Add material for GoLab 2020 ws

Author: pippolo84

README.md

@@ -0,0 +1,16 @@
+# Design patterns for production grade Go services
+## Material for the GoLab 2020 Workshop
+
+## Prerequisites
+
+As an intermediate workshop, familiarity with the basics of the Go programming language is expected. As a reference, you have already completed (or should be able to complete) [A Tour of Go](https://tour.golang.org/).
+
+A previous experience in writing Go services may be useful, but not required.
+
+To install Go 1.15 and configure your environment properly, follow the instructions [here](https://golang.org/doc/install).
+
+During the workshop, we will try the example code with some HTTP requests. `curl` is perfectly fine, but it may be easier to use a tool like [Insomnia Core](https://insomnia.rest/download/core/?) or [Postman](https://www.postman.com/downloads/).
+
+## Setup test
+
+see [this repo](https://github.com/pippolo84/golab2020-ws-setup-test) for more information regarding your local dev environment setup

part1/graceful-shutdown/go.mod

@@ -0,0 +1,8 @@
+module github.com/Pippolo84/go-services-patterns/part1/graceful-shutdown
+
+go 1.15
+
+require (
+	go.uber.org/goleak v1.1.10
+	nhooyr.io/websocket v1.8.6
+)

part1/graceful-shutdown/go.sum

@@ -0,0 +1,55 @@
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part1/graceful-shutdown/graceful/server.go

@@ -0,0 +1,118 @@
+package graceful
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"sync"
+	"time"
+
+	"nhooyr.io/websocket"
+)
+
+// Server is a HTTP server that supports graceful shutdown
+type Server struct {
+	http.Server
+}
+
+// NewServer returns a reference to a new Server listening on addr
+func NewServer(addr string) *Server {
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("/", handler)
+	mux.HandleFunc("/slow", slowHandler)
+	// see https://github.com/hashrocket/ws for a websocket client
+	mux.HandleFunc("/ws", wsHandler)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	srv := &Server{
+		Server: http.Server{
+			Addr:    addr,
+			Handler: mux,
+			// use the context with cancellation to be able to gracefully shutdown websocket connections
+			BaseContext: func(_ net.Listener) context.Context {
+				return ctx
+			},
+		},
+	}
+
+	// on shutdown, cancel the context
+	srv.Server.RegisterOnShutdown(cancel)
+
+	return srv
+}
+
+// Shutdown makes the server stop listening and refuse further connections
+// It takes a context to limit the shutdown duration and a wait group to signal
+// the caller when the shutdown process has finished
+func (srv *Server) Shutdown(ctx context.Context, wg *sync.WaitGroup) error {
+	defer wg.Done()
+	return srv.Server.Shutdown(ctx)
+}
+
+// Run starts the server, making it listening on specified address
+// it returns a channel where all errors are relayed
+func (srv *Server) Run() <-chan error {
+	errs := make(chan error)
+
+	go func() {
+		defer close(errs)
+
+		log.Printf("server: start listening on %s\n", srv.Addr)
+
+		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			errs <- err
+		}
+
+		log.Println("server: bye!")
+	}()
+
+	return errs
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello, world!")
+}
+
+func slowHandler(w http.ResponseWriter, r *http.Request) {
+	// Shutdown won't close this connection until it returns to idle
+	time.Sleep(10 * time.Second)
+	fmt.Fprintf(w, "Hello, slow world!")
+}
+
+func wsHandler(w http.ResponseWriter, r *http.Request) {
+	c, err := websocket.Accept(w, r, nil)
+	if err != nil {
+		fmt.Printf("websocket upgrade error: %v\n", err)
+	}
+	// Additional calls to Close are no-ops
+	defer c.Close(websocket.StatusInternalError, "internal server error")
+
+	// to cancel the write in case of a slow reader
+	ctx, cancel := context.WithTimeout(r.Context(), time.Second*10)
+	defer cancel()
+
+	if err := c.Write(ctx, websocket.MessageText, []byte("Hello, ws world!")); err != nil {
+		if !errors.Is(err, context.Canceled) {
+			log.Printf("ws write error: %v\n", err)
+		}
+		return
+	}
+
+	mtype, buf, err := c.Read(ctx)
+	if err != nil {
+		if !errors.Is(err, context.Canceled) {
+			log.Printf("ws read error: %v\n", err)
+		}
+		return
+	}
+
+	if mtype == websocket.MessageText {
+		fmt.Printf("received: %s\n", string(buf))
+	}
+
+	c.Close(websocket.StatusNormalClosure, "")
+}

