Google App Engine Go 应用中的状态管理与持久化策略

package main

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

    "google.golang.org/appengine"
    "google.golang.org/appengine/memcache"
)

func main() {
    http.HandleFunc("/", handleRequest)
    appengine.Main()
}

func handleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := appengine.NewContext(r)

    key := "my_counter"
    var counter int

    // 尝试从Memcache获取计数器
    item, err := memcache.Get(ctx, key)
    if err == memcache.ErrCacheMiss {
        // 如果缓存中没有，初始化为0
        counter = 0
        log.Printf("Cache miss for key %s, initializing counter to %d", key, counter)
    } else if err != nil {
        http.Error(w, fmt.Sprintf("Error getting from memcache: %v", err), http.StatusInternalServerError)
        return
    } else {
        // 如果缓存命中，解析计数器值
        _, err := fmt.Sscanf(string(item.Value), "%d", &counter)
        if err != nil {
            http.Error(w, fmt.Sprintf("Error parsing counter from memcache: %v", err), http.StatusInternalServerError)
            return
        }
        log.Printf("Cache hit for key %s, current counter: %d", key, counter)
    }

    // 增加计数器
    counter++

    // 将新值存回Memcache
    newItem := &memcache.Item{
        Key:   key,
        Value: []byte(fmt.Sprintf("%d", counter)),
    }
    if err := memcache.Set(ctx, newItem); err != nil {
        http.Error(w, fmt.Sprintf("Error setting to memcache: %v", err), http.StatusInternalServerError)
        return
    }

    fmt.Fprintf(w, "Counter: %d", counter)
}

package main

import (
    "context"
    "fmt"
    "log"
    "net/http"
    "time"

    "cloud.google.com/go/datastore"
    "google.golang.org/appengine"
)

// 定义一个结构体来表示要存储的数据
type Visit struct {
    Timestamp time.Time
    Message   string
}

func main() {
    http.HandleFunc("/", handleRequest)
    appengine.Main()
}

func handleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := appengine.NewContext(r)

    // 创建Datastore客户端
    client, err := datastore.NewClient(ctx, appengine.AppID(ctx))
    if err != nil {
        http.Error(w, fmt.Sprintf("Failed to create Datastore client: %v", err), http.StatusInternalServerError)
        return
    }
    defer client.Close()

    // 存储新的访问记录
    visit := Visit{
        Timestamp: time.Now(),
        Message:   "User visited the page",
    }
    key := datastore.IncompleteKey("Visit", nil) // 自动生成ID
    if _, err := client.Put(ctx, key, &visit); err != nil {
        http.Error(w, fmt.Sprintf("Failed to save visit: %v", err), http.StatusInternalServerError)
        return
    }
    log.Printf("Saved new visit at %v", visit.Timestamp)

    // 查询最近的5条访问记录
    var visits []Visit
    query := datastore.NewQuery("Visit").Order("-Timestamp").Limit(5)
    if _, err := client.GetAll(ctx, query, &visits); err != nil {
        http.Error(w, fmt.Sprintf("Failed to query visits: %v", err), http.StatusInternalServerError)
        return
    }

    fmt.Fprintf(w, "Last 5 visits:\n")
    for _, v := range visits {
        fmt.Fprintf(w, "- %v: %s\n", v.Timestamp.Format(time.RFC3339), v.Message)
    }
}