Freepascal socket unit use
lazarus / 38-Networking and Web Programming

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Jack.R · 2019-11-01 15:39

Dear All,

Many years ago, I was programming with Delphi.
I restart programming now with Lazarus and need to play with sockets.

The expected application will have a GUI which will display some data
got through socket, can be a server or a client and must accept many
client at the same time when acting as a server

When you search what to use, you found sockets unit, synapse or indy.
I qucikly try those 3.
I remove indy as it seems API change between versions and I do not
want to rewrite the application at each new indy version.
I try to decide if I go to sockets unit or synapse.

The example I have found in the sockets unit documentation are
relative to older version and deprecated functions.
I try to build below working example.
Currently the server is single thread, so accept a single client but
the goal is to write also a multithread one to accept many clients.

My current issue is to detect on the server side that the client has
close the connection in order to close the socket and came back to
listening for another client connection.

Could someone point me on what to check to detect client disconnection
?

Server
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 program
server; {  Program to test sockets and get working example of Sockets
unit.  This is the single thread server part.  Use the client part to
send data to that server.  Inspired from fpConnect / fpAccept
examples} uses  Sockets,  SysUtils; var  // Sockets descriptors 
SockDesc: longint;  clientId: longint;  // Sockets addresses 
SockAddr: TInetSockAddr;  ClientAddr: TInetSockAddr;  // Message 
Buffer: string [255];   AddrSize: longint;  RecvSize: longint; 
StartTimer: longint;   procedure perror(const S: string);  var   
ErrorMsg: string;  begin    case socketerror of      EsockADDRINUSE:
ErrorMsg := 'Error number when socket address is already in use';    
EsockEACCESS: ErrorMsg := 'Access forbidden error';      EsockEBADF:
ErrorMsg := 'Alias: bad file descriptor';      EsockEFAULT: ErrorMsg
:= 'Alias: an error occurred';      EsockEINTR: ErrorMsg := 'Alias :
operation interrupted';      EsockEINVAL: ErrorMsg := 'Alias: Invalid
value specified';      EsockEMFILE: ErrorMsg := 'Error code ?';     
EsockEMSGSIZE: ErrorMsg := 'Wrong message size error';     
EsockENOBUFS: ErrorMsg := 'No buffer space available error';     
EsockENOTCONN: ErrorMsg := 'Not connected error';      EsockENOTSOCK:
ErrorMsg := 'File descriptor is not a socket error';     
EsockEPROTONOSUPPORT: ErrorMsg := 'Protocol not supported error';    
EsockEWOULDBLOCK: ErrorMsg := 'Operation would block error';     
else        ErrorMsg := 'Undescribed error : ' +
IntToStr(socketerror);    end;    writeln(S, ErrorMsg);    halt(100); 
end; begin  SockDesc := fpSocket(AF_INET, SOCK_STREAM, 0);  if
SockDesc = -1 then    Perror('[Server] Socket : '); 
SockAddr.sin_family := AF_INET;  // Port 8008  SockAddr.sin_port :=
htons(8008);  // Look on all interfaces so address 0.0.0.0 
SockAddr.sin_addr := StrToNetAddr('0.0.0.0');  // Bind socket  if
fpBind(SockDesc, @SockAddr, sizeof(SockAddr)) = -1 then   
PError('[Server] Bind : ');  // Turn socket into listening state  if
fpListen(SockDesc, 1) = -1 then    PError('[Server] Listen : ');  //
Waiting client connection  Writeln('Waiting for client connection, run
now client in an other tty');  // Accept client connection  AddrSize
:= sizeof(ClientAddr);  clientId := fpAccept(SockDesc, @ClientAddr,
@AddrSize);  if clientId = -1 then    PError('[Server] Accept : ' +
NetAddrToStr(ClientAddr.sin_addr));  // Read data  RecvSize :=
fprecv(clientId, @Buffer, 255, 0);  while RecvSize <> -1 do  begin   
if RecvSize > 0 then      writeln('[Server] Receive : ' + buffer + '
[' + IntToStr(RecvSize) + ']');    RecvSize := fprecv(clientId,
@Buffer, 255, 0);  end;  if RecvSize = -1 then    PError('[Server]
Read failed : ');end.  

