[SOLVED] SOCKETS fpsend fails, loses 1 character.

[arturogr]

Hello,

when SENDING 20 BYTES or more, OF DATA using "fpsend" SOCKETS function in a client applicatilon:

//in the client side, Buffer is 20 bytes long
Result := fpsend(SockDesc, @Buffer, SizeOf(Buffer), 1); // the flag is 1 (I got it from an example)

the server application, "RecvSize" does not report the same number of characters sent by the client when using "fprecv":

//in the server side, Buffer is 30 bytes long
RecvSize := fprecv(clientId, @Buffer, SizeOf(Buffer), 0);  // the flag is 0 (I got it from an example)


if I change an increase the Buffer size in the client side to:
Result := fpsend(SockDesc, @Buffer, SizeOf(Buffer)+1, 1); // the flag is 1 (I got it from an example)

the server side get the total of the message transmited by the client.

In the example code provided, you can view it only when transmiting 20 or more characters. But I think the server does not get the last byte of the message in the transmition.

¿Any idea of the problem?

Regards.

===========
SERVER:

Code: Pascal  [Select][+][-]

1. program socket_server;
2.  {$mode objfpc}{$H+}
3. {
4.   Program to test sockets and get working example of Sockets unit.
5.   This is the single thread server part.
6.   Use the client part to send data to that server.
7.   Inspired from fpConnect / fpAccept examples
8. }
9.  
10. uses
11.   {$IFDEF UNIX}
12.   cthreads,
13.   {$ENDIF}
14.   Classes,
15.   Sockets,
16.   SysUtils
17.   { you can add units after this };
18.  
19. var
20.   // Sockets descriptors
21.   SockDesc: longint;
22.   clientId: longint;
23.   // Sockets addresses
24.   SockAddr: TInetSockAddr;
25.   ClientAddr: TInetSockAddr;
26.   // Message
27.   Buffer: array [1..30] of char;
28.  
29.   Mensaje: string;
30.   AddrSize: longint;
31.   RecvSize: longint;
32.   StartTimer: longint;
33.  
34.   procedure perror(const S: string);
35.   var
36.     ErrorMsg: string;
37.   begin
38.     case socketerror of
39.       EsockADDRINUSE: ErrorMsg := 'Error number when socket address is already in use';
40.       EsockEACCESS: ErrorMsg := 'Access forbidden error';
41.       EsockEBADF: ErrorMsg := 'Alias: bad file descriptor';
42.       EsockEFAULT: ErrorMsg := 'Alias: an error occurred';
43.       EsockEINTR: ErrorMsg := 'Alias : operation interrupted';
44.       EsockEINVAL: ErrorMsg := 'Alias: Invalid value specified';
45.       EsockEMFILE: ErrorMsg := 'Error code ?';
46.       EsockEMSGSIZE: ErrorMsg := 'Wrong message size error';
47.       EsockENOBUFS: ErrorMsg := 'No buffer space available error';
48.       EsockENOTCONN: ErrorMsg := 'Not connected error';
49.       EsockENOTSOCK: ErrorMsg := 'File descriptor is not a socket error';
50.       EsockEPROTONOSUPPORT: ErrorMsg := 'Protocol not supported error';
51.       EsockEWOULDBLOCK: ErrorMsg := 'Operation would block error';
52.       else
53.         ErrorMsg := 'Undescribed error : ' + IntToStr(socketerror);
54.     end;
55.     writeln(S, ErrorMsg);
56.     halt(100);
57.   end;
58.  
59. begin
60.   SockDesc := fpSocket(AF_INET, SOCK_STREAM, 0);
61.   if SockDesc = -1 then
62.     Perror('[Server] Socket : ');
63.   SockAddr.sin_family := AF_INET;
64.   // Port 8008
65.   SockAddr.sin_port := htons(8008);
66.   // Look on all interfaces so address 0.0.0.0
67.   SockAddr.sin_addr := StrToNetAddr('0.0.0.0');
68.   // Bind socket
69.   if fpBind(SockDesc, @SockAddr, sizeof(SockAddr)) = -1 then
70.     PError('[Server] Bind : ');
71.   // Turn socket into listening state
72.   if fpListen(SockDesc, 1) = -1 then
73.     PError('[Server] Listen : ');
74.   // Waiting client connection
75.   Writeln('Waiting for client connection, run now client in an other tty');
76.   // Accept client connection
77.   AddrSize := sizeof(ClientAddr);
78.  
79.   while True do
80.   begin
81.     clientId := fpAccept(SockDesc, @ClientAddr, @AddrSize);
82.     if clientId = -1 then
83.       PError('[Server] Accept : ' + NetAddrToStr(ClientAddr.sin_addr))
84.     else
85.       writeln('[Server] New client connected from: ' + NetAddrToStr(ClientAddr.sin_addr));
86.     // Read data
87.     RecvSize := fprecv(clientId, @Buffer, SizeOf(Buffer), 0);
88.     Mensaje := Buffer;
89.     while RecvSize > 0 do
90.     begin
91.       if RecvSize > 0 then
92.         writeln('[Server] Receive : ' + Mensaje + ' [' + IntToStr(RecvSize) + ']');
93.       RecvSize := fprecv(clientId, @Buffer, SizeOf(Buffer), 0);
94.       Mensaje := Buffer;
95.     end;
96.     if (RecvSize = 0) and (SocketError = 0) then
97.     begin
98.       writeln('[Server] Client disconnect.');
99.       writeln('');
100.     end;
101.     if RecvSize = -1 then
102.       PError('[Server] Read failed : ');
103.   end;
104. end.            
105.  

