The full error text is Remote error: [FireDAC][Phys][FB]Unable to complete network request to host "dataserver16". Error writing data to the connection. Now it seems that others have had this problem then once they sorted it, it went away, but I have the problem sporadically.
My Datasnap ISAPI.dll which contains the FireDAC Firebird connection, is running on an IIS server on a different machine to the one where the database is hosted (dataserver16) but on the same subnet. I know everything is configured correctly, because the application works to expectations about 70% of the time! The other 30% of the time, my Datasnap client receives this error (as passed back from the dll).
IMHO it looks like there is a Network issue. If the Connection is Etablished and you can read and write Data to this connection it seams to be correct.
Have you tried to do a Ping from your Source System to the Target and log that Ping so you can See if the hole Connection to the Server disapears?
Open Commandwindow as Admin and Type:
Ping {TARGET} -t >> c:\ping.log
Than wait until the Error apears and check the Logfile if your Target was available the hole Time.
For more Help we need more Background Information, like Firebird Version or If you are able to reproduce the Error + Source Code how you set up your Connection.
For completeness, I am posting my solution here. Perhaps others will gain benefit from this answer. The solution is to perform retries of the Firebird connection. The way I did it, is every TSQLQuery's BeforeOpen event handler is wired to the same method. This has improved reliability considerably (even if it slowed it down a little). The code for FireDAC is similar. Both DBX and FireDac work equally well here.
const
retrycount = 3;
procedure TServerMethodsDBX.QueryBeforeOpen(DataSet: TDataSet);
begin
TryConnect(TSQLQuery(DataSet).SQLConnection);
// ...
end;
procedure TServerMethodsDBX.TryConnect(SQLConn: TSQLConnection);
var
i: Integer;
Error: String;
begin
i := 0;
SQLConn.Close;
while (not SQLConn.Connected) and (i < retrycount) do
begin
try
SQLConn.Connected := True
except
on e: exception do
begin
Error := Error + ' ' + e.Message;
Sleep(500);
Inc(i);
end;
end;
end;
if i = retrycount then
LogMessage('Tryconnect error: ' + Error);
end;
Related
I thought converting a mapped drive letter to a UNC path would be enough to be able to open a .GDB file,
but alas:
function ConvertToUNCPath(AMappedDrive: string) : string;
var
lRemoteString : array[0..255] of char;
lpRemote : PChar;
lStringLen : Cardinal;
begin
lpRemote := #lRemoteString;
lStringLen := 255;
If WNetGetConnection(Pchar(ExtractFileDrive(AMappedDrive)) ,
lpRemote,
lStringLen) = NO_ERROR Then
Result := lRemoteString
else
Result := ''; // No mapping found
end;
function TDataModuleData.OpenGDBDatabase(AGDBName: string) : Boolean;
var
lDlgLogin: TFrmLogin;
p : Integer;
lUNC,
lErrMsg : String;
begin
Result := False;
with FDConnection do // TFDConnection
begin
Close;
TxOptions.Isolation := xiDirtyRead;
p := Pos(':',AGDBName);
if p = 2 then
begin
lUNC := ConvertToUNCPath(Copy(AGDBName,1,2));
if lUNC <> '' then
begin
lUNC := Copy(lUNC,3);
p := pos('\',lUNC);
AGDBName := Copy(lUNC,p) + Copy(AGDBName,3);
lUNC := copy(lUNC,1,p-1);
end;
end;
DriverName := S_FD_IBId;
Params.Database := AGDBName;
if lUNC <> '' then
Params.Add('Server=' + lUNC)
else
Params.Add('Server=localhost'); // Not strictly necessary
Params.UserName := 'SYSDBA';
Params.Password := 'masterkey';
try
Open;
Result := Connected;
except
on E:Exception do
begin
lErrMsg := LowerCase(E.Message);
end;
end;
end;
end;
Depending on how I parse the ConvertToUNCPath result I get different error messages:
[firedac][phys][ib]unavailable database
[firedac][phys][ib]i/o error during "createfile (open)" operation for file "persoonlijk\jan\klanten.gdb"'#$D#$A'error while trying to open file'#$D#$A'the system cannot find the path specified.
