From 2c54ee703fb0cc23a808eb40099845368c581e41 Mon Sep 17 00:00:00 2001
From: Joel  Speed <joel.speed@hotmail.co.uk>
Date: Sun, 14 Feb 2021 17:39:36 +0000
Subject: [PATCH] Add server group implementation for running multiple servers
 at once

---
 pkg/http/server_group.go      |  35 ++++++++++++
 pkg/http/server_group_test.go | 102 ++++++++++++++++++++++++++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 pkg/http/server_group.go
 create mode 100644 pkg/http/server_group_test.go

diff --git a/pkg/http/server_group.go b/pkg/http/server_group.go
new file mode 100644
index 00000000..261d9837
--- /dev/null
+++ b/pkg/http/server_group.go
@@ -0,0 +1,35 @@
+package http
+
+import (
+	"context"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// NewServerGroup creates a new Server to start and gracefully stop a collection
+// of Servers.
+func NewServerGroup(servers ...Server) Server {
+	return &serverGroup{
+		servers: servers,
+	}
+}
+
+// serverGroup manages the starting and graceful shutdown of a collection of
+// servers.
+type serverGroup struct {
+	servers []Server
+}
+
+// Start runs the servers in the server group.
+func (s *serverGroup) Start(ctx context.Context) error {
+	g, groupCtx := errgroup.WithContext(ctx)
+
+	for _, server := range s.servers {
+		srv := server
+		g.Go(func() error {
+			return srv.Start(groupCtx)
+		})
+	}
+
+	return g.Wait()
+}
diff --git a/pkg/http/server_group_test.go b/pkg/http/server_group_test.go
new file mode 100644
index 00000000..97748b4d
--- /dev/null
+++ b/pkg/http/server_group_test.go
@@ -0,0 +1,102 @@
+package http
+
+import (
+	"context"
+	"errors"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Server Group", func() {
+	var m1, m2, m3 *mockServer
+	var ctx context.Context
+	var cancel context.CancelFunc
+	var group Server
+
+	BeforeEach(func() {
+		ctx, cancel = context.WithCancel(context.Background())
+
+		m1 = newMockServer()
+		m2 = newMockServer()
+		m3 = newMockServer()
+		group = NewServerGroup(m1, m2, m3)
+	})
+
+	AfterEach(func() {
+		cancel()
+	})
+
+	It("starts each server in the group", func() {
+		go func() {
+			defer GinkgoRecover()
+			Expect(group.Start(ctx)).To(Succeed())
+		}()
+
+		Eventually(m1.started).Should(BeClosed(), "mock server 1 not started")
+		Eventually(m2.started).Should(BeClosed(), "mock server 2 not started")
+		Eventually(m3.started).Should(BeClosed(), "mock server 3 not started")
+	})
+
+	It("stop each server in the group when the context is cancelled", func() {
+		go func() {
+			defer GinkgoRecover()
+			Expect(group.Start(ctx)).To(Succeed())
+		}()
+
+		cancel()
+		Eventually(m1.stopped).Should(BeClosed(), "mock server 1 not stopped")
+		Eventually(m2.stopped).Should(BeClosed(), "mock server 2 not stopped")
+		Eventually(m3.stopped).Should(BeClosed(), "mock server 3 not stopped")
+	})
+
+	It("stop each server in the group when the an error occurs", func() {
+		err := errors.New("server error")
+		go func() {
+			defer GinkgoRecover()
+			Expect(group.Start(ctx)).To(MatchError(err))
+		}()
+
+		m2.errors <- err
+		Eventually(m1.stopped).Should(BeClosed(), "mock server 1 not stopped")
+		Eventually(m2.stopped).Should(BeClosed(), "mock server 2 not stopped")
+		Eventually(m3.stopped).Should(BeClosed(), "mock server 3 not stopped")
+	})
+})
+
+// mockServer is used to test the server group can start
+// and stop multiple servers simultaneously.
+type mockServer struct {
+	started     chan struct{}
+	startClosed bool
+	stopped     chan struct{}
+	stopClosed  bool
+	errors      chan error
+}
+
+func newMockServer() *mockServer {
+	return &mockServer{
+		started: make(chan struct{}),
+		stopped: make(chan struct{}),
+		errors:  make(chan error),
+	}
+}
+
+func (m *mockServer) Start(ctx context.Context) error {
+	if !m.startClosed {
+		close(m.started)
+		m.startClosed = true
+	}
+	defer func() {
+		if !m.stopClosed {
+			close(m.stopped)
+			m.stopClosed = true
+		}
+	}()
+	select {
+	case <-ctx.Done():
+		return nil
+	case err := <-m.errors:
+		return err
+	}
+}