Client
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 program
client; {  Program to test sockets and get working example of Sockets
unit.  This is the client part. The server part must be start before
using this one.  Inspired from fpConnect / fpAccept examples} uses 
Sockets,  SysUtils;   procedure PError(const S: string);  var   
ErrorMsg: string;  begin    case socketerror of      EsockADDRINUSE:
ErrorMsg := 'Error number when socket address is already in use';    
EsockEACCESS: ErrorMsg := 'Access forbidden error';      EsockEBADF:
ErrorMsg := 'Alias: bad file descriptor';      EsockEFAULT: ErrorMsg
:= 'Alias: an error occurred';      EsockEINTR: ErrorMsg := 'Alias :
operation interrupted';      EsockEINVAL: ErrorMsg := 'Alias: Invalid
value specified';      EsockEMFILE: ErrorMsg := 'Error code ?';     
EsockEMSGSIZE: ErrorMsg := 'Wrong message size error';     
EsockENOBUFS: ErrorMsg := 'No buffer space available error';     
EsockENOTCONN: ErrorMsg := 'Not connected error';      EsockENOTSOCK:
ErrorMsg := 'File descriptor is not a socket error';     
EsockEPROTONOSUPPORT: ErrorMsg := 'Protocol not supported error';    
EsockEWOULDBLOCK: ErrorMsg := 'Operation would block error';     
else        ErrorMsg := 'Undescribed error : ' +
IntToStr(socketerror);    end;    writeln(S, ErrorMsg);  end; var  //
Socket descriptor  SockDesc: longint;  // Socket address  SockAddr:
TInetSockAddr;  // Message  Buffer: array [0..255] of char; 
//string[255];  i: longint;  Result: longint; begin  SockDesc :=
fpSocket(AF_INET, SOCK_STREAM, 0);  if SockDesc = -1 then   
Perror('[Client] Socket : ');  SockAddr.sin_family := AF_INET;  //
Port 8008  SockAddr.sin_port := htons(8008);  // Address 127.0.0.1 
SockAddr.sin_addr := StrToNetAddr('127.0.0.1');  // Connection  if
fpconnect(SockDesc, @SockAddr, SizeOf(SockAddr)) = -1 then   
PError('[Client] Connect : ');  // Send data  for i := 1 to 100 do 
begin    Buffer := 'This is a textstring sent by the client. (' +
IntToStr(i) + ')';    Result := fpsend(SockDesc, @Buffer,
SizeOf(Buffer), 1);    writeln(Buffer + ' [' + IntToStr(Result) +
']');    if Result <> SizeOf(Buffer) then      PError('[Client] Send :
');    sleep(5);  end;  // Shutdown communication  if
fpshutdown(SockDesc, 2) = -1 then    PError('[Client] Shutdown : '); 
// Close socket  if CloseSocket(SockDesc) = -1 then   
PError('[Client] Close : ');end.

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Thaddy · 2019-11-01 15:51

the standard fcl-net package comes with many examples.

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Jack.R · 2019-11-01 16:56

Where did you find them ?

In the examples folder of fcl-net on my installation I have :
cnslookup.pp, ip6test.pp, rpccli.pp, rpcserv.pp, svrclass.pp,
svrclass_xmlrpc.pp,testdns.pp, testhosts.pp, testhst.pp, testnet.pp,
testproto.pp, testsvc.pp, testuri.pp

I have had a look but they did not seems to suit my needs.
fpSock.pp seems to be interresting but the only example of use I found
was "fcl-net, the undocumented treasure" on "Pascal Warrior's Journey
".