The part of the code using ConvertToUNCPath succesfully converts e.g. P:\Jan\KLANTEN.GDB to \\tt2012server\persoonlijk\Jan\KLANTEN.GDB.
How can I open a GDB file when the path points to a mapped drive letter?
Added: I tried these hardcoded variations, they all fail:
// lUNC := '\\2012server'; // Unable to complete network request to host
lUNC := 'tt2012server';
//AGDBName := '\\tt2012server\persoonlijk\jan\klanten.gdb';
//AGDBName := 'tt2012server\persoonlijk\jan\klanten.gdb';
//AGDBName := '\persoonlijk\jan\klanten.gdb';
//AGDBName := 'persoonlijk\jan\klanten.gdb';
//AGDBName := '\jan\klanten.gdb';
//AGDBName := 'jan\klanten.gdb';
//AGDBName := 'p:\jan\klanten.gdb'; (original input)
(P: maps to \\tt2012server\persoonlijk)
Added:
Sorry, I was not clear in my initial text: this is not about connecting to a database on a remote server per se. I just want my local 'DB inspection' tool to be able to open a GDB file if someone places it in my network share for inspection (instead of having to copy it to local disk first).
To only intention of using WNetGetConnection was to resolve drive letter to UNC path (some I code I found on the web).
1. Firebird explicitly denies attempts to open database files on non-local disks
Firebird is database server, and as such it focuses on performance and reliability.
http://www.firebirdfaq.org/faq46/
Performance means lots of data is cached, both cached for reading and cached for writing.
Reliability means Firebird has to gain worthy warrants from OS that:
a. no other process would tinker with the database file while the server has some data from it cached for reading.
b. at any moment in time the server might wish to write any data to the file from its cache and it is warranted that that data - at any moment in time - ends persistently written to the persistent media.
Network-connected disks nullify both warranties and consequently Firebird Server refuses to trust them.
You may hack Firebird configuration or source files on your own discretion to remove this safety check and open network-shared files, if you really need this more than safety and speed.
But proper solution would be installing Firebird server on the machine whose disks do carry the database file.
2. Connection String is not a database file name
AGDBName := '\\tt2012server\persoonlijk\jan\klanten.gdb'
This does NOT mean "local Firebird server should connect to tt2012server server using LOCAL_SYSTEM credentials and read the database file from persoonlijk shared resource", as you probably intended it to mean.
http://www.firebirdfaq.org/faq260/
If anything, Windows LOCAL_SYSTEM user is explicitly barred from most network operations to contain intruders and viruses. Even if you hack Firebird into opening network files, most probably Windows would prohibit this access anyway, unless you would setup your Windows to run Firebird Server service with some user account other than the default LOCAL_SYSTEM.
Anyway, what \\tt2012server\persoonlijk\jan\klanten.gdb Connection String actually means is that you request your application to connect to tt2012server using WNET (aka Microsoft Named Pipes) protocol and find Firebird server running on that server and communicating by WNET protocol, as opposed to TCP/IP protocol.
Judging by the error you quote - lUNC := '\\2012server'; // Unable to complete network request to host - the said tt2012server computer perhaps does not have a Firebird Server running and accepting Named Pipes connections.
The WNET protocol is considered obsoleted and would most probably be removed from the future Firebird Server versions. As of now it is working, but few people use it, thus little up to date experience exists in that area. It is suggested you would use TCP/IP protocol by default to connect your application to the Firebird Server running on the tt2012server machine, not WNET protocol.
PS. This question has duplicates:
Connecting to Firebird database from Windows local network
ibase_connect: remote computer host and shared db file from windows
PPS. Firebird is a multi-generation database engine.
Consequently, there is no "dirty read" transactions possible in Interbase/Yaffil/Firebird family.
TxOptions.Isolation := xiDirtyRead; - this line would not work. Most probably it would silently change the transaction class to "READ COMMITTED", less probably it would give an explicit error.
