Problem

Add the current time stamp to the file name, preserving the original file's extension when doing a Server Initiated Pull.

For example:

The source file on the remote server test.txt to be pulled and stored on SecureTransport as test_20190930145433.txt

Resolution

The following Expression Language should be put in the Transfer Site, in the Post Transmission setting -> Receive file as field:

${basename(stenv.target)}_${date('yyyyddMMHHmmss')}${extension(stenv.target)}

The date() function accepts as parameter the format in which the time stamp should be printed out. The format follows the Java Simple Date Format notation as explained here.