Building WEB APPS with GO

BuildingWebAppswithGo

TableofContents
Introduction

0

GoMakesThingsSimple

1

Thenet/httppackage

2

CreatingaBasicWebApp

3

Deployment

4

URLRouting

5

Middleware

6

Rendering

7

JSON

7.1

HTMLTemplates

7.2

UsingTherenderpackage

7.3

Testing

8

UnitTesting

8.1

EndtoEndTesting

8.2

Controllers

9

Databases

10

TipsandTricks

11

MovingForward

12

2


BuildingWebAppswithGo

Introduction
WelcometoBuildingWebAppswithGo!Ifyouarereadingthisthenyouhavejuststarted
yourjourneyfromnoobtopro.Noseriously,webprogramminginGoissofunandeasythat
youwon'tevennoticehowmuchinformationyouarelearningalongtheway!
Keepinmindthattherearestillportionsofthisbookthatareincompleteandneedsome
love.ThebeautyofopensourcepublishingisthatIcangiveyouanincompletebookandit
isstillofvaluetoyou.
Beforewegetintoallthenittygrittydetails,let'sstartwithsomegroundrules:

Prerequisites

Tokeepthistutorialsmallandfocused,I'massumingthatyouarepreparedinthefollowing
ways:
1. YouhaveinstalledtheGoProgrammingLanguage.
2. Youhavesetupa GOPATHbyfollowingtheHowtoWriteGoCodetutorial.
3. YouaresomewhatfamiliarwiththebasicsofGo.(TheGoTourisaprettygoodplaceto
start)
4. Youhaveinstalledalltherequiredpackages
5. YouhaveinstalledtheHerokuToolbelt
6. YouhaveaHerokuaccount

RequiredPackages
Forthemostpartwewillbeusingthebuiltinpackagesfromthestandardlibrarytobuildout
ourwebapps.CertainlessonssuchasDatabases,MiddlewareandURLRoutingwillrequire
athirdpartypackage.Hereisalistofallthegopackagesyouwillneedtoinstallbefore
starting:

Introduction

3


BuildingWebAppswithGo

Name

ImportPath

Description

httprouter

github.com/julienschmidt/httprouter

AhighperformanceHTTPrequest
routerthatscaleswell

Negroni

github.com/codegangsta/negroni

IdiomaticHTTPMiddleware

Black
Friday

github.com/russross/blackfriday

amarkdownprocessor

Render

gopkg.in/unrolled/render.v1

EasyrenderingforJSON,XML,and
HTML

SQLite3

github.com/mattn/go-sqlite3

sqlite3driverforgo

Youcaninstall(orupdate)thesepackagesbyrunningthefollowingcommandinyour
console
goget-u<import_path>

Forinstance,ifyouwishtoinstallNegroni,thefollowingcommandwouldbe:
goget-ugithub.com/codegangsta/negroni

Introduction

4


BuildingWebAppswithGo

GoMakesThingsSimple
Ifyouhavebuiltawebapplicationbefore,yousurelyknowthattherearequitealotof
conceptstokeepinyourhead.HTTP,HTML,CSS,JSON,databases,sessions,cookies,
forms,middleware,routingandcontrollersarejustafewamongthemanythingsyourweb
appmayneedtointeractwith.
Whileeachoneofthesethingscanbeimportantinthebuildingofyourwebapplications,not
everyoneofthemisimportantforanygivenapp.Forinstance,awebAPImayjustuse
JSONasitsserializationformat,thusmakingconceptslikeHTMLnotrelevantforthat
particularwebapp.

TheGoWay
TheGocommunityunderstandsthisdilemma.Ratherthanrelyonlarge,heavyweight
frameworksthattrytocoverallthebases,Goprogrammerspullinthebarenecessitiesto
getthejobdone.Thisminimalistapproachtowebprogrammingmaybeoff-puttingatfirst,

buttheresultofthiseffortisamuchsimplerprogramintheend.
Gomakesthingssimple,it'saseasyasthat.Ifwetrainourselvestoalignwiththe"Go
way"ofprogrammingfortheweb,wewillendupwithmoresimple,flexible,and
maintainablewebapplications.