I created a stand-alone Datasnap TCP/IP server using the Wizard. I selected sample methods (echostring and reversestring). I saved the server and ran it. Then I created a client application, and using the file-new-other, added a ClientModule to that client project, along with the ClientClasses unit. On the main form. I added a button. On the button's onclick event handler, I added the following code:
procedure TForm1.Button1Click(Sender: TObject);
begin
if ClientModule1.SQLConnection1.Connected then
begin
Button1.Text := 'Open';
ClientModule1.SQLConnection1.Close;
end
else
begin
Button1.Text := 'Close';
// ClientModule1.SQLConnection1.Open;
ClientModule1.ServerMethods1Client.ReverseString('myteststring');
end;
end;
The purpose here is to simulate a situation where the client is logging into and logging out of the server regularly rather than keeping a connection. This is especially important on apps deployed to mobile.
You can see I commented out the Connection.Open, because the first call to the ServerMethods1client opens the connection. The generated code is shown here:
function TClientModule1.GetServerMethods1Client: TServerMethods1Client;
begin
if FServerMethods1Client = nil then
begin
SQLConnection1.Open;
FServerMethods1Client := TServerMethods1Client.Create(SQLConnection1.DBXConnection, FInstanceOwner);
end;
Result := FServerMethods1Client;
end;
Now the problem arises. On first click to the button, the connection is opened, and the method is called. On the second click to the button, the connection is closed.
On the 3rd click, an exception is raised "Operation Failed. Connection was Closed" is raised from with the TDBXCommand code.
As a workaround, I tried this:
procedure TForm1.Button1Click(Sender: TObject);
begin
if ClientModule1.SQLConnection1.Connected then
begin
Button1.Text := 'Open';
ClientModule1.SQLConnection1.Close;
ClientModule1.ServerMethods1Client := nil;
end
else
begin
Button1.Text := 'Close';
// ClientModule1.SQLConnection1.Open;
ClientModule1.ServerMethods1Client.ReverseString('myteststring');
end;
end;
This does sort-of solve the problem, since the ClientModule1's FServerMethods1Client instance is reset so the create code runs again like it did on the first run.
The only other problem now, is (I am using Eurekalog) it creates a memory leak.
What am I doing wrong? What's the right way to connected/disconnect from a Datasnap server repeatedly without restarting the app?
The reason for the first error is that the code that binds the client side proxy (which allows server methods to be called) is tied to the local SQL connection. Note the call to create the proxy class:
FServerMethods1Client := TServerMethods1Client.Create(SQLConnection1.DBXConnection, ...)
The underlying DBExpress connection is passed by reference, and the proxy class uses that connection to call the server. You closed and re-opened the connection, but the underlying DBExpress connection that ServerMethodsClient1 was using has been destroyed. Thus, you receive the "Connection was closed" exception. The connection that ServerMethodsClient1 was using has been closed. You have to recreate ServerMethodsClient1 as you did in your second example.
I can't answer your second question, as I believe it is ARC specific. For a VCL DataSnap app, I would call ServerMethodsClient1.Free rather than setting it to nil. Based on my very, very limited understanding of Delphi's ARC implementation (which is all from the newsgroups), I believe you should call ServerMethodsClient1.DisposeOf, since the class descends from TComponent
But I'm not sure about that. I'm sure someone will jump on here that understands ARC and the proper solution to destroy the object rather than having a memory leak.
In my Android FMX implementation, I only call servermethods to get stuff done. (ie I don't use Datasnap data components). There's too much uncontrolled data transmission overhead to the Datasnap architecture to contemplate anything else realistically on a mobile device... To get around it (and not have memory leaks), I now create local instances of the TServermethods1Client as and when I need them and free them in context:
function TClientModule1.PostTheLog: Boolean;
var
Server: TServerMethods1Client;
begin
Server := TServerMethods1Client.Create(ClientModule1.SQLConnection1.DBXConnection);
try
UserID := Server.GetUserID;
...
finally
Server.Free;
end;
end;
Now the ClientModule1.SQLConnection1 can be connected and disconnected at will (preferably connected just before any call to a servermethod, and disconnected thereafter) and no further issues arise.
