From 21913a8304c76dbc7fff0f3a1bda75d8e3a667ec Mon Sep 17 00:00:00 2001
From: Vladimir Mihailenco <vladimir.webdev@gmail.com>
Date: Tue, 12 Mar 2019 12:40:08 +0200
Subject: [PATCH] pubsub: drop a message when the channel is full

---
 pubsub.go      | 38 +++++++++++++++++++++++++++++++-------
 pubsub_test.go |  7 +++++++
 2 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/pubsub.go b/pubsub.go
index 0afb47c..e185511 100644
--- a/pubsub.go
+++ b/pubsub.go
@@ -3,6 +3,7 @@ package redis
 import (
 	"errors"
 	"fmt"
+	"strings"
 	"sync"
 	"time"
 
@@ -29,8 +30,9 @@ type PubSub struct {
 	cn       *pool.Conn
 	channels map[string]struct{}
 	patterns map[string]struct{}
-	closed   bool
-	exit     chan struct{}
+
+	closed bool
+	exit   chan struct{}
 
 	cmd *Cmd
 
@@ -39,6 +41,12 @@ type PubSub struct {
 	ping   chan struct{}
 }
 
+func (c *PubSub) String() string {
+	channels := mapKeys(c.channels)
+	channels = append(channels, mapKeys(c.patterns)...)
+	return fmt.Sprintf("PubSub(%s)", strings.Join(channels, ", "))
+}
+
 func (c *PubSub) init() {
 	c.exit = make(chan struct{})
 }
@@ -389,16 +397,23 @@ func (c *PubSub) ReceiveMessage() (*Message, error) {
 // It periodically sends Ping messages to test connection health.
 // The channel is closed with PubSub. Receive* APIs can not be used
 // after channel is created.
+//
+// If the Go channel is full for 30 seconds the message is dropped.
 func (c *PubSub) Channel() <-chan *Message {
 	c.chOnce.Do(c.initChannel)
 	return c.ch
 }
 
 func (c *PubSub) initChannel() {
+	const timeout = 30 * time.Second
+
 	c.ch = make(chan *Message, 100)
-	c.ping = make(chan struct{}, 10)
+	c.ping = make(chan struct{}, 1)
 
 	go func() {
+		timer := time.NewTimer(timeout)
+		timer.Stop()
+
 		var errCount int
 		for {
 			msg, err := c.Receive()
@@ -413,6 +428,7 @@ func (c *PubSub) initChannel() {
 				errCount++
 				continue
 			}
+
 			errCount = 0
 
 			// Any message is as good as a ping.
@@ -427,16 +443,24 @@ func (c *PubSub) initChannel() {
 			case *Pong:
 				// Ignore.
 			case *Message:
-				c.ch <- msg
+				timer.Reset(timeout)
+				select {
+				case c.ch <- msg:
+					if !timer.Stop() {
+						<-timer.C
+					}
+				case <-timer.C:
+					internal.Logf(
+						"redis: %s channel is full for %s (message is dropped)",
+						c, timeout)
+				}
 			default:
-				internal.Logf("redis: unknown message: %T", msg)
+				internal.Logf("redis: unknown message type: %T", msg)
 			}
 		}
 	}()
 
 	go func() {
-		const timeout = 5 * time.Second
-
 		timer := time.NewTimer(timeout)
 		timer.Stop()
 
diff --git a/pubsub_test.go b/pubsub_test.go
index 7f0021f..2d072fa 100644
--- a/pubsub_test.go
+++ b/pubsub_test.go
@@ -27,6 +27,13 @@ var _ = Describe("PubSub", func() {
 		Expect(client.Close()).NotTo(HaveOccurred())
 	})
 
+	It("implements Stringer", func() {
+		pubsub := client.PSubscribe("mychannel*")
+		defer pubsub.Close()
+
+		Expect(pubsub.String()).To(Equal("PubSub(mychannel*)"))
+	})
+
 	It("should support pattern matching", func() {
 		pubsub := client.PSubscribe("mychannel*")
 		defer pubsub.Close()