Unless there's something wrong with the system's TCP stack, no FIN should be sent on application crash or on force termination, only a RST.
Only some legacy mainframe servers implement these. Haven't actually ever seen these modes used elsewhere.[/quote]
Yes and no.
Receiving a FIN means that the client has wanted to close the connection. As such, the server can see whether the transfer has ended successfully or whether the connection has been forcefully terminated (barring broken TCP stacks, consumer-grade routers, firewalls and the like).
What the server cannot see is whether a successful transfer includes the complete file. The server shouldn't even know, its something the client takes care of.
Last but not least, there's always the possibility of a flipped bit. To ensure correctness, the connection as a whole needs to be integrity protected, e.g. through FTP over TLS.
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1) Is block and compressed mode supported by any FTP clients/servers?
Only some legacy mainframe servers implement these. Haven't actually ever seen these modes used elsewhere.[/quote]
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2) In stream mode is it at all possible to tell reliably if the whole file has transferred correctly?
Yes and no.
Receiving a FIN means that the client has wanted to close the connection. As such, the server can see whether the transfer has ended successfully or whether the connection has been forcefully terminated (barring broken TCP stacks, consumer-grade routers, firewalls and the like).
What the server cannot see is whether a successful transfer includes the complete file. The server shouldn't even know, its something the client takes care of.
Last but not least, there's always the possibility of a flipped bit. To ensure correctness, the connection as a whole needs to be integrity protected, e.g. through FTP over TLS.