如何使用Golang开发Web请求上下文管理功能_Golang Web请求上下文实践

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func handleUser(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    
    // 将ctx传入下游服务
    user, err := fetchUser(ctx, "123")
    if err != nil {
        if ctx.Err() == context.Canceled {
            log.Println("请求被取消")
            return
        }
        if ctx.Err() == context.DeadlineExceeded {
            log.Println("请求超时")
            http.Error(w, "timeout", http.StatusGatewayTimeout)
            return
        }
        http.Error(w, "server error", http.StatusInternalServerError)
        return
    }

    json.NewEncoder(w).Encode(user)
}
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func loggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        ctx := r.Context()
        requestID := generateRequestID()
        
        // 创建带value的子context（仅用于存储数据）
        ctx = context.WithValue(ctx, "requestID", requestID)
        
        // 设置5秒超时
        ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
        defer cancel()

        // 使用新context构建新request
        r = r.WithContext(ctx)

        log.Printf("start request %s", requestID)
        next.ServeHTTP(w, r)
        log.Printf("end request %s", requestID)
    })
}
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func fetchUser(ctx context.Context, id string) (*User, error) {
    var user User
    query := `SELECT name, email FROM users WHERE id = $1`
    
    // 将ctx传给QueryRowContext
    err := db.QueryRowContext(ctx, query, id).Scan(&user.Name, &user.Email)
    if err != nil {
        return nil, err
    }
    return &user, nil
}
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