PowerinSimplicity
Aswegothroughtheexercisesinthisbook,Ithinkyouwillbesurprisedbyhowsimple
someoftheseprogramscanbewhilststillaffordingabunchoffunctionality.
WhensittingdowntocraftyourownwebapplicationsinGo,thinkhardaboutthe
componentsandconceptsthatyourappwillbefocusedon,andusejustthosepieces.This
bookwillbecoveringawidearrayofwebtopics,butdonotfeelobligatedtousethemall.In
thewordsofourfriendLonestar,"Takeonlywhatyouneedtosurvive".

GoMakesThingsSimple

5


BuildingWebAppswithGo

GoMakesThingsSimple

6


BuildingWebAppswithGo

Thenet/httpPackage
YouhaveprobablyheardthatGoisfantasticforbuildingwebapplicationsofallshapesand
sizes.Thisispartlyduetothefantasticworkthathasbeenputintomakingthestandard

libraryclean,consistent,andeasytouse.
PerhapsoneofthemostimportantpackagesforanybuddingGowebdeveloperisthe
net/httppackage.ThispackageallowsyoutobuildHTTPserversinGowithitspowerful

compositionalconstructs.Beforewestartcoding,let'sdoanextremelyquickoverviewof
HTTP.

HTTPBasics
Whenwetalkaboutbuildingwebapplications,weusuallymeanthatwearebuildingHTTP
servers.HTTPisaprotocolthatwasoriginallydesignedtotransportHTMLdocumentsfrom
aservertoaclientwebbrowser.Today,HTTPisusedtotransportawholelotmorethan
HTML.

Theimportantthingtonoticeinthisdiagramisthetwopointsofinteractionbetweenthe
ServerandtheBrowser.TheBrowsermakesanHTTPrequestwithsomeinformation,the
ServerthenprocessesthatrequestandreturnsaResponse.

Thenet/httppackage

7


BuildingWebAppswithGo

Thispatternofrequest-responseisoneofthekeyfocalpointsinbuildingwebapplicationsin
Go.Infact,the net/httppackage'smostimportantpieceisthe http.HandlerInterface.

Thehttp.HandlerInterface
AsyoubecomemorefamiliarwithGo,youwillnoticehowmuchofanimpactinterfaces
makeinthedesignofyourprograms.The net/httpinterfaceencapsulatestherequestresponsepatterninonemethod:

typeHandlerinterface{
ServeHTTP(ResponseWriter,*Request)
}

Implementorsofthisinterfaceareexpectedtoinspectandprocessdatacomingfromthe
http.Requestobjectandwriteoutaresponsetothe http.ResponseWriterobject.

The http.ResponseWriterinterfacelookslikethis:
typeResponseWriterinterface{
Header()Header
Write([]byte)(int,error)
WriteHeader(int)
}

ComposingWebServices
Becausemuchofthe net/httppackageisbuiltoffofwelldefinedinterfacetypes,wecan
(andareexpectedto)buildourwebapplicationswithcompositioninmind.Each
http.Handlerimplementationcanbethoughtofasitsownwebserver.

Manypatternscanbefoundinthatsimplebutpowerfulassumption.Throughoutthisbook
wewillcoversomeofthesepatternsandhowwecanusethemtosolverealworld
problems.

Exercise:1LineFileServer
Let'ssolvearealworldproblemin1lineofcode.

