LazWebsocket How to identify IP adress during connect
lazarus / 38-Networking and Web Programming

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hgbk · 2021-04-20 13:47

I have implemented a game as client server solution using
LazWebsockets. It may happen that during the game the connection from
a client breaks. In order to implement the possibility for this
specific client to reconnect I need to identify the IP address during
accept and compare it with
ACommunication.SocketStream.RemoteAddress.Address of this client 
which I have stored before failure. In accept I have TRequestData as
parameter which delivers Host (Domain but not IP address). Any idea
how to solve this?

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Warfley · 2021-04-21 01:02

There is currently no way implemented to identify the client during
the handshake. This is defenetly something I will consider adding to
the library.

But, I should point out that identifying clients based on their IPs is
bad style, as due to the use of NAT networks, multiple devices usually
share an external IP. While in Europe and the US it is usually
something like one per household, for some (cheaper) internet
providers or providers in other countries that haven't been so lucky
with getting large shares of the IP address space, multiple homes or
even larger parts like city blocks can share the same IP address. So
there could be potentially hundreds of people with the same IP.

Therefore you should give the client a unique ID to reconnect. Like
when a game starts, you could generate a game ID, which every client
gets. If a client looses it's connection it can reconnect by sending
this game ID to the server and the server can recognize this and put
it back into the right game

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hgbk · 2021-04-21 11:17

Understand - I will implement the "reconnect" according to your
proposal. Thanks a lot for the quick and helpful answer!

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r.lukasiak · 2021-09-28 18:38

Quote from: Warfley on April 21, 2021, 03:02:55 amThere is currently
no way implemented to identify the client during the handshake. This
is defenetly something I will consider adding to the library.

But, I should point out that identifying clients based on their IPs is
bad style, as due to the use of NAT networks, multiple devices usually
share an external IP. While in Europe and the US it is usually
something like one per household, for some (cheaper) internet
providers or providers in other countries that haven't been so lucky
with getting large shares of the IP address space, multiple homes or
even larger parts like city blocks can share the same IP address. So
there could be potentially hundreds of people with the same IP.

Therefore you should give the client a unique ID to reconnect. Like
when a game starts, you could generate a game ID, which every client
gets. If a client looses it's connection it can reconnect by sending
this game ID to the server and the server can recognize this and put
it back into the right game

Hi everyone!
I've been trying to figure out how to use LazWebSocket for some 3
days. I'm analyzing the example  server and client files. I managed to
figure out how the client works (at least some basic functions), I
created some basic GUI and applied the "client" code to it, I was able
to run it iin StartReceiveMessageThread mode. My app is able to sent
and receive the message (OnReceiveMessage). But when I run more than 1
instance, messages from the server are sent randomly. I even tried to
start my client app from different IPs, local 192.168.x.x and through
HamachiLogMeIn 25.x.x.x. Both instances can send messages to the
server but the server answers randomly. I understand that it may
happen when there are more than 1 client with the same IP but if 2
clients have a different IP address?
How can I make the server answer to a specific client?
Quoteyou could generate a game ID, which every client gets how could I
use a client ID to make the server contact the specific client by his
ID, not IP?

thanks for any hint.

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Warfley · 2021-09-29 12:27

In LazWebsockets the connection is handled by the
TWebsocketCommunicator instance given as Parameter to the handler.

If you want to handle multiple connections, you need to identify
these. The (threaded) base handler already provides a list of all
connections, you could use the index to identify these:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   procedure
TSocketHandler.IdentifyClients;  var    ConnectionList:
TConnectionList;    i: Integer;  begin    ConnectionList :=
Connections.Lock;    try      for i := 0 to ConnectionList.Count - 1
do        ConnectionList[i].WriteStringMessage('You are client number
' + i.ToString);    finally      Connections.Unlock;    end;  end;
The problem here is, when a client disconnects, it changes the indices
of all clients connected after that one (as all move by one). So you
could rather than that generate an ID (e.g. by simply having a counter
counting up) and use a TDictionary or TFPGMap or similar to manage the
connections. You might also need a reverse lookup to map the
communicator to it's ID (some extendibility option for the
communicator might be also useful here, to store such data right in
the communicator).

