GoLang 101 for ITPros

Patrick Riel, priel@cisco.com

Stève Sfartz, stsfartz@cisco.com

DEVNET-1808

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How

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• Why Golang ?

• Hello World (in Python / Golang in VSCode)

• Setting up your dev env, code formating, compiling, VSCode

• CLI example, Mac/Win/Linux binaries

• Advanced: goroutines & channels

• Deployment: docker packaging

Agenda

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Why Go?

• Released by Google in 2009

• conceived in 2007, popular since 2015

• Designed to address software engineering issues faced in the construction of large server software

• Influenced by: C, Python, Smalltalk, Alef, CSP, Modula, Pascal, Limbo, BCPL

• Focus on clarity, simplicity and composability

• resulted in a productive, fun, expressive and powerful language

• No class inheritance but ‘Embedding’ & ‘Interfaces’ to provide polymorphism

• Built-in concurrency (parallelism & asynchrony) via ‘Channels’ & ‘goroutines’

• Includes a - debugging, profiling, formatting and testing - toolset

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Software engineering guided the design of Go

• Clear dependencies

• Clear syntax

• Clear semantics

• Composition over inheritance

• Simplicity provided by the programming model (garbage collection, concurrency)

• Easy tooling (the go tool, gofmt, godoc, gofix)

• TRY IT: https://tour.golang.org

https://talks.golang.org/2012/splash.article

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Variableshttps://tour.golang.org/basics

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Functions: mutiple & named resultshttps://tour.golang.org/basics/6

Go Tour

Setting up go on your machine

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Installing Go

• Download the PKG on Mac (or MSI for Windows), and Install

• by default installs in /usr/local/go (or c:\Go for Windows).

• adds the Go binary to your PATH environment variable

• Set the GOROOT environment variable if you install to a different location

• Type ‘go version’ to check your installation is successful

• Create a Go workspace directory

• under $HOME/go on Mac (or %USERPROFILE%\go for Windows)

• Set a GOPATH environment variable is preferable (and mandatory if elsewhere)

• Add the $GOPATH/bin directory to your path

https://golang.org/doc/install

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Hello World (on Windows)

• Create a “src/hello” directory in your workspace

• Create a file named hello.go

• Build it with the go tool

• Produces an executable named hello.exe

• Run go install to install the binary into your workspace's bin directory or go clean to remove it.

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File: src/hello/hello.go

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Hello World (on a Mac)

• Create a “src/hello” directory in your workspace

• Create a file named hello.go

• Build it with the go tool

• Produces an executable named hello.exe

• Run go install to install the binary into your workspace's bin directory or go clean to remove it.

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File: src/hello/hello.go2

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Typical go folder structure

• go tooling requires to organize your code in a specific way

• Go programmers typically keep all their Go code in a single workspace.

• A workspace contains many version controlrepositories (managed by Git, for example).

• Each repository contains one or more packages.

• Each package consists of one or more Go source files in a single directory.

• The path to a package's directory determines its import path.

https://golang.org/doc/code.html

GOPATH = C:\Local\gowork

mkdir ‘$GOPATH/src/github.com/<username>/hello’

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Creating a Library

> mkdir $GOPATH/src/github.com/<user>/stringutil

https://golang.org/doc/code.html

filename: reverse.go

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Creating a Library

> mkdir $GOPATH/src/github.com/user/hello

https://golang.org/doc/code.html

filename: hello.go

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Creating a Libraryhttps://golang.org/doc/code.html

> go install github.com/<user>/hello• the ‘stringutil’ package is automatically installed as well

• Go command executables are statically linked

Setting up your IDE

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Go Extension for Visual Studio Code

Installs automatically at launchor manually via go get –v:

github.com/nsf/gocodegithub.com/uudashr/gopkgs/cmd/gopkgs

github.com/ramya-rao-a/go-outlinegithub.com/acroca/go-symbolsgolang.org/x/tools/cmd/guru

golang.org/x/tools/cmd/gorenamegithub.com/fatih/gomodifytags

github.com/haya14busa/goplay/cmd/goplaygithub.com/josharian/implgithub.com/rogpeppe/godef

golang.org/x/tools/cmd/godocsourcegraph.com/sqs/goreturnsgithub.com/golang/lint/golint

github.com/cweill/gotestsgithub.com/derekparker/delve/cmd/dlv

golang.org/x/tools/cmd/guru

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VS Code golang extension: Installation Tips

• If any go tools dependency is missing, install it manually

• Make sure the $GOPATH/bin directory appears in your path

• To install the Delve debugger, type

> go get -u github.com/derekparker/delve/cmd/dlv

• If having issue with the debugger on Mac: ‘lldb-server’ not found, type

> xcode-select –install

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readword.go

Demo

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Pointershttps://tour.golang.org/moretypes/1

CLI with golangdoing chatops

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Methods and Interfaces

• Remember: a method is just a function with a receiver argument

• To implement an interface in Go

• Implement all the methods in the interface

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https://tour.golang.org/methods

https://gobyexample.com/interfaces

https://github.com/ObjectIsAdvantag/CLEUR-1814/blob/master/7-spark/main.go

https://github.com/ObjectIsAdvantag/CLEUR-1814/blob/master/6-interfaces/main.go

CLI Demo

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Deferhttps://tour.golang.org/flowcontrol/12

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Defer

• defers the execution of a function until the surrounding function returns

• deferred function calls are pushed onto a stack (executed in LIFO)

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counting

done

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HTTP API Clients

• https://www.scaledrone.com/blog/posts/creating-an-api-client-in-go

• simplify development

• speed up development

• clean code

• abstraction

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Concurrency

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Channels & GoRoutines

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Channels & GoRoutines

More about #golang

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Structureshttps://tour.golang.org/moretypes/2

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Arrayshttps://tour.golang.org/moretypes/6

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Sliceshttps://tour.golang.org/moretypes/13

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Mapshttps://tour.golang.org/moretypes/22

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Closureshttps://tour.golang.org/moretypes/25

Deployment & packaging

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Packaging for various platforms

• The go toolchain natively cross-build executables for any Go-supported foreign platform

• Example:

> env GOOS=linux GOARCH=amd64 go build -o dist/demo.linux -v main.go

• https://www.digitalocean.com/community/tutorials/how-to-build-go-executables-for-multiple-platforms-on-ubuntu-16-04

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Dockerfile examplehttps://github.com/ObjectIsAdvantag/CLEUR-1814/tree/master/8-docker

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Wrapup

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Wrapup… go for ITPros

CLI

Proxy

Reverse Proxy

Web API

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Cisco Community Contributions

• golang samples

• https://github.com/ObjectIsAdvantag/CLEUR-1814

• Cisco Spark REST API wrapper

• https://github.com/jbogarin/go-cisco-spark

• Cisco ACI from golang

• https://github.com/udhos/acigo

• Answering Machine backed by Tropo

• https://github.com/ObjectIsAdvantag/answering-machine

• Proxy incoming web hooks to established web sockets

• https://github.com/sgrimee/whproxy

https://blog.golang.org

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Cisco Spark

Questions? Use Cisco Spark to communicate with the speaker after the session

1. Find this session in the Cisco Live Mobile App

2. Click “Join the Discussion”

3. Install Spark or go directly to the space

4. Enter messages/questions in the space

How

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