How to use context to pass request parameters in Go

The context package in the Go language is used to pass request context information in the program. It can pass parameters, intercept requests and cancel operations between functions across multiple Goroutines.

To use the context package in Go, we first need to import the "context" package. Below is an example that demonstrates how to use the context package to implement request parameter passing.

package main

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

type key string

func main() {
    // 创建一个根context
    ctx := context.Background()

    // 在根context中添加一个参数
    ctx = context.WithValue(ctx, key("name"), "Alice")

    // 创建一个HTTP处理函数
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        // 从请求中获取参数
        name := r.Context().Value(key("name")).(string)

        // 打印参数
        fmt.Fprintf(w, "Hello, %s!", name)
    })

    // 启动HTTP服务器
    http.ListenAndServe(":8080", nil)
}

In the above example, we first created a root context and added a name parameter to it. Then, we created an HTTP processing function in which we use r.Context().Value(key("name")) to obtain the parameters in the request.

By creating a subcontext in the request and passing it to other Goroutines, we can pass parameters between multiple functions without passing parameters directly. This is very useful in complex applications.

In addition to passing parameters, the context package can also be used to intercept requests and cancel operations. For example, we can use context.WithTimeout() to set a timeout. If the request is not completed within that time, the request can be canceled.

package main

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

func main() {
    // 创建一个带有超时的context
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel() // 确保在函数结束时取消context

    // 创建一个HTTP客户端
    client := &http.Client{}

    // 创建一个GET请求
    req, err := http.NewRequest("GET", "http://example.com", nil)
    if err != nil {
        fmt.Println("创建请求失败:", err)
        return
    }

    // 使用context发送请求
    resp, err := client.Do(req.WithContext(ctx))
    if err != nil {
        fmt.Println("发送请求失败:", err)
        return
    }
    defer resp.Body.Close()

    // 处理响应
    fmt.Println("响应状态码:", resp.StatusCode)
}

In the above example, we use context.WithTimeout() to create a context with a 5-second timeout and pass it to the http.NewRequest() function . Then, we use req.WithContext(ctx) to pass the context to the http.Client.Do() method.

By using the context package, it becomes very simple to implement request parameter passing in Go. We can pass data through context, intercept requests and implement cancellation operations. This makes it easier to manage requests in complex applications.

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