Thenet/httppackage

8

BuildingWebAppswithGo

Mostofthetimepeoplejustneedtoservestaticfiles.MaybeyouhaveastaticHTML
landingpageandjustwanttoserveupsomeHTML,images,andCSSandcallitaday.
Sure,youcouldpullinApacheorPython's SimpleHTTPServer,butApacheistoomuchfor
thislittlesiteand SimpleHTTPServeris,well,tooslow.
Wewillbeginbycreatinganewprojectinour GOPATH.
cdGOPATH/src
mkdirfileserver&&cdfileserver

Createamain.gowithourtypicalgoboilerplate.
packagemain
import"net/http"
funcmain(){
}

Allweneedtoimportisthe net/httppackageforthistowork.Rememberthatthisisall
partofthestandardlibraryinGo.
Let'swriteourfileservercode:
http.ListenAndServe(":8080",http.FileServer(http.Dir(".")))

The http.ListenAndServefunctionisusedtostarttheserver,itwillbindtotheaddresswe
gaveit( :8080)andwhenitreceivesanHTTPrequest,itwillhanditofftothe
http.Handlerthatwesupplyasthesecondargument.Inourcaseitisthebuilt-in
http.FileServer.

The http.FileServerfunctionbuildsan http.Handlerthatwillserveanentiredirectoryof
filesandfigureoutwhichfiletoservebasedontherequestpath.WetoldtheFileServerto
servethecurrentworkingdirectorywith http.Dir(".").

Theentireprogramlookslikethis:
packagemain
import"net/http"
funcmain(){
http.ListenAndServe(":8080",http.FileServer(http.Dir(".")))
}

Thenet/httppackage

9


BuildingWebAppswithGo

Let'sbuildandrunourfileserverprogram:
gobuild
./fileserver

Ifwevisit localhost:8080/main.goweshouldseethecontentsofourmain.gofileinourweb
browser.Wecanrunthisprogramfromanydirectoryandservethetreeasastaticfile
server.Allin1lineofGocode.

Thenet/httppackage

10


BuildingWebAppswithGo

CreatingaBasicWebApp

NowthatwearedonegoingoverthebasicsofHTTP,let'screateasimplebutusefulweb
applicationinGo.
Pullingfromourfileserverprogramthatweimplementedlastchapter,wewillimplementa
Markdowngeneratorusingthe github.com/russross/blackfridaypackage.

HTMLForm
Forstarters,wewillneedabasicHTMLformforthemarkdowninput:
<html>
<head>
<linkhref="/css/bootstrap.min.css"rel="stylesheet">
</head>
<body>
<divclass="container">
<divclass="page-title">

MarkdownGenerator

GenerateyourmarkdownwithGo

<hr/>
</div>
<formaction="/markdown"method="POST">
<divclass="form-group">
<textareaclass="form-control"name="body"cols="30"rows="10"></textarea>
</div>
<divclass="form-group">
<inputtype="submit"class="btnbtn-primarypull-right"/>
</div>
</form>
</div>
<scriptsrc="/js/bootstrap.min.js"></script>
</body>
</html>

PutthisHTMLintoafilenamed index.htmlinthe"public"folderofourapplicationandthe
bootstrap.min.cssfrominthe"public/css"folder.Noticethatthe

formmakesanHTTPPOSTtothe"/markdown"endpointofourapplication.Wedon't
actuallyhandlethatrouterightnow,solet'saddit.

CreatingaBasicWebApp

11


BuildingWebAppswithGo

The"/markdown"route
Theprogramtohandlethe'/markdown'routeandservethepublic index.htmlfilelookslike
this:
packagemain
import(
"net/http"
"github.com/russross/blackfriday"
)
funcmain(){
http.HandleFunc("/markdown",GenerateMarkdown)
http.Handle("/",http.FileServer(http.Dir("public")))
http.ListenAndServe(":8080",nil)
}
funcGenerateMarkdown(rwhttp.ResponseWriter,r*http.Request){
markdown:=blackfriday.MarkdownCommon([]byte(r.FormValue("body")))
rw.Write(markdown)

}

Let'sbreakitdownintosmallerpiecestogetabetterideaofwhatisgoingon.
http.HandleFunc("/markdown",GenerateMarkdown)
http.Handle("/",http.FileServer(http.Dir("public")))