That is why I get back to the socket unit.
Did I make a mistake and should invertigate more deeper to use fpSock
?

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Jack.R · 2019-11-03 13:45

fpSock from fcl-net is unix only as it has a use clause with
baseunix,Unix;

Regarding my original issue,'Detecting on the server side that the
client has disconnect', we are using blocking sockets, this means that
if fpReceive return a 0 size, the client has disconnect gracefully.

The code thus became:
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 program
server; {  Program to test sockets and get working example of Sockets
unit.  This is the single thread server part.  Use the client part to
send data to that server.  Inspired from fpConnect / fpAccept
examples} uses  Sockets,  SysUtils,  baseunix; var  // Sockets
descriptors  SockDesc: longint;  clientId: longint;  // Sockets
addresses  SockAddr: TInetSockAddr;  ClientAddr: TInetSockAddr;  //
Message  Buffer: string [255];   AddrSize: longint;  RecvSize:
longint;  StartTimer: longint;   procedure perror(const S: string); 
var    ErrorMsg: string;  begin    case socketerror of     
EsockADDRINUSE: ErrorMsg := 'Error number when socket address is
already in use';      EsockEACCESS: ErrorMsg := 'Access forbidden
error';      EsockEBADF: ErrorMsg := 'Alias: bad file descriptor';   
 EsockEFAULT: ErrorMsg := 'Alias: an error occurred';      EsockEINTR:
ErrorMsg := 'Alias : operation interrupted';      EsockEINVAL:
ErrorMsg := 'Alias: Invalid value specified';      EsockEMFILE:
ErrorMsg := 'Error code ?';      EsockEMSGSIZE: ErrorMsg := 'Wrong
message size error';      EsockENOBUFS: ErrorMsg := 'No buffer space
available error';      EsockENOTCONN: ErrorMsg := 'Not connected
error';      EsockENOTSOCK: ErrorMsg := 'File descriptor is not a
socket error';      EsockEPROTONOSUPPORT: ErrorMsg := 'Protocol not
supported error';      EsockEWOULDBLOCK: ErrorMsg := 'Operation would
block error';      else        ErrorMsg := 'Undescribed error : ' +
IntToStr(socketerror);    end;    writeln(S, ErrorMsg);    halt(100); 
end; begin  SockDesc := fpSocket(AF_INET, SOCK_STREAM, 0);  if
SockDesc = -1 then    Perror('[Server] Socket : '); 
SockAddr.sin_family := AF_INET;  // Port 8008  SockAddr.sin_port :=
htons(8008);  // Look on all interfaces so address 0.0.0.0 
SockAddr.sin_addr := StrToNetAddr('0.0.0.0');  // Bind socket  if
fpBind(SockDesc, @SockAddr, sizeof(SockAddr)) = -1 then   
PError('[Server] Bind : ');  // Turn socket into listening state  if
fpListen(SockDesc, 1) = -1 then    PError('[Server] Listen : ');  //
Waiting client connection  Writeln('Waiting for client connection, run
now client in an other tty');  // Accept client connection  AddrSize
:= sizeof(ClientAddr);   while True do  begin    clientId :=
fpAccept(SockDesc, @ClientAddr, @AddrSize);    if clientId = -1 then 
   PError('[Server] Accept : ' + NetAddrToStr(ClientAddr.sin_addr))  
else      writeln('[Server] New client connected.');    // Read data 
 RecvSize := fprecv(clientId, @Buffer, 255, 0);    while RecvSize > 0
do    begin      if RecvSize > 0 then        writeln('[Server] Receive
: ' + buffer + ' [' + IntToStr(RecvSize) + ']');      RecvSize :=
fprecv(clientId, @Buffer, 255, 0);    end;    if (RecvSize = 0) and
(SocketError = 0) then    begin      writeln('[Server] Client
disconnect.');      writeln('');    end;    if RecvSize = -1 then    
PError('[Server] Read failed : ');  end;end.