ESocketError with fphttpserver
lazarus / 38-Networking and Web Programming

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FlKo · 2016-11-06 19:52

Hi there. In my "work life", beside VBS, LabVIEW and PLCs if required,
I'm mostly a C++ programmer (for the major part with C++ Builder).

As a "spare-time-approach", I'm trying my best to get into Object
Pascal with Lazarus/Free Pascal because I'm used to the VCL from
CBuilder and it never hurts learning another language.

Now I'm trying to implement a simple webserver with Lazarus 1.6, FPC
3.0.0 and fphttpserver.
I've created a form, put 2 buttons on it and copy-pasted the major
part of the code from Michaël Van Canneyt's tutorial Creating a simple
webserver in Lazarus. Everything works as expected, except for the
server shutdown.

When I click on 'Stop Server', the following exception is raised:

Exception class "ESocketError" at $005415CA with message "Could not
accept a client connection on socket: 584, error 10038

Stack trace is:
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  
FServer.Active := True (in procedure THTTPServerThread.Execute;)   
procedure TFPCustomHttpServer.SetActive(const AValue: Boolean);     
procedure TFPCustomHttpServer.StartServerSocket;        Procedure
TSocketServer.StartAccepting;          Function
TInetServer.GetConnection : TSocketStream;            Function
TInetServer.Accept : Longint;              <-------- Error is raised
here 
And here is my code:

frmmain.pas:
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 unit
frmmain; {$mode objfpc}{$H+} interface uses  Classes, SysUtils,
FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls, 
httpserverthread, fphttpserver, fpweb, fpwebfile; type   { TMainForm
}   TMainForm = class(TForm)    btnStart: TButton;    btnStop:
TButton;    meLog: TMemo;    Panel1: TPanel;    procedure
btnStopClick(Sender: TObject);    procedure btnStartClick(Sender:
TObject);    procedure FormCreate(Sender: TObject);  private   
FHandler: TFPCustomFileModule;    FURL: string;    FServer:
THTTPServerThread;    procedure DoHandleRequest(Sender: TObject; var
ARequest: TFPHTTPConnectionRequest;      var AResponse:
TFPHTTPConnectionResponse);    procedure ShowURL;  public  end; var 
MainForm: TMainForm; implementation {$R *.lfm} { TMainForm } procedure
TMainForm.btnStartClick(Sender: TObject);begin 
meLog.Lines.Add('Starting server');  FServer :=
THTTPServerThread.Create(8080, @DoHandleRequest);end; procedure
TMainForm.FormCreate(Sender: TObject);begin  DoubleBuffered := true;  
RegisterFileLocation('files', 'C:\Users\FlKo\Documents\lazarus\project
\bin\i386-win32\debug\data\');  MimeTypesFile := 'C:\Users\FlKo\Docume
nts\lazarus\project\bin\i386-win32\debug\etc\mime.types';  FHandler :=
TFPCustomFileModule.CreateNew(Self);  FHandler.BaseURL :=
'files/';end; procedure TMainForm.btnStopClick(Sender: TObject);begin 
meLog.Lines.Add('Stopping server'); 
FServer.DoTerminate;end; procedure TMainForm.DoHandleRequest(Sender:
TObject;  var ARequest: TFPHTTPConnectionRequest; var AResponse:
TFPHTTPConnectionResponse);begin  FURL := ARequest.URL; 
FServer.Synchronize(FServer, @ShowURL); 
FHandler.HandleRequest(ARequest, AResponse);end; procedure
TMainForm.ShowURL;begin  meLog.Lines.Add('Handling request: ' +
FURL);end; end. 
httpserverthread.pas:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
HTTPServerThread; {$mode objfpc}{$H+} interface uses  Classes,
SysUtils,  fphttpserver, fpweb, fpwebfile; type  THTTPServerThread =
class(TThread)  private    FServer: TFPHTTPServer;  public   
constructor Create(APort: word; const OnRequest:
THTTPServerRequestHandler);    procedure Execute; override;   
procedure DoTerminate; override;    property Server: TFPHTTPServer
read FServer;  end;  implementation constructor
THTTPServerThread.Create(APort: word; const OnRequest:
THTTPServerRequestHandler);begin  inherited Create(False);  FServer :=
TFPHTTPServer.Create(nil);  FServer.Threaded:=true;  FServer.Port :=
APort;  FServer.OnRequest := OnRequest;end; procedure
THTTPServerThread.Execute;begin  try    FServer.Active := True; 
finally    FreeAndNil(FServer);  end;end; procedure
THTTPServerThread.DoTerminate;begin  FServer.Active := False; 
inherited DoTerminate;end; end. 
Am I doing something wrong?

Thanks for all answers.

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Leledumbo · 2016-11-07 00:08

10038 is socket error code for "Socket operation on nonsocket", i.e.
the socket identifier is either not valid or no longer valid.
You shouldn't call DoTerminate directly, but let thread class calls it
after Execute terminates. You should expose something in the thread
class that will set FServer.Active to false, but NOT in DoTerminate,
and call it somewhere in frmmain.

With your current code, DoTerminate will be called twice. The first
one is your explicit call, the second one is after Execute. In the
second call, FServer is no longer valid because finally block in
Execute already FreeAndNil it.

P.S.:
DoTerminate is a protected method in FPC trunk, it really isn't meant
to be called directly.