HTTP/2, full json support and a great networking stack, all that is part of Go’s standard library. Just like everything else you need for a smashing web application. You can run your Go application on AWS Lambda, any operating system or in your browser with WebAssembly thanks to Go’s extreme portability. You will learn the basics of web development with Go very hands on and with just the standard library of Go. Along the way we will touch essential tooling and dev setup. By then building a REST API or simple server rendered frontend is a piece of cake. And let us not forget to properly test the bastard, before putting it out in the wild.

1. GO WEB
DEVELOPMENT 101

2. 3 MONTHS to be productive
74% write API SERVICES
45% write WEB APPS
*
Go Developer Survey 2020 Results

4. HELLO GOPHER
package main
import "fmt"
func main() {
fmt.Println("Hello Gopher!")
}
Run Code
go build hellogopher.go // 1. Compile code
./hellogopher // 2. Run binary
go run hellogopher.go // Compile code + run binary

5. DEVELOPMENT
JetBrains
GoLand
Visual
Studio Code
Vim Go

6. 5 FACTS ABOUT GO
1 static type system
2 garbage collection
3 no inheritance
4 built-in concurrency
5 native execution
Linux,
Win, z/OS, 386, amd64, ARM, wasm, ...

7. VARIABLES, SLICES, LOOPS
// Variable
var kitty string = "Kitty"
bella := "Bella"
1
2
3
4
// Array (fixed length)
5
namesArray := [3]string{kitty, bella, "Cleo"}
6
7
// Slice (variable length)
8
namesSlice := make([]string, 2)
9
namesSlice[0] = kitty
10
11
// Loop
12
for i, name := range namesSlice {
13
fmt.Println("Hello " + name + "!")
14
}
15
// Array (fixed length)
namesArray := [3]string{kitty, bella, "Cleo"}
// Variable
1
var kitty string = "Kitty"
2
bella := "Bella"
3
4
5
6
7
// Slice (variable length)
8
namesSlice := make([]string, 2)
9
namesSlice[0] = kitty
10
11
// Loop
12
for i, name := range namesSlice {
13
fmt.Println("Hello " + name + "!")
14
}
15
// Slice (variable length)
namesSlice := make([]string, 2)
namesSlice[0] = kitty
// Variable
1
var kitty string = "Kitty"
2
bella := "Bella"
3
4
// Array (fixed length)
5
namesArray := [3]string{kitty, bella, "Cleo"}
6
7
8
9
10
11
// Loop
12
for i, name := range namesSlice {
13
fmt.Println("Hello " + name + "!")
14
}
15
// Loop
for i, name := range namesSlice {
fmt.Println("Hello " + name + "!")
}
// Variable
1
var kitty string = "Kitty"
2
bella := "Bella"
3
4
// Array (fixed length)
5
namesArray := [3]string{kitty, bella, "Cleo"}
6
7
// Slice (variable length)
8
namesSlice := make([]string, 2)
9
namesSlice[0] = kitty
10
11
12
13
14
15

8. STRUCT
type Cat struct {
Name string
}
1
2
3
4
func main() {
5
c := Cat{Name: "Kitty"}
6
fmt.Println("Hello " + c.Name + "!")
7
}
8
c := Cat{Name: "Kitty"}
fmt.Println("Hello " + c.Name + "!")
type Cat struct {
1
Name string
2
}
3
4
func main() {
5
6
7
}
8
type Cat struct {
Name string
}
func main() {
c := Cat{Name: "Kitty"}
fmt.Println("Hello " + c.Name + "!")
}
1
2
3
4
5
6
7
8

9. ERRORS
// Error as return value
func (c Cat) feed(food string) error {
if c.Name == "Kitty" && food != "Steak Tartare" {
return errors.New("Won't eat!")
}
return nil
}
1
2
3
4
5
6
7
8
func main() {
9
c := Cat{Name: "Kitty"}
10
11
// Handle error
12
err := c.feed("Caviar")
13
if err != nil {
14
fmt.Printf("%v won't eat it.", c.Name)
15
}
16
}
17
// Handle error
err := c.feed("Caviar")
if err != nil {
fmt.Printf("%v won't eat it.", c.Name)
}
}
// Error as return value
1
func (c Cat) feed(food string) error {
2
if c.Name == "Kitty" && food != "Steak Tartare" {
3
return errors.New("Won't eat!")
4
}
5
return nil
6
}
7
8
func main() {
9
c := Cat{Name: "Kitty"}
10
11
12
13
14
15
16
17

