I’ve been working with that are built on Go.

A lot of these tools have a lot of open issues around the Windows build and I can’t contribute if I don’t understand Go and the community is huge. The PowerShell Summit had about 250 attendees.

GopherCon started in 2014, with an amazing first year attendance of over 700 people. Since then, we’ve doubled in attendance. We expect to sell out early this year, with a maximum capacity of 1500 people. -https://www.gophercon.com/

I find in PowerShell that I have to build a lot of supporting functionality just to be able to build the valuable bit of functionality I originally wanted. In Go, the problem is that when you go looking for a package you have to choose from three or more. My first Go app has 20 dependencies and that’s a lot of code I didn’t have to write myself. Package management in PowerShell is still not mature enough to handle that kind of dependency chain.

I also like the language. It has nice programmery things like Interfaces and Goroutines.

Getting started with Go as a PowerShell developer

There is a number of good getting started resources.

However, thinking about the features of Go compared to PowerShell helped me get my head around the language. So, here are some of those analogies.

GOPATH

$env:GOPATH is your $env:PSModulePath for Go. It doesn’t get set to some default when you install Go and without this nothing works. I have mine set to ~\go.

Packages

Packages are obviously like Modules. At the top of each file, you define what package the file is part of. If you want to build a binary, you need to have a main package with a func main(). Or, you can just name your package whatever if you are going to distribute it like a library. Packages also function a bit like a .Net Namespace and Go has a clever feature where if your function name starts with an uppercase letter it is exported, otherwise it stays private to the package.

Cobra

I initially used the flag package to handle command-line flags (parameters), but I found them lacking compared to PowerShell’s fantastic parameter handling. A coworker suggested Cobra (the package powering the CLI for Hugo.exe).

The syntax to use Cobra is looks nothing like PowerShell parameter declarations, but it provides a lot of equivalent functionality. You can define commands and flags and Cobra takes care of building the Help output for you.

Here’s an example command declaration:

var RootCmd = &cobra.Command{
    Use:   "hugo",
    Short: "Hugo is a very fast static site generator",
    Aliases: []string{"url", "address"},
    Example:    "An example of usage",
    Long: `A Fast and Flexible Static Site Generator built with
                love by spf13 and friends in Go.
                Complete documentation is available at http://hugo.spf13.com`,
    Run: func(cmd *cobra.Command, args []string) {
        // Do Stuff Here
    },
}

Use is the usage (syntax) string of the command. Short is like the PowerShell Synopsis and Long is like Description. There is even an Example section — Use it or June will find you. Yes, even if you are using Go! On top of that, there is an Aliases property.

Let me back up a second and cover something that took me the better part of a day to think about clearly. In PowerShell, you typically just invoke some function. That function probably is part of a Module and represents a small bit of the functionality the Module offers. When I started with Go I equated the executable I was building to a cmdlet. Cobra implements a CLI convention of exe command -flag and thinking of the exe as a cmdlet got me confused when I was trying to figure out what my commands should be. However, the exe is really like a Module and each command is like a cmdlet. 💡 It seems obvious in hindsight. It even says so in the README.

The pattern to follow is APPNAME VERB NOUN –ADJECTIVE. or APPNAME COMMAND ARG –FLAG

The other common pattern of Cobra is putting each command in a separate file. Similar to how I like to put each public function for a PowerShell module in a separate file. This is extra useful when you do cross-platform compiling and not all commands should be included for every platform.

Glide

Remember when I said Go has a lot of options for packages? It even has options for package management. Glide makes package management easier. Glide up is basically like nuget restore and it uses reflection to examine your source files and figure out which packages need to be installed. Super handy for CI.

GOX

Gox like Glide is about making a part of Go development single-line simple.

Gox is a simple, no-frills tool for Go cross compilation

You can do cross compilation with go build, but Gox automates it and does it fast.

This is the command I use in AppVeyor for creating amd64 builds for both Windows and Linux. If you leave off the os and arch flags it compiles for over a dozen platforms.

gox.exe -os="windows" -os="linux" -arch="amd64" -ldflags="-X cmd.version=$env:APPVEYOR_BUILD_VERSION" -output="./build/{{.OS}}_{{.Arch}}/spinner_v$env:APPVEYOR_BUILD_VERSION"

The -ldflags part is sort of the community recommended way of versioning your binary in Go. This is setting the value of the version variable in cmd package.

Speaking of AppVeyor

AppVeryor includes Go on all of its build agent flavors, however, Glide and Gox are not included. I also found I needed to set the environment variables to get Go builds working on AppVeyor.

Here’s the install section of my AppVeryor.yml.

install:
  - set PATH=%GOPATH%\bin;%PATH%
  - ps: Start-FileDownload 'https://github.com/Masterminds/glide/releases/download/v0.12.3/glide-v0.12.3-windows-amd64.zip'
  - ps: Expand-Archive -Path glide-v0.12.3-windows-amd64.zip
  - ps: Copy-Item .\glide-v0.12.3-windows-amd64\windows-amd64\glide.exe .\glide.exe
  - go get github.com/mitchellh/gox
  - go version
  - go env

AppVeyor includes a cmdlet called Start-FileDownload that seems to work better in their agent than Invoke-WebRequest -outfile.

After that, the rest of the rest of the yml isn’t that complicated.

test_script:
  - go test .\cmd --coverprofile=cover.cov

before_build:
  - glide up

build_script:
  - ps: gox.exe -os="windows" -os="linux" -arch="amd64" -ldflags="-X cmd.version=$env:APPVEYOR_BUILD_VERSION" -output="./build/{{.OS}}_{{.Arch}}/spinner_v$env:APPVEYOR_BUILD_VERSION"

after_build:
  - ps: .\create_archives.ps1

  - path: build/spinner*.zip
    name: spinner

The create_archive.ps1 script just loops through all of the directories created by Gox and creates a zip file for each.

All of this was learned while developing Spinner, a replacement for the closed source ServiceMoniter.exe included in some Microsoft published Docker images.

I think I missed some stuff. I crammed a lot of learning into a few days. If you’re interested in Go development on Windows and the above didn’t answer your question, leave a comment or hit me up on Twitter.

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