Weareusingthe http.HandleFuncand http.Handlemethodstodefinesomesimple
routingforourapplication.Itisimportanttonotethatcalling http.Handleonthe"/"pattern
willactasacatch-allroute,sowedefinethatroutelast. http.FileServerreturnsan
http.Handlersoweuse http.Handletomapapatternstringtoahandler.Thealternative

method, http.HandleFunc,usesan http.HandlerFuncinsteadofan http.Handler.This
maybemoreconvenient,tothinkofhandlingroutesviaafunctioninsteadofanobject.
funcGenerateMarkdown(rwhttp.ResponseWriter,r*http.Request){
markdown:=blackfriday.MarkdownCommon([]byte(r.FormValue("body")))
rw.Write(markdown)
}

OurGenerateMarkdownfunctionimplementsthestandard http.HandlerFuncinterfaceand
rendersHTMLfromaformfieldcontainingmarkdown-formattedtext.Inthiscase,the
contentisretrievedwith r.FormValue("body").Itisverycommontogetinputfromthe

CreatingaBasicWebApp

12


BuildingWebAppswithGo

http.Requestobjectthatthe http.HandlerFuncreceivesasanargument.Someother

examplesofinputarethe r.Header, r.Body,and r.URLmembers.
Wefinalizetherequestbywritingitouttoour http.ResponseWriter.Noticethatwedidn't
explicitlysendaresponsecode.Ifwewriteouttotheresponsewithoutacode,the
net/httppackagewillassumethattheresponseisa 200OK.Thismeansthatif

somethingdidhappentogowrong,weshouldsettheresponsecodeviathe
rw.WriteHeader()method.

http.ListenAndServe(":8080",nil)

Thelastbitofthisprogramstartstheserver,wepass nilasourhandler,whichassumes
thattheHTTPrequestswillbehandledbythe net/httppackagesdefault http.ServeMux,
whichisconfiguredusing http.Handleand http.HandleFunc,respectively.
AndthatisallyouneedtobeabletogeneratemarkdownasaserviceinGo.Itisa
surprisinglysmallamountofcodefortheamountofheavyliftingitdoes.Inthenextchapter
wewilllearnhowtodeploythisapplicationtothewebusingHeroku.

CreatingaBasicWebApp

13


BuildingWebAppswithGo

Deployment
Herokumakesdeployingapplicationseasy.Itisaperfectplatformforsmalltomediumsize
webapplicationsthatarewillingtosacrificealittlebitofflexibilityininfrastructuretogaina
fairlypain-freeenvironmentfordeployingandmaintainingwebapplications.
IamchoosingtodeployourwebapplicationtoHerokuforthesakeofthistutorialbecausein

myexperienceithasbeenthefastestwaytogetawebapplicationupandrunninginno
time.RememberthatthefocusofthistutorialishowtobuildwebapplicationsinGoandnot
gettingcaughtupinallofthedistractionofprovisioning,configuring,deploying,and
maintainingthemachinesthatourGocodewillberunon.

Gettingsetup
Ifyoudon'talreadyhaveaHerokuaccount,signupatid.heroku.com/signup.It'squick,easy
andfree.
ApplicationmanagementandconfigurationisdonethroughtheHerokutoolbelt,whichisa
freecommandlinetoolmaintainedbyHeroku.Wewillbeusingittocreateourapplication
onHeroku.Youcangetitfromtoolbelt.heroku.com.

ChangingtheCode
TomakesuretheapplicationfromourlastchapterwillworkonHeroku,wewillneedtomake
afewchanges.Herokugivesusa PORTenvironmentvariableandexpectsourweb
applicationtobindtoit.Let'sstartbyimportingthe"os"packagesowecangrabthat PORT
environmentvariable:
import(
"net/http"
"os"
"github.com/russross/blackfriday"
)

Next,weneedtograbthe PORTenvironmentvariable,checkifitisset,andifitisweshould
bindtothatinsteadofourhardcodedport(8080).