10. THE CATS APP

12. CATS APP
API

13. SET UP CATS APP
# Create directory
mkdir cats
cd cats
# Enable dependency tracking
go mod init goday.com/cats
# Create go file
touch main.go

14. CAT API SIMPLE
func main() {
http.HandleFunc("/api/cats", catAPIHandler)
http.ListenAndServe(":8080", nil)
}
func catAPIHandler(w http.ResponseWriter, r *http.Request)
1
fmt.Fprintf(w, "Meow!")
2
w.WriteHeader(http.StatusOK)
3
}
4
5
6
7
8
9
func catAPIHandler(w http.ResponseWriter, r *http.Request)
fmt.Fprintf(w, "Meow!")
w.WriteHeader(http.StatusOK)
}
1
2
3
4
5
func main() {
6
http.HandleFunc("/api/cats", catAPIHandler)
7
http.ListenAndServe(":8080", nil)
8
}
9

15. CAT API WITH JSON
func catAPIHandler(w http.ResponseWriter, r *http.Request) {
cats := make([]Cat, 1)
cats[0] = Cat{Name: "Ginger"}
json.NewEncoder(w).Encode(c)
type Cat struct {
1
Name string
2
}
3
4
5
6
7
8
}
9
10
func main() {
11
http.HandleFunc("/api/cats", catAPIHandler)
12
http.ListenAndServe(":8080", nil)
13
}
14
type Cat struct {
Name string
}
1
2
3
4
func catAPIHandler(w http.ResponseWriter, r *http.Request) {
5
cats := make([]Cat, 1)
6
cats[0] = Cat{Name: "Ginger"}
7
json.NewEncoder(w).Encode(c)
8
}
9
10
func main() {
11
http.HandleFunc("/api/cats", catAPIHandler)
12
http.ListenAndServe(":8080", nil)
13
}
14
type Cat struct {
Name string
}
func catAPIHandler(w http.ResponseWriter, r *http.Request) {
cats := make([]Cat, 1)
cats[0] = Cat{Name: "Ginger"}
json.NewEncoder(w).Encode(c)
1
2
3
4
5
6
7
8
}
9
10
func main() {
11
http.HandleFunc("/api/cats", catAPIHandler)
12
http.ListenAndServe(":8080", nil)
13
}
14
type Cat struct {
Name string
}
func catAPIHandler(w http.ResponseWriter, r *http.Request) {
cats := make([]Cat, 1)
cats[0] = Cat{Name: "Ginger"}
json.NewEncoder(w).Encode(c)
}
func main() {
http.HandleFunc("/api/cats", catAPIHandler)
http.ListenAndServe(":8080", nil)
1
2
3
4
5
6
7
8
9
10
11
12
13
}
14

16. CAT API WITH JSON
# Query cat API
curl -s http://localhost:8080/api/cats | jq
1
2
[
3
{
4
"Name": "Ginger"
5
}
6
]
7
[
{
"Name": "Ginger"
}
]
# Query cat API
1
curl -s http://localhost:8080/api/cats | jq
2
3
4
5
6
7

17. CAT API WITH JSON
type Cat struct {
Name string
}
func catAPIHandler(w http.ResponseWriter, r *http.Request) {
cats := make([]Cat, 1)
cats[0] = Cat{Name: "Ginger"}
json.NewEncoder(w).Encode(cats)
1
2 `json:"name"`
3
4
5
6
7
8
}
9
10
func main() {
11
http.HandleFunc("/api/cats", catAPIHandler)
12
http.ListenAndServe(":8080", nil)
13
}
14