Which then begs the question: In which ideal world would the publicly accessible ServerMethods1Client actually be useful?
I'm working to an application with a login form at the start-up.
Until user is writing the login data, I would like to connect discreetly to the SQL server.
The problem is that, when I have a slow connection or a wrong path to the server, the application is looking for the server or trying to connect and in this time the application is not responding.
For connection I use this procedure:
//-- SQL connect --//
procedure TSql.Connect;
var
DriverId: String;
i: Byte;
begin
try
Screen.Cursor:=crAppStart;
//connection DriverName
DriverId:=Server[FServerType].DriverId;
FConnection.DriverName:=DriverId;
//connection Params
FConnection.Params.Clear;
FConnection.Params.Add('DriverID='+DriverId); //mandatory
if FConnString.Count>0 then
for i := 0 to FConnString.Count-1 do FConnection.Params.Add(FConnString.Strings[i]);
try
FConnection.Open;
FQuery.Connection:=FConnection;
except
on E : Exception do ShowError(_('Connection could not be established!'),E);
end;
finally
Screen.Cursor:=crdefault;
end;
end;
Please help me with some suggestion about how this can be done. I've read about threads and Application.ProcessMessages but I did not succeed to make it work smoothly.
Create a new thread, and do everything you need on it, that will not hang the main form and the user will not see anything you can see simillar functionality here
I've been struggling with the crap documentation of Google and can't get the program to join the channel even though it connects to the server fine. (It says Connected to server)
//On Form Make
procedure TForm2.FormCreate(Sender: TObject);
begin
IdIRC1.Connect();
end;
//on connected
procedure TForm2.IdIRC1Connected(Sender: TObject);
begin
ShowMessage('Connected to server');
IdIRC1.Join('#TheChannel', 'password');
end;
Once i close the form an error comes up saying:
Project raised exception class EIdException with message 'Not Connected'
Also once connected what functions do i use to talk on the channel/check input?
And what other IRC connection options (components) are there for Delphi applications?
ANY HELP WOULD BE APPRECIATED, GOOGLE HAS NOTHING ON THIS REALLY.
All i want is to be able to connect/check channel chat messages & talk on the chat; Simple String IO through IRC...
Guess you are not filling all the server requirements. Just IdIrc.Connect isn't enought, this works for me:
FIRC.Host:= 'irc.freenode.org';
FIRC.Port := 6667;
FIRC.Username:= 'SapoIndy';
FIRC.Nickname:= 'SapoIndy';
FIRC.RealName:= 'Fabio Gomes';
FIRC.Connect;
FIRC.Join('#TheChannel');
To figure out what is going on, you need to get the output of some events, I had implemented these:
FIRC.OnStatus:= #Status;
FIRC.OnNotice:= #Notice;
FIRC.OnMOTD:= #MOTD;
Get some events up and you should figure out what the server is telling you, don't go with trial and error.
And about sending and receiving messages, I've implemented some of this some time ago, here is the project, it was made using Lazarus.
https://bitbucket.org/fabioxgn/irc/src/b510d73e553d/main.pas
Do not call Join() in the OnConnected event. That event simply means the underlying socket connection is established. Connect() is still running, and has not actually logged into the IRC server yet when the OnConnected event is triggered. Wait until Connect() exits before issuing any commands:
procedure TForm2.FormCreate(Sender: TObject);
begin
IdIRC1.Connect;
ShowMessage('Connected to server');
IdIRC1.Join('#TheChannel', 'password');
end;
I tried to employ Indy 10.5.5 (shipped with Delphi 2010) for:
connecting to telnet server
performing username/password authentication (gaining access to the command shell)
executing a command with returning resulting data back to application
and had no success, additionally i'm completely lost in spaghetti logic of Indy's internals and now have no idea why it didnt work or how i supposed to send strings to the server and grab the results. Need some sample code to study.
