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【解答】Go言語 初心者向けハンズオン

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※これは解答です。どうしても課題が解けない場合、ご利用ください。

練習問題 #1: FizzBuzz APIを作ろう

package main

import (
    "fmt"
    "log"
    "net/http"
    "strconv"

    "github.com/julienschmidt/httprouter"
)

func FizzBuzz(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    num, err := strconv.Atoi(p.ByName("num"))
    if err != nil || num < 1 {
        http.Error(w, fmt.Sprintf("%d Bad Request", http.StatusBadRequest), http.StatusBadRequest)
        return
    }

    var str string
    for i := 1; i <= num; i++ {
        if i%15 == 0 {
            str += fmt.Sprintf("%d: %s\n", i, "FizzBuzz!")
        } else if i%5 == 0 {
            str += fmt.Sprintf("%d: %s\n", i, "Buzz")
        } else if i%3 == 0 {
            str += fmt.Sprintf("%d: %s\n", i, "Fizz")
        } else {
            str += fmt.Sprintf("%d:\n", i)
        }
    }
    fmt.Fprintf(w, str)
}

func main() {
    router := httprouter.New()
    router.GET("/FizzBuzz/:num", FizzBuzz)

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        log.Fatal(err)
    }
}

練習問題 #2: プロフィール取得APIを作ろう

package main

import (
    "encoding/json"
    "fmt"
    "log"
    "net/http"

    "github.com/julienschmidt/httprouter"
)

type Profile struct {
    Name          string   `json:"name"`
    Age           int      `json:"age"`
    Gender        string   `json:"gender"`
    FavoriteFoods []string `json:"favorite_foods"`
}

var bob Profile = Profile{
    Name:          "Bob",
    Age:           25,
    Gender:        "Man",
    FavoriteFoods: []string{"Hamburger", "Cookie", "Chocolate"},
}

var alice Profile = Profile{
    Name:          "Alice",
    Age:           24,
    Gender:        "Woman",
    FavoriteFoods: []string{"Apple", "Orange", "Melon"},
}

func GetProfile(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    name := p.ByName("name")

    var resProfile Profile
    if name == "Bob" {
        resProfile = bob
    } else if name == "Alice" {
        resProfile = alice
    } else {
        http.Error(w, fmt.Sprintf("%d Not Found", http.StatusNotFound), http.StatusNotFound)
        return
    }

    bytes, err := json.Marshal(resProfile)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
    }
    fmt.Fprintf(w, string(bytes))
}

func main() {
    router := httprouter.New()
    router.GET("/Profile/:name", GetProfile)

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        log.Fatal(err)
    }
}

練習問題 #3: プロフィール保存APIを作ろう

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"

    "github.com/julienschmidt/httprouter"
)

type Profile struct {
    Name          string   `json:"name"`
    Age           int      `json:"age"`
    Gender        string   `json:"gender"`
    FavoriteFoods []string `json:"favorite_foods"`
}

var savedProfiles map[string]Profile = map[string]Profile{}

func PostProfile(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    defer r.Body.Close()
    body, err := ioutil.ReadAll(r.Body)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    var reqProfile Profile
    err = json.Unmarshal(body, &reqProfile)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    if reqProfile.Name == "" {
        http.Error(w, "name is required.", http.StatusBadRequest)
        return
    }

    savedProfiles[reqProfile.Name] = reqProfile
    fmt.Fprintf(w, fmt.Sprintf("%d Created", http.StatusCreated))
}

func main() {
    router := httprouter.New()
    router.POST("/Profile", PostProfile)

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        log.Fatal(err)
    }
}

練習問題 #4: プロフィール取得APIを拡張しよう

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"

    "github.com/julienschmidt/httprouter"
)

type Profile struct {
    Name          string   `json:"name"`
    Age           int      `json:"age"`
    Gender        string   `json:"gender"`
    FavoriteFoods []string `json:"favorite_foods"`
}

var savedProfiles map[string]Profile = map[string]Profile{}

func PostProfile(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    defer r.Body.Close()
    body, err := ioutil.ReadAll(r.Body)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    var reqProfile Profile
    err = json.Unmarshal(body, &reqProfile)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    if reqProfile.Name == "" {
        http.Error(w, "name is required.", http.StatusBadRequest)
        return
    }

    savedProfiles[reqProfile.Name] = reqProfile
    fmt.Fprintf(w, fmt.Sprintf("%d Created", http.StatusCreated))
}

func GetProfile(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    name := p.ByName("name")
    resProfile, found := savedProfiles[name]

    if !found {
        http.Error(w, fmt.Sprintf("%d Not Found", http.StatusNotFound), http.StatusNotFound)
        return
    }

    bytes, err := json.Marshal(resProfile)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
    }
    fmt.Fprintf(w, string(bytes))
}

func main() {
    router := httprouter.New()
    router.POST("/Profile", PostProfile)
    router.GET("/Profile/:name", GetProfile)