18. TEST CAT API cat_api_test.go
func TestCatAPIHandler(t *testing.T) {
}
1
// 1. Create test request
2
req, _ := http.NewRequest("GET", "/api/cats", nil)
3
4
// 2. Create recorder (which satisfies http.ResponseWriter)
5
recorder := httptest.NewRecorder()
6
7
// 3. Invoke handler
8
catAPIHandler(recorder, req)
9
10
// 4. Check the response
11
if recorder.Code != http.StatusOK {
12
t.Errorf("Wrong status: got %v expected %v", recorder.Code, http.Sta
13
}
14
15
// 1. Create test request
req, _ := http.NewRequest("GET", "/api/cats", nil)
func TestCatAPIHandler(t *testing.T) {
1
2
3
4
// 2. Create recorder (which satisfies http.ResponseWriter)
5
recorder := httptest.NewRecorder()
6
7
// 3. Invoke handler
8
catAPIHandler(recorder, req)
9
10
// 4. Check the response
11
if recorder.Code != http.StatusOK {
12
t.Errorf("Wrong status: got %v expected %v", recorder.Code, http.Sta
13
}
14
}
15
// 2. Create recorder (which satisfies http.ResponseWriter)
recorder := httptest.NewRecorder()
func TestCatAPIHandler(t *testing.T) {
1
// 1. Create test request
2
req, _ := http.NewRequest("GET", "/api/cats", nil)
3
4
5
6
7
// 3. Invoke handler
8
catAPIHandler(recorder, req)
9
10
// 4. Check the response
11
if recorder.Code != http.StatusOK {
12
t.Errorf("Wrong status: got %v expected %v", recorder.Code, http.Sta
13
}
14
}
15
// 3. Invoke handler
catAPIHandler(recorder, req)
func TestCatAPIHandler(t *testing.T) {
1
// 1. Create test request
2
req, _ := http.NewRequest("GET", "/api/cats", nil)
3
4
// 2. Create recorder (which satisfies http.ResponseWriter)
5
recorder := httptest.NewRecorder()
6
7
8
9
10
// 4. Check the response
11
if recorder.Code != http.StatusOK {
12
t.Errorf("Wrong status: got %v expected %v", recorder.Code, http.Sta
13
}
14
}
15
// 4. Check the response
if recorder.Code != http.StatusOK {
t.Errorf("Wrong status: got %v expected %v", recorder.Code, http.Sta
}
func TestCatAPIHandler(t *testing.T) {
1
// 1. Create test request
2
req, _ := http.NewRequest("GET", "/api/cats", nil)
3
4
// 2. Create recorder (which satisfies http.ResponseWriter)
5
recorder := httptest.NewRecorder()
6
7
// 3. Invoke handler
8
catAPIHandler(recorder, req)
9
10
11
12
13
14
}
15
func TestCatAPIHandler(t *testing.T) {
// 1. Create test request
req, _ := http.NewRequest("GET", "/api/cats", nil)
// 2. Create recorder (which satisfies http.ResponseWriter)
recorder := httptest.NewRecorder()
// 3. Invoke handler
catAPIHandler(recorder, req)
// 4. Check the response
if recorder.Code != http.StatusOK {
t.Errorf("Wrong status: got %v expected %v", recorder.Code, http.Sta
}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

19. RUN TEST
# Run tests
go test -v ./...
1
2
=== RUN TestCatAPIHandler
3
--- PASS: TestCatAPIHandler (0.00s)
4
PASS
5
coverage: 50.0% of statements
6
ok devopscon.com/cats 0.127s coverage: 50.0% of stateme
7
=== RUN TestCatAPIHandler
--- PASS: TestCatAPIHandler (0.00s)
PASS
coverage: 50.0% of statements
ok devopscon.com/cats 0.127s coverage: 50.0% of statem
# Run tests
1
go test -v ./...
2
3
4
5
6
7

20. BUILD WITH Makefile
build:
go build -o dist/"${BIN_FILE}"
.DEFAULT_GOAL := build
1
BIN_FILE=cats
2
3
4
5
6
test:
7
go test -v ./...
8
9
run:
10
./"${BIN_FILE}"
11
12
clean:
13
go clean
14
test:
go test -v ./...
.DEFAULT_GOAL := build
1
BIN_FILE=cats
2
3
build:
4
go build -o dist/"${BIN_FILE}"
5
6
7
8
9
run:
10
./"${BIN_FILE}"
11
12
clean:
13
go clean
14
run:
./"${BIN_FILE}"
.DEFAULT_GOAL := build
1
BIN_FILE=cats
2
3
build:
4
go build -o dist/"${BIN_FILE}"
5
6
test:
7
go test -v ./...
8
9
10
11
12
clean:
13
go clean
14
clean:
go clean
.DEFAULT_GOAL := build
1
BIN_FILE=cats
2
3
build:
4
go build -o dist/"${BIN_FILE}"
5
6
test:
7
go test -v ./...
8
9
run:
10
./"${BIN_FILE}"
11
12
13
14
.DEFAULT_GOAL := build
BIN_FILE=cats
build:
go build -o dist/"${BIN_FILE}"
test:
go test -v ./...
run:
./"${BIN_FILE}"
clean:
go clean
1
2
3
4
5
6
7
8
9
10
11
12
13
14

