server/shard: added UpdatePlayer(), which should be used whenever player struct state needs to be updated to prevent race conditions

README.md

@@ -2,9 +2,9 @@
 
 A toy implementation of the [Fusionfall Packet Protocol](https://openpunk.com/pages/fusionfall-openfusion/) written in Go.
 
-## Login Sever
+## Landwalker demo
 
-An example login server implementation exists in `server/`. This implementation should be compatible with existing OpenFusion databases, however this only exists as an example and doesn't direct clients to a shard server (they're softlocked after the tutorial, or during character selection).
+An implementation of a landwalker server is located in `server/`. This includes a functional login server and a dummy shard (supporting the minimum amount of packets necessary). The DB implementation in `core/db/` matches the OpenFusion 1.4 SQLite tables, which the login server located in `server/` uses. There's no support for NPCs nor other players, and is liable to softlock the client.
 
 ## Generating structures
 

core/protocol/cnpeer.go

@@ -120,7 +120,7 @@ func (peer *CNPeer) Handler() {
 		}
 
 		// grab buffer && read packet body
-		if err := func() error { // we wrap this in a closure so we can easily defer the buffer return to pool
+		if err := func() error {
 			buf := pool.Get()
 			defer pool.Put(buf)
 			if _, err := buf.ReadFrom(io.LimitReader(peer.conn, int64(sz))); err != nil {

server/join.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/CPunch/gopenfusion/core"
 	"github.com/CPunch/gopenfusion/core/protocol"
 )
 
@@ -18,21 +19,30 @@ func (server *ShardServer) RequestEnter(peer *protocol.CNPeer, pkt protocol.Pack
 		return err
 	}
 
-	plr, err := server.dbHndlr.GetPlayer(int(loginData.PlayerID))
-	if err != nil {
-		peer.Send(protocol.P_FE2CL_REP_PC_ENTER_FAIL, protocol.SP_FE2CL_REP_PC_ENTER_FAIL{})
-		return err
+	// attach player
+	var resp *protocol.SP_FE2CL_REP_PC_ENTER_SUCC
+	if err := server.UpdatePlayer(peer, func(old *core.Player) (*core.Player, error) {
+		if old != nil { // resending a shard enter packet?
+			return nil, fmt.Errorf("resent enter packet!")
 		}
 
-	// attach player
-	server.JoinPlayer(peer, plr)
+		plr, err := server.dbHndlr.GetPlayer(int(loginData.PlayerID))
+		if err != nil {
+			return nil, err
+		}
 
-	resp := &protocol.SP_FE2CL_REP_PC_ENTER_SUCC{
+		resp = &protocol.SP_FE2CL_REP_PC_ENTER_SUCC{
 			IID:           int32(plr.PlayerID),
 			PCLoadData2CL: plr.ToPCLoadData2CL(),
 			UiSvrTime:     uint64(time.Now().Unix()),
 		}
 
+		return plr, nil
+	}); err != nil {
+		peer.Send(protocol.P_FE2CL_REP_PC_ENTER_FAIL, protocol.SP_FE2CL_REP_PC_ENTER_FAIL{})
+		return err
+	}
+
 	// setup key
 	peer.E_key = protocol.CreateNewKey(resp.UiSvrTime, uint64(resp.IID+1), uint64(resp.PCLoadData2CL.IFusionMatter+1))
 	peer.FE_key = loginData.FEKey
@@ -45,7 +55,7 @@ func (server *ShardServer) LoadingComplete(peer *protocol.CNPeer, pkt protocol.P
 	var loadComplete protocol.SP_CL2FE_REQ_PC_LOADING_COMPLETE
 	pkt.Decode(&loadComplete)
 
-	plr := server.GetPlayer(peer)
+	plr := server.LoadPlayer(peer)
 	if plr == nil {
 		return fmt.Errorf("peer has no player attached!")
 	}

server/shardServer.go

@@ -23,8 +23,9 @@ type ShardServer struct {
 	port               int
 	dbHndlr            *db.DBHandler
 	packetHandlers     map[uint32]PacketHandler
-	peers              sync.Map // [*protocol.CNPeer]*core.Player
 	loginMetadataQueue sync.Map // [int64]*LoginMetadata w/ int64 = serialKey
+	peersLock          sync.Mutex
+	peers              sync.Map // [*protocol.CNPeer]core.Player
 }
 
 func NewShardServer(dbHndlr *db.DBHandler, port int) (*ShardServer, error) {
@@ -90,7 +91,7 @@ func (server *ShardServer) Connect(peer *protocol.CNPeer) {
 	server.peers.Store(peer, nil)
 }
 
-func (server *ShardServer) GetPlayer(peer *protocol.CNPeer) *core.Player {
+func (server *ShardServer) LoadPlayer(peer *protocol.CNPeer) *core.Player {
 	val, ok := server.peers.Load(peer)
 	if !ok {
 		return nil
@@ -104,7 +105,25 @@ func (server *ShardServer) GetPlayer(peer *protocol.CNPeer) *core.Player {
 	return plr
 }
 
-func (server *ShardServer) JoinPlayer(peer *protocol.CNPeer, player *core.Player) {
+// UpdatePlayer locks the peers map, and calls the provided callback. The returned new pointer will be stored, however if an error returns it will be passed back.
+// Since it is UNSAFE to write to the returned pointer from LoadPlayer, this wrapper is for the cases that state in the player struct needs to be updated.
+// TODO: maybe LoadPlayer should return a player by value instead?
+// The pointers new and old may be the same if you are just updating struct fields.
+func (server *ShardServer) UpdatePlayer(peer *protocol.CNPeer, f func(old *core.Player) (new *core.Player, err error)) error {
+	server.peersLock.Lock()
+	defer server.peersLock.Unlock()
+
+	// on fail, the player should not be stored
+	new, err := f(server.LoadPlayer(peer))
+	if err != nil {
+		return err
+	}
+
+	server.storePlayer(peer, new)
+	return nil
+}
+
+func (server *ShardServer) storePlayer(peer *protocol.CNPeer, player *core.Player) {
 	server.peers.Store(peer, player)
 }