3 Implement two-way realiable acked lock-step protocol
6 uses NetAddr
,ServerLoop
,MemStream
;
16 callback
: procedure(msg
:tSMsg
; data
:boolean) of object; {client must maintain active chats}
17 TMhook
: procedure(willwait
:LongWord
) of object;
18 DisposeHook
: procedure of object; {called instead of freeing self}
19 procedure Init(const iremote
:tNetAddr
);
20 procedure AddHeaders(var s
:tMemoryStream
);
21 procedure StreamInit(var s
:tMemoryStream
; l
:word);
22 procedure Send(s
:tMemoryStream
);
23 {the stream can be invalidated, but the buffer must not be modified or freed}
27 txPk
:pointer; txLen
:word; {last sent, not acked msg}
29 procedure InitFrom(const iremote
:tNetAddr
; iopcode
:byte);
32 procedure OnReply(msg
:tSMsg
);
35 type tChatHandler
=procedure(var nchat
:tChat
; msg
:tSMsg
);
36 procedure SetChatHandler(initcode
:byte; handler
:tChatHandler
);
38 { download manager create FileRequest
39 File Request open chat session to server
40 upmgr accepts chat and send reply
41 FileRequest acks, chat is then closed after TimeWait
42 upmgr starts TC transfer
43 transfer finished, upmgr send new Chat to FileRequest
44 FileRequest acks, chat is closed on both ends
45 FileRequest can open new chat if blocks are missing
47 => chat msgs must be created with New, disposed by Chat
48 => there is TimeWait, no references are to the Chat, except Sheduler, it Disposes itself.
51 { Chats are the HiMsg. Use hash table from ServerLoop, works for HiMsg too. }
55 procedure tChat
.Init(const iremote
:tNetAddr
);
59 while ServerLoop
.IsMsgHandled(opcode
,remote
) do inc(opcode
);
60 InitFrom(remote
,opcode
);
62 procedure tChat
.InitFrom(const iremote
:tNetAddr
; iopcode
:byte);
66 SetMsgHandler(opcode
,remote
,@OnReply
);
69 rxAcked
:=true; {to not ack pk 0}
76 RTT
:=200; {a default for timeouts}
86 procedure tCHat
.AddHeaders(var s
:tMemoryStream
);
88 procedure tChat
.StreamInit(var s
:tMemoryStream
; l
:word);
90 s
.Init(GetMem(l
+5),0,l
+5);
94 procedure tChat
.Send(s
:tMemoryStream
);
97 //assert(assigned(callback));
101 s
.WriteWord(txSeq
,2);
102 if not rxAcked
then begin
103 s
.WriteWord(rxSeq
,2);
105 end else s
.WriteWord(0,2);
108 ServerLoop
.SendMessage(txPk
^,txLen
,remote
);
109 ServerLoop
.Shedule(RTT
*2,@Resend
);
116 if not rxAcked
then begin
117 s
.Init(GetMem(5),0,5);
120 s
.WriteWord(rxSeq
,2);
121 ServerLoop
.SendMessage(s
.base
^,s
.length
,remote
);
122 FreeMem(s
.base
,s
.length
);
127 procedure tChat
.Close
;
132 //writeln('Chat: closing');
133 if txLen
=0 {no packets in flight} then begin
134 Shedule(15000{todo},@Done
); {wait for something lost}
135 callback
:=nil; {avoid calling}
140 procedure tChat
.Done
;
142 {called from sheduler, Done is unsheduled, Resend is not sheduled since ack was received when Done was sheduled}
143 if txLen
>0 then FreeMem(txPk
,txLen
);
144 SetMsgHandler(opcode
,remote
,nil);
145 if assigned(DisposeHook
) then DisposeHook
146 else FreeMem(@self
,sizeof(self
));
147 //writeln('Chat: closed');
150 procedure tChat
.Resend
;
151 {timeout waiting for ack}
153 {resend and reshedule}
154 if txLen
=0 then exit
;
156 if RTT
<1 then RTT
:=2;
158 if assigned(TMhook
) and (not closed
) then begin
161 Done
; {if hook decided to close then abort}
165 if closed
and (RTT
<400) then RTT
:=400;
166 if (RTT
>=5000) and closed
then begin
169 {finally resend the msg}
170 //writeln('Chat: retry');
171 ServerLoop
.SendMessage(txPk
^,txLen
,remote
);
172 ServerLoop
.Shedule(RTT
,@Resend
);
176 procedure tChat
.OnReply(msg
:tSMsg
);
180 msg
.stream
.skip(1{opcode});
181 seq
:=msg
.stream
.ReadWord(2);
182 aseq
:=msg
.stream
.ReadWord(2);
183 if aseq
>0 then {ack of our msg} begin
184 if (aseq
=txSeq
)and(txLen
>0) {it is current} then begin
185 if txTime
>0 then RTT
:=Round((Now
-txTime
)*MsecsPerDay
);
189 if assigned(callback
) then callback(msg
,false);
190 ServerLoop
.UnShedule(@Resend
);
191 if Closed
then ServerLoop
.Shedule(5000,@Done
);
192 end else {write(' old-ack')it is ack of old data, do nothing};
194 if seq
>0 then {some data} begin
195 if seq
<=rxSeq
then {remote didnt get our ack} begin
196 s
.Init(GetMem(5),0,5);
199 s
.WriteWord(rxSeq
,2);
200 ServerLoop
.SendMessage(s
.base
^,s
.length
,remote
);
201 FreeMem(s
.base
,s
.length
);
202 if seq
=rxSeq
then rxacked
:=true;
207 if assigned(callback
) then callback(msg
,true);
212 var ChatHandlers
: array [1..32] of tChatHandler
;
214 procedure SetChatHandler(initcode
:byte; handler
:tChatHandler
);
216 assert(ChatHandlers
[initcode
]=nil);
217 ChatHandlers
[initcode
]:=handler
;
220 procedure OnHiMsg(msg
:tSMsg
);
221 {new chat was received!}
224 var hnd
:tChatHandler
;
228 opcode
:=msg
.stream
.ReadByte
;
229 assert(not IsMsgHandled(opcode
,msg
.source
^));
230 seq
:=msg
.stream
.ReadWord(2);
231 aseq
:=msg
.stream
.ReadWord(2);
232 if (seq
<>1)or(aseq
>0) then exit
; {invalid initial state}
233 ix
:=msg
.stream
.ReadByte
;
234 if (ix
<1)or(ix
>high(ChatHandlers
)) then exit
;
235 hnd
:=ChatHandlers
[ix
];
236 if not assigned(hnd
) then raise eXception
.Create('No handler for initcode '+IntToStr(ix
));
237 msg
.stream
.seek(msg
.stream
.position
-1);{unskip the initcode}
238 nchat
:=GetMem(sizeof(tChat
));
239 nchat
^.InitFrom(msg
.Source
^,opcode
);
240 nchat
^.rxacked
:=false;
246 FillChar(ChatHandlers
,sizeof(chathandlers
),0);
247 ServerLoop
.SetHiMsgHandler(@OnHiMsg
);