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Golang：使用 httprouter 构建 API 服务器

2020-06-10 04:13:26 admin 772

> [https://medium.com/@gauravsingharoy/build-your-first-api-server-with-
> httprouter-in-
> golang-732b7b01f6ab](https://links.jianshu.com/go?to=https%3A%2F%2Fmedium.com%2F%40gauravsingharoy%2Fbuild-
> your-first-api-server-with-httprouter-in-golang-732b7b01f6ab)  
>  作者：Gaurav Singha Roy  
>  译者：oopsguy.com

10 个月前，我成为了一名 Gopher，没有后悔。像许多其他 gopher
一样，我很快发现简单的语言特性对于快速构建快速、可扩展的软件非常有用。当我刚开始学习 Go 时，我正在捣鼓不同的路由器，它可以当做 API
服务器使用。如果你跟我一样有 Rails 背景，你也可能会在构建 Web 框架提供的所有功能方面遇到困难。回到路由器话题，我发现了 3
个是非常有用的好东西： [Gorilla
mux](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgorilla%2Fmux)、[httprouter](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fjulienschmidt%2Fhttprouter)
和 [bone](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgo-
zoo%2Fbone)（按性能从低到高）。即便 bone 的性能最高且有更简单的 handler
签名，但对我来说，它仍然不够成熟，无法应用于生产环境中。因此，我最终使用了 httprouter。在本教程中，我将使用 httprouter 构建一个简单的
REST API 服务器。

如果你想偷懒，只想获取源码，则可以在[这里](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-
tutorial%2Ftree%2Fmaster%2Fpart4)[4]直接克隆我的 github 仓库。

让我们开始吧。首先创建一个基本端点：

package main
    
    import (
        "fmt"
        "log"
        "net/http"
    
        "github.com/julienschmidt/httprouter"
    )
    
    func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
        fmt.Fprint(w, "Welcome!\n")
    }
    
    func main() {
        router := httprouter.New()
        router.GET("/", Index)
    
        log.Fatal(http.ListenAndServe(":8080", router))
    }

在上面的代码段中，`Index` 是一个 handler 函数，需要传入三个参数。之后，该 handler 将在 `main` 函数中被注册到 GET
`/` 路径上。现在编译并运行你的程序，转到 `http:// localhost:8080` 来查看你的 API
服务器。点击[这里](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-
tutorial%2Ftree%2Fmaster%2Fpart1)[1]获取当前代码。

我们可以让 API 变得复杂一点。现在有一个名为 `Book` 的实体，可以把 `ISDN` 字段作为唯一标识。让我们创建更多的
handler，即分表代表着 Index 和 Show 动作的 GET `/books` 和 GET `/books/:isdn`。`main.go`
文件此时如下：

package main
    
    import (
        "encoding/json"
        "fmt"
        "log"
        "net/http"
    
        "github.com/julienschmidt/httprouter"
    )
    
    func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
        fmt.Fprint(w, "Welcome!\n")
    }
    
    type Book struct {
        // The main identifier for the Book. This will be unique.
        ISDN   string `json:"isdn"`
        Title  string `json:"title"`
        Author string `json:"author"`
        Pages  int    `json:"pages"`
    }
    
    type JsonResponse struct {
        // Reserved field to add some meta information to the API response
        Meta interface{} `json:"meta"`
        Data interface{} `json:"data"`
    }
    
    type JsonErrorResponse struct {
        Error *ApiError `json:"error"`
    }
    
    type ApiError struct {
        Status int16  `json:"status"`
        Title  string `json:"title"`
    }
    
    // A map to store the books with the ISDN as the key
    // This acts as the storage in lieu of an actual database
    var bookstore = make(map[string]*Book)
    
    // Handler for the books index action
    // GET /books
    func BookIndex(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
        books := []*Book{}
        for _, book := range bookstore {
            books = append(books, book)
        }
        response := &JsonResponse{Data: &books}
        w.Header().Set("Content-Type", "application/json; charset=UTF-8")
        w.WriteHeader(http.StatusOK)
        if err := json.NewEncoder(w).Encode(response); err != nil {
            panic(err)
        }
    }
    
