Streaming a zip file over http in .net with SharpZipLib - asp.net

Question

I'm making a simple download service so a user can download all his images from out site.
To do that i just zip everything to the http stream.
However it seems everything is stored in memory, and the data isn't sent til zip file is complete and the output closed.
I want the service to start sending at once, and not use too much memory.
public void ProcessRequest(HttpContext context)
{
List<string> fileNames = GetFileNames();
context.Response.ContentType = "application/x-zip-compressed";
context.Response.AppendHeader("content-disposition", "attachment; filename=files.zip");
context.Response.ContentEncoding = Encoding.Default;
context.Response.Charset = "";
byte[] buffer = new byte[1024 * 8];
using (ICSharpCode.SharpZipLib.Zip.ZipOutputStream zipOutput = new ICSharpCode.SharpZipLib.Zip.ZipOutputStream(context.Response.OutputStream))
{
foreach (string fileName in fileNames)
{
ICSharpCode.SharpZipLib.Zip.ZipEntry zipEntry = new ICSharpCode.SharpZipLib.Zip.ZipEntry(fileName);
zipOutput.PutNextEntry(zipEntry);
using (var fread = System.IO.File.OpenRead(fileName))
{
ICSharpCode.SharpZipLib.Core.StreamUtils.Copy(fread, zipOutput, buffer);
}
}
zipOutput.Finish();
}
context.Response.Flush();
context.Response.End();
}
I can see the the worker process memory growing while it makes the file, and then releases the memory when its done sending. How do i do this without using too much memory?

Answer 1

Disable response buffering with context.Response.BufferOutput = false; and remove the Flush call from the end of your code.

Answer 2

use Response.BufferOutput = false; at start of ProcessRequest and flush response after each file.

Answer 3

FYI. This is working code to recursively add an entire tree of files, with streaming to browser:
string path = #"c:\files";
Response.Clear();
Response.ContentType = "application/zip";
Response.AddHeader("Content-Disposition", string.Format("attachment; filename=\"{0}\"", "hive.zip"));
Response.BufferOutput = false;
byte[] buffer = new byte[1024 * 1024];
using (ZipOutputStream zo = new ZipOutputStream(Response.OutputStream, 1024 * 1024)) {
zo.SetLevel(0);
DirectoryInfo di = new DirectoryInfo(path);
foreach (string file in Directory.GetFiles(di.FullName, "*.*", SearchOption.AllDirectories)) {
string folder = Path.GetDirectoryName(file);
if (folder.Length > di.FullName.Length) {
folder = folder.Substring(di.FullName.Length).Trim('\\') + #"\";
} else {
folder = string.Empty;
}
zo.PutNextEntry(new ZipEntry(folder + Path.GetFileName(file)));
using (FileStream fs = File.OpenRead(file)) {
ICSharpCode.SharpZipLib.Core.StreamUtils.Copy(fs, zo, buffer);
}
zo.Flush();
Response.Flush();
}
zo.Finish();
}
Response.Flush();