api: add ConnectionListener to the connection_pool

ConnectionListener provides an observer semantics for components interested
in knowing the role changes of connections in a ConnectionPool.

Closes #178

Author: oleg-jukovec

CHANGELOG.md

@@ -11,6 +11,8 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 ### Added
 
 - Support queue 1.2.0 (#177)
+- RoleListener interface for knowing the role changes of connections in
+  ConnectionPool (#178)
 
 ### Changed
 

connection_pool/connection_pool.go

@@ -32,17 +32,35 @@ var (
 	ErrNoHealthyInstance = errors.New("can't find healthy instance in pool")
 )
 
+// ConnectionListener provides an observer semantics for components interested
+// in knowing the role changes of connections in a ConnectionPool.
+type ConnectionListener interface {
+	// Added is called before a connection with a role added into a list of
+	// active connections.
+	Added(conn *tarantool.Connection, role Role)
+	// Removed is called after a connection with a role removed from a list
+	// of active connections.
+	Removed(conn *tarantool.Connection, role Role)
+	// Updated is called if a connection with a role updated in a list
+	// of active connections.
+	Updated(conn *tarantool.Connection, oldRole, newRole Role)
+}
+
 /*
 Additional options (configurable via ConnectWithOpts):
 
 - CheckTimeout - time interval to check for connection timeout and try to switch connection.
+
+- ConnectionListener - a listener for connection updates.
 */
 type OptsPool struct {
 	// timeout for timer to reopen connections
 	// that have been closed by some events and
 	// to relocate connection between subpools
 	// if ro/rw role has been updated
 	CheckTimeout time.Duration
+	// ConnectionListener provides an ability to observe connection updates.
+	ConnectionListener ConnectionListener
 }
 
 /*
@@ -174,9 +192,22 @@ func (connPool *ConnectionPool) closeImpl() []error {
 			if err := conn.Close(); err != nil {
 				errs = append(errs, err)
 			}
+			if conn := connPool.rwPool.DeleteConnByAddr(addr); conn != nil {
+				if connPool.opts.ConnectionListener != nil {
+					connPool.opts.ConnectionListener.Removed(conn, MasterRole)
+				}
+				continue
+			}
+			if conn := connPool.roPool.DeleteConnByAddr(addr); conn != nil {
+				if connPool.opts.ConnectionListener != nil {
+					connPool.opts.ConnectionListener.Removed(conn, ReplicaRole)
+				}
+				continue
+			}
+			if connPool.opts.ConnectionListener != nil {
+				connPool.opts.ConnectionListener.Removed(conn, UnknownRole)
+			}
 		}
-		connPool.rwPool.DeleteConnByAddr(addr)
-		connPool.roPool.DeleteConnByAddr(addr)
 	}
 
 	return errs
@@ -659,10 +690,22 @@ func (connPool *ConnectionPool) getConnectionFromPool(addr string) (*tarantool.C
 }
 
 func (connPool *ConnectionPool) deleteConnectionFromPool(addr string) {
-	_ = connPool.anyPool.DeleteConnByAddr(addr)
-	conn := connPool.rwPool.DeleteConnByAddr(addr)
-	if conn == nil {
-		connPool.roPool.DeleteConnByAddr(addr)
+	if conn := connPool.anyPool.DeleteConnByAddr(addr); conn != nil {
+		if conn := connPool.rwPool.DeleteConnByAddr(addr); conn != nil {
+			if connPool.opts.ConnectionListener != nil {
+				connPool.opts.ConnectionListener.Removed(conn, MasterRole)
+			}
+			return
+		}
+		if conn := connPool.roPool.DeleteConnByAddr(addr); conn != nil {
+			if connPool.opts.ConnectionListener != nil {
+				connPool.opts.ConnectionListener.Removed(conn, ReplicaRole)
+			}
+			return
+		}
+		if connPool.opts.ConnectionListener != nil {
+			connPool.opts.ConnectionListener.Removed(conn, UnknownRole)
+		}
 	}
 }
 
@@ -672,6 +715,10 @@ func (connPool *ConnectionPool) setConnectionToPool(addr string, conn *tarantool
 		return err
 	}
 
+	if connPool.opts.ConnectionListener != nil {
+		connPool.opts.ConnectionListener.Added(conn, role)
+	}
+
 	connPool.anyPool.AddConn(addr, conn)
 
 	switch role {
@@ -684,16 +731,32 @@ func (connPool *ConnectionPool) setConnectionToPool(addr string, conn *tarantool
 	return nil
 }
 
+func (connPool *ConnectionPool) updateConnectionInPool(addr string, conn *tarantool.Connection, oldRole Role, newRole Role) {
+	switch oldRole {
+	case MasterRole:
+		connPool.rwPool.DeleteConnByAddr(addr)
+	case ReplicaRole:
+		connPool.roPool.DeleteConnByAddr(addr)
+	}
+
+	if connPool.opts.ConnectionListener != nil {
+		connPool.opts.ConnectionListener.Updated(conn, oldRole, newRole)
+	}
+
+	switch newRole {
+	case MasterRole:
+		connPool.rwPool.AddConn(addr, conn)
+	case ReplicaRole:
+		connPool.roPool.AddConn(addr, conn)
+	}
+}
+
 func (connPool *ConnectionPool) refreshConnection(addr string) {
 	if conn, oldRole := connPool.getConnectionFromPool(addr); conn != nil {
 		if !conn.ClosedNow() {
-			curRole, _ := connPool.getConnectionRole(conn)
-			if oldRole != curRole {
-				connPool.deleteConnectionFromPool(addr)
-				err := connPool.setConnectionToPool(addr, conn)
-				if err != nil {
-					conn.Close()
-					log.Printf("tarantool: storing connection to %s failed: %s\n", addr, err.Error())
+			if curRole, err := connPool.getConnectionRole(conn); err == nil {
+				if oldRole != curRole {
+					connPool.updateConnectionInPool(addr, conn, oldRole, curRole)
 				}
 			}
 		}