    // Handler for the books Show action
    // GET /books/:isdn
    func BookShow(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
        isdn := params.ByName("isdn")
        book, ok := bookstore[isdn]
        w.Header().Set("Content-Type", "application/json; charset=UTF-8")
        if !ok {
            // No book with the isdn in the url has been found
            w.WriteHeader(http.StatusNotFound)
            response := JsonErrorResponse{Error: &ApiError{Status: 404, Title: "Record Not Found"}}
            if err := json.NewEncoder(w).Encode(response); err != nil {
                panic(err)
            }
        }
        response := JsonResponse{Data: book}
        if err := json.NewEncoder(w).Encode(response); err != nil {
            panic(err)
        }
    }
    
    func main() {
        router := httprouter.New()
        router.GET("/", Index)
        router.GET("/books", BookIndex)
        router.GET("/books/:isdn", BookShow)
    
        // Create a couple of sample Book entries
        bookstore["123"] = &Book{
            ISDN:   "123",
            Title:  "Silence of the Lambs",
            Author: "Thomas Harris",
            Pages:  367,
        }
    
        bookstore["124"] = &Book{
            ISDN:   "124",
            Title:  "To Kill a Mocking Bird",
            Author: "Harper Lee",
            Pages:  320,
        }
    
        log.Fatal(http.ListenAndServe(":8080", router))
    }

你如果现在尝试请求 `GET https:// localhost:8080/books`，将得到以下响应：

{
        "meta": null,
        "data": [
            {
                "isdn": "123",
                "title": "Silence of the Lambs",
                "author": "Thomas Harris",
                "pages": 367
            },
            {
                "isdn": "124",
                "title": "To Kill a Mocking Bird",
                "author": "Harper Lee",
                "pages": 320
            }
        ]
    }

我们在 `main` 函数中硬编码了这两个 book
实体。点击[这里](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-
tutorial%2Ftree%2Fmaster%2Fpart2)[2]获取当前代码。

让我们来重构一下代码。到目前为止，所有的代码都放置在同一个文件中：`main.go`。我们可以把它们划分移到不同的文件中。此时我们有一个目录：

.
    ├── handlers.go
    ├── main.go
    ├── models.go
    └── responses.go

我们把所有与 `JSON` 响应相关的结构体移动到 `responses.go`，将 handler 函数移动到 `Handlers.go`，将
`Book` 结构体移动到
`models.go`。点击[这里](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-
tutorial%2Ftree%2Fmaster%2Fpart3)[3]查看当前代码。现在，我们跳过来写一些测试。在 Go 中，`*_test.go`
文件是用作测试用途。因此让我们创建一个 `handlers_test.go`。

package main
    
    import (
        "net/http"
        "net/http/httptest"
        "testing"
    
        "github.com/julienschmidt/httprouter"
    )
    
    func TestBookIndex(t *testing.T) {
        // Create an entry of the book to the bookstore map
        testBook := &Book{
            ISDN:   "111",
            Title:  "test title",
            Author: "test author",
            Pages:  42,
        }
        bookstore["111"] = testBook
        // A request with an existing isdn
        req1, err := http.NewRequest("GET", "/books", nil)
        if err != nil {
            t.Fatal(err)
        }
        rr1 := newRequestRecorder(req1, "GET", "/books", BookIndex)
        if rr1.Code != 200 {
            t.Error("Expected response code to be 200")
        }
        // expected response
        er1 := "{\"meta\":null,\"data\":[{\"isdn\":\"111\",\"title\":\"test title\",\"author\":\"test author\",\"pages\":42}]}\n"
        if rr1.Body.String() != er1 {
            t.Error("Response body does not match")
        }
    }
    
    // Mocks a handler and returns a httptest.ResponseRecorder
    func newRequestRecorder(req *http.Request, method string, strPath string, fnHandler func(w http.ResponseWriter, r *http.Request, param httprouter.Params)) *httptest.ResponseRecorder {
        router := httprouter.New()
        router.Handle(method, strPath, fnHandler)
        // We create a ResponseRecorder (which satisfies http.ResponseWriter) to record the response.
        rr := httptest.NewRecorder()
        // Our handlers satisfy http.Handler, so we can call their ServeHTTP method
        // directly and pass in our Request and ResponseRecorder.
        router.ServeHTTP(rr, req)
        return rr
    }