Another solution is, each handler call gets executed in their own
Thread (assuming you use a threaded handler). The best way is to have
all the communication happen within that handler and you interact
though messages in a message queue. When you receive something you can
send a message to the GUI to handle the data. When the GUI wants to
send something it sends a message to the handler.

But: no matter what approach you choose, you must always make sure to
use sufficient thread locks. All the default  datastructures (arrays,
Lists, Maps, Dictionaries, etc.) are not thread safe, so when dealing
with the threaded websockets, you should always use locks

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gucao · 2021-10-06 10:46

The accepted socket is the SocketStream.handle?
can get the ip and port from the accepted  socket
The code need test
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
sockets var  VRtInt,VL:Integer;  VAddr:TSockAddr;  VSocketErr: cint;
 VIP:string;  VPort:integer; begin  VL:=SizeOf(VAddr);   
VRtInt:=fpgetpeername(ASocket,@VAddr,@VL);  if VRtInt=0 then begin   
 VIp:=NetAddrToStr(VAddr.sin_addr);     VPort:=NToHs(VAddr.sin_port); 
end else begin     Result:='faild`````';     Exit;  end;  end;

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r.lukasiak · 2021-10-14 08:35

Hi there!
I'm sorry for the delay in answering.

Warfley, thanks for the explanation, it seems pretty clear, however
I'd have several questions:
1. Quote"The (threaded) base handler"
socket.AcceptingMethod:=samThreaded?

2. Does a new client always get the highest number in ConnectionList?
If there are 5 connected clients, I suppose they are numbered 0..4 so
the new one will get 5, right?
Clients have their user names so basing on ConnectionList, I could
have some list linking ConnectionList's client number to the user name
but...

3. Quote"when a client disconnects, it changes the indices of all
clients connected" Is there any event going on in this situation? how
can I know that someone disconnected to update my list?

gucao, I haven't tested it it but quickly analyzing the code, I
understand that it's extracting IP and port from the handler?

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Warfley · 2021-10-14 12:47

Quote from: r.lukasiak on October 14, 2021, 10:35:19 amWarfley, thanks
for the explanation, it seems pretty clear, however I'd have several
questions:
1. Quote"The (threaded) base handler"
socket.AcceptingMethod:=samThreaded?
Nope, that makes the accepting handshake threaded (basically before
establishing a connection a HTTP request is made, with samThreaded or
samThreadPool this will be threaded).

What I meant is when implementing the handler you create a class
inheriting from TWebsocketHandler. If you inherit from 
TThreadedWebsocketHandler you make use of the threaded handler.
In the ChatServer example this would be this line:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
TSocketHandler = class(TThreadedWebsocketHandler) // inherit from
TThreadedWebsocketHandler
Quote from: r.lukasiak on October 14, 2021, 10:35:19 am2. Does a new
client always get the highest number in ConnectionList? If there are 5
connected clients, I suppose they are numbered 0..4 so the new one
will get 5, right?
Clients have their user names so basing on ConnectionList, I could
have some list linking ConnectionList's client number to the user name
but...
Yes it is a simple TFPGList used. When a client connects it is added
to the list via .Add at the end of the list and if it disconnects it
is removed via .Delete.

Quote from: r.lukasiak on October 14, 2021, 10:35:19 am3. Quote"when a
client disconnects, it changes the indices of all clients connected"
Is there any event going on in this situation? how can I know that
someone disconnected to update my list?
The list is automatically updated. To be notified on a disconnect you
can register an event handler. In the ChatServer example this is done
in:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i    
ACommunication.OnClose := @ConnectionClosed;

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r.lukasiak · 2021-10-14 22:30

QuoteTSocketHandler = class(TThreadedWebsocketHandler) ok, got it.

QuoteThe list is automatically updated. To be notified on a disconnect
you can register an event handler. In the ChatServer example this is
done in: of course... :| I don't know what I was thinking of when
asking this question. I even use that event to do some stuff. What I
really wanted to know is how can I figure out which client
disconnected, is there any way get its number in ConnectionsList?

