fix(pool): wip, pool reauth should not interfere with handoff

auth/conn_reauth_credentials_listener.go

@@ -0,0 +1,114 @@
+package auth
+
+import (
+	"runtime"
+	"time"
+
+	"github.com/redis/go-redis/v9/internal/pool"
+)
+
+// ConnReAuthCredentialsListener is a struct that implements the CredentialsListener interface.
+// It is used to re-authenticate the credentials when they are updated.
+// It holds reference to the connection to re-authenticate and will pass it to the reAuth and onErr callbacks.
+// It contains:
+// - reAuth: a function that takes the new credentials and returns an error if any.
+// - onErr: a function that takes an error and handles it.
+// - conn: the connection to re-authenticate.
+// - checkUsableTimeout: the timeout to wait for the connection to be usable - default is 1 second.
+type ConnReAuthCredentialsListener struct {
+	// reAuth is called when the credentials are updated.
+	reAuth func(conn *pool.Conn, credentials Credentials) error
+	// onErr is called when an error occurs.
+	onErr func(conn *pool.Conn, err error)
+	// conn is the connection to re-authenticate.
+	conn *pool.Conn
+	// checkUsableTimeout is the timeout to wait for the connection to be usable
+	// when the credentials are updated.
+	// default is 1 second
+	checkUsableTimeout time.Duration
+}
+
+// OnNext is called when the credentials are updated.
+// It calls the reAuth function with the new credentials.
+// If the reAuth function returns an error, it calls the onErr function with the error.
+func (c *ConnReAuthCredentialsListener) OnNext(credentials Credentials) {
+	if c.conn.IsClosed() {
+		return
+	}
+
+	if c.reAuth == nil {
+		return
+	}
+
+	var err error
+
+	// this hard-coded timeout is not ideal
+	timeout := time.After(c.checkUsableTimeout)
+	// wait for the connection to be usable
+	// this is important because the connection pool may be in the process of reconnecting the connection
+	// and we don't want to interfere with that process
+	// but we also don't want to block for too long, so incorporate a timeout
+	for err == nil && !c.conn.Usable.CompareAndSwap(true, false) {
+		select {
+		case <-timeout:
+			err = pool.ErrConnUnusableTimeout
+		default:
+			runtime.Gosched()
+		}
+	}
+	if err == nil {
+		defer c.conn.SetUsable(true)
+	}
+
+	for err == nil && !c.conn.Used.CompareAndSwap(false, true) {
+		select {
+		case <-timeout:
+			err = pool.ErrConnUnusableTimeout
+		default:
+			runtime.Gosched()
+		}
+	}
+
+	// we timed out waiting for the connection to be usable
+	// do not try to re-authenticate, instead call the onErr function
+	// which will handle the error and close the connection if needed
+	if err != nil {
+		c.OnError(err)
+		return
+	}
+
+	defer c.conn.Used.Store(false)
+	// we set the usable flag, so restore it back to usable after we're done
+	if err = c.reAuth(c.conn, credentials); err != nil {
+		c.OnError(err)
+	}
+}
+
+// OnError is called when an error occurs.
+// It can be called from both the credentials provider and the reAuth function.
+func (c *ConnReAuthCredentialsListener) OnError(err error) {
+	if c.onErr == nil {
+		return
+	}
+
+	c.onErr(c.conn, err)
+}
+
+// SetCheckUsableTimeout sets the timeout for the connection to be usable.
+func (c *ConnReAuthCredentialsListener) SetCheckUsableTimeout(timeout time.Duration) {
+	c.checkUsableTimeout = timeout
+}
+
+// NewConnReAuthCredentialsListener creates a new ConnReAuthCredentialsListener.
+// Implements the auth.CredentialsListener interface.
+func NewConnReAuthCredentialsListener(conn *pool.Conn, reAuth func(conn *pool.Conn, credentials Credentials) error, onErr func(conn *pool.Conn, err error)) *ConnReAuthCredentialsListener {
+	return &ConnReAuthCredentialsListener{
+		conn:               conn,
+		reAuth:             reAuth,
+		onErr:              onErr,
+		checkUsableTimeout: 1 * time.Second,
+	}
+}
+
+// Ensure ConnReAuthCredentialsListener implements the CredentialsListener interface.
+var _ CredentialsListener = (*ConnReAuthCredentialsListener)(nil)

auth/reauth_credentials_listener.go

@@ -44,4 +44,4 @@ func NewReAuthCredentialsListener(reAuth func(credentials Credentials) error, on
 }
 
