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c#arraysexceptionout-of-memorymemorystream
user5663970
user5663970

Reputation: 129

OutOfMemory Exception while converting MemoryStream to Array

I use the following code to return a byte array in HttpResponseMessage:

using (WebResponse response = (HttpWebResponse)request.GetResponse())
{
   byte[] bytes = ReadFully(response.GetResponseStream());
   ......
}
public static byte[] ReadFully(Stream input)
{
  byte[] buffer = new byte[16*1024];
  using (MemoryStream ms = new MemoryStream())
  {
    int read;
    while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
    {
        ms.Write(buffer, 0, read);
    }
    return ms.ToArray(); // This line throws OutOfMemory exception
  }
}

An OutOfMemory exception is thrown in the last return ms.ToArray() statement.

I need to set the resulting byte[] as HttpResponseMessage.Content.

Upvotes: 1

Views: 1985

Answers (2)

Igor
Igor

Reputation: 62318

You should return the stream directly instead of reading it into memory first.

public HttpResponseMessage CreateMessage(Stream input)
{
    HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
    result.Content = new StreamContent(input);
    return result;
}

Do not forget to set the appropriate headers etc.

Edit

... i need to write the byte array from the HttpResponseMessage into a file

Based on your last comment you changed your question and want to go the other way. Here is an example of writing to a file from a web response.

public void writetoFile(HttpWebResponse response)
{
    var inStream = response.GetResponseStream();
    using (var file = System.IO.File.OpenWrite("your file path here"))
    {
        inStream.CopyTo(file);
    }
}

Upvotes: 2

Panagiotis Kanavos
Panagiotis Kanavos

Reputation: 131774

Igor posted the solution, and the correct way to deal with stream content. Use one of the MVC helper functions like File(stream,contentype) or classes like StreamContent to send the stream contents directly to the client, eg:

return File(myStream,myExcelContentTypeString);

or 

return File(myStream,myExcelContentTypeString,"ReallyBigFile.xlsx");

The reason for the error, is that OOM can occur because memory is too fragmented to allocate a new object. A MemoryStream stores data in a buffer. When it exceeds the buffer limits, it allocates a new one with double the capacity and copies the old data. Copying 250MB of data like this is going to cause a lot of reallocations and thus a lot of memory fragmentation.

This can be avoided by specifying the desired capacity in the stream's constructor. This will allocate a large enough buffer immediatelly.

It's even better though to avoid caching this content though, by sending it to the browser directly.

Upvotes: 1

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