And there is another question about OnConnectionClosed. I testing the
server using my gui and the HTML example. The server notices when the
HTML client disconnects, whether I use the disconnect button, refresh
the page or even kill the browser process, the server always triggers
the OnConnectionClosed event but it doesn't happen with my GUI,
whether I close it or just kill the process, the server doesn't notice
it. How could I notify the server I disconnect?

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Warfley · 2021-10-15 15:21

Quote from: r.lukasiak on October 15, 2021, 12:30:26 amof course... :|
I don't know what I was thinking of when asking this question. I even
use that event to do some stuff. What I really wanted to know is how
can I figure out which client disconnected, is there any way get its
number in ConnectionsList?
Currently there is no nice way of getting it, you basically need to
iterate that list and search for it

Quote from: r.lukasiak on October 15, 2021, 12:30:26 amAnd there is
another question about OnConnectionClosed. I testing the server using
my gui and the HTML example. The server notices when the HTML client
disconnects, whether I use the disconnect button, refresh the page or
even kill the browser process, the server always triggers the
OnConnectionClosed event but it doesn't happen with my GUI, whether I
close it or just kill the process, the server doesn't notice it. How
could I notify the server I disconnect?
Thats because you don't perform the closing handshake of websockets,
but rather break the TCP connection (which will result in an
exception).

To close the connection gracefully just call
"TWebsocketCommunicator.Close" and wait until
TWebsocketCommunicator.Open is false

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r.lukasiak · 2021-10-20 16:18

QuoteTo close the connection gracefully just call
"TWebsocketCommunicator.Close" and wait until
TWebsocketCommunicator.Open is falseworked perfectly!

QuoteCurrently there is no nice way of getting it, you basically need
to iterate that list and search for itI see... anyway I managed to
somehow solve it.  I dug through your code to find out how you
implemented ConnectionList and what info it exactly stores.
I created something like:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
ConnectedUser = record  UserName: string;  Handler:
TWebsocketCommunicator;end;...varConnectedUserList = array of
ConnectedUser; OnConnect I add the client to the list and the client
after connecting automatically sends some kind of "hello message" with
its username so the server adds it to the list.
So far so good, thanks a lot!

I tried to use these libs with LAMW for Android and I came across a
problem with:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i FCommunicat
or.OnClose:=@StreamClosed;FCommunicator.OnReceiveMessage:=@ReceiveMess
age; The compiler (for aarch64) is giving me:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
unit1.pas(138,26) Error: Variable identifier expectedchanging it to:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i FCommunicat
or.OnClose:=StreamClosed;FCommunicator.OnReceiveMessage:=ReceiveMessag
e; helps to compile but it's obviously causing some problems.
I ran the app on my phone and it connected to the server, server
showed info about the connected client but the app crashed
immediately.

Have you tried it with LAMW? any hint?

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r.lukasiak · 2021-10-25 05:15

This solution seems to work, it stores the handlers and the usernames.
However I'm stuck at sending messages from one client to another. All
clients can communicate with the server and server can communicate
with the clients, but the problem appears when the server receives a
message and tries to send it to another clients.
What I did is:
1. SERVER: Server starts
2. SERVER: Client connects - server stores the handler in
ConnectionList and I added my ConnectedUsersList(record of
TWebsocketCommunicator and string), it add the handler to my array in
TSocketHandler.DoHandleCommunication
3. CLIENT: right after chat.FCommunicator.StartReceiveMessageThread,
if chat.FCommunicator.Open is true, it sends a message to the server
providing the client's username (each client has its unique username).
4. SERVER: Server receives this message
(TSocketHandler.MessageReceived) and updates my array adding the
username to the handler.
5. Steps 2-4 for every client (I've tested with just 3)
At this point all clients are able to talk to the server and receive
messages from the server.
But if a client sends a message that's supposed to be send to another
client, I come across a problem. Some client (apparently the last one)
can send messages and these are delivered to another client with no
problem but others can't.
How I did it:
1. Client A sends a message that's supposed to get to Client B.
2. Server receives the message (TSocketHandler.MessageReceived). The
message contains the Client B's username .
3. Server looks up my array to find the B's username:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i for i:=0 to
length(ConnectedUsersList)-1 do if
ConnectedUsersList[i].UserID=ClientB then
ConnectedUsersList[i].Handler.WriteStringMessage.....4. Client B
receives the message.
I use locks whenever I  use the connection list or send messages.

