How to get a MemoryStream from a Stream in .NET?

Question

I have the following constructor method which opens a MemoryStream from a file path:

MemoryStream _ms;

public MyClass(string filePath)
{
    byte[] docBytes = File.ReadAllBytes(filePath);
    _ms = new MemoryStream();
    _ms.Write(docBytes, 0, docBytes.Length);
}

I need to change this to accept a Stream instead of a file path. Whats the easiest/most efficient way to get a MemoryStream from the Stream object?

Answer 1

If you're modifying your class to accept a Stream instead of a filename, don't bother converting to a MemoryStream. Let the underlying Stream handle the operations:

public class MyClass
{ 
    Stream _s;

    public MyClass(Stream s) { _s = s; }
}

But if you really need a MemoryStream for internal operations, you'll have to copy the data out of the source Stream into the MemoryStream:

public MyClass(Stream stream)
{
    _ms = new MemoryStream();
    CopyStream(stream, _ms);
}

// Merged From linked CopyStream below and Jon Skeet's ReadFully example
public static void CopyStream(Stream input, Stream output)
{
    byte[] buffer = new byte[16*1024];
    int read;
    while((read = input.Read (buffer, 0, buffer.Length)) > 0)
    {
        output.Write (buffer, 0, read);
    }
}