============
CLIENT:

Code: Pascal  [Select][+][-]

1. program socket_client;
2.  
3. {
4.   Program to test sockets and get working example of Sockets unit.
5.   This is the client part. The server part must be start before using this one.
6.   Inspired from fpConnect / fpAccept examples
7. }
8.  
9. {$mode objfpc}{$H+}
10.  
11. uses
12.   {$IFDEF UNIX}
13.   cthreads,
14.   {$ENDIF}
15.   Classes,
16.   Sockets,
17.   SysUtils
18.   { you can add units after this };
19.  
20.   procedure PError(const S: string);
21.   var
22.     ErrorMsg: string;
23.   begin
24.     case socketerror of
25.       EsockADDRINUSE: ErrorMsg := 'Error number when socket address is already in use';
26.       EsockEACCESS: ErrorMsg := 'Access forbidden error';
27.       EsockEBADF: ErrorMsg := 'Alias: bad file descriptor';
28.       EsockEFAULT: ErrorMsg := 'Alias: an error occurred';
29.       EsockEINTR: ErrorMsg := 'Alias : operation interrupted';
30.       EsockEINVAL: ErrorMsg := 'Alias: Invalid value specified';
31.       EsockEMFILE: ErrorMsg := 'Error code ?';
32.       EsockEMSGSIZE: ErrorMsg := 'Wrong message size error';
33.       EsockENOBUFS: ErrorMsg := 'No buffer space available error';
34.       EsockENOTCONN: ErrorMsg := 'Not connected error';
35.       EsockENOTSOCK: ErrorMsg := 'File descriptor is not a socket error';
36.       EsockEPROTONOSUPPORT: ErrorMsg := 'Protocol not supported error';
37.       EsockEWOULDBLOCK: ErrorMsg := 'Operation would block error';
38.       else
39.         ErrorMsg := 'Undescribed error : ' + IntToStr(socketerror);
40.     end;
41.     writeln(S, ErrorMsg);
42.   end;
43.  
44. var
45.   // Socket descriptor
46.   SockDesc: longint;
47.   // Socket address
48.   SockAddr: TInetSockAddr;
49.   // Message
50.   Buffer: array [1..20] of char;
51.   //string[255];
52.   i, j: longint;
53.   Result: longint;
54.  
55.   Mensaje: string;
56. begin
57.   SockDesc := fpSocket(AF_INET, SOCK_STREAM, 0);
58.   if SockDesc = -1 then
59.     Perror('[Client] Socket : ');
60.   SockAddr.sin_family := AF_INET;
61.   // Port 8008
62.   SockAddr.sin_port := htons(8008);
63.   // Address 127.0.0.1
64.   SockAddr.sin_addr := StrToNetAddr('127.0.0.1');
65.   // Connection
66.   if fpconnect(SockDesc, @SockAddr, SizeOf(SockAddr)) = -1 then
67.     PError('[Client] Connect : ');
68.   // Send data
69.   i:=1;
70.   writeln('send a "-", and the client will disconnect (exit).');
71.   Mensaje := '(' + IntToStr(i) + ') >1st Msg.';
72.   while copy(Mensaje,length(Mensaje),1) <> '-' do
73.   begin
74.     Buffer := Mensaje;
75.     Result := fpsend(SockDesc, @Buffer, SizeOf(Buffer), 1);
76.     writeln(Buffer + ' [TX=' + IntToStr(Result) + ' / Data=' + IntToStr(SizeOf(Buffer)) + ']');
77.     if Result <> (SizeOf(Buffer)) then
78.       PError('[ERROR Client] Send : ');
79.     sleep(5);
80.     i := i+1;
81.     readln(Mensaje);
82.     Mensaje := '(' + IntToStr(i) + ') >' + Mensaje;
83.  
84.   end;
85.   writeln('>>> press ENTER to disconnet and EXIT.');
86.   readln();
87.   writeln('>bye!');
88.   // Shutdown communication
89.   if fpshutdown(SockDesc, 2) = -1 then
90.     PError('[Client] Shutdown : ');
91.   // Close socket
92.   if CloseSocket(SockDesc) = -1 then
93.     PError('[Client] Close : ');
94.   sleep(2000);
95. end.                      
96.  

