Detailed explanation of middleware of Gin framework and its application

The Gin framework is a lightweight web framework based on the Go language. It has the advantages of high efficiency, flexibility, and easy scalability, and is loved by many developers. The middleware mechanism is a highlight of the Gin framework. In this article, we will explore the middleware mechanism of the Gin framework and its application in detail.

1. What is middleware

Middleware refers to a plug-in that intercepts and rewrites the processing logic of requests and responses during the process of processing network requests. In Go language, middleware is usually implemented using function types. The middleware of the Gin framework is implemented by passing these functions as formal parameters to the functions that handle requests and responses.

In the Gin framework, middleware is divided into two types: global middleware and local middleware. Global middleware acts on all routes, while local middleware acts on a certain route or routing group.

2. The middleware mechanism of the Gin framework

The middleware mechanism of the Gin framework is very simple. You only need to pass the middleware as a function type to the function that handles the request and response.

For example, the following code is a simple middleware:

func MyMiddleware() gin.HandlerFunc {
  return func(c *gin.Context) {
    // do something
    c.Next()
    // do something after
  }
}

Among them, the MyMiddleware function defines a middleware function, which returns a function type. The function type returned is the function that handles requests and responses, usually called HandlerFunc.

HandlerFunc is defined as follows:

type HandlerFunc func(*Context)

It accepts a parameter of type *Context, which represents the context of the request. The *Context type contains various information in the request, such as request headers, request bodies, request parameters, etc.

In the middleware function, we can operate on the context and call the c.Next() method to transfer control to the next middleware or route processing function.

For example, if we want to add a request header to the middleware, we can do it in the following way:

func AddHeader() gin.HandlerFunc {
  return func(c *gin.Context) {
    c.Header("X-Request-Id", "123456")
    c.Next()
  }
}

This middleware will add a X-Request-Id# to the request. ##Header, and then transfer control to the next handler function. In the routing processing function, we can obtain the value of this request header through the c.GetHeader method.

Use, GET, POST, PUT, DELETE and other methods. Can. For example:

import (
    "github.com/gin-gonic/gin"
)

func main() {
    r := gin.Default()

    // 使用全局中间件
    r.Use(MyGlobalMiddleware())

    // 定义路由组，并使用局部中间件
    v1 := r.Group("/v1")
    {
        v1.Use(AddHeader())
        v1.GET("/hello", Hello)
    }

    r.Run(":8080")
}

func MyGlobalMiddleware() gin.HandlerFunc {
  return func(c *gin.Context) {
    // do something
    c.Next()
    // do something after
  }
}

func AddHeader() gin.HandlerFunc {
  return func(c *gin.Context) {
    c.Header("X-Request-Id", "123456")
    c.Next()
  }
}

func Hello(c *gin.Context) {
    headers := c.Request.Header
    requestId := headers.Get("X-Request-Id")
    c.JSON(200, gin.H{
        "message": "hello",
        "request_id": requestId,
    })
}

MyGlobalMiddleware(), which will act on all routes. We also use a local middleware AddHeader(), which only acts before the /v1/hello route. In the Hello function, we obtain the value of the X-Request-Id request header and return it to the caller.

Logger middleware

r := gin.New()
r.Use(gin.Logger())

Recovery middleware

r := gin.Default()
r.Use(gin.Recovery())

Cors middleware

r := gin.Default()
r.Use(cors.Default())

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