Introduction to Google's Go programming language

Introduction to Google's Go
Stratio / Datio (May 2016)
Mario Castro

For those who don’t know me…

For those who don’t know me…
Mario Castro
DevOps @ Stratio
Started coding with 13 yo
Java (J++) since 2000
PHP, Python, Java Android, Objective-C, Node.js
Pixar's Certi ed in Renderman's render engine
Other scripting languages (MEL, HScript)

History
Design began in late 2007.
Robert Griesemer, Rob Pike, and Ken Thompson.
Ian Lance Taylor and Russ Cox.
Open source since 2009 with a very active community.
Language stable as of Go 1, early 2012.

Who's Go
The men behind it...
Ken Thompson (Ex Bell labs, Unix designer, B programming language)
Rob Pike (Ex Bell labs, Unix Team, Inferno, Plan 9, UTF-8)
Robert Griesemer (V8 Chrome engine, Sawzall)

Why a new language
slow builds
uncontrolled dependencies
poor program understanding (code hard to read, poorly documented...)
Computers are enormously quicker but software development is not faster.
Some fundamental concepts such as garbage collection and parallel computation
are not well supported by popular systems languages.

What's Go (as a programming language)
Statically typed (duck typing)
Compiled language (no more virtual machines... thanks...)
Structure oriented (no inheritance)
Concise and simple syntax, easy to get started with
Good facilities for writing concurrent programs that share state by communicating
Uni ed formatting style for the language
Compilation is fast even with large projects
No need to know a new paradigm or awkward syntax

Go and Java have much in common

Go and Java have much in common
C family (imperative, braces)
Statically typed
Garbage collected
Methods
Interfaces
Type assertions (instanceof)
Re ection

Classes vs Structs. Interfaces vs... Interfaces?

This is not a competition
Go is not trying to replace Java
Go has focus on productivity and consolidating Google's experience in large
distributed systems
Google uses Java, Javascript, C++, Python, Go, Sawzal and probably a few other
languages are supported (Je Nelson, inventor of Chrome OS)

Go di ers from Java in several ways
Programs compile to machine code. There's no VM.
Statically linked binaries
Built-in strings (UTF-8)
Built-in generic maps and arrays/slices
Built-in concurrency

Go intentionally leaves out many features
No classes
No constructors
No inheritance
No user-de ned generics
No final, exceptions, annotations...

Go intentionally leaves out many features

Seriously...
No, there are not generics nor algebraic types, monads...

Why does Go leave out those features?
Clarity is critical.
classFoo[F[+_]:Monad,A,B](valexecute:Foo.Request[A]=>F[B],valjoins:Foo.Request[A]=>B=
defbar:Foo[({typel[+a]=WriterT[F,Log[A,B],a]})#l,A,B]={
typeTraceW[FF[+_],+AA]=WriterT[FF,Log[A,B],AA]
defexecute(request:Request[A]):WriterT[F,Log[A,B],B]=
self.execute(request).liftM[TraceW]:++>>(repr=>List(request->request.response(repr,self
When reading code, it should be clear what the program will do.
When writing code, it should be clear how to make the program do what you
want.
Sometimes this means writing out a loop instead of invoking an obscure function.

So, Go is not...
...a functional language
...a new fancy way of coding
...a completely open-source project (no pull-requests)
...a super language that will replace us
...talking about replacement... is not the replacement of Java... or C++... or Cobol...

Why Go
Make programming fast
Safety: type-safe and memory-safe
E cient gargage collector
Reduce typing. No more:
foo.Foo*myFoo=newfoo.Foo(foo.FOO_INIT)
Focus on productivity and concurrency of distributed systems with CSP
concurrency model

CSP Concurrency
Actor model: Entities passing messages to each other that are queued (Erlang,
Scala, Java...)
CSP (Communicating sequential processes) model. Proccesses passing messages
to channels that blocks until the messages are taken but with possibility of using
queues
CSP represents the best known way to write software and organize services together
to form a system. Nature itself provides the best examples; even the human body is a
system of interconnected services — respiratory, cardiovascular, nervous, immune,
etc.
The Tao of Hashicorp https://www.hashicorp.com/blog/tao-of-hashicorp.html(https://www.hashicorp.com/blog/tao-of-hashicorp.html)
This was my face when I read the Tao of Hashicorp...

