A proper way to set up a listening socket (WebHook)

plastkort · August 31, 2019

hi!

I have been using TWSocket erarlier to create listening sockets, but this is several years back, now i have a case where i need to make it work again.

I got it to listen, but it eventually dies after some time, it could be 1 hour or 1 day.

I do the following:

First i create the listening socket:

wsTradingWebHook.addr:='0.0.0.0';

wsTradingWebHook.port:='80';
wsTradingWebHook.Listen;

When incoming I do the following:

procedure TDataFunctions.wsTradingWebHookSessionAvailable(Sender: TObject;
ErrCode: Word);
var
html : TStringlist;
FMySocket : TWSocket;
begin
FMySocket := Twsocket.create(self);
html := TStringlist.Create;
with FMySocket do
try
OnDataAvailable := wsTradingWebHookDataAvailable;

HSocket := twsocket(sender).Accept;

html.add('<html><head>');
html.add('<title>Welcome to WhaleAlert</title>');
html.add('</head><body>');
html.add('Usage: <br>');
html.add('{ "signal": "short", "message": "short signal on 5 minutes" } <br>');
html.add('{ "signal": "long", "message": "long signal on 5 minutes" } <br>');
html.add('</body></html>

sendstr('HTTP/1.1 200 OK'#13#10);
sendstr(format('Date: %s GMT+2'#13#10,[formatdatetime('ddd, dd mmm yyyy hh:mm:ss', date)]));
sendstr('Server; myserver'#13#10);
sendstr('Content-Type: text/html; charset=iso-8859-1'#13#10);
sendstr(format('Content-length=%d'#13#10,[length(html.Text)]));
sendstr(#13#10);
sendstr(html.Text);
sendstr(#13#10);
finally
freeAndNil(html);
end;
end;

When I receive data from the server i handle it like this: ( I just want the json data received, so any data prior to the { and } will be deleted)

I am unsure if i need the "TWSocket(sender).Free;" is needed, or the socket will just clean itself, if i try connect with a normal webserver i receive the "info" message, but the client still seem to wait for more data...i.e. the waiting circle keeps spinning...

function TDataFunctions.ProcessWebHook(Received : string) : string;
var
PostCommand : string;
begin
result := '';
if pos('POST',received) <> 0 then
begin
PostCommand := received;
if (pos('{',PostCommand) <> 0) and
(pos('}',PostCommand) <> 0) then
begin
Delete(postcommand, 1, pred(pos('{',PostCommand)));
Result := PostCommand;
end;
end;

end;

procedure TDataFunctions.wsTradingWebHookDataAvailable(Sender: TObject;
ErrCode: Word);
var
ProcessedCommand : string;
Signal : string;
TrayIcon : TRzTrayIcon;

UserData : ISuperObject;
ReceivedJSON : AnsiString;
begin
try
ProcessedCommand := ProcessWebHook(AnsiString(TSslWSocket(Sender).ReceiveStr));
if (trim(ProcessedCommand) <> '') then
try
TrayIcon := frmMain.MyTrayicon;
UserData := SO(ProcessedCommand);
if userdata.s['signal'] = 'short' then
begin
Signal := userdata.s['message'];
AddSignal(signal, false);
end;

if userdata.s['signal'] = 'long' then
begin
Signal := userdata.s['message'];
AddSignal(signal, true);
end;
finally
TWSocket(sender).Free;
end;

except
AddSignal(ProcessedCommand, false,true);
end;
end;

FPiette · August 31, 2019

It looks like you are rewriting HTTP protocol. Why don't you use the HTTP server component. It does everything for you. See sample programs containing HTTP server component.

plastkort · August 31, 2019

I looked at it, and it seems it needed a HTML folder, I just need to answer a few lines.

this works for me. for a short time. but the listening socket seems to die

FPiette · August 31, 2019

HTTP protocol is more complex than you think...

There is also THttpAppSrv component and his demo application OverbyteIcsWebAppServer.

THttpAppSrv is more oriented to answer with "computed" responses.

plastkort · August 31, 2019

1 hour ago, FPiette said:

HTTP protocol is more complex than you think...

There is also THttpAppSrv component and his demo application OverbyteIcsWebAppServer.

THttpAppSrv is more oriented to answer with "computed" responses.

That one might do the trick, but i hope it can be simplified. I just require it to receive a POST message, and just reply a simple instruction page on the default.

but I would also appreciate if you have any answer to why my listening socket just stops listening after a while, im concerned that this happens on other projects i might be planning to do in the future. are there any sample codes around I can take a look at so i know that i do everything right ?

plastkort · August 31, 2019

hmm.. it seems this appserver will overcomplicate my simple project.. I did however notice something in your sample files called:

OverbyteIcsSrv5

i use "FNewSocket := _TWSocket(sender).Accept;"

but i did not apply the FnewSocket := TWSocket(sender).dup

is this a very important part i was missing ?

also i have added :

ShutDown(2);
Close;

and will see if this allows my server to live longer, note, it's only the listening socket that died earlier, and not the rest of my program. however im not sure if it just stopped listen or something else messed it up

FPiette · September 1, 2019

Quote

is this a very important part i was missing ?

Look at TWSocketServer if you want something basic able to listen for client and instanciate new TWSocket for each client. It doesn't do anything special related to HTTP protocol which is handled by THttpSrv component. As you can see there is a full hierarchy of classes each one being more intelligent. TWSocket is below everything, TWSocketServer add support for server features above TWSocket. THttpServer add HTTP protocol support (server side) to TWSocketServer. THttpAppSrv add REST application layer to THttpServer. In this hierarchy, there are some more intermediate classes for "custom", "Line mode", "proxy", "SSL/TLS" and more.

Angus Robertson · September 1, 2019

As François says, you should be using TWSocketServer which handles aspects of accepting and closing connections, you just plug in your existing onDataAvailable code. Also makes it easier to move to SSL in the future.

If you are using the HTTP protocol, there is a new component TSimpleWebSrv in OverbyteIcsSslHttpRest,pas which uses TWSocketServer and adds a simple HTTP protocol, just a few lines of code, ICS uses it for lightweight HTTP servers for OAuth2 and Lets Encrypt.

Angus

plastkort · September 2, 2019

I can take a look at TWSocketServer, I think i used it before, but maybe 6-7 years ago.

As a sidenote, i think the shutdown(2) and close did the trick i think. program still accepting connections after 2 days.

Angus Robertson · September 2, 2019

Years ago I had TWSocketServers running and accepting thousands of short connections a day for a few months at a tine, had to workaround the 49 day GetTickCount wrap around. Now my servers never run for more than 35 days, due to Microsoft being more aggressive with Windows Update and forcing reboots.

Angus

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A proper way to set up a listening socket (WebHook)

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