我们使用 `httptest` 包的 Recorder 来 mock handler。同样，你也可以为 handler `BookShow` 编写测试用例。

让我们稍微做些重构。我们仍然把所有路由都定义在了 `main` 函数中，handler 看起来有点臃肿，需要做点
DRY。我们仍然在终端中输出一些日志消息，并且可以添加一个 `BookCreate` handler 来创建一个新的 Book。

首先先解决 `handlers.go`。

package main
    
    import (
        "encoding/json"
        "fmt"
        "io"
        "io/ioutil"
        "net/http"
    
        "github.com/julienschmidt/httprouter"
    )
    
    func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
        fmt.Fprint(w, "Welcome!\n")
    }
    
    // Handler for the books Create action
    // POST /books
    func BookCreate(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
        book := &Book{}
        if err := populateModelFromHandler(w, r, params, book); err != nil {
            writeErrorResponse(w, http.StatusUnprocessableEntity, "Unprocessible Entity")
            return
        }
        bookstore[book.ISDN] = book
        writeOKResponse(w, book)
    }
    
    // Handler for the books index action
    // GET /books
    func BookIndex(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
        books := []*Book{}
        for _, book := range bookstore {
            books = append(books, book)
        }
        writeOKResponse(w, books)
    }
    
    // Handler for the books Show action
    // GET /books/:isdn
    func BookShow(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
        isdn := params.ByName("isdn")
        book, ok := bookstore[isdn]
        if !ok {
            // No book with the isdn in the url has been found
            writeErrorResponse(w, http.StatusNotFound, "Record Not Found")
            return
        }
        writeOKResponse(w, book)
    }
    
    // Writes the response as a standard JSON response with StatusOK
    func writeOKResponse(w http.ResponseWriter, m interface{}) {
        w.Header().Set("Content-Type", "application/json; charset=UTF-8")
        w.WriteHeader(http.StatusOK)
        if err := json.NewEncoder(w).Encode(&JsonResponse{Data: m}); err != nil {
            writeErrorResponse(w, http.StatusInternalServerError, "Internal Server Error")
        }
    }
    
    // Writes the error response as a Standard API JSON response with a response code
    func writeErrorResponse(w http.ResponseWriter, errorCode int, errorMsg string) {
        w.Header().Set("Content-Type", "application/json; charset=UTF-8")
        w.WriteHeader(errorCode)
        json.
            NewEncoder(w).
            Encode(&JsonErrorResponse{Error: &ApiError{Status: errorCode, Title: errorMsg}})
    }
    
    //Populates a model from the params in the Handler
    func populateModelFromHandler(w http.ResponseWriter, r *http.Request, params httprouter.Params, model interface{}) error {
        body, err := ioutil.ReadAll(io.LimitReader(r.Body, 1048576))
        if err != nil {
            return err
        }
        if err := r.Body.Close(); err != nil {
            return err
        }
        if err := json.Unmarshal(body, model); err != nil {
            return err
        }
        return nil
    }

我创建了两个函数，`writeOKResponse` 用于将 `StatusOK` 写入响应，其返回一个 model 或一个 model
slice，`writeErrorResponse` 将在发生预期或意外错误时将 `JSON` 错误作为响应。像任何一个优秀的 gopher
一样，我们不应该 panic。我还添加了一个名为 `populateModelFromHandler` 的函数，它将内容从 body 中解析成所需的
model（struct）。在这种情况下，我们在 `BookCreate` handler 中使用它来填充一个 `Book`。

现在来看看日志。我们简单地创建一个 `Logger` 函数，它包装了 handler 函数，并在执行 handler 函数之前和之后打印日志消息。

package main
    
    import (
        "log"
        "net/http"
        "time"
    
        "github.com/julienschmidt/httprouter"
    )
    