 // Ensure ReAuthCredentialsListener implements the CredentialsListener interface.
-var _ CredentialsListener = (*ReAuthCredentialsListener)(nil)
+var _ CredentialsListener = (*ReAuthCredentialsListener)(nil)

error.go

@@ -108,10 +108,12 @@ func isRedisError(err error) bool {
 
 func isBadConn(err error, allowTimeout bool, addr string) bool {
 	switch err {
-	case nil:
-		return false
-	case context.Canceled, context.DeadlineExceeded:
-		return true
+		case nil:
+			return false
+		case context.Canceled, context.DeadlineExceeded:
+			return true
+		case pool.ErrConnUnusableTimeout:
+			return true
 	}
 
 	if isRedisError(err) {

internal/pool/buffer_size_test.go

@@ -3,7 +3,6 @@ package pool_test
 import (
 	"bufio"
 	"context"
-	"net"
 	"unsafe"
 
 	. "github.com/bsm/ginkgo/v2"
@@ -124,20 +123,27 @@ var _ = Describe("Buffer Size Configuration", func() {
 })
 
 // Helper functions to extract buffer sizes using unsafe pointers
+// The struct layout must match pool.Conn exactly to avoid checkptr violations
 func getWriterBufSizeUnsafe(cn *pool.Conn) int {
+	// Import required for atomic types
+	type atomicBool struct{ _ uint32 }
+	type atomicInt64 struct{ _ int64 }
+
 	cnPtr := (*struct {
-		usedAt  int64
-		netConn net.Conn
-		rd      *proto.Reader
-		bw      *bufio.Writer
-		wr      *proto.Writer
-		// ... other fields
+		id            uint64        // First field in pool.Conn
+		usedAt        int64         // Second field (atomic)
+		netConnAtomic interface{}   // atomic.Value (interface{} has same size)
+		rd            *proto.Reader
+		bw            *bufio.Writer
+		wr            *proto.Writer
+		// We only need fields up to bw, so we can stop here
 	})(unsafe.Pointer(cn))
 
 	if cnPtr.bw == nil {
 		return -1
 	}
 
+	// bufio.Writer internal structure
 	bwPtr := (*struct {
 		err error
 		buf []byte
@@ -150,18 +156,20 @@ func getWriterBufSizeUnsafe(cn *pool.Conn) int {
 
 func getReaderBufSizeUnsafe(cn *pool.Conn) int {
 	cnPtr := (*struct {
-		usedAt  int64
-		netConn net.Conn
-		rd      *proto.Reader
-		bw      *bufio.Writer
-		wr      *proto.Writer
-		// ... other fields
+		id            uint64        // First field in pool.Conn
+		usedAt        int64         // Second field (atomic)
+		netConnAtomic interface{}   // atomic.Value (interface{} has same size)
+		rd            *proto.Reader
+		bw            *bufio.Writer
+		wr            *proto.Writer
+		// We only need fields up to rd, so we can stop here
 	})(unsafe.Pointer(cn))
 
 	if cnPtr.rd == nil {
 		return -1
 	}
 
+	// proto.Reader internal structure
 	rdPtr := (*struct {
 		rd *bufio.Reader
 	})(unsafe.Pointer(cnPtr.rd))
@@ -170,6 +178,7 @@ func getReaderBufSizeUnsafe(cn *pool.Conn) int {
 		return -1
 	}
 
+	// bufio.Reader internal structure
 	bufReaderPtr := (*struct {
 		buf          []byte
 		rd           interface{}

internal/pool/conn.go

@@ -40,6 +40,9 @@ func generateConnID() uint64 {
 }
 
 type Conn struct {
+	// Connection identifier for unique tracking
+	id uint64 // Unique numeric identifier for this connection
+
 	usedAt int64 // atomic
 
 	// Lock-free netConn access using atomic.Value
@@ -54,7 +57,34 @@ type Conn struct {
 	// Only used for the brief period during SetNetConn and HasBufferedData/PeekReplyTypeSafe
 	readerMu sync.RWMutex
 
-	Inited    atomic.Bool
+	// Design note:
+	// Why have both Usable and Used?
+	// _Usable_ is used to mark a connection as safe for use by clients, the connection can still
+	// be in the pool but not Usable at the moment (e.g. handoff in progress).
+	// _Used_ is used to mark a connection as used when a command is going to be processed on that connection.
+	// this is going to happen once the connection is picked from the pool.
+	//
+	// If a background operation needs to use the connection, it will mark it as Not Usable and only use it when it
+	// is not in use. That way, the connection won't be used to send multiple commands at the same time and
+	// potentially corrupt the command stream.
+
+	// Usable flag to mark connection as safe for use
+	// It is false before initialization and after a handoff is marked
+	// It will be false during other background operations like re-authentication
+	Usable atomic.Bool
+
+	// Used flag to mark connection as used when a command is going to be
+	// processed on that connection. This is used to prevent a race condition with
+	// background operations that may execute commands, like re-authentication.
+	Used atomic.Bool
+
+	// Inited flag to mark connection as initialized, this is almost the same as usable
+	// but it is used to make sure we don't initialize a network connection twice
+	// On handoff, the network connection is replaced, but the Conn struct is reused
+	// this flag will be set to false when the network connection is replaced and
+	// set to true after the new network connection is initialized
+	Inited atomic.Bool
+
 	pooled    bool
 	pubsub    bool
 	closed    atomic.Bool
@@ -75,11 +105,7 @@ type Conn struct {
 	// Connection initialization function for reconnections
 	initConnFunc func(context.Context, *Conn) error
 
