Chapter 3: Memory Uploads

The Path parameter to the method Upload.Save is optional: the method can be called with no arguments at all, as follows:

If a folder path is not passed in, the Save method does not save uploaded files to disk. Instead it creates memory images of the files that can be accessed via the Upload.Files collection. A memory file can then be saved to disk via the File.SaveAs method. You may also use the property File.Binary to save the file in the database, as shown in the next chapter.

Note that AspUpload 2.x used the method Upload.SaveToMemory to perform memory uploads. This method is still supported for backwards compatibility, but it is equivalent to Upload.Save with the Path argument omitted.

Memory uploads provide several major advantages over regular uploads:

• Access to form items. You cannot access text fields on your form until after the Save method is called. Therefore, if you need to access a form item before saving a file to disk, uploading to memory is the only way to do it.
• Access to file names. You can check whether a file with the same name already exists in a directory before saving the uploaded file to disk.
• Simplified renaming and copying. A regular upload saves all the files in the same directory, and under their original names. Uploading to memory makes the task of renaming and copying files easier to code.
• Performance and security. If the ultimate destination of an uploaded file is a database table, you can use memory uploads to save your file in the database directly from memory without saving it to disk first.

The main disadvantage of memory uploads is that it cannot be used with large files as it is very memory-intensive. You should always use SetMaxSize with memory uploads to limit the size of the memory imprints of files.

The following code sample enables a user to select a destination subdirectory underneath the c:\upload folder to upload a file to. The sample form (file formitems.asp) contains a file item and a drop-down list box:

The corresponding upload script formitems_upload.asp uploads the file to memory, then creates a user-specified subfolder and saves the file in it:

Click the link below to run this code sample:

http://localhost/aspupload/03_memory/formitems.asp

The next code sample uploads a file to memory, the checks whether a file with the same name already exists in the destination directory, and if so, alerts a user. Otherwise the file is saved to disk. The form file filename.asp contains a single file item and is not shown here. The corresponding upload script filename_upload.asp uses the method FileExists to determine whether the file already exists:

Click the link below to run this code sample:

http://localhost/aspupload/03_memory/filename.asp

Using regular uploads, all the files uploaded at once are saved in the same directory, and under their original names. Memory uploads enable you to save files individually in any directory and under arbitrary names.

The next code sample enables a user to upload two files. One file is saved in the directory "c:\upload\folder1", the other in "c:\upload\folder2", both under the name derived from the current session ID.

The file twofolders.asp contains a form with two file items, FILE1 and FILE2. This file is not shown here. The corresponding upload script twofolders_upload.asp creates two subdirectories and saves FILE1 in Folder1 and FILE2 in Folder2. Both files are saved under the same name derived from SessionID and the original extension:

Click the link below to run this code sample:

http://localhost/aspupload/03_memory/twofolders.asp

Using uploads to memory to save files in the database is covered in the next chapter.

To copy and/or rename files, you don't have to use memory uploading. The same effect can be achieved using regular (disk) uploading in conjunction with the methods File.Copy, File.Move and File.Delete, which copy, move and delete an uploaded file, respectively.

The code sample twofoders2_upload.asp does essentially the same as twofolders_upload described above, but without the use of memory uploading:

Click the link below to run this code sample:

http://localhost/aspupload/03_memory/twofolders2.asp