21. DEMO

22. CATS APP
WEB

23. CATS HANDLER BASIC TEMPLATE SETUP
func indexHandler(w http.ResponseWriter, r *http.Request) {
var tpl = template.Must(template.ParseFiles("index.html"))
tpl.Execute(w, nil)
1
2
3
}
4
5
func main() {
6
http.HandleFunc("/", indexHandler)
7
http.ListenAndServe(":8080", nil)
8
}
9
func indexHandler(w http.ResponseWriter, r *http.Request) {
var tpl = template.Must(template.ParseFiles("index.html"))
tpl.Execute(w, nil)
}
func main() {
http.HandleFunc("/", indexHandler)
http.ListenAndServe(":8080", nil)
}
1
2
3
4
5
6
7
8
9
func indexHandler(w http.ResponseWriter, r *http.Request) {
var tpl = template.Must(template.ParseFiles("index.html"))
tpl.Execute(w, nil)
}
func main() {
http.HandleFunc("/", indexHandler)
http.ListenAndServe(":8080", nil)
}
1
2
3
4
5
6
7
8
9

24. CATS HANDLER WITH MULTIPLEXER
mux := http.NewServeMux()
mux.HandleFunc("/", indexHandler)
func indexHandler(w http.ResponseWriter, r *http.Request) {
1
var tpl = template.Must(template.ParseFiles("index.html"))
2
tpl.Execute(w, nil)
3
}
4
5
func main() {
6
7
8
9
http.ListenAndServe(":8080", mux)
10
}
11
http.ListenAndServe(":8080", mux)
func indexHandler(w http.ResponseWriter, r *http.Request) {
1
var tpl = template.Must(template.ParseFiles("index.html"))
2
tpl.Execute(w, nil)
3
}
4
5
func main() {
6
mux := http.NewServeMux()
7
mux.HandleFunc("/", indexHandler)
8
9
10
}
11
func indexHandler(w http.ResponseWriter, r *http.Request) {
var tpl = template.Must(template.ParseFiles("index.html"))
tpl.Execute(w, nil)
}
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/", indexHandler)
http.ListenAndServe(":8080", mux)
}
1
2
3
4
5
6
7
8
9
10
11

25. SERVE FILES FROM FILESYSTEM
// Serve files
fs := http.FileServer(http.Dir("assets"))
mux.Handle("/assets/", http.StripPrefix("/assets/", fs))
func main() {
1
mux := http.NewServeMux()
2
mux.HandleFunc("/", indexHandler)
3
4
5
6
7
8
http.ListenAndServe(":8080", mux)
9
}
10

26. SERVE FILES EMBEDDED IN BINARY
// Serve files
mux.Handle("/assets/", http.FileServer(http.FS(assets)))
//go:embed assets
1
var assets embed.FS
2
3
func main() {
4
mux := http.NewServeMux()
5
mux.HandleFunc("/", indexHandler)
6
7
8
9
10
http.ListenAndServe(":8080", mux)
11
}
12
//go:embed assets
var assets embed.FS
// Serve files
mux.Handle("/assets/", http.FileServer(http.FS(assets)))
1
2
3
func main() {
4
mux := http.NewServeMux()
5
mux.HandleFunc("/", indexHandler)
6
7
8
9
10
http.ListenAndServe(":8080", mux)
11
}
12
mux.HandleFunc("/", indexHandler)
mux.Handle("/assets/", http.FileServer(http.FS(assets)))
//go:embed assets
1
var assets embed.FS
2
3
func main() {
4
mux := http.NewServeMux()
5
6
7
// Serve files
8
9
10
http.ListenAndServe(":8080", mux)
11
}
12

27. HANDLER AND HANDLEFUNC

28. CATS HANDLER TEMPLATE WITH DATA
main.go
type Cat struct {
Name string
}
func indexHandler(w ResponseWriter, r *Request) {
// Create cat slice
cat := make([]Cat, 1)
// Add cat ginger
cat[0] = Cat{Name: "Ginger"}
// Render template
tpl.Execute(w, cat)
}
index.html
<body>
<h1>Cats App</h1>
{{ range. }}
<h2>{{ .Name }}</h2>
{{ end }}
</body>