part1/graceful-shutdown/graceful/server_test.go

@@ -0,0 +1,148 @@
+package graceful
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"go.uber.org/goleak"
+)
+
+// FIXME: add a test for the ws handler
+
+// go test -v -timeout=20s .
+
+func startServer(t *testing.T, addr string) (*Server, <-chan error) {
+	t.Helper()
+
+	srv := NewServer(addr)
+
+	errs := make(chan error)
+
+	go func() {
+		defer close(errs)
+
+		for err := range srv.Run() {
+			errs <- err
+		}
+	}()
+
+	// wait for the server to listen on addr
+	for {
+		_, err := net.Dial("tcp", fmt.Sprintf("localhost%s", addr))
+		if err == nil {
+			break
+		}
+		if strings.Contains(err.Error(), "connection refused") {
+			time.Sleep(100 * time.Millisecond)
+			continue
+		}
+
+		log.Fatal(err)
+	}
+
+	return srv, errs
+}
+
+func TestGetRequest(t *testing.T) {
+	defer goleak.VerifyNone(t)
+
+	srv, srvErrs := startServer(t, ":8080")
+
+	res, err := http.Get("http://localhost:8080")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+
+	if res.StatusCode != http.StatusOK {
+		t.Fatalf("expected status code %d, got %d\n", http.StatusOK, res.StatusCode)
+	}
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	if err := srv.Shutdown(context.Background(), &wg); err != nil {
+		t.Fatal(err)
+	}
+
+	wg.Wait()
+
+	// srvErrs should have been closed without errors
+	for err := range srvErrs {
+		t.Fatal(err)
+	}
+}
+
+func TestGracefulShutdown(t *testing.T) {
+	defer goleak.VerifyNone(t)
+
+	srv, srvErrs := startServer(t, ":8080")
+
+	shutdownCtx, cancelShutdown := context.WithTimeout(context.Background(), 20*time.Second)
+	defer cancelShutdown()
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	if err := srv.Shutdown(shutdownCtx, &wg); err != nil {
+		t.Fatal(err)
+	}
+
+	wg.Wait()
+
+	// srvErrs should have been closed without errors
+	for err := range srvErrs {
+		t.Fatal(err)
+	}
+}
+
+func slowRequest(t *testing.T, addr string) <-chan error {
+	t.Helper()
+
+	reqErrs := make(chan error)
+
+	go func() {
+		defer close(reqErrs)
+
+		var err *net.OpError
+		if _, e := http.Get(addr); !errors.As(e, &err) {
+			reqErrs <- err
+		}
+	}()
+
+	return reqErrs
+}
+
+func TestGracefulShutdownTimeout(t *testing.T) {
+	srv, srvErrs := startServer(t, ":8081")
+
+	reqErrs := slowRequest(t, "http://localhost:8081/slow")
+
+	shutdownCtx, cancelShutdown := context.WithTimeout(context.Background(), time.Second)
+	defer cancelShutdown()
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	if err := srv.Shutdown(shutdownCtx, &wg); !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("expected context deadline exceeded, got: %v\n", err)
+	}
+
+	wg.Wait()
+
+	// srvErrs and reqErrs should have been closed without errors
+	for err := range srvErrs {
+		t.Fatal(err)
+	}
+	for err := range reqErrs {
+		t.Fatal(err)
+	}
+}

part1/graceful-shutdown/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/Pippolo84/go-services-patterns/part1/graceful-shutdown/graceful"
+)
+
+const cooldown time.Duration = 5 * time.Second
+
+func main() {
+	srv := graceful.NewServer(":8080")
+
+	errs := srv.Run()
+
+	// trap incoming SIGINT and SIGKTERM
+	signalChan := make(chan os.Signal, 1)
+	signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM)
+
+	// block until a signal or an error from the server is received
+	select {
+	case err := <-errs:
+		log.Println(err)
+	case sig := <-signalChan:
+		log.Printf("got signal: %v, shutting down...\n", sig)
+	}
+
+	// graceful shutdown the server
+	shutdownCtx, cancelShutdown := context.WithTimeout(context.Background(), cooldown)
+	defer cancelShutdown()
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	if err := srv.Shutdown(shutdownCtx, &wg); err != nil {
+		log.Println(err)
+	}
+
+	wg.Wait()
+}