server/group: refactor with shared abstractions and fix concurrency issues (#5222)

* server/group: refactor group package with shared abstractions and fix concurrency issues

Extract common patterns into reusable components:
- groupRegistry[G]: generic concurrent map for group lifecycle management
- baseGroup: shared plumbing for listener-based groups (TCP, HTTPS, TCPMux)
- Listener: unified virtual listener replacing 3 identical implementations

Fix concurrency issues:
- Stale-pointer race: isCurrent check + errGroupStale + controller retry loops
- Worker generation safety: pass realLn and acceptCh as params instead of reading mutable fields
- Connection leak: close conn on worker panic recovery path
- ABBA deadlock in HTTP UnRegister: consistent lock ordering (group.mu -> registry.mu)
- Round-robin overflow in HTTPGroup: use unsigned modulo

Add unit tests (17 tests) for registry, listener, and baseGroup.
Add TCPMux group load balancing e2e test.

* server/group: replace tautological assertion with require.NotPanics

* server/group: remove blank line between doc comment and type declaration

server/group/tcpmux.go

@@ -18,118 +18,100 @@ import (
 	"context"
 	"fmt"
 	"net"
-	"sync"
-
-	gerr "github.com/fatedier/golib/errors"
 
 	v1 "github.com/fatedier/frp/pkg/config/v1"
 	"github.com/fatedier/frp/pkg/util/tcpmux"
 	"github.com/fatedier/frp/pkg/util/vhost"
 )
 
-// TCPMuxGroupCtl manage all TCPMuxGroups
+// TCPMuxGroupCtl manages all TCPMuxGroups.
 type TCPMuxGroupCtl struct {
-	groups map[string]*TCPMuxGroup
-
-	// portManager is used to manage port
+	groupRegistry[*TCPMuxGroup]
 	tcpMuxHTTPConnectMuxer *tcpmux.HTTPConnectTCPMuxer
-	mu                     sync.Mutex
 }
 
-// NewTCPMuxGroupCtl return a new TCPMuxGroupCtl
+// NewTCPMuxGroupCtl returns a new TCPMuxGroupCtl.
 func NewTCPMuxGroupCtl(tcpMuxHTTPConnectMuxer *tcpmux.HTTPConnectTCPMuxer) *TCPMuxGroupCtl {
 	return &TCPMuxGroupCtl{
-		groups:                 make(map[string]*TCPMuxGroup),
+		groupRegistry:          newGroupRegistry[*TCPMuxGroup](),
 		tcpMuxHTTPConnectMuxer: tcpMuxHTTPConnectMuxer,
 	}
 }
 
-// Listen is the wrapper for TCPMuxGroup's Listen
-// If there are no group, we will create one here
+// Listen is the wrapper for TCPMuxGroup's Listen.
+// If there is no group, one will be created.
 func (tmgc *TCPMuxGroupCtl) Listen(
 	ctx context.Context,
 	multiplexer, group, groupKey string,
 	routeConfig vhost.RouteConfig,
 ) (l net.Listener, err error) {
-	tmgc.mu.Lock()
-	tcpMuxGroup, ok := tmgc.groups[group]
-	if !ok {
-		tcpMuxGroup = NewTCPMuxGroup(tmgc)
-		tmgc.groups[group] = tcpMuxGroup
-	}
-	tmgc.mu.Unlock()
+	for {
+		tcpMuxGroup := tmgc.getOrCreate(group, func() *TCPMuxGroup {
+			return NewTCPMuxGroup(tmgc)
+		})
 
-	switch v1.TCPMultiplexerType(multiplexer) {
-	case v1.TCPMultiplexerHTTPConnect:
-		return tcpMuxGroup.HTTPConnectListen(ctx, group, groupKey, routeConfig)
-	default:
-		err = fmt.Errorf("unknown multiplexer [%s]", multiplexer)
-		return
+		switch v1.TCPMultiplexerType(multiplexer) {
+		case v1.TCPMultiplexerHTTPConnect:
+			l, err = tcpMuxGroup.HTTPConnectListen(ctx, group, groupKey, routeConfig)
+			if err == errGroupStale {
+				continue
+			}
+			return
+		default:
+			return nil, fmt.Errorf("unknown multiplexer [%s]", multiplexer)
+		}
 	}
 }
 
-// RemoveGroup remove TCPMuxGroup from controller
-func (tmgc *TCPMuxGroupCtl) RemoveGroup(group string) {
-	tmgc.mu.Lock()
-	defer tmgc.mu.Unlock()
-	delete(tmgc.groups, group)
-}
-
-// TCPMuxGroup route connections to different proxies
+// TCPMuxGroup routes connections to different proxies.
 type TCPMuxGroup struct {
-	group           string
-	groupKey        string
+	baseGroup
+
 	domain          string
 	routeByHTTPUser string
 	username        string
 	password        string
-
-	acceptCh chan net.Conn
-	tcpMuxLn net.Listener
-	lns      []*TCPMuxGroupListener
-	ctl      *TCPMuxGroupCtl
-	mu       sync.Mutex
+	ctl             *TCPMuxGroupCtl
 }
 
-// NewTCPMuxGroup return a new TCPMuxGroup
+// NewTCPMuxGroup returns a new TCPMuxGroup.
 func NewTCPMuxGroup(ctl *TCPMuxGroupCtl) *TCPMuxGroup {
 	return &TCPMuxGroup{
-		lns:      make([]*TCPMuxGroupListener, 0),
-		ctl:      ctl,
-		acceptCh: make(chan net.Conn),
+		ctl: ctl,
 	}
 }
 
