ASP.NET C# OutofMemoryException On Large File Upload

Question

I have the following file upload handler:

public class FileUploader : IHttpHandler
{
 public void ProcessRequest(HttpContext context)
 {
    HttpRequest request = context.Request;

    context.Response.ContentType = "text/html";
    context.Response.ContentEncoding = System.Text.Encoding.UTF8;
    context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
    var tempPath = request.PhysicalApplicationPath + "\\Files\\TempFiles\\";        
    byte[] buffer = new byte[request.ContentLength];
    using (BinaryReader br = new BinaryReader(request.InputStream))
    {
        br.Read(buffer, 0, buffer.Length);
    }
    var tempName = WriteTempFile(buffer, tempPath);
    context.Response.Write("{\"success\":true}");
    context.Response.End();
 }

 public bool IsReusable
 {
    get { return true; }
 }

 private string WriteTempFile(byte[] buffer, string tempPath)
 {
    var fileName = GetUniqueFileName(tempPath);
    File.WriteAllBytes(tempPath + fileName, buffer);
    return fileName;
 }
 private string GetUniqueFileName(string tempPath)
 {
    var guid = Guid.NewGuid().ToString().ToUpper();
    while (File.Exists(tempPath + guid))
    {
        guid = Guid.NewGuid().ToString().ToUpper();
    }
    return guid;
 }
}

When I upload large files, this is causing OutOfMemoryException. Could someone tell what's right way to upload large files using such a handler?

Answer 1

There is no need to load a file into memory to write it to somewhere. You should be using a small buffer (maybe 8k), and looping over the streams. Or, with 4.0, the CopyTo method. For example:

using(var newFile = File.Create(tempPath)) {
    request.InputStream.CopyTo(newFile);
}

(which does the small-buffer/loop for you, using a 4k buffer by default, or allowing a custom buffer-size to be passed via an overload)

Answer 2

You get an OutOfMemoryException because you load your uploaded file into memory. Avoid this by writing your stream directly to a file.

public void ProcessRequest(HttpContext context)
 {
    const int BufferSize = 4096;    

    HttpRequest request = context.Request;

    context.Response.ContentType = "text/html";
    context.Response.ContentEncoding = System.Text.Encoding.UTF8;
    context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
    var tempFilePath = Path.GetTempFileName();        

    using (Stream fs = File.OpenWrite(tempFilePath));
    {
        byte[] buffer = new byte[BufferSize];
        int read = -1;
        while(read = request.InputStream.Read(buffer, 0, buffer.Length) > 0)
        {            
             fs.Write(buffer, 0, buffer.Length);             
        }
    }

    context.Response.Write("{\"success\":true}");
    context.Response.End();
 }

edit: removed binaryreader