go - 使用GO导航时如何使用Context？

Question

我正在使用以下代码来从Google Cloud获得指导:

import (
    "google.golang.org/appengine"
    "google.golang.org/appengine/urlfetch"
    "fmt"
    "io/ioutil"
    "net/http"
)

const directionAPIKey = "APIKey"
const directionURL = "https://maps.googleapis.com/maps/api/directions/json?origin=%s&destination=%s&mode=%s&key=%s"

func main() {
    http.HandleFunc("/", handler)
}

func handler(w http.ResponseWriter, r *http.Request) {
    ctx := appengine.NewContext(r)
    direction, err := fetchDirection(ctx, r.FormValue("origin"), r.FormValue("destination"), r.FormValue("mode"))
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    w.Header().Add("Content-Type", "application/json; charset=utf-8")
    w.Write(direction)
}

func fetchDirection(ctx appengine.Context, origin string, destination string, mode string) ([]byte, error) {
    client := urlfetch.Client(ctx)
    resp, err := client.Get(fmt.Sprintf(directionURL, origin, destination, mode, directionAPIKey))
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    return ioutil.ReadAll(resp.Body)
}

但我得到一个错误:

未定义:appengine.Context

尝试部署应用程序时。我试图改变的是:

ctx := appengine.NewContext(r)

进入

ctx := r.Context()

和

func fetchDirection(ctx appengine.Context, origin string...)

进入

func fetchDirection(ctx Context, origin string...)

但是我得到:

undefined: Context

我完全迷路了。我是Go和GCP的新手，所以请耐心等待。谢谢

Answer 1

如果您检查godoc for urlfetch，您会看到它链接到where the Context type is defined。这反过来又告诉您“从Go 1.7开始，该程序包在标准库中的名称上下文为https://golang.org/pkg/context可用。”

因此添加一个导入:

import "context"

并将其称为:

func fetchDirection(ctx context.Context, origin string...)