[MarkMLl]

Full marks for trying, but please chop all of that example code from your message and give us a proper example as an attachment.

Basically, if you just plonk code in like that it's unusable for the rest of us because it's mangled by the forum software.

A first glance doesn't show any of the "usual suspects", i.e. things like trying to take the address of (the data structure describing) a string or a dynamic array rather than taking the address of the first byte. Ditto the current size... you'd be amazed by how many people are caught by that one.

You shouldn't really be trusting random examples. The *documentation* for the sockets unit is at https://www.freepascal.org/docs-html/current/rtl/sockets/index.html and from that you'll see that the final parameter of fpSend() should be zero. I don't recall using anything else, and I work at this level a lot.

MarkMLl

[bytebites]

https://www.freepascal.org/docs-html/current/rtl/sockets/fpsend.html

says flag can be 1 or 4, but if you change it to zero, the server gets 20 chars.

[Remy Lebeau]

Full marks for trying, but please chop all of that example code from your message and give us a proper example as an attachment.

Basically, if you just plonk code in like that it's unusable for the rest of us because it's mangled by the forum software.

Or, just use proper code formatting using [ code ][ /code ] tags instead.

[Warfley]

Why are you using flags if you don't seem to know what they are doing? Usually in most cases you don't need or want to set any flags and should just pass 0. For further info on what flags exist and what they do check out the man pages:
https://www.man7.org/linux/man-pages/man2/send.2.html
https://www.man7.org/linux/man-pages/man2/recv.2.html

Flag 1 is, at least according to the fpc doc the MSG_OOB flag. also never use numeral constants because this makes finding out what they do difficult. Always use the named constants like MSG_OOB.

About OOB, this flag is specifically for very short messages that need to be handled specially (out of band), see this: https://stackoverflow.com/questions/589928/socket-programming-how-do-i-handle-out-of-band-data

It's only for things like exceptions or similar, and is very limited. Do not use it just for arbitrary data

[arturogr]

Thanks to Warfley, MarkMLl and Bytebites users, the solution was to change from 1 to 0, the FLAG used at the fpsend function from the client program:

original FLAG in fpsend function:

Code: Pascal  [Select][+][-]

1. .
2. .
3. .
4. Result := fpsend(SockDesc, @Buffer, SizeOf(Buffer), 1);
5. .
6. .
7. .

correct FLAG in fpsend function:

Code: Pascal  [Select][+][-]

1. .
2. .
3. .
4. Result := fpsend(SockDesc, @Buffer, SizeOf(Buffer), 0);
5. .
6. .
7. .
8.  

Thanks to MarkMLl and Remy Lebeau users, I used the [ code ] tags to improve my post in this forum.

Now, I just do not know how to mark this topic as [SOLVED].

[dseligo]

Now, I just do not know how to mark this topic as [SOLVED].

Modify your first post and change Subject so it has [SOLVED] in front of it.