I performed some tests:
1#
-Client A connects
-Client B connects
-Client A sends a message to the Server (the message doesn't reach the
server)
-Client B sends a message to the Server (the message goes through)
-Server sends a message to Client A (the message goes through)
-Server sends a message to Client B (the message goes through)
at this point Server can send messages to both clients but only Client
B can send messages to the Server
-Client B sends a message to Client A (it goes through)
-Client A sends a message to Client B (the message doesn't even reach
the Server)
at this point Server can still send message to both Clients but only
Client B can send to the Server.
What's even more disturbing, Client B's GUI closes properly, Client
A's GUI doesn't want to close, I need to kill the process.

2#
-3 clients connect
-Server can send messages to all 3 clients
-Only Client C can send message to the server

I've tried to do the same using my ConnectedUserList and the original
ConnectionList. Another solution was adding UserID: string variable to
TWebsocketCommunicator class (wsstream), since it's threaded, each
thread keeps it's UserID. No matter which solution I use, the result
is the same.

any idea what's wrong?

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Warfley · 2021-11-04 19:15

This sounds like a deadlock, have you checked when a thread acquires a
lock and when it is released (e.g. by adding simple writeln with debug
output)?

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r.lukasiak · 2021-11-05 15:21

I was taking care of the locks, as far as I understand how to use
them. Anyway the code was kinda messy, I was implementing several
ideas and then changing them if they didn't work so I decided to start
from 0. I took the example client and server and implemented just 2
simple things but I have already faced the same problem, not all
clients can send messages.

First off, I added UserID: string to TWebsocketCommunicator class so
the handler stores the user name:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
TWebsocketCommunincator = class  private ...  public    UserID:
string;... end;
The client just connects and sends its user name right after
connecting:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
Ttestchat.FormCreate(Sender: TObject);begin  if paramCount()>0 then
MyUserID:=ParamStr(1) else MyUserID:='Client';   
 writeln(paramCount().ToString+' MyUserID='+MyUserID);   client :=
TWebsocketClient.Create(MyServerIP, MyServerPort);  try    chat :=
TSimpleChat.Create(client.Connect(TSocketHandler.Create));    finally 
  client.Free;  end;    
chat.FCommunicator.StartReceiveMessageThread;     while not
chat.FCommunicator.Open do              begin               
writeln('not open, sleeping...');                Sleep(100);         
   end;     if chat.FCommunicator.Open then      begin       
Writeln('chat.FCommunicator.Open=true');       
chat.FCommunicator.WriteStringMessage(mtHello+MyUserID);       
Writeln('Hello message sent');      end      else
Writeln('chat.FCommunicator.Open=false');end;
on the server side, when the client connects and sends the "hello"
message:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TSocketHandler.MessageRecieved(Sender: TObject);  var    Messages:
TWebsocketMessageOwnerList;    m: TWebsocketMessage;    Comm:
TWebsocketCommunincator;    CL: TConnectionList;    i: integer; 
begin    Comm := TWebsocketCommunincator(Sender);    Messages :=
TWebsocketMessageOwnerList.Create(True);    try     
Comm.GetUnprocessedMessages(Messages);      for m in Messages do     
 if m is TWebsocketStringMessage then        begin         
WriteLn('Message from ', Comm.SocketStream.RemoteAddress.Address,    
      ': ', TWebsocketStringMessage(m).Data);           //Hello
message          if TWebsocketStringMessage(m).Data[1]=mtHello then  
      begin            writeln('Hello message received');           
write('(MessageReceived) LOCK... ');            CL:=Connections.Lock; 
          writeln('...locked');            try            for i:=0 to
CL.Count-1 do              begin                if CL[i]=Comm then   
             begin                    CL[i].UserID:=copy(TWebsocketStr
ingMessage(m).Data,2,length(TWebsocketStringMessage(m).Data)-1);     
            