Deployment

14

BuildingWebAppswithGo

port:=os.Getenv("PORT")
ifport==""{
port="8080"
}

Lastly,wewanttobindtothatportinour http.ListenAndServecall:
http.ListenAndServe(":"+port,nil)

Thefinalcodeshouldlooklikethis:
packagemain
import(
"net/http"
"os"
"github.com/russross/blackfriday"
)
funcmain(){
port:=os.Getenv("PORT")
ifport==""{
port="8080"
}
http.HandleFunc("/markdown",GenerateMarkdown)
http.Handle("/",http.FileServer(http.Dir("public")))
http.ListenAndServe(":"+port,nil)
}
funcGenerateMarkdown(rwhttp.ResponseWriter,r*http.Request){
markdown:=blackfriday.MarkdownCommon([]byte(r.FormValue("body")))
rw.Write(markdown)

}

Configuration
WeneedacouplesmallconfigurationfilestotellHerokuhowitshouldrunourapplication.
Thefirstoneisthe Procfile,whichallowsustodefinewhichprocessesshouldberunfor
ourapplication.Bydefault,Gowillnametheexecutableafterthecontainingdirectoryofyour
mainpackage.Forinstance,ifmywebapplicationlivedin
GOPATH/github.com/codegangsta/bwag/deployment,my Procfilewilllooklikethis:

Deployment

15


BuildingWebAppswithGo

web:deployment

SpecificallytorunGoapplications,weneedtoalsospecifya .godirfiletotellHeroku
whichdirisinfactourpackagedirectory.
deployment

Deployment
Onceallthesethingsinplace,Herokumakesiteasytodeploy.
InitializetheprojectasaGitrepository:
gitinit
gitadd-A
gitcommit-m"InitialCommit"

CreateyourHerokuapplication(specifyingtheGobuildpack):

herokucreate-b />
PushittoHerokuandwatchyourapplicationbedeployed!
gitpushherokumaster

Viewyourapplicationinyourbrowser:
herokuopen

Deployment

16


BuildingWebAppswithGo

URLRouting
Forsomesimpleapplications,thedefault http.ServeMuxcantakeyouprettyfar.Ifyouneed
morepowerinhowyouparseURLendpointsandroutethemtotheproperhandler,youmay
needtopullinathirdpartyroutingframework.Forthistutorial,wewillusethepopular
github.com/julienschmidt/httprouterlibraryasourrouter.
github.com/julienschmidt/httprouterisagreatchoiceforarouterasitisaverysimple

implementationwithoneofthebestperformancebenchmarksoutofallthethirdpartyGo
routers.
Inthisexample,wewillcreatesomeroutingforaRESTfulresourcecalled"posts".Belowwe
definemechanismstoviewindex,show,create,update,destroy,andeditposts.
packagemain
import(
"fmt"
"net/http"
"github.com/julienschmidt/httprouter"

)
funcmain(){
r:=httprouter.New()
r.GET("/",HomeHandler)
//Postscollection
r.GET("/posts",PostsIndexHandler)
r.POST("/posts",PostsCreateHandler)
//Postssingular
r.GET("/posts/:id",PostShowHandler)
r.PUT("/posts/:id",PostUpdateHandler)
r.GET("/posts/:id/edit",PostEditHandler)
fmt.Println("Startingserveron:8080")
http.ListenAndServe(":8080",r)
}
funcHomeHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
fmt.Fprintln(rw,"Home")
}
funcPostsIndexHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
fmt.Fprintln(rw,"postsindex")
}

URLRouting

17


BuildingWebAppswithGo

funcPostsCreateHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
fmt.Fprintln(rw,"postscreate")

}
funcPostShowHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
id:=p.ByName("id")
fmt.Fprintln(rw,"showingpost",id)
}
funcPostUpdateHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
fmt.Fprintln(rw,"postupdate")
}
funcPostDeleteHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
fmt.Fprintln(rw,"postdelete")
}
funcPostEditHandler(rwhttp.ResponseWriter,r*http.Request,phttprouter.Params){
fmt.Fprintln(rw,"postedit")
}

Exercises
1. Explorethedocumentationfor github.com/julienschmidt/httprouter.
2. Findouthowwell github.com/julienschmidt/httprouterplaysnicelywithexisting
http.Handlerslike http.FileServer

3.

httprouterhasaverysimpleinterface.Explorewhatkindofabstractionscanbebuilt

ontopofthisfastroutertomakebuildingthingslikeRESTfulroutingeasier.

