Question

I only need to copy a file from a remote server to a local PC if:

1. No target file on local PC yet.
2. Source file on server is newer than target on local PC.

Source file is 4 MB so I want to avoid copying every time.

// File copy if target doesn't exist or source is newer:
if (File.Exists(filenameSource))
{
  if (File.Exists(filenameTarget))
  {
    DateTime dateSource = File.GetLastWriteTimeUtc(filenameSource);
    DateTime dateTarget = File.GetLastWriteTimeUtc(filenameTarget);

    if (dateTarget < dateSource)
    {
      File.Copy(filenameSource, filenameTarget, true);
    }
  }
  else
  {
    File.Copy(filenameSource, filenameTarget);
  }
}

My questions are:

1. Does the above code still have to stream 4 MB of data in order to obtain the source’s modified timestamp?

2. Is comparing the modified timestamps sufficient for what I am trying to do? Or should I also compare created timestamps?

(#2 Might seem like a dumb question, but what if I drop a new source file with a modified timestamp that is older than the target’s modified timestamp?)

Bonus:

What if I write the above code in VBScript? Does the code below have to stream 4 MB of data in order to create the fileSource object?

if filesys.FileExists(strSource) then
  if filesys.FileExists(strTarget) then
    set fileSource = filesys.GetFile(strSource)
    set fileTarget = filesys.GetFile(strTarget)
    dateSource = fileSource.DateLastModified 
    dateTarget = fileTarget.DateLastModified 
    if dateTarget < dateSource then
      filesys.CopyFile strSource, strTarget, true
    end if
  else
    filesys.CopyFile strSource, strTarget, false
  end if
end if 

Answer 1

1. Accessing size and timestamps does not require the entire file to be yanked over the network.

2. I would include created, modified and size. To be perfectly safe, you’d have to calculate a hash, but that does require accessing the 4MB. Only you can determine whether this is an acceptable risk.

And VBScript should be the same thing.