Hooks

Hook is a generic concept that indicates the action that accompanies an event when it is triggered.

Hertz provides a global Hook for injecting your processing logic on the server-side after triggering startup and before exiting.

StartHook

StartHook is a function to be called after the server-side has triggered a start, represented in Hertz by the type CtxErrCallback. Hertz uses the OnRun property to store the StartHook list.

// CtxErrCallback refer to it's function signatures below
OnRun []CtxErrCallback

Hook functions get triggered sequentially after triggering the startup. Once the call is completed, Hertz will officially start listening on the port, or terminate the service immediately if any error occurs.

Function signatures:

type CtxErrCallback func(ctx context.Context) error

Sample Code:

package main

import (
    "context"
    
    "github.com/cloudwego/hertz/pkg/app"
    "github.com/cloudwego/hertz/pkg/app/server"
    "github.com/cloudwego/hertz/pkg/common/hlog"
    "github.com/cloudwego/hertz/pkg/common/utils"
    "github.com/cloudwego/hertz/pkg/protocol/consts"
)

func main() {
    h := server.Default()

    h.OnRun = append(h.OnRun, func(ctx context.Context) error {
        hlog.Info("run the first start hook")
        return nil
    })
    h.OnRun = append(h.OnRun, func(ctx context.Context) error {
        hlog.Info("run the second start hook")
        return nil
    })
    h.OnRun = append(h.OnRun, func(ctx context.Context) error {
        hlog.Info("run the third start hook")
        return nil
    })

    h.GET("/ping", func(c context.Context, ctx *app.RequestContext) {
        ctx.JSON(consts.StatusOK, utils.H{"ping": "pong"})
    })

    h.Spin()
}

Note: After triggering startup, The logs of the three StartHook functions will be printed in the terminal in order.

main.go:17: [Info] run the first start hook
main.go:21: [Info] run the second start hook
main.go:25: [Info] run the third start hook

ShutdownHook

ShutdownHook is a function to be called before the server-side exiting, represented in Hertz by the type CtxCallback. Hertz uses the OnShutdown property to store the ShutdownHook list.

Hook functions get triggered simultaneously before the server-side exiting. The user can configure the max expiration time by server.WithExitWaitTime, the default is 5 seconds, and once timeout, the server is terminated.

The ShutdownHook call process is essentially a part of the Hertz Graceful Shutdown.

Function signatures:

type CtxCallback func(ctx context.Context)

Sample Code1:

package main

import (
    "context"

    "github.com/cloudwego/hertz/pkg/app"
    "github.com/cloudwego/hertz/pkg/app/server"
    "github.com/cloudwego/hertz/pkg/common/hlog"
    "github.com/cloudwego/hertz/pkg/common/utils"
    "github.com/cloudwego/hertz/pkg/protocol/consts"
)

func main() {
    h := server.Default()

    h.OnShutdown = append(h.OnShutdown, func(ctx context.Context) {
        hlog.Info("run the first shutdown hook")
    })
    h.OnShutdown = append(h.OnShutdown, func(ctx context.Context) {
        hlog.Info("run the second shutdown hook")
    })
    h.OnShutdown = append(h.OnShutdown, func(ctx context.Context) {
        hlog.Info("run the third shutdown hook")
    })

    h.GET("/ping", func(c context.Context, ctx *app.RequestContext) {
        ctx.JSON(consts.StatusOK, utils.H{"ping": "pong"})
    })

    h.Spin()
}

Note: Before exiting, the logs of the three ShutdownHook functions will be printed in the terminal disorderly.

main.go:17: [Info] run the first shutdown hook
main.go:23: [Info] run the third shutdown hook
main.go:20: [Info] run the second shutdown hook

Sample Code2:

package main

import (
    "context"
    "time"
    
    "github.com/cloudwego/hertz/pkg/app"
    "github.com/cloudwego/hertz/pkg/app/server"
    "github.com/cloudwego/hertz/pkg/common/hlog"
    "github.com/cloudwego/hertz/pkg/common/utils"
    "github.com/cloudwego/hertz/pkg/protocol/consts"
)

func main() {
    h := server.Default(server.WithExitWaitTime(time.Second * 2))

    h.OnShutdown = append(h.OnShutdown, func(ctx context.Context) {
        hlog.Info("run shutdown hook")
        time.Sleep(time.Second * 5)
    })

    h.GET("/ping", func(c context.Context, ctx *app.RequestContext) {
        ctx.JSON(consts.StatusOK, utils.H{"ping": "pong"})
    })

    h.Spin()
}

Note: When terminating the service, the timeout log is printed because the hook function took more than 2 seconds to execute.

hertz.go:77: [Info] HERTZ: Begin graceful shutdown, wait at most num=2 seconds...
main.go:17: [Info] run shutdown hook
engine.go:276: [Info] HERTZ: Execute OnShutdownHooks timeout: error=context deadline exceeded

Last modified December 2, 2022 : chore: add lark footer link (#460) (f41a884)