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I developped an application that uses indy component to download updates from a remote server.
The problem is that if the FTP server is down or the IP address is not correct, the idFTP.connect() takes too long to give the result (connection failure).
What is the best way to accelerate the connection answer, or may be checking ip address before connection to idFTP.
Thanks in advance.
Well, native connect() API timeouts are notoriously lengthy by design, (to accommodate high latency links like modems). Artificially shortening the timeout may result in premature failure notification, (though as many developers have never seen a modem, it’s not that much of a problem today:).
FTP is a reasonably complex transfer requiring two TCP connections and perhaps a DNS lookup – any of these could conceivably generate long connection delays. TidFTP has an inherited ‘ReadTimeout’ property and a connect() overload with a timeout parameter, but I’m not sure how effective they are.
Historically, I have always timed out such operations myself using a TTimer or similar – if the FTP thread does not respond with a suitable signal, (eg. TThread.Sychronize or user-defined Windows message SendMessage()’d to the GUI), in time, a ‘FTP failed’ actions are taken and a flag is set in the FTP thread that tells it to ignore any replies and self-terminate. Don’t use PostMessage – if you do, there is a small window of time in which a posted response my be queued up while the TTimer is firing – a race.
Oh – and if you are just plonking a TidFTP onto the form, (or creating one in TForm.FormCreate), and trying to run it from the main GUI thread, (with, or without, TidAntiFreeze), stop doing it and thread off the FTP.