URLRouting

18

BuildingWebAppswithGo

Middleware
Ifyouhavesomecodethatneedstoberunforeveryrequest,regardlessoftheroutethatit
willeventuallyendupinvoking,youneedsomewaytostack http.Handlersontopofeach
otherandruntheminsequence.Thisproblemissolvedelegantlythroughmiddleware
packages.Negroniisapopularmiddlewarepackagethatmakesbuildingandstacking
middlewareveryeasywhilekeepingthecomposablenatureoftheGowebecosystemintact.
NegronicomeswithsomedefaultmiddlewaresuchasLogging,ErrorRecovery,andStatic
fileserving.SooutoftheboxNegroniwillprovideyouwithalotofvaluewithoutalotof
overhead.
TheexamplebelowshowshowtouseaNegronistackwiththebuiltinmiddlewareandhow
tocreateyourowncustommiddleware.

Middleware

19


BuildingWebAppswithGo

packagemain
import(
"log"
"net/http"
"github.com/codegangsta/negroni"
)
funcmain(){
//Middlewarestack

n:=negroni.New(
negroni.NewRecovery(),
negroni.HandlerFunc(MyMiddleware),
negroni.NewLogger(),
negroni.NewStatic(http.Dir("public")),
)
n.Run(":8080")
}
funcMyMiddleware(rwhttp.ResponseWriter,r*http.Request,nexthttp.HandlerFunc){
log.Println("Loggingonthewaythere...")
ifr.URL.Query().Get("password")=="secret123"{
next(rw,r)
}else{
http.Error(rw,"NotAuthorized",401)
}
log.Println("Loggingonthewayback...")
}

Exercises
1. ThinkofsomecoolmiddlewareideasandtrytoimplementthemusingNegroni.
2. ExplorehowNegronicanbecomposedwith github.com/gorilla/muxusingthe
http.Handlerinterface.

3. PlaywithcreatingNegronistacksforcertaingroupsofroutesinsteadoftheentire
application.

Middleware

20

BuildingWebAppswithGo

Rendering
Renderingistheprocessoftakingdatafromyourapplicationordatabaseandpresentingit
fortheclient.TheclientcanbeabrowserthatrendersHTML,oritcanbeanother
applicationthatconsumesJSONasitsserializationformat.Inthischapterwewilllearnhow
torenderbothoftheseformatsusingthemethodsthatGoprovidesforusinthestandard
library.

Rendering

21


BuildingWebAppswithGo

JSON
JSONisquicklybecomingtheubiquitousserializationformatforwebAPIs,soitmaybethe
mostrelevantwhenlearninghowtobuildwebappsusingGo.Fortunately,Gomakesit
simpletoworkwithJSON--itisextremelyeasytoturnexistingGostructsintoJSONusing
the encoding/jsonpackagefromthestandardlibrary.
packagemain
import(
"encoding/json"
"net/http"
)
typeBookstruct{
Titlestring`json:"title"`
Authorstring`json:"author"`

}
funcmain(){
http.HandleFunc("/",ShowBooks)
http.ListenAndServe(":8080",nil)
}
funcShowBooks(whttp.ResponseWriter,r*http.Request){
book:=Book{"BuildingWebAppswithGo","JeremySaenz"}
js,err:=json.Marshal(book)
iferr!=nil{
http.Error(w,err.Error(),http.StatusInternalServerError)
return
}
w.Header().Set("Content-Type","application/json")
w.Write(js)
}

Exercises
1. ReadthroughtheJSONAPIdocsandfindouthowtorenameandignorefieldsfor
JSONserialization.
2. Insteadofusingthe json.Marshalmethod,tryusingthe json.EncoderAPI.
3. FigureourhowtoprettyprintJSONwiththe encoding/jsonpackage.

