Middleware Overview

There are various types of Hertz middleware, which are simply divided into two categories.

• Server-side middleware
• Client-side middleware

Server-side middleware

Server-side middleware is a function in the HTTP request-response cycle that provides a convenient mechanism for inspecting and filtering HTTP requests entering your application, such as logging each request or enabling CORS.

Figure 1: middleware call chain

Middleware can perform tasks before or after passing the request deeper into the application:

• Middleware can be executed before the request reaches business processing, such as performing identity authentication and authorization authentication. When the middleware only has pre-handle logic and there is no requirement to be in a function call stack with real handler, the .Next can be omitted.
• Middleware can also be executed after business processing has been performed, such as logging response times and recovering from a panic. If there is other processing logic (post-handle) after the business handler, or there is a strong requirement for the function call chain (stack), then the .Next must be called explicitly, see middleware C in Figure 1.

Implement customized middleware

// One way
func MyMiddleware() app.HandlerFunc {
   return func(ctx context.Context, c *app.RequestContext) {
      // pre-handle
      // ...
      // if there is no 'post-handle' logic, the 'c.Next(ctx)' can be omitted.
      c.Next(ctx)
   }
}

// The other way
func MyMiddleware() app.HandlerFunc {
   return func(ctx context.Context, c *app.RequestContext) {
      c.Next(ctx) // call the next middleware(handler)
      // post-handle
      ...
   }
}

The middleware will be executed in the order defined, If you want to terminate the middleware call quickly, you can use the following methods, noting that the current middleware will still execute.

• Abort()：terminate subsequent calls
• AbortWithMsg(msg string, statusCode int)：terminates subsequent calls and sets the body and status code for the Response
• AbortWithStatus(code int)：terminates subsequent calls and sets the status code

Server-level middleware

Server-level middleware will take effect on all routing of the server

h := server.Default()
h.Use(MyMiddleware())

Group-level middleware

The group-level middleware takes effect on the paths under the current routing group

h := server.Default()
group := h.Group("/group")
group.Use(GroupMiddleware())

or

package main

import (
	"context"
	"fmt"

	"github.com/cloudwego/hertz/pkg/app"
	"github.com/cloudwego/hertz/pkg/app/server"
)

func GroupMiddleware() []app.HandlerFunc {
	return []app.HandlerFunc{func(ctx context.Context, c *app.RequestContext) {
		fmt.Println("group middleware")
		c.Next(ctx)
	}}
}

func main() {
	h := server.Default(server.WithHostPorts("127.0.0.1:8888"))

	group := h.Group("/group", append(GroupMiddleware(),
        func(ctx context.Context, c *app.RequestContext) {
            fmt.Println("group middleware 2")
            c.Next(ctx)
        })...)
	// ...
	h.Spin()
}

Route-level middleware

A route-level middleware only takes effect on the current route

package main

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

	"github.com/cloudwego/hertz/pkg/app"
	"github.com/cloudwego/hertz/pkg/app/server"
)

func PathMiddleware() []app.HandlerFunc {
	return []app.HandlerFunc{func(ctx context.Context, c *app.RequestContext) {
		fmt.Println("path middleware")
		c.Next(ctx)
	}}
}

func main() {
	h := server.Default(server.WithHostPorts("127.0.0.1:8888"))

	h.GET("/path", append(PathMiddleware(),
		func(ctx context.Context, c *app.RequestContext) {
			c.String(http.StatusOK, "path")
		})...)

	h.Spin()
}

If you use the hz tool and IDL to develop a project, the router folder will automatically generate group-level middleware and route-level middleware templates based on services and methods. You can add corresponding logic to it and customize your own personalized middleware.

Activate default middleware

The Hertz framework already presets the commonly used Recover middleware, which can be registered by Default with server.Default().

Middlewares we provided

Hertz provides frequently-used middlewares such as BasicAuth, CORS, JWT etc., more implementations can be found at hertz-contrib. If you need others, please make an issue.

Client-side Middleware

Client-side middleware can be executed before the request is made or after the response is obtained:

• Middleware can be executed before the request is sent, such as adding a signature or other fields to the request.
• Middleware can also be executed after receiving the response, such as modifying the response result to adapt to the business logic.

Implement customized middleware

The middleware implementation on the Client side is different from that on the Server side. The Client side cannot get the index of the middleware to increase, so the Client middleware uses nested functions to build the middleware in advance. When implementing client-side customized middleware, you can refer to the following code.

func MyMiddleware(next client.Endpoint) client.Endpoint {
    return func(ctx context.Context, req *protocol.Request, resp *protocol.Response) (err error) {
        // pre-handle
        // ...
        err = next(ctx, req, resp)
        if err != nil {
            return
        }
        // post-handle
        // ...
    }
}

Note: the next method must be executed to continue calls to the subsequent middleware. If you want to stop the middleware call, just return before next.

Register customized middleware

Registering custom middleware is the same as on the server side.

c, err := client.NewClient()
c.Use(MyMiddleware)

Full example

package main

import (
	"context"
	"fmt"

	"github.com/cloudwego/hertz/pkg/app/client"
	"github.com/cloudwego/hertz/pkg/protocol"
)

func MyMiddleware(next client.Endpoint) client.Endpoint {
	return func(ctx context.Context, req *protocol.Request, resp *protocol.Response) (err error) {
		// pre-handle
		// ...
		fmt.Println("before request")

		req.AppendBodyString("k1=v1&")

		err = next(ctx, req, resp)
		if err != nil {
			return
		}
		// post-handle
		// ...
		fmt.Println("after request")

		return nil
	}
}

func main() {
	client, _ := client.NewClient()
	client.Use(MyMiddleware)
	statusCode, body, err := client.Post(context.Background(),
		[]byte{},
		"http://httpbin.org/redirect-to?url=http%3A%2F%2Fhttpbin.org%2Fpost&status_code=302",
		&protocol.Args{})
	fmt.Printf("%d, %s, %s", statusCode, body, err)
}

Middleware may be executed more than once, such as redirect, etc., idempotency needs to be considered