-	// Connection identifier for unique tracking
-	id uint64 // Unique numeric identifier for this connection
-
 	// Handoff state - using atomic operations for lock-free access
-	usableAtomic         atomic.Bool   // Connection usability state
 	handoffRetriesAtomic atomic.Uint32 // Retry counter for handoff attempts
 
 	// Atomic handoff state to prevent race conditions
@@ -116,7 +142,7 @@ func NewConnWithBufferSize(netConn net.Conn, readBufSize, writeBufSize int) *Con
 	cn.netConnAtomic.Store(&atomicNetConn{conn: netConn})
 
 	// Initialize atomic state
-	cn.usableAtomic.Store(false)     // false initially, set to true after initialization
+	cn.Usable.Store(false)           // false initially, set to true after initialization
 	cn.handoffRetriesAtomic.Store(0) // 0 initially
 
 	// Initialize handoff state atomically
@@ -162,12 +188,12 @@ func (cn *Conn) setNetConn(netConn net.Conn) {
 
 // isUsable returns true if the connection is safe to use (lock-free).
 func (cn *Conn) isUsable() bool {
-	return cn.usableAtomic.Load()
+	return cn.Usable.Load()
 }
 
 // setUsable sets the usable flag atomically (lock-free).
 func (cn *Conn) setUsable(usable bool) {
-	cn.usableAtomic.Store(usable)
+	cn.Usable.Store(usable)
 }
 
 // getHandoffState returns the current handoff state atomically (lock-free).
@@ -455,9 +481,24 @@ func (cn *Conn) MarkQueuedForHandoff() error {
 	const maxRetries = 50
 	const baseDelay = time.Microsecond
 
+	connAcquired := false
 	for attempt := 0; attempt < maxRetries; attempt++ {
-		currentState := cn.getHandoffState()
+		// If CAS failed, add exponential backoff to reduce contention
+		// the delay will be 1, 2, 4... up to 512 microseconds
+		// Moving this to the top of the loop to avoid "continue" without delay
+		if attempt > 0 && attempt < maxRetries-1 {
+			delay := baseDelay * time.Duration(1<<uint(attempt%10)) // Cap exponential growth
+			time.Sleep(delay)
+		}
+
+		// first we need to mark the connection as not usable
+		// to prevent the pool from returning it to the caller
+		if !connAcquired && !cn.Usable.CompareAndSwap(true, false) {
+			continue
+		}
+		connAcquired = true
 
+		currentState := cn.getHandoffState()
 		// Check if marked for handoff
 		if !currentState.ShouldHandoff {
 			return errors.New("connection was not marked for handoff")
@@ -472,16 +513,12 @@ func (cn *Conn) MarkQueuedForHandoff() error {
 
 		// Atomic compare-and-swap to update state
 		if cn.handoffStateAtomic.CompareAndSwap(currentState, newState) {
-			cn.setUsable(false)
+			// queue the handoff for processing
+			// the connection is now "acquired" (marked as not usable) by the handoff
+			// and it won't be returned to any other callers until the handoff is complete
 			return nil
 		}
 
-		// If CAS failed, add exponential backoff to reduce contention
-		// the delay will be 1, 2, 4... up to 512 microseconds
-		if attempt < maxRetries-1 {
-			delay := baseDelay * time.Duration(1<<uint(attempt%10)) // Cap exponential growth
-			time.Sleep(delay)
-		}
 	}
 
 	return fmt.Errorf("failed to mark connection as queued for handoff after %d attempts due to high contention", maxRetries)
@@ -527,7 +564,8 @@ func (cn *Conn) ClearHandoffState() {
 	// Atomically set clean state
 	cn.setHandoffState(cleanState)
 	cn.setHandoffRetries(0)
-	cn.setUsable(true) // Connection is safe to use again after handoff completes
+	// Clearing handoff state also means the connection is usable again
+	cn.setUsable(true)
 }
 
 // IncrementAndGetHandoffRetries atomically increments and returns handoff retries (lock-free).