CSP Concurrency
"Gophers" = processes
Arrows = channels
One "Gopher" could listen to zero or more channels
One "Gopher" can send messages to zero or more channels

CSP Concurrency
Process are anonymous (you can just reach them using a channel)
Channels can be bu ered or unbe ered
Channels can be bi-directional or uni-directional
More than one proccess could be listening the same channel
One process could listen more than one channel
More about this in the workshop

An opinionated language
Can be weird at the beginning
No brackets in new line (formatter will put them up again)
An Uppercase name means that some method or variable is public, lowercase for
private
Comments of public methods must start with the name of the method
Your project must reside within $GOPATH
Parameters in the de nition of a function must be one character
If you return more than one value, last must be an error
No more than one le with "package main" even if you only have one "main"
function (just works with `go build` but not with `go run [ le]`)
Imports points to some kind of URL that must match a path within your $GOPATH

Hello World
packagemain
funcmain(){
println("HelloWorld!")
} Run

Hello web-server
packagemain
import(
"fmt"
"log"
"net/http"
)
funcmain(){
http.HandleFunc("/hello",handleHello)
fmt.Println("servingonhttp://localhost:7777/hello")
log.Fatal(http.ListenAndServe("localhost:7777",nil))
}
funchandleHello(whttp.ResponseWriter,req*http.Request){
fmt.Fprintln(w,"Hello,Stratio")
} Run

More examples: Native Unix piping
funcmain(){
c1:=exec.Command("ls","-lh","/")
c2:=exec.Command("awk","{print$5,"011"$9}")
r1,w1:=io.Pipe()
c1.Stdout=w1
c2.Stdin=r1
c2.Stdout=os.Stdout
c1.Start()
c2.Start()
c1.Wait()
w1.Close()
} Run

Inferred types
No need to write variables types
packagemain
import(
"fmt"
"reflect"
)
funcmain(){
me:="JebediahKerman"
fmt.Println(reflect.TypeOf(me))
} Run

Some common coding features and patterns
More than one object on return (error always at the end)
funcmyFunc()(struct1,struct2,error)
Delegate error pattern
returnnil,err //Errorocurred,delegatetocaller
returno,nil //Noerror
Pointers and references
o:=myObject{} //"o"isanobject
doSomething(&o) //Passingapointer."o"isstillanobject
o:=&myObject{} //Pointertoobject."o"isapointer
funcuseObject(o*myObject) //Areceivedpointer"o"isapointer

Some commong coding features and patterns
Handle every error
iferr!=nil{
log.Fatal(err)
}
Ignore a returned variable (very bad practice, don't trust code that do this)
myobj,_:=myFuncThatReturnsAnObjectAndAnError()
Return anything (quite common in Consul code)
funcmyFunc()interface{}
Do some type assertion
obj:=myFunc()
myString,ok:=obj.(string)
ifok{
println(myString)
}

Testing
Comes with its own test suite
$gotest.
$ok github.com/thehivecorporation/raccoon/parser 0.003s
Getting output...
$gotest-v.
$INFO[0000]------------------------------>Readingzombiebookfile zombiebook=/tmp/i-do-not-exist
$INFO[0000]------------------------------>Readingzombiebookfile zombiebook=/tmp/wrongJson81990
$INFO[0000]------------------------------>Readingzombiebookfile zombiebook=../examples/example
$INFO[0000]------------------------------>Readingzombiebookfile zombiebook=/tmp/no-content6184
$INFO[0000]------------------------------>Readingzombiebookfile zombiebook=/tmp/incorrect-keys
$---PASS:TestReadZbookFile(0.00s)
$ zbook_test.go:18:Errorreadingzombiebookfile:open/tmp/i-do-not-exist:nosuchfileordir
$ zbook_test.go:32:ErrorparsingJSON:invalidcharacter'w'lookingforbeginningofobjectke
$PASS