connection_pool/connection_pool_test.go

@@ -208,6 +208,128 @@ func TestClose(t *testing.T) {
 	require.Nil(t, err)
 }
 
+type testListener struct {
+	added, closed, updated int
+	errs                   []error
+}
+
+func (tl *testListener) addErr(err error) {
+	tl.errs = append(tl.errs, err)
+}
+
+func (tl *testListener) Added(conn *tarantool.Connection, role connection_pool.Role) {
+	tl.added++
+
+	if conn == nil {
+		tl.addErr(fmt.Errorf("added conn == nil"))
+		return
+	}
+
+	addr := conn.Addr()
+	if addr == servers[0] {
+		if role != connection_pool.MasterRole {
+			tl.addErr(fmt.Errorf("unexpected added role %d for addr %s", role, addr))
+		}
+	} else if addr == servers[1] {
+		if role != connection_pool.ReplicaRole {
+			tl.addErr(fmt.Errorf("unexpected added role %d for addr %s", role, addr))
+		}
+	} else {
+		tl.addErr(fmt.Errorf("unexpected added addr %s", addr))
+	}
+}
+
+func (tl *testListener) Removed(conn *tarantool.Connection, role connection_pool.Role) {
+	tl.closed++
+
+	if conn == nil {
+		tl.addErr(fmt.Errorf("removed conn == nil"))
+		return
+	}
+
+	addr := conn.Addr()
+	if addr == servers[0] || addr == servers[1] {
+		if role != connection_pool.ReplicaRole {
+			tl.addErr(fmt.Errorf("unexpected removed role %d for addr %s", role, addr))
+		}
+	} else {
+		tl.addErr(fmt.Errorf("unexpected removed addr %s", addr))
+	}
+}
+
+func (tl *testListener) Updated(conn *tarantool.Connection, oldRole, newRole connection_pool.Role) {
+	tl.updated++
+
+	if oldRole != connection_pool.MasterRole {
+		tl.addErr(fmt.Errorf("unexpected oldRole = %d", oldRole))
+	}
+
+	if newRole != connection_pool.ReplicaRole {
+		tl.addErr(fmt.Errorf("unexpected newRole = %d", newRole))
+	}
+
+	if conn == nil {
+		tl.addErr(fmt.Errorf("updated conn == nil"))
+		return
+	}
+
+	addr := conn.Addr()
+	if addr != servers[0] {
+		tl.addErr(fmt.Errorf("unexpected updated addr: %s", addr))
+	}
+}
+
+func TestConnectionListener(t *testing.T) {
+	poolServers := []string{servers[0], servers[1]}
+	roles := []bool{false, true}
+
+	err := test_helpers.SetClusterRO(poolServers, connOpts, roles)
+	require.Nilf(t, err, "fail to set roles for cluster")
+
+	tl := &testListener{}
+	poolOpts := connection_pool.OptsPool{
+		CheckTimeout:       100 * time.Microsecond,
+		ConnectionListener: tl,
+	}
+	connPool, err := connection_pool.ConnectWithOpts(poolServers, connOpts, poolOpts)
+	require.Nilf(t, err, "failed to connect")
+	require.NotNilf(t, connPool, "conn is nil after Connect")
+
+	_, err = connPool.Call17("box.cfg", []interface{}{map[string]bool{
+		"read_only": true,
+	}}, connection_pool.RW)
+	require.Nilf(t, err, "failed to make ro")
+	for i := 0; i < 10; i++ {
+		if tl.updated == 1 {
+			break
+		}
+		time.Sleep(poolOpts.CheckTimeout)
+	}
+
+	connPool.Close()
+
+	args := test_helpers.CheckStatusesArgs{
+		ConnPool:           connPool,
+		Mode:               connection_pool.ANY,
+		Servers:            poolServers,
+		ExpectedPoolStatus: false,
+		ExpectedStatuses: map[string]bool{
+			poolServers[0]: false,
+			poolServers[1]: false,
+		},
+	}
+
+	err = test_helpers.Retry(test_helpers.CheckPoolStatuses, args, defaultCountRetry, defaultTimeoutRetry)
+	require.Nil(t, err)
+
+	for _, err := range tl.errs {
+		t.Errorf("Unexpected error: %s", err)
+	}
+	require.Equalf(t, tl.added, len(poolServers), "unexpected added count")
+	require.Equalf(t, tl.closed, len(poolServers), "unexpected closed count")
+	require.Equalf(t, tl.updated, 1, "unexpected updated count")
+}
+
 func TestRequestOnClosed(t *testing.T) {
 	server1 := servers[0]
 	server2 := servers[1]