JSON

22


BuildingWebAppswithGo

HTMLTemplates

ServingHTMLisanimportantjobforsomewebapplications.Gohasoneofmyfavorite
templatinglanguagestodate.Notforitsfeatures,butforitssimplicityandoutofthebox
security.RenderingHTMLtemplatesisalmostaseasyasrenderingJSONusingthe
'html/template'packagefromthestandardlibrary.Hereiswhatthesourcecodeforrendering
HTMLtemplateslookslike:
packagemain
import(
"html/template"
"net/http"
"path"
)
typeBookstruct{
Titlestring
Authorstring
}
funcmain(){
http.HandleFunc("/",ShowBooks)
http.ListenAndServe(":8080",nil)
}
funcShowBooks(whttp.ResponseWriter,r*http.Request){
book:=Book{"BuildingWebAppswithGo","JeremySaenz"}
fp:=path.Join("templates","index.html")
tmpl,err:=template.ParseFiles(fp)
iferr!=nil{
http.Error(w,err.Error(),http.StatusInternalServerError)
return
}
iferr:=tmpl.Execute(w,book);err!=nil{
http.Error(w,err.Error(),http.StatusInternalServerError)
}

}

Thisisthefollowingtemplatewewillbeusing.Itshouldbeplacedina
templates/index.htmlfileinthedirectoryyourprogramisrunfrom:

HTMLTemplates

23


BuildingWebAppswithGo

<html>

{{.Title}}

by{{.Author}}

</html>

Exercises
1. Lookthroughthedocsfor text/templateand html/templatepackage.Playwiththe
templatinglanguageabittogetafeelforitsgoals,strengths,andweaknesses.
2. Intheexampleweparsethefilesoneveryrequest,whichcanbealotofperformance
overhead.Experimentwithparsingthefilesatthebeginningofyourprogramand
executingtheminyour http.Handler(hint:makeuseofthe Copy()methodon
html.Template).

3. Experimentwithparsingandusingmultipletemplates.

HTMLTemplates

24

BuildingWebAppswithGo

Usingtherenderpackage
IfyouwantrenderingJSONandHTMLtobeevensimpler,thereisthe
github.com/unrolled/renderpackage.Thispackagewasinspiredbythe martinicontrib/renderpackageandismygotowhenitcomestorenderingdataforpresentationin

mywebapplications.
packagemain
import(
"net/http"
"gopkg.in/unrolled/render.v1"
)
funcmain(){
r:=render.New(render.Options{})
mux:=http.NewServeMux()
mux.HandleFunc("/",func(whttp.ResponseWriter,req*http.Request){
w.Write([]byte("Welcome,visitsubpagesnow."))
})
mux.HandleFunc("/data",func(whttp.ResponseWriter,req*http.Request){
r.Data(w,http.StatusOK,[]byte("Somebinarydatahere."))
})
mux.HandleFunc("/json",func(whttp.ResponseWriter,req*http.Request){
r.JSON(w,http.StatusOK,map[string]string{"hello":"json"})
})
mux.HandleFunc("/html",func(whttp.ResponseWriter,req*http.Request){
//Assumesyouhaveatemplatein./templatescalled"example.tmpl"
//$mkdir-ptemplates&&echo"

Hello{{.}}.

">templates/example.tmpl
r.HTML(w,http.StatusOK,"example",nil)

})
http.ListenAndServe(":8080",mux)
}

Exercises
1. Havefunplayingwithalloftheoptionsavailablewhencalling render.New()
2. Tryusingthe .yieldhelperfunction(withthecurlybraces)andalayoutwithHTML

UsingTherenderpackage

25