Testing
Race condition evaluation integrated
$gotest-race.
Comes with its own coverage support
$gotest-race-cover.
$ok github.com/thehivecorporation/raccoon/parser 1.011s coverage:68.3%ofstatements

gofmt
gofmtformats indentation, spaces, newlines and syntax
Makes most code familiar.

golint
golintwarns you about good practices and suggestions
Example:
typeExecutorinterface{
Execute()
}
linter.go:3:6:exportedtypeExecutorshouldhavecommentorbeunexported
Ok so...
//Interfaceforexecution
Execute()
}
linter2.go:3:1:commentonexportedtypeExecutorshouldbeoftheform"Executor..."(withoptiona
//Executoristhestrategypatternfora...
Execute()
}

Introduction to Google's Go programming language

golint
If the name always begins the comment, the output of godoc can usefully be run
through grep. Imagine you couldn't remember the name "Compile" but were
looking for the parsing function for regular expressions, so you ran the command,
$godocregexp|grepparse
Compileparsesaregularexpressionandreturns,ifsuccessful,aRegexp
parsed.Itsimplifiessafeinitializationofglobalvariablesholding
cannotbeparsed.Itsimplifiessafeinitializationofglobalvariables
$
Found in "E ective Go"(https://golang.org/doc/e ective_go.html#commentary)

GoDoc
All core packages at your ngertips
You can perform queries in command line
Or open a web server to search
godocindex=true-http=:6060
Search in a speci c package
godocfmt|grep-iread
funcFscanln(rio.Reader,a...interface{})(nint,errerror)
Scanscanstextreadfromstandardinput,storingsuccessive
Scanfscanstextreadfromstandardinput,storingsuccessive
//ReadRunereadsthenextrune(Unicodecodepoint)fromtheinput.
//IfinvokedduringScanln,Fscanln,orSscanln,ReadRune()will
//returnEOFafterreturningthefirst'n'orwhenreadingbeyond
ReadRune()(rrune,sizeint,errerror)
//UnreadRunecausesthenextcalltoReadRunetoreturnthesamerune.
UnreadRune()error
//BecauseReadRuneisimplementedbytheinterface,Readshouldneverbe
//ScanStatemaychoosealwaystoreturnanerrorfromRead.
Read(buf[]byte)(nint,errerror)

Go Get
Useful for dependency management
As simple as
$gogetgithub.com/kubernetes/kubernetes
import"github.com/4ad/doozer"
varclientdoozer.Conn
Most IDE's has an auto-import (on save) features

Installing Go
From repositories
- Ubuntu users: `sudo apt-get install -y golang`
- Centos/RHEL users: `sudo yum install -y golang`
- Fedora: `sudo dnf install -y golang`

Ok... the slightly harder one: Installing Go
Latest build
golang.org(http://golang.org)
Select your distro
unpack it `tar -zxvf go1.6.2.linux-amd64.tar.gz`
Move the gofolder to your favorite destination (assign permissions according to
destination)
Add a $GOROOT environment variable pointing to your go folder (not the bin
folder within your go folder) to /etc/pro le, ${HOME}/.bashrc, etc.
Add a $GOPATH environment variable pointing to an empty folder that will
represent your global workspace for Go
Add $GOPATH/bin and $GOROOT/bin to your $PATH

The workspace
Workspace is global and it's de ned as an environment variable called $GOPATH.
$exportGOPATH=${HOME}/go
So a `go get github.com/docker/docker` will put the source in
$gogetgithub.com/docker/docker
$cd$GOPATH/src/github.com/docker/docker
Easy, uh?

