问题
I want to download a file from FTP. If the file is small (usually under 1000MB) it works. However, if the file is big I get an EIdReadTimeout. Why? Should I keep the connection alive? From what I know reading data has its own channel so I don't have to keep the connection alive.
What is odd is that the exception appears at the end of the Get (after Get successfully downloads the whole file): FTP.Get(Name, TempGzFile, TRUE, FALSE) !!!!
Documentation:
TIdFTP.ReadTimeout - Number of milliseconds to wait for an FTP protocol response.
TIdFTP.TransferTimeout - Timeout value for read operations on the data channel for the FTP client.
By default ReadTimeout is set to 60sec and TransferTimeout to 10sec.
I a using Delphi XE7 (which I guess uses Indy 10). The Passive property for my IdFTP is set to false.
回答1:
The FTP protocol uses multiple TCP/IP connections - one for the main command/response connection, and separate connections for data transfers. While a data transfer is in progress, the main command connection sits idle. Once the transfer is finished, the command connection receives a response.
If you are passing through a router/firewall that is not FTP-aware, the command connection is likely to get killed if it sits idle for too long during a large transfer. The connection is usually not killed "gracefully", so even the OS does not know the connection is gone. When TIdFTP then tries to read a transfer response that never arrives, it times out.
To account for that, use the TIdFTP.NATKeepAlive property to enable TCP/IP level keep-alives on the command connection during transfers. Set NATKeepAlive.UseKeepAlive to True, and set NATKeepAlive.IdleTimeMS (the idle timeout before keepalives start sending) and NATKeepAlive.IntervalMS (the interval between each keepalive) to suitable values.
Note, however, that IdleTimeMS and IntervalMS are only implemented for Windows 2000+, Linux, and BSD at this time. Other platforms use defaults provided by the OS (which tend to be very large). If you need to customize the values on those platforms, you can use the TIdFTP.OnDataChannelCreate and TIdFTP.OnDataChannelDestroy events to call TIdFTP.Socket.Binding.SetSocketOption() directly as needed.
来源：https://stackoverflow.com/questions/29244462/exception-class-eidreadtimeout-with-message-read-timed-out-indy-idftp