    // A Logger function which simply wraps the handler function around some log messages
    func Logger(fn func(w http.ResponseWriter, r *http.Request, param httprouter.Params)) func(w http.ResponseWriter, r *http.Request, param httprouter.Params) {
        return func(w http.ResponseWriter, r *http.Request, param httprouter.Params) {
            start := time.Now()
            log.Printf("%s %s", r.Method, r.URL.Path)
            fn(w, r, param)
            log.Printf("Done in %v (%s %s)", time.Since(start), r.Method, r.URL.Path)
        }
    }

之后来看看路由。首先，在统一一个地方定义所有路由，比如 `routes.go`。

package main
    
    import "github.com/julienschmidt/httprouter"
    
    /*
    Define all the routes here.
    A new Route entry passed to the routes slice will be automatically
    translated to a handler with the NewRouter() function
    */
    type Route struct {
        Name        string
        Method      string
        Path        string
        HandlerFunc httprouter.Handle
    }
    
    type Routes []Route
    
    func AllRoutes() Routes {
        routes := Routes{
            Route{"Index", "GET", "/", Index},
            Route{"BookIndex", "GET", "/books", BookIndex},
            Route{"Bookshow", "GET", "/books/:isdn", BookShow},
            Route{"Bookshow", "POST", "/books", BookCreate},
        }
        return routes
    }

让我们创建了一个 `NewRouter` 函数，它可以在 `main` 函数中调用，它读取上面定义的所有路由，并返回一个可用的
`httprouter.Router`。因此创建一个文件 `router.go`。我们还将使用新创建的 `Logger` 函数来包装 handler。

package main
    
    import "github.com/julienschmidt/httprouter"
    
    //Reads from the routes slice to translate the values to httprouter.Handle
    func NewRouter(routes Routes) *httprouter.Router {
    
        router := httprouter.New()
        for _, route := range routes {
            var handle httprouter.Handle
    
            handle = route.HandlerFunc
            handle = Logger(handle)
    
            router.Handle(route.Method, route.Path, handle)
        }
    
        return router
    }

你的目录此时应该像这样：

.
    ├── handlers.go
    ├── handlers_test.go
    ├── logger.go
    ├── main.go
    ├── models.go
    ├── responses.go
    ├── router.go
    └── routes.go

在[这里](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-
tutorial%2Ftree%2Fmaster%2Fpart4)[4]查看完整代码。

到这里，这些代码应该可以帮助你开始编写自己的 API 服务器了。当然，你需要把你的功能放在不同的包中，以下目录结构是一个参照：

.
    ├── LICENSE
    ├── README.md
    ├── handlers
    │   ├── books_test.go
    │   └── books.go
    ├── models
    │   ├── book.go
    │   └── *
    ├── store
    │   ├── *
    └── lib
    |   ├── *
    ├── main.go
    ├── router.go
    ├── rotes.go

如果你有一个大的单体服务，你还可以将 `handlers`、`models` 和所有路由功能都放在另一个名为 `app` 的包中。你只要记住，go 不像
Java 或 Scala 那样可以有循环的包引用。因此你必须格外注意你的包结构。

这就是全部内容，希望本教程能帮助到你。?

## 注

* [1] [https://github.com/gsingharoy/httprouter-tutorial/tree/master/part1](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-tutorial%2Ftree%2Fmaster%2Fpart1)
  * [2] [https://github.com/gsingharoy/httprouter-tutorial/tree/master/part2](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-tutorial%2Ftree%2Fmaster%2Fpart2)
  * [3] [https://github.com/gsingharoy/httprouter-tutorial/tree/master/part3](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-tutorial%2Ftree%2Fmaster%2Fpart3)
  * [4] [https://github.com/gsingharoy/httprouter-tutorial/tree/master/part4](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgsingharoy%2Fhttprouter-tutorial%2Ftree%2Fmaster%2Fpart4)
  * [Gorilla mux] [https://github.com/gorilla/mux](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgorilla%2Fmux)
  * [httprouter] [https://github.com/julienschmidt/httprouter](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fjulienschmidt%2Fhttprouter)
  * [bone] [https://github.com/go-zoo/bone](https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fgo-zoo%2Fbone)

转载文章，原文链接： Golang：使用 httprouter 构建 API 服务器

关键字词golang httprouter

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