30. CATS HANDLER WITH CATS API
Query Cats API
GET https://api.thecatapi.com/v1/breeds?limit=5
[
{
"id": "abys",
"name": "Abyssinian",
"image": {
"url": "https://cdn2.thecatapi.com/images/0XYvRd7oD.jpg
}
},
{
"id": "aege",
"name": "Aegean",
"image": {
"url": "https://cdn2.thecatapi.com/images/ozEvzdVM-.jpg
}
},
...
]
Map JSON
type Cat struct {
ID string `json:"id"`
Name string `json:"name"`
Image struct {
URL string `json:"url"`
} `json:"image"`
}

32. CATS HANDLER WITH CATS API
resp, err := http.Get("https://api.thecatapi.com/v1/breeds?limit=5")
if err != nil {
http.Error(w, "Cats API error", http.StatusInternalServerError)
return
}
func indexHandler(w http.ResponseWriter, r *http.Request) {
1
2
3
4
5
6
7
// Create cat slice
8
cat := make([]Cat, 5)
9
10
// Read and parse body
11
defer resp.Body.Close()
12
body, _ := ioutil.ReadAll(resp.Body)
13
json.Unmarshal(body, &cat)
14
15
tpl.Execute(w, cat)
16
}
17
// Create cat slice
cat := make([]Cat, 5)
func indexHandler(w http.ResponseWriter, r *http.Request) {
1
resp, err := http.Get("https://api.thecatapi.com/v1/breeds?limit=5")
2
if err != nil {
3
http.Error(w, "Cats API error", http.StatusInternalServerError)
4
return
5
}
6
7
8
9
10
// Read and parse body
11
defer resp.Body.Close()
12
body, _ := ioutil.ReadAll(resp.Body)
13
json.Unmarshal(body, &cat)
14
15
tpl.Execute(w, cat)
16
}
17
// Read and parse body
defer resp.Body.Close()
body, _ := ioutil.ReadAll(resp.Body)
json.Unmarshal(body, &cat)
func indexHandler(w http.ResponseWriter, r *http.Request) {
1
resp, err := http.Get("https://api.thecatapi.com/v1/breeds?limit=5")
2
if err != nil {
3
http.Error(w, "Cats API error", http.StatusInternalServerError)
4
return
5
}
6
7
// Create cat slice
8
cat := make([]Cat, 5)
9
10
11
12
13
14
15
tpl.Execute(w, cat)
16
}
17
func indexHandler(w http.ResponseWriter, r *http.Request) {
resp, err := http.Get("https://api.thecatapi.com/v1/breeds?limit=5")
if err != nil {
http.Error(w, "Cats API error", http.StatusInternalServerError)
return
}
// Create cat slice
cat := make([]Cat, 5)
// Read and parse body
defer resp.Body.Close()
body, _ := ioutil.ReadAll(resp.Body)
json.Unmarshal(body, &cat)
tpl.Execute(w, cat)
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

33. MIDDLEWARE
cross cutting functionality for all requests
(e.g. logging, authentication)
#
create a chain of handlers
router => middleware handler => application handler
#
satisfy the interface http.Handler
#

34. MIDDLEWARE TO LOG REQUESTS
http.ListenAndServe(":8080", loggingMiddleware(mux))
func loggingMiddleware(next http.Handler) http.Handler {
1
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Reque
2
log.Printf("%v requested URL %v", r.Host, r.URL)
3
next.ServeHTTP(w, r)
4
})
5
}
6
7
func main() {
8
mux := http.NewServeMux()
9
mux.HandleFunc("/", indexHandler)
10
11
12
}
13
func loggingMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Reque
log.Printf("%v requested URL %v", r.Host, r.URL)
next.ServeHTTP(w, r)
})
}
1
2
3
4
5
6
7
func main() {
8
mux := http.NewServeMux()
9
mux.HandleFunc("/", indexHandler)
10
11
http.ListenAndServe(":8080", loggingMiddleware(mux))
12
}
13
func loggingMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Reque
log.Printf("%v requested URL %v", r.Host, r.URL)
next.ServeHTTP(w, r)
})
}
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/", indexHandler)
http.ListenAndServe(":8080", loggingMiddleware(mux))
1
2
3
4
5
6
7
8
9
10
11
12
}
13

35. DEMO

36. BASICS
Dev Setup
Variables,
Slices, Loops
Struct
Errors
#
#
#
#
CATS APP
API
Handler (with
JSON)
Http Test
Build
#
#
#
CATS APP
WEB
Multiplexer
(Router)
File Server
Template
Middleware
#
#
#
#

38. JAN STAMER
Solution Architect
jan.stamer@comdirect.de