Gracefully shutdown a http server in golang

To gracefully shutdown a http server requires a few steps.

The http library’s serving function will block over there when getting started, until we call http.Server.Close(). As for us, we can invoke the starting function in a goroutine, and call close in another one.

Here is a full simple example:

package main

import (
    "context"
    "fmt"
    "github.com/argcv/stork/log"
    "github.com/gin-gonic/gin"
    "github.com/pkg/errors"
    "net/http"
    "os"
    "os/signal"
    "sync"
    "time"
)

type HttpSrv struct {
    Port int

    server    *http.Server
    isStarted bool
    mtx       *sync.Mutex
}

func NewHttpSrv(port int) *HttpSrv {
    return &HttpSrv{
        Port:      port,
        server:    nil,
        isStarted: false,
        mtx:       &sync.Mutex{},
    }
}

func (srv *HttpSrv) Start() (err error) {
    srv.mtx.Lock()
    defer srv.mtx.Unlock()

    if srv.isStarted {
        return errors.New("Server is already started")
    }

    srv.isStarted = true

    // prepare router
    router := gin.Default()

    router.GET("/*uri", func(c *gin.Context) {
        uri := c.Param("uri")
        c.JSON(200, map[string]interface{}{
            "status": "ok",
            "uri":    uri,
        })
    })

    // prepare address
    addr := fmt.Sprintf(":%v", srv.Port)

    // prepare http server
    srv.server = &http.Server{
        Addr:    addr,
        Handler: router,
    }

    log.Infof("Starting http server: %v", srv)

    go func() {
        if err = srv.server.ListenAndServe(); err != nil {
            if err == http.ErrServerClosed {
                log.Infof("Server closed under request: %v", err)
            } else {
                log.Fatalf("Server closed unexpect: %v", err)
            }
        }
        // in case of closed normally
        srv.isStarted = false
    }()

    time.Sleep(10 * time.Millisecond)

    return
}

func (m *HttpSrv) Shutdown(ctx context.Context) (err error) {
    m.mtx.Lock()
    defer m.mtx.Unlock()

    if !m.isStarted || m.server == nil {
        return errors.New("Server is not started")
    }

    stop := make(chan bool)
    go func() {
        // dummy preprocess before interrupted
        //time.Sleep(4 * time.Second)

        // Close immediately closes all active net.Listeners and any
        // connections in state StateNew, StateActive, or StateIdle. For a
        // graceful shutdown, use Shutdown.
        //
        // Close does not attempt to close (and does not even know about)
        // any hijacked connections, such as WebSockets.
        //
        // Close returns any error returned from closing the Server's
        // underlying Listener(s).
        //err = m.server.Close()
        // We can use .Shutdown to gracefully shuts down the server without
        // interrupting any active connection
        err = m.server.Shutdown(ctx)
        stop <- true
    }()

    select {
    case <-ctx.Done():
        log.Errorf("Timeout: %v", ctx.Err())
        break
    case <-stop:
        log.Infof("Finished")
    }

    return
}

func main() {
    srv := NewHttpSrv(9990)
    if err := srv.Start(); err != nil {
        log.Fatalf("Start failed: %v", err)
        return
    }

    quit := make(chan os.Signal)
    signal.Notify(quit, os.Interrupt)
    // holding here
    // waiting for a interrupt signal
    <-quit
    log.Infof("[Control-C] Get signal: shutdown server ...")
    signal.Reset(os.Interrupt)

    // starting shutting down progress...
    log.Infof("Server shutting down")
    // context: wait for 3 seconds
    ctx, cancel := context.WithTimeout(
        context.Background(),
        3*time.Second)

    defer cancel()
    // call for shutdown
    if err := srv.Shutdown(ctx); err != nil {
        log.Errorf("Server Shutdown failed: %v", err)
    }
    log.Infof("Server exiting")
}