Detect if files are being downloaded

I need to know if anyone is busy downloaded specific files from my Apache web server. The 10 files (all in same path) are +100mb each, and I do not want to upload / replace them if someone if currently busy downloading one of them. Solution should be either php script or Putty commands that give the file name being downloaded, and (if possible) the IP address or the user downloading the file. An added advantage would be the progress of the download so that I can estimate the time remaining. Please specify the solution type you would use ( php / putty ), as well as which of the preferred info it would provide.