Formal form of the question: Where can i get 3-rd party contributed demo covering TIdTelnet component? (indyproject.org demos webpage do not have one)
The main problem with Telnet is that it DOES NOT utilize a command/response model like most other Internet protocols do. Either party can send data at any time, and each direction of data is independant from the other direction. This is reflected in TIdTelnet by the fact that it runs an internal reading thread to receive data. Because of this, you cannot simply connect, send a command, and wait for a response in a single block of code like you can with other Indy components. You have to write the command, then wait for the OnDataAvailable event to fire, and then parse the data to determine what it actually is (and be prepared to handle situations where partial data may be received, since that is just how TCP/IP works).
If you are connecting to a server that actually implements a command/response model, then you are better off using TIdTCPClient directly instead of TIdTelnet (and then implement any Telnet sequence decoding manually if the server really is using Telnet, which is rare nowadays but not impossible). For Indy 11, we might refactor TIdTelnet's logic to support a non-threaded version, but that is undecided yet.
done with indy.
no comments.. just som old code :-)
telnet don't like the send string kommand.. use sendch.
telnetdude.Host := 1.1.1.1;
try
telnetdude.connect;
except
on E: Exception do begin
E.CleanupInstance;
end; {except}
if telnetdude.Connected then begin
for i := 1 to length(StringToSend) do telnetdude.sendch(StringToSend[i]);
telnetdude.sendch(#13);
end;
end; {while}
end; {if}
if telnetdude.Connected then telnetdude.Disconnect;
end;
I hope this helps anyone looking for answers to a similar question.
Firstly, It would seem the typical command/response model (as mentioned above, does indeed NOT apply).
So I just got it working for some very simple application (rebooting my router).
Specific additions to above code from Johnny Lanewood (and perhaps some clarification)
a) You have to send #13 to confirm the command
b) I got "hangs" on every command I sent / response I requested UNTIL I enabled ThreadedEvent. (this was my big issue)
c) the OnDataAvailable event tells you when new data is available from the Telnet Server - however there are no guarantees as to what this data is - i.e. it's pretty what you get in the command line / what ever is appended to the previous responses. But is is NOT a specific response line to your command - it's whatever the telnet server returns (could be welcome info, ASCII drawings etc etc.)
Given (c) above, one would rather check the OnDataAvailable event and parse the data (knowing what you'd expect). When the output stops (i.e. you need build a mechanism for this), you can parse the data and determine whether the server is ready for something new from the client. For the purpose of my code below, I set a read timemout and I just used Sleep(2000) - ignorantly expecting no errors and that the server would be ready after the sleep for the next command.
My biggest stumbling block was ThreadedEvent := True (see above in b)
Thus, my working solution (for specific application, and possibly horrible to some).
lIDTelnet := TIdTelnet.Create(nil);
try
lIdTelnet.ReadTimeout := 30000;
lIDTelnet.OnDataAvailable := TDummy.Response;
lIDTelnet.OnStatus := TDummy.Status;
lIdTelnet.ThreadedEvent := True;
try
lIDTelnet.Connect('192.168.0.1', 23);
if not lIDTelnet.Connected then
Raise Exception.Create('192.168.0.1 TELNET Connection Failed');
Sleep(2000);
lIdtelnet.SendString(cst_user + #13);
Sleep(2000);
lIdtelnet.SendString(cst_pass + #13);
Sleep(2000);
lIdtelnet.SendString(cst_reboot + #13);
Sleep(2000);
if lIDTelnet.Connected then
lIDTelnet.Disconnect;
except
//Do some handling
end;
finally
FreeAndNil(lIdTelnet);
end;
and then
class procedure TDummy.Response(Sender: TIdTelnet; const Buffer: TIdBytes);
begin
Write(TDummy.ByteToString(Buffer));
end;
class function TDummy.ByteToString(
const aBytes: TIdBytes): String;
var
i : integer;
begin
result := '';
for i := 0 to Length(aBytes) -1 do
begin
result := result + Char(aBytes[i]);
end;
end;