Implemented Nickname cancellation using context, the good way

channel.go

@@ -1,6 +1,7 @@
 package mock
 
 import (
+	"context"
 	"math/rand"
 	"strconv"
 	"strings"
@@ -40,7 +41,8 @@ type Channel struct {
 	// up to about 12 or so. check sameAuthorLimit.
 	incrAuthor uint8
 
-	busyWg sync.WaitGroup
+	// single-use write-once context, written on every JoinServer
+	ctx context.Context
 }
 
 var (
@@ -61,15 +63,25 @@ func (ch *Channel) Name() text.Rich {
 	return text.Rich{Content: ch.name}
 }
 
+// Nickname sets the labeler to the nickname. It simulates heavy IO. This
+// function stops as cancel is called in JoinServer, as Nickname is specially
+// for that.
 func (ch *Channel) Nickname(labeler cchat.LabelContainer) error {
-	// Simulate IO.
-	simulateAustralianInternet()
+	// Borrow the parent's context and stop fetching if the context expires.
+	ctx, cancel := context.WithCancel(ch.ctx)
+	defer cancel()
+
+	// Simulate IO with cancellation. Ignore the error if it's a simulated time
+	// out, else return.
+	if err := simulateAustralianInternetCtx(ctx); err != nil && err != ErrTimedOut {
+		return err
+	}
 
 	labeler.SetLabel(ch.username)
 	return nil
 }
 
-func (ch *Channel) JoinServer(container cchat.MessagesContainer) (func(), error) {
+func (ch *Channel) JoinServer(container cchat.MessagesContainer) (stop func(), err error) {
 	// Is this a fresh channel? If yes, generate messages with some IO latency.
 	if len(ch.messages) == 0 || ch.messageixs == nil {
 		// Simulate IO.
@@ -94,8 +106,8 @@ func (ch *Channel) JoinServer(container cchat.MessagesContainer) (func(), error)
 		}
 	}
 
-	// Initialize channels for use.
-	doneCh := make(chan struct{})
+	// Initialize context for cancellation.
+	ch.ctx, stop = context.WithCancel(context.Background())
 
 	go func() {
 		ticker := time.NewTicker(4 * time.Second)
@@ -126,13 +138,13 @@ func (ch *Channel) JoinServer(container cchat.MessagesContainer) (func(), error)
 				var old = ch.randomOldMsg()
 				ch.deleteMessage(MessageHeader{old.id, time.Now()}, container)
 
-			case <-doneCh:
+			case <-ch.ctx.Done():
 				return
 			}
 		}
 	}()
 
-	return func() { doneCh <- struct{}{} }, nil
+	return
 }
 
 func (ch *Channel) RawMessageContent(id string) (string, error) {
@@ -272,8 +284,8 @@ func (ch *Channel) nextID() (id uint32) {
 }
 
 func (ch *Channel) SendMessage(msg cchat.SendableMessage) error {
-	if simulateAustralianInternet() {
-		return errors.New("Failed to send message: Australian Internet unsupported.")
+	if err := simulateAustralianInternet(); err != nil {
+		return errors.Wrap(err, "Failed to send message")
 	}
 
 	go func() {
@@ -360,12 +372,29 @@ func randClamp(min, max int) int {
 	return rand.Intn(max-min) + min
 }
 
+// ErrTimedOut is returned when the simulated IO decides to fail.
+var ErrTimedOut = errors.New("Australian Internet unsupported.")
+
 // simulate network latency
-func simulateAustralianInternet() (lost bool) {
+func simulateAustralianInternet() error {
+	return simulateAustralianInternetCtx(context.Background())
+}
+
+func simulateAustralianInternetCtx(ctx context.Context) (err error) {
 	var ms = randClamp(internetMinLatency, internetMaxLatency)
-	<-time.After(time.Duration(ms) * time.Millisecond)
+
+	select {
+	case <-time.After(time.Duration(ms) * time.Millisecond):
+		// noop
+	case <-ctx.Done():
+		return ctx.Err()
+	}
 
 	// because australia, drop packet 20% of the time if internetCanFail is
 	// true.
-	return internetCanFail && rand.Intn(100) < 20
+	if internetCanFail && rand.Intn(100) < 20 {
+		return ErrTimedOut
+	}
+
+	return nil
 }

service.go

@@ -3,13 +3,13 @@ package mock
 
 import (
 	"encoding/json"
-	"errors"
 	"strconv"
 	"time"
 
 	"github.com/diamondburned/cchat"
 	"github.com/diamondburned/cchat/services"
 	"github.com/diamondburned/cchat/text"
+	"github.com/pkg/errors"
 )
 
 func init() {
@@ -32,8 +32,8 @@ func (s Service) Name() text.Rich {
 }
 
 func (s Service) RestoreSession(storage map[string]string) (cchat.Session, error) {
-	if simulateAustralianInternet() {
-		return nil, errors.New("Restore failed: server machine broke")
+	if err := simulateAustralianInternet(); err != nil {
+		return nil, errors.Wrap(err, "Restore failed")
 	}
 
 	username, ok := storage["username"]
@@ -70,8 +70,8 @@ func (Authenticator) AuthenticateForm() []cchat.AuthenticateEntry {
 
 func (Authenticator) Authenticate(form []string) (cchat.Session, error) {
 	// SLOW IO TIME.
-	if simulateAustralianInternet() {
-		return nil, errors.New("Authentication timed out.")
+	if err := simulateAustralianInternet(); err != nil {
+		return nil, errors.Wrap(err, "Authentication failed")
 	}
 
 	return newSession(form[0]), nil