What is the working principle and execution flow of Gin middleware?

The working principle and execution flow of Gin middleware are as follows:

1. Concept of middleware Middleware is an interceptor pattern that can execute code before and after the request reaches the final handler function. Each middleware is a function that receives gin.Context as a parameter.

2. Middleware registration methods

• Global middleware: Registered using engine.Use(), applies to all routes
• Route group middleware: Registered using group.Use(), applies to all routes in the group
• Single route middleware: Added directly when defining the route, only applies to that route

3. Execution flow Gin's middleware uses a chain call approach with the following execution order:

1. After the request arrives, execute the pre-logic of each middleware in the order of registration
2. When the middleware calls c.Next(), it passes control to the next middleware
3. After all middleware pre-logic is executed, execute the final handler function
4. After the handler function is executed, execute the post-logic of the middleware in reverse order

4. Middleware example code

go
func Logger() gin.HandlerFunc {
    return func(c *gin.Context) {
        // Pre-logic
        start := time.Now()
        
        // Call next middleware or handler
        c.Next()
        
        // Post-logic
        duration := time.Since(start)
        fmt.Printf("Request took %v\n", duration)
    }
}

5. Common uses of middleware

• Authentication and authorization
• Request logging
• CORS cross-domain handling
• Error recovery and unified handling
• Rate limiting
• Data compression

6. Middleware control

• c.Next(): Continue executing subsequent middleware
• c.Abort(): Interrupt request processing, no longer execute subsequent middleware
• c.AbortWithStatusJSON(): Interrupt and return JSON response

Understanding the execution order and control of middleware is very important for building complex application logic.