If an application is copying a large file into a folder that is being polled by a DataPower FTP Poller, and if the file name matches the pattern being polled for, does the FTP Poller know when the file has been copied completely?
Outside application copying a large file into a folder being polled by a DataPower FTP Poller.
The FTP poller has no way to know if the "feeder" application has copied the file completely. The "feeder" application needs to write the file to a name on the FTP server that does NOT match the DataPower configured match pattern for the poller. When the feeder finishes writing the file, and ideally uses the STAT command for a size check (to verify no truncation), then the feeder should use RNFR/RNTO to rename the file to a name that does match the configured match pattern.
Note that some FTP servers do this "automatically", That is, while they are writing the file, they use a temporary name (ex. files starting with a period) and then rename the file when the data connection closes. But that is not universal among FTP servers and it is not part of the FTP specification. The approach described in the previous paragraph, particularly using the STAT call wisely, is "best practice".