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golang 實現一個restful微服務的操作

如何用net/http構建一個簡單的web服務

Golang提供了簡潔的方法來構建web服務

package main 
import (
    "net/http"
)
 
func HelloResponse(rw http.ResponseWriter, request *http.Request) {
    fmt.Fprintf(w, "Hello world.")
}
 
func main() {
    http.HandleFunc("/", HelloResponse)
    http.ListenAndServe(":3000", nil)
}

其中核心的兩個方法：

func HandleFunc(pattern string, handler func(ResponseWriter, *Request))：HandleFunc注冊一個handler function對應到給定的pattern。

func ListenAndServe(addr string, handler Handler) error：ListenAndServe監聽給定的TCP網絡地址，接著帶上handler調用Serve方法來接收請求。

在go build之后，執行編譯后的文件就能在客戶端看到hello world了

有了web服務，就可以制定小目標了

我認為作為第一版本，不需要復雜的設計，只需要接收到用戶的請求，并且找到對應的handler，執行其邏輯，然后返回JSON響應就好了。

小目標有了，那怎么實現呢？

1.設計用戶如何注冊Controller和Action

據我觀察，一些框架是在Controller里預先設定了GET,POST,PUT等一系列方法，負責接收GET,POST,PUT的HTTP請求。

我認為這樣設計的確有其優勢，因為用戶只需要實現這些方法就好了，但在業務層面也有其劣勢，因為我們沒有辦法保證負責一個頁面或者功能的Controller只接收一個GET請求，如果有2個GET請求，那就需要再建立一個Controller，單單實現其GET方法。

因此我借鑒了PHP社區中Laravel注冊Controller和Action的語法：Get("/", "IndexController@Index")。

用戶只需要定義:

type IndexController struct {
}
 
func (IndexController *IndexController) Index(//params) (//return values) {
}

當然這樣思考后，就給框架帶入了一點動態腳本語言的特性，肯定會用到Golang的reflect庫。

2.設計Path和Controller還有Action的關系容器

我運用了Golang的map，定義了map[string]map[string]map[string]string這樣的數據結構

以["/":["GET":["IndexController":"Get"], "POST":["IndexController":"Post"]], "/foo":["GET":["IndexController":"Foo"]]]舉例：

這個說明了在"/"這個PATH下面，有GET和POST請求，分別對應了IndexController下的Get和Post方法，在"/foo"這個PATH下面，有GET請求，對應IndexController下的Foo方法。

在接受請求時候，如果沒有找到對應的方法，就返回405。

3.如何將注冊了的一系列Method與PATH綁定來接收外部請求

我們可以看到，func HandleFunc(pattern string, handler func(ResponseWriter, *Request))要求的handler類型是func(ResponseWriter, *Request))，這和我們設計的functionfunc (IndexController *IndexController) Index(//params) (//return values) {}有所差距。

這時候我發現由于Golang具備First Class Functions特性，因此我們可以將函數做如下處理：

http.HandleFunc(path, HandleRequest()) 
func HandleRequest() {
    return func(rw http.ResponseWriter, request *http.Request) {
        // do your logic
    }
}

4.和encoding/json說Hi

當我們接收到function的返回值后，我們就需要對結果進行json encode，而encoding/json正是負責這個功能。我用的是json.Marshal():

func Marshal(v interface{}) ([]byte, error): Marshal返回v的encoding結果。

如何使用

package main 
import (
    "net/url"
    "net/http"
    "github.com/ZhenhangTung/GoGym"
)
 
type IndexController struct {
}
 
func (IndexController *IndexController) Index(request map[string]url.Values, headers http.Header) (statusCode int, response interface{}) {
    return 200, map[string]string{"hello": "world"}
}
 
type BarController struct {
}
 
func (*BarController) Bar(request map[string]url.Values, headers http.Header) (statusCode int, response interface{}, responseHeader http.Header) {
    return 200, map[string]string{"GoTo": "Bar"}, http.Header{"Foo": {"Bar", "Baz"}}
}
 
func main() {
    var apiService = GoGym.Prepare()
    apiService.Get("index", "IndexController@Index")
    apiService.Post("bar", "BarController@Bar")
    controllers := []interface{}{IndexController{}}
    apiService.RegisterControllers(controllers)
    apiService.RegisterController(BarController{})
    apiService.Serve(3000)
}

項目完整代碼

package GoGym 
import (
    "encoding/json"
    "fmt"
    "net/http"
    "net/url"
    "reflect"
    "strings"
)
 
const (
    GETMethod     = "GET"
    POSTMethod    = "POST"
    PUTMethod     = "PUT"
    PATCHMethod   = "PATCH"
    DELETEMethod  = "DELETE"
    OPTIONSMethod = "OPTIONS"
)
 
const (
    HTTPMethodNotAllowed = 405
)
 