-// Listen will return a new TCPMuxGroupListener
-// if TCPMuxGroup already has a listener, just add a new TCPMuxGroupListener to the queues
-// otherwise, listen on the real address
+// HTTPConnectListen will return a new Listener.
+// If TCPMuxGroup already has a listener, just add a new Listener to the queues,
+// otherwise listen on the real address.
 func (tmg *TCPMuxGroup) HTTPConnectListen(
 	ctx context.Context,
 	group, groupKey string,
 	routeConfig vhost.RouteConfig,
-) (ln *TCPMuxGroupListener, err error) {
+) (ln *Listener, err error) {
 	tmg.mu.Lock()
 	defer tmg.mu.Unlock()
+	if !tmg.ctl.isCurrent(group, func(cur *TCPMuxGroup) bool { return cur == tmg }) {
+		return nil, errGroupStale
+	}
 	if len(tmg.lns) == 0 {
 		// the first listener, listen on the real address
 		tcpMuxLn, errRet := tmg.ctl.tcpMuxHTTPConnectMuxer.Listen(ctx, &routeConfig)
 		if errRet != nil {
 			return nil, errRet
 		}
-		ln = newTCPMuxGroupListener(group, tmg, tcpMuxLn.Addr())
 
-		tmg.group = group
-		tmg.groupKey = groupKey
 		tmg.domain = routeConfig.Domain
 		tmg.routeByHTTPUser = routeConfig.RouteByHTTPUser
 		tmg.username = routeConfig.Username
 		tmg.password = routeConfig.Password
-		tmg.tcpMuxLn = tcpMuxLn
-		tmg.lns = append(tmg.lns, ln)
-		if tmg.acceptCh == nil {
-			tmg.acceptCh = make(chan net.Conn)
-		}
-		go tmg.worker()
+		tmg.initBase(group, groupKey, tcpMuxLn, func() {
+			tmg.ctl.removeIf(tmg.group, func(cur *TCPMuxGroup) bool {
+				return cur == tmg
+			})
+		})
+		ln = tmg.newListener(tcpMuxLn.Addr())
+		go tmg.worker(tcpMuxLn, tmg.acceptCh)
 	} else {
 		// route config in the same group must be equal
 		if tmg.group != group || tmg.domain != routeConfig.Domain ||
@@ -141,90 +123,7 @@ func (tmg *TCPMuxGroup) HTTPConnectListen(
 		if tmg.groupKey != groupKey {
 			return nil, ErrGroupAuthFailed
 		}
-		ln = newTCPMuxGroupListener(group, tmg, tmg.lns[0].Addr())
-		tmg.lns = append(tmg.lns, ln)
+		ln = tmg.newListener(tmg.lns[0].Addr())
 	}
 	return
 }
-
-// worker is called when the real TCP listener has been created
-func (tmg *TCPMuxGroup) worker() {
-	for {
-		c, err := tmg.tcpMuxLn.Accept()
-		if err != nil {
-			return
-		}
-		err = gerr.PanicToError(func() {
-			tmg.acceptCh <- c
-		})
-		if err != nil {
-			return
-		}
-	}
-}
-
-func (tmg *TCPMuxGroup) Accept() <-chan net.Conn {
-	return tmg.acceptCh
-}
-
-// CloseListener remove the TCPMuxGroupListener from the TCPMuxGroup
-func (tmg *TCPMuxGroup) CloseListener(ln *TCPMuxGroupListener) {
-	tmg.mu.Lock()
-	defer tmg.mu.Unlock()
-	for i, tmpLn := range tmg.lns {
-		if tmpLn == ln {
-			tmg.lns = append(tmg.lns[:i], tmg.lns[i+1:]...)
-			break
-		}
-	}
-	if len(tmg.lns) == 0 {
-		close(tmg.acceptCh)
-		tmg.tcpMuxLn.Close()
-		tmg.ctl.RemoveGroup(tmg.group)
-	}
-}
-
-// TCPMuxGroupListener
-type TCPMuxGroupListener struct {
-	groupName string
-	group     *TCPMuxGroup
-
-	addr    net.Addr
-	closeCh chan struct{}
-}
-
-func newTCPMuxGroupListener(name string, group *TCPMuxGroup, addr net.Addr) *TCPMuxGroupListener {
-	return &TCPMuxGroupListener{
-		groupName: name,
-		group:     group,
-		addr:      addr,
-		closeCh:   make(chan struct{}),
-	}
-}
-
-// Accept will accept connections from TCPMuxGroup
-func (ln *TCPMuxGroupListener) Accept() (c net.Conn, err error) {
-	var ok bool
-	select {
-	case <-ln.closeCh:
-		return nil, ErrListenerClosed
-	case c, ok = <-ln.group.Accept():
-		if !ok {
-			return nil, ErrListenerClosed
-		}
-		return c, nil
-	}
-}
-
-func (ln *TCPMuxGroupListener) Addr() net.Addr {
-	return ln.addr
-}
-
-// Close close the listener
-func (ln *TCPMuxGroupListener) Close() (err error) {
-	close(ln.closeCh)
-
-	// remove self from TcpMuxGroup
-	ln.group.CloseListener(ln)
-	return
-}