How to Build Your First Web App in Go

Building Your First Web
App in Go
Andy Watson
Ionic Security
#ATOWebGo #ATO2015
All Things Open
2015

About Me
Who: Andy Watson
What: Code Flinger
Where: Ionic Security
http://ionic.com/ @andrewwatson

I used to write PHP
Lots of PHP.
Tons.

Web Apps in Go
• No need for a wrapper like Apache or Nginx
• Create a self-contained, statically compiled
binary
• Cross Compile from your laptop to your
server architecture

Simple Web App
package main
import (
"fmt"
"net/http"
)
func main() {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
fmt.Fprint(w, "Hello, worldn")
})
fmt.Print("Listening on :8080n")
http.ListenAndServe(":8080", nil)
}

Templates
Easily render well formed HTML using data
from your application
Nest templates inside each other (partials) for
easy re-use

Simple Template Example
func handleRoot(w http.ResponseWriter, req *http.Request) {
var templateStr =
"<html><body><h1>{{.}}</h1></body></html>n"
var templ =
template.Must(template.New("qr").Parse(templateStr))
templ.Execute(w, "Hello!")
}
func main() {
http.HandleFunc("/", handleRoot)
fmt.Print("Listening on :8080n")
http.ListenAndServe(":8080", nil)
}

Simple Logic
{{if .}}
<h1><a
href="{{.}}">Something!</a>
{{else}}
<h1>None</h1>
{{end}}

Iterations
type Book struct {
Author, Title string
}
func handler(w http.ResponseWriter, r *http.Request) {
// var bookList Book[]
bookList, err := lookupBooksForSale()
templ.Execute(w, bookList)
}

Template with range Operator
<h1>Books For Sale</h1>
{{range .}}
<h3>{{.Title}} by {{.Author}} </h3>
{{else}}
<h3>Sorry.</h3>
{{end}}

Outputs
<h3>Sorry.</h3> <h3>The Thing by
Stephen King</h3>
<h3>Moby Dick by
Herman Melville</h3>
With Empty List With Data

It’s the Methods, man!
func uploadHandler(…) {
if r.Method != "POST" {
err := doPostThings()
handleErrors(err)
return
}
}

Routing
Use a routing library like httprouter or mux to
match requests to handlers
Routes defined using paths and HTTP verbs
r := httprouter.New()
r.POST(”/login", LoginHandler)
r.GET("/", HomeHandler)

MiddleWare
Gets executed with every request
Used for logging, instrumentation, error
handling and more

Negroni
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
fmt.Fprintf(w, "Welcome to the home page!")
})
n := negroni.Classic()
n.UseHandler(mux)
n.Run(":3000")
}
https://github.com/codegangsta/negroni

Negroni Classic
Common set of middleware
• Logging
• Recovery (from panics)
• Static Content Handling

Render
• Cleans Up boilerplate template rendering code
• Handles Errors
• Takes care of headers for HTML, JSON, XML
etc
https://github.com/unrolled/render

Context
• Stores values shared during a request
lifetime
• Useful for easily passing the full context of a
request to multiple handlers
http://www.gorillatoolkit.org/pkg/context

Sessions
Keep data between requests to maintain state
• User information
• Shopping Cart
• ETC
http://www.gorillatoolkit.org/pkg/sessions

Setting up Session Handling
var sessionstore = sessions.NewCookieStore([]byte(secret))
func init() {
sessionstore.Options = &sessions.Options{
Path: "/",
MaxAge: 3600,
HttpOnly: true,
}
}

Using Sessions
session, _ := sessionstore.Get(req, "OthrNumbr-session")
session.Values["loggedin"] = true
session.Values["cust_id"] = cust.CustomerId
session.Values["description"] = cust.Description
session.Save(req, w)
http.Redirect(w, req, "/home/", 302)

Rapid Development
• Gin wraps your process
• Recompiles and Restarts Automatically
• https://github.com/codegangsta/gin

Deploy to Production
• Cross Compile for Linux
• SCP to production
• Wrap in upstart script etc

Contain Yourself
The GoLang library Docker images make it
easy to build and run your Go app in a
container
https://hub.docker.com/_/golang/

Dockerfile
FROM golang:1.5-onbuild

Docker Commands
$ docker build -t hello-world .
$ docker run --rm -it --name fred hello-world

Google App Engine
• GAE supports Go runtime
• Automatically scales up instances
• Provides highly available datastore
• Supports Go 1.4 at this time
• Soon: Migrate GAE to Managed VMs
https://cloud.google.com/appengine/

GAE DataStore
type Greeting struct {
Author string
Content string
Date time.Time
}

Fetch from DataStore
func root(w http.ResponseWriter, r *http.Request) {
c := appengine.NewContext(r)
q := datastore.NewQuery("Greeting").
Ancestor(guestbookKey(c)).Order("-Date").Limit(10)
greetings := make([]Greeting, 0, 10)
if _, err := q.GetAll(c, &greetings); err != nil {
http.Error(w, err.Error(),500)
return
}
}

GAE Example
https://github.com/GoogleCloudPlatform/appen
gine-guestbook-go
Shows session handling, data storage,
authentication and more

Other Resources
Building Web Apps with Go – by codegangtsa
http://bit.ly/WebAppsWithGo
Google Cloud Platform - Go
http://bit.ly/GoGoogleCloud

Deployed To GAE
SMS Voting Application for CSS Dev Conf
• Takes votes via SMS (Twilio) and stores
them in GAE Datastore
• Outputs them as CSV

Deployed to GAE
OthrNumbr
• Burner Numbers for
texting with strangers
• Written in Go, Deployed
on App Engine
• Users Datastore,
memcache, Twilio, Stripe
http://othrnumbr.com/

@andrewwatson
http://about.me/andrewwatson
Thank You

Kitty wants to learn concurrency

Concurrency in Go
• In Go, concurrency is accomplished by
passing shared values around on channels
• Not by sharing memory between threads

Repeat After Me
“Do not communicate by sharing
memory; instead, share memory by
communicating.”

Concurrent Routines
Created by putting “go” in front of function calls
func Announce(message string, delay time.Duration) {
go func() {
time.Sleep(delay)
fmt.Println(message)
}() // Note the parentheses - must call the function.
}
https://golang.org/doc/effective_go.html#concurrency

Channels
Go has a built in primitive types for
communicating between goroutines
c := make(chan int) // Allocate a channel.
// Start the sort in a goroutine; when it completes, signal on the channel.
go func() {
list.Sort()
c <- 1 // Send a signal; value does not matter.
}()
doSomethingForAWhile()
<-c // Wait for sort to finish; discard sent value.

Channels
• Can be buffered or unbuffered
• Can be declared to carry any other type,
even channels!

Concurrency in Go
The essential guides:
http://bit.ly/ConcurrentGo
http://bit.ly/AdvancedGoConcurrency

How to Build Your First Web App in Go

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