feat: add proactive push notification processing to WithReader

- Add push notification processing to Conn.WithReader method
- Process notifications immediately before every read operation
- Provides proactive notification handling vs reactive processing
- Add proper error handling with internal.Logger
- Non-blocking implementation that doesn't break Redis operations
- Complements existing processing in Pool.Put and isHealthyConn

Benefits:
- Immediate processing when notifications arrive
- Called before every read operation for optimal timing
- Prevents notification backlog accumulation
- More responsive to Redis cluster changes
- Better user experience during migrations
- Optimal placement for catching asynchronous notifications

Implementation:
- Type-safe interface assertion for processor
- Context-aware error handling with logging
- Maintains backward compatibility
- Consistent with existing pool patterns
- Three-layer processing strategy: WithReader (proactive) + Pool.Put + isHealthyConn (reactive)

Use cases:
- MOVING/MIGRATING/MIGRATED notifications for slot migrations
- FAILING_OVER/FAILED_OVER notifications for failover scenarios
- Real-time cluster topology change awareness
- Improved connection utilization efficiency

Author: ndyakov

internal/pool/conn.go

@@ -7,6 +7,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/redis/go-redis/v9/internal"
 	"github.com/redis/go-redis/v9/internal/proto"
 	"github.com/redis/go-redis/v9/internal/pushnotif"
 )
@@ -77,11 +78,23 @@ func (cn *Conn) RemoteAddr() net.Addr {
 func (cn *Conn) WithReader(
 	ctx context.Context, timeout time.Duration, fn func(rd *proto.Reader) error,
 ) error {
+	// Process any pending push notifications before executing the read function
+	// This ensures push notifications are handled as soon as they arrive
+	if cn.PushNotificationProcessor != nil {
+		// Type assert to the processor interface
+		if err := cn.PushNotificationProcessor.ProcessPendingNotifications(ctx, cn.rd); err != nil {
+			// Log the error but don't fail the read operation
+			// Push notification processing errors shouldn't break normal Redis operations
+			internal.Logger.Printf(ctx, "push: error processing pending notifications in WithReader: %v", err)
+		}
+	}
+
 	if timeout >= 0 {
 		if err := cn.netConn.SetReadDeadline(cn.deadline(ctx, timeout)); err != nil {
 			return err
 		}
 	}
+
 	return fn(cn.rd)
 }
 

redis.go

@@ -386,7 +386,7 @@ func (c *baseClient) initConn(ctx context.Context, cn *pool.Conn) error {
 
 	// for redis-server versions that do not support the HELLO command,
 	// RESP2 will continue to be used.
-  if err = conn.Hello(ctx, c.opt.Protocol, username, password, c.opt.ClientName).Err(); err == nil {
+	if err = conn.Hello(ctx, c.opt.Protocol, username, password, c.opt.ClientName).Err(); err == nil {
 		// Authentication successful with HELLO command
 	} else if !isRedisError(err) {
 		// When the server responds with the RESP protocol and the result is not a normal
@@ -813,25 +813,25 @@ func (c *Client) Options() *Options {
 
 // initializePushProcessor initializes the push notification processor for any client type.
 // This is a shared helper to avoid duplication across NewClient, NewFailoverClient, and NewSentinelClient.
-func initializePushProcessor(opt *Options, useVoidByDefault bool) PushNotificationProcessorInterface {
+func initializePushProcessor(opt *Options) PushNotificationProcessorInterface {
 	// Always use custom processor if provided
 	if opt.PushNotificationProcessor != nil {
 		return opt.PushNotificationProcessor
 	}
 
 	// For regular clients, respect the PushNotifications setting
-	if !useVoidByDefault && opt.PushNotifications {
+	if opt.PushNotifications {
 		// Create default processor when push notifications are enabled
 		return NewPushNotificationProcessor()
 	}
 
-	// Create void processor when push notifications are disabled or for specialized clients
+	// Create void processor when push notifications are disabled
 	return NewVoidPushNotificationProcessor()
 }
 
 // initializePushProcessor initializes the push notification processor for this client.
 func (c *Client) initializePushProcessor() {
-	c.pushProcessor = initializePushProcessor(c.opt, false)
+	c.pushProcessor = initializePushProcessor(c.opt)
 }
 
 // RegisterPushNotificationHandler registers a handler for a specific push notification name.
@@ -987,7 +987,7 @@ func newConn(opt *Options, connPool pool.Pooler, parentHooks *hooksMixin) *Conn
 
 	// Initialize push notification processor using shared helper
 	// Use void processor by default for connections (typically don't need push notifications)
-	c.pushProcessor = initializePushProcessor(opt, true)
+	c.pushProcessor = initializePushProcessor(opt)
 
 	c.cmdable = c.Process
 	c.statefulCmdable = c.Process

sentinel.go

@@ -433,7 +433,7 @@ func NewFailoverClient(failoverOpt *FailoverOptions) *Client {
 
 	// Initialize push notification processor using shared helper
 	// Use void processor by default for failover clients (typically don't need push notifications)
-	rdb.pushProcessor = initializePushProcessor(opt, true)
+	rdb.pushProcessor = initializePushProcessor(opt)
 
 	connPool = newConnPool(opt, rdb.dialHook)
 	rdb.connPool = connPool
@@ -503,7 +503,7 @@ func NewSentinelClient(opt *Options) *SentinelClient {
 
 	// Initialize push notification processor using shared helper
 	// Use void processor by default for sentinel clients (typically don't need push notifications)
-	c.pushProcessor = initializePushProcessor(opt, true)
+	c.pushProcessor = initializePushProcessor(opt)
 
 	c.initHooks(hooks{
 		dial:    c.baseClient.dial,