Our rst Go App
packagemain
funcmain(){
println("Helloworld")
} Run

Our second Go App
packagemain
import"fmt"
funcmain(){
fmt.Printf("(P1)Hello")
goWorld()
}
funcWorld(){
fmt.Printf("world(P2)n")
}

Our third Go App
packagemain
import"fmt"
funcmain(){
fori:=0;i<10000;i++{
gofunc(jint){
fmt.Printf("Proccess#%dn",j)
}(i)
}
varinputstring
fmt.Scanln(&input)
}

Our fourth Go App
funcmain(){
workersCh:=make(chanint,20)
fori:=0;i<20;i++{
goworker(i,workersCh)
}
iter:=0
for{
workersCh<-iter
iter++
time.Sleep(100*time.Millisecond)
}
}
funcworker(idint,wchanint){
for{
select{
casenumber:=<-w:
fmt.Printf("Worker%dgotthenumber%dn",id,number)
time.Sleep(3*time.Second)
}
}
}//END

Our fth Go App
vardelaytime.Duration=5000
funcmain(){
dispatcherCh:=make(chanint,100)
workersCh:=make(chanint)
fori:=0;i<20;i++{
goworker(i,workersCh)
}
godispatcher(dispatcherCh,workersCh)
iter:=0
for{
fmt.Printf("Queuehassize%dn",len(dispatcherCh))
iflen(dispatcherCh)==100{
delay=100
}elseiflen(dispatcherCh)==0{
delay=5000
}
dispatcherCh<-iter
iter++
time.Sleep(100*time.Millisecond)
}
}

funcdispatcher(c,wchanint){
for{
v:=<-c
w<-v
}
}
funcworker(idint,wchanint){
for{
select{
casenumber:=<-w:
fmt.Printf("Worker%dgotthenumber%dn",id,number)
time.Sleep(delay*time.Millisecond)
}
}
}//END

Contributing in Github
Work ow is slightly di erent
Fork the project into your own github account
Don't clone your fork! Use `go get` of the original git project
As mentioned earlier, it will create a folder within your
$GOPATH/src/[project_owner]/[repo]
Add your fork as a di erente remote (`git remote add my_fork
https://github.com/[my_account]/[my_fork]`)
Work as usual
Push your changes to your fork
Open pull request as usual
(At least, this is how I do it)

Part of Tens
No inheritance
Strongly typed
No “git clone”. Use “go get”
Strongly opinionated
No generics
Has pointers and references
No unused variables nor imports
Strings and structs can’t be nil
You must work always in $GOPATH
No need of locks or semaphores with channels

IDE's and other editing tools
vim + vim-go
emacs + go-model.el
Intellij Idea (has debugging support already. Thanks Abel!)
Atom + go-plus (Has debugging support using Delve plugin)
Sublime Text + GoSublime
Visual Studio Code + vscode-go
LiteIde

Companies using Go
Google
Docker
Net ix
Parse
Digital Ocean
Ebay
AirBnB
Dropbox
Uber
VMWare

Famous software written in Go
Docker
Kubernetes (Google)
Hashicorp's stack (Consul, Terraform, Vault, Serf, Otto, Nomad, Packer)
Prometheus (SoundClound)
CoreOS stack (ETCD, Fleet, Rkt, Flannel)
In uxDB
Grafana

Best resources to learn Go (ordered)
A Tour of Go (interactive tutorial)
https://tour.golang.org/list(https://tour.golang.org/list)
Go By Example
https://gobyexample.com/(https://gobyexample.com/)
How to install Go workspace
https://golang.org/doc/code.html(https://golang.org/doc/code.html)
Go bootcamp (free ebook)
http://www.golangbootcamp.com/(http://www.golangbootcamp.com/)
"E ective Go" Wait a week or two to read
https://golang.org/doc/e ective_go.html(https://golang.org/doc/e ective_go.html)

Other references
Docker and Go: Why we decide to write Docker in Go?
http://www.slideshare.net/jpetazzo/docker-and-go-why-did-we-decide-to-write-
docker-in-go(http://www.slideshare.net/jpetazzo/docker-and-go-why-did-we-decide-to-write-docker-in-go)

This presentation...
...isalsodonewithaGotool

Thank you
Mario Castro
Gopher @ StratioBD(mailto:Gopher%20@%20StratioBD)
@110010111101011(http://twitter.com/110010111101011)
github.com/sayden
mcastro@stratio.com(mailto:mcastro@stratio.com)

Introduction to Google's Go programming language

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