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        log.Fatal(err)
    }
}

練習問題 #5: APIクライアントを作ろう

get_client.go

package main

import (
    "flag"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
)

func main() {
    name := flag.String("name", "", "Name")
    flag.Parse()
    resp, err := http.Get(fmt.Sprintf("http://localhost:8080/Profile/%s", *name))
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    bytes, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(string(bytes))
}

post_client.go

package main

import (
    "bytes"
    "encoding/json"
    "flag"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "strings"
)

type Profile struct {
    Name          string   `json:"name"`
    Age           int      `json:"age"`
    Gender        string   `json:"gender"`
    FavoriteFoods []string `json:"favorite_foods"`
}

func main() {
    profile := parseArgs()
    fmt.Printf("%+v\n", profile)

    jsonStr, err := json.Marshal(profile)
    if err != nil {
        log.Fatal(err)
    }

    req, err := http.NewRequest("POST", "http://localhost:8080/Profile", bytes.NewBuffer([]byte(jsonStr)))
    if err != nil {
        log.Fatal(err)
    }

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()
    body, err := ioutil.ReadAll(resp.Body)

    fmt.Println(string(body))
}

func parseArgs() Profile {
    name := flag.String("name", "", "Name")
    age := flag.Int("age", 0, "Age")
    gender := flag.String("gender", "", "Gender")
    foods := flag.String("foods", "", "Favorite foods")
    flag.Parse()

    return Profile{
        Name:          *name,
        Age:           *age,
        Gender:        *gender,
        FavoriteFoods: strings.Split(*foods, " "),
    }
}

練習問題 #6: HTMLを返そう

index.html.tpl

<html>
<body>
    <h1>Hello golang!</h1>
    <div><a href="/profile/Alice">Alice</a></div>
    <div><a href="/profile/Bob">Bob</a></div>
</body>
</html>

profile.html.tpl

<html>
<body>
    <h1>Hello golang!</h1>

    <div>Name: {{ .Name }}</div>
    <div>Age: {{ .Age }}</div>
    <div>Gender: {{ .Gender }}</div>
    <div>Favorite Foods: {{ .FavoriteFoods }}</div>
</body>
</html>

html_server.go

package main

import (
    "fmt"
    "html/template"
    "log"
    "net/http"

    "github.com/julienschmidt/httprouter"
)

type Profile struct {
    Name          string   `json:"name"`
    Age           int      `json:"age"`
    Gender        string   `json:"gender"`
    FavoriteFoods []string `json:"favorite_foods"`
}

var bob Profile = Profile{
    Name:          "Bob",
    Age:           25,
    Gender:        "Man",
    FavoriteFoods: []string{"Hamburger", "Cookie", "Chocolate"},
}

var alice Profile = Profile{
    Name:          "Alice",
    Age:           24,
    Gender:        "Woman",
    FavoriteFoods: []string{"Apple", "Orange", "Melon"},
}

func Index(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    t := template.Must(template.ParseFiles("templates/index.html.tpl"))
    err := t.ExecuteTemplate(w, "index.html.tpl", nil)
    if err != nil {
        log.Fatal(err)
    }
}

func GetProfile(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    name := p.ByName("name")

    var resProfile Profile
    if name == "Bob" {
        resProfile = bob
    } else if name == "Alice" {
        resProfile = alice
    } else {
        http.Error(w, fmt.Sprintf("%d Not Found", http.StatusNotFound), http.StatusNotFound)
        return
    }

    t := template.Must(template.ParseFiles("templates/profile.html.tpl"))
    err := t.ExecuteTemplate(w, "profile.html.tpl", resProfile)
    if err != nil {
        log.Fatal(err)
    }
}

func main() {
    router := httprouter.New()
    router.GET("/", Index)
    router.GET("/profile/:name", GetProfile)

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        log.Fatal(err)
    }
}
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