ASP Classic, Download large files does not work on some servers


I have the following script, which works good, locally (Windows 10 IIS, windows 2003 Server), but not on our hosting server (Windows 2003 Server). Anything over 4mb will download really slow and then timeout before it gets to the end of the file. However, locally, it downloads fast and full.

Doing a Direct Download (link to the file itself) downloads a 26.5mb file in 5 seconds from our hosting provider server. So, there is not an issue with a download limit. There is an issue it seems, with the hosting server and this script. Any ideas?

Response.AddHeader "content-disposition","filename=" & strfileName
Response.ContentType = "application/x-zip-compressed" 'here your content -type

Dim strFilePath, lSize, lBlocks
'Const CHUNK = 2048
' Thanks to Lankymart. I have set this and it download at 1.5MB a second, so that is running pretty well for what I need it to be.
Const CHUNK = 2048000
set objStream = CreateObject("ADODB.Stream")
objStream.Type = 1
objStream.LoadFromfile Server.MapPath("up/"&strfileName&"")
lSize = objStream.Size
Response.AddHeader "Content-Size", lSize
lBlocks = 1
Response.Buffer = False
Do Until objStream.EOS Or Not Response.IsClientConnected


Just looking at the code snippet it appear to be fine and is the very approach I would use for downloading large files (especially like the use of Response.IsClientConnected).

However having said that, it's likely the size of the chunks being read in relation to the size of the file.

Very roughly the formula is something like this...

time to read = ((file size / chunk size) * read time)

So if we use your example of a 4 MB file (4194304 bytes) and say it takes 100 milliseconds to read each chunk then the following applies;

  • Chunk Size of 2048 bytes (2 KB) will take approx. 3 minutes to read.

  • Chunk Size of 20480 bytes (20 KB) will take approx. 20 seconds to read.

Classic ASP pages on IIS 7 and above have a default scriptTimeout of 00:01:30 so in the example above a 4 MB file constantly read at 100 milliseconds in 2 KB chunks would timeout before the script could finish.

Now these are just rough statistics your read time won't constantly stay the same and it's likely faster then 100 milliseconds (depending on disk read speeds) but I think you get the point.

So just try increasing the CHUNK.

Const CHUNK = 20480 'Read in chunks of 20 KB