// APIService for now is the struct for containing controllerRegistry and registeredPathAndController,
// and it is the core service provider
type APIService struct {
    // controllerRegistry is where all registered controllers exist
    controllerRegistry map[string]interface{}
    //registeredPathAndController is a mapping of paths and controllers
    registeredPathAndController map[string]map[string]map[string]string
    requestForm                 map[string]url.Values
}
 
func (api *APIService) Get(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(GETMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Post(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(POSTMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Put(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(PUTMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Patch(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(PATCHMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Options(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(OPTIONSMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Delete(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(DELETEMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
// mappingRequestMethodWithControllerAndActions is a function for mapping request method with controllers
// which containing actions
func (api *APIService) mappingRequestMethodWithControllerAndActions(requestMethod, path, controllerWithActionString string) map[string]map[string]string {
    mappingResult := make(map[string]map[string]string)
    if length := len(api.registeredPathAndController[path]); length > 0 {
        mappingResult = api.registeredPathAndController[path]
    }
    controllerAndActionSlice := strings.Split(controllerWithActionString, "@")
    controller := controllerAndActionSlice[0]
    action := controllerAndActionSlice[1]
    controllerAndActionMap := map[string]string{controller: action}
    mappingResult[requestMethod] = controllerAndActionMap
    return mappingResult
}
 
// HandleRequest is a function to handle http request
func (api *APIService) HandleRequest(controllers map[string]map[string]string) http.HandlerFunc {
    return func(rw http.ResponseWriter, request *http.Request) {
        request.ParseForm()
        method := request.Method
        api.requestForm["query"] = request.Form
        api.requestForm["form"] = request.PostForm
        macthedControllers, ok := controllers[method]
        if !ok {
            rw.WriteHeader(HTTPMethodNotAllowed)
        }
        for k, v := range macthedControllers {
            controllerKey := "*" + k
            controller := api.controllerRegistry[controllerKey]
            in := make([]reflect.Value, 2)
            in[0] = reflect.ValueOf(api.requestForm)
            in[1] = reflect.ValueOf(request.Header)
            returnValues := reflect.ValueOf(controller).MethodByName(v).Call(in)
            statusCode := returnValues[0].Interface()
            intStatusCode := statusCode.(int)
            response := returnValues[1].Interface()
            responseHeaders := http.Header{}
            if len(returnValues) == 3 {
                responseHeaders = returnValues[2].Interface().(http.Header)
            }
            api.JSONResponse(rw, intStatusCode, response, responseHeaders)
        }
    }
}
 
// RegisterHandleFunc is a function registers a handle function to handle request from path
func (api *APIService) RegisterHandleFunc() {
    for k, v := range api.registeredPathAndController {
        path := k
        if !strings.HasPrefix(k, "/") {
            path = fmt.Sprintf("/%v", k)
        }
        http.HandleFunc(path, api.HandleRequest(v))
    }
}
 
// RegisterControllers is a function registers a struct of controllers into controllerRegistry
func (api *APIService) RegisterControllers(controllers []interface{}) {
    for _, v := range controllers {
        api.RegisterController(v)
    }
}
 
// RegisterControllers is a function registers a controller into controllerRegistry
func (api *APIService) RegisterController(controller interface{}) {
    controllerType := getType(controller)
    api.controllerRegistry[controllerType] = controller
}
 
// getType is a function gets the type of value
func getType(value interface{}) string {
    if t := reflect.TypeOf(value); t.Kind() == reflect.Ptr {
        return "*" + t.Elem().Name()
    } else {
        return t.Name()
    }
}
 
// Serve is a function
func (api *APIService) Serve(port int) {
    api.RegisterHandleFunc()
    fullPort := fmt.Sprintf(":%d", port)
    http.ListenAndServe(fullPort, nil)
}
 
// JSONResponse is a function return json response
func (api *APIService) JSONResponse(rw http.ResponseWriter, statusCode int, response interface{}, headers http.Header) {
    for k, v := range headers {
        for _, header := range v {
            rw.Header().Add(k, header)
        }
    }
    rw.Header().Add("Content-Type", "application/json")
    rw.WriteHeader(statusCode)
    rsp, err := json.Marshal(response)
    if err != nil {
        // TODO: logging error
        fmt.Println("JSON err:", err)
    }
    rw.Write(rsp)
}
 
// Prepare is a fucntion prepare the service and return prepared service to the user
func Prepare() *APIService {
    var apiService = new(APIService)
    apiService.controllerRegistry = make(map[string]interface{})
    apiService.registeredPathAndController = make(map[string]map[string]map[string]string)
    apiService.requestForm = make(map[string]url.Values)
    return apiService
}

以上為個人經驗，希望能給大家一個參考，也希望大家多多支持腳本之家。如有錯誤或未考慮完全的地方，望不吝賜教。

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