writeln('CL['+i.ToString+'].UserID:='+QuotedStr(CL[i].UserID));      
            Break;                  end;              end;           
finally              write('(MessageReceived) UNLOCK... ');          
  Connections.Unlock;              writeln('...unlocked');           
end;          end;        end;    finally      Messages.Free;    end; 
end;                        
I also implemented some command so I can peek on ConnectionList:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TSocketHandler.DoHandleCommunication(    ACommunication:
TWebsocketCommunincator);  var    str: string;    i: integer;    CL:
TConnectionList;  begin    WriteLn('Connected to ',
ACommunication.SocketStream.RemoteAddress.Address);   
ACommunication.OnRecieveMessage := @MessageRecieved;   
ACommunication.OnClose := @ConnectionClosed;    while
ACommunication.Open do    begin      ReadLn(str);       if str='cl'
then      begin        Write('(DoHandleCommunication) LOCK... ');    
  CL:=Connections.Lock;        Writeln('...locked');        try      
begin          Writeln('Count='+CL.Count.ToString);          if
CL.Count>0 then             for i:=0 to CL.Count-1 do             
 writeln(i.ToString+' '+CL[i].UserID);        end;        finally    
    Write('(DoHandleCommunication) UNLOCK... ');         
Connections.Unlock;          Writeln('...unlocked');        end;     
end;       if not ACommunication.Open then        Break;    end;   
socket.Stop(True);  end;                   
Server output:
Quote$ ./chatServer
Server is starting
Connected to 192.168.1.1                       <- Client A connects
Message from 192.168.1.1: ClientA          <- and everything is ok,
it's able to send the Hello message
Hello message received
(MessageReceived) LOCK... ...locked
CL[0].UserID:='ClientA'
(MessageReceived) UNLOCK... ...unlocked
Connected to 192.168.1.3                        <-The same with Client
B, everything is ok. It connects from another PC
Message from 192.168.1.3: ClientB
Hello message received
(MessageReceived) LOCK... ...locked
CL[1].UserID:='ClientB'
(MessageReceived) UNLOCK... ...unlocked
                                                                   
 <-here I fired Client C but it didn't reach the server. I ran it on
the same PC that ClientA
cl                                                                 
 <-I typed 'cl' on the server to see what's in ConnectionList
(DoHandleCommunication) LOCK... ...locked
Count=2
0 ClientA
1 ClientB                                                         
<-and there is no info about Client C
(DoHandleCommunication) UNLOCK... ...unlocked


Client A and Client B close without a problem but Client C doesn't, I
need to kill the process.

In case of ClientC, according to logs, it connected and sent the
message:
Quote$ ./TestChat ClientC
1 MyUserID=ClientC
chat.FCommunicator.Open=true
Hello message sent

Another scenario, I ran just 2 clients, from the same PC:
Quote$ ./chatServer
Server is starting
Connected to 192.168.1.3       <-Client1 connects and sends the Hello
message but Server doesn't receive it
Connected to 192.168.1.3       <-Client2 connects
Message from 192.168.1.3: Client2   <-and Server receives the Hello
message
Hello message received
(MessageReceived) LOCK... ...locked
CL[1].UserID:='Client2'                              <-it's added to
the handler
(MessageReceived) UNLOCK... ...unlocked
cl                                                                 <-I
fire 'cl' command and....
(DoHandleCommunication) LOCK... ...locked
Count=2
0                                                                 
 <-...both clients are connected but the Hello message from Client1
never reached Server
1 Client2                                                           
so there is no user name.
(DoHandleCommunication) UNLOCK... ...unlocked

I performed several tests and random clients weren't able to connect
or send the first message. It looks like I'm doing something wrong
right in the beginning but I can't figure it out. Any clue?