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?

Pasteboard

Once you have the Stream, why bother converting it to a MemoryStream? Can't you just work with the Stream directly? – Lacuna

I need a MemoryStream due to other dependencies. – Pasteboard

There are also instances where poor performance working with Streams causes a MemoryStream to be more efficient. Like my question here: #50399981 – Countermine

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);
    }
}

Lacuna

I'm presuming that's > 0 at the end of the while line? – Pasteboard

@Pasteboard - Correct. I got a little delete happy. Fixed. – Lacuna

looks like one closing parenthesis is missing. should be while((read = input.Read(buffer,0,buffer.Length)) > 0) – Useless

Might want to add output.Position = 0; as the very last line otherwise you'll need to remember to reset it later. – Aeromedical

Answer 2

In .NET 4, you can use Stream.CopyTo to copy a stream, instead of the home-brew methods listed in the other answers.

MemoryStream _ms;
    
public MyClass(Stream sourceStream)
{
    _ms = new MemoryStream();
    sourceStream.CopyTo(_ms);
}

Pulitzer

Make sure you first set sourceStream.Position = 0; – Ointment

You will need to set _ms.Position = 0; prior to using it as well. – Abolition

Answer 3

Use this:

var memoryStream = new MemoryStream();
stream.CopyTo(memoryStream);

This will convert Stream to MemoryStream.

Vigen

Answer 4

You can simply do:

var ms = new MemoryStream(File.ReadAllBytes(filePath));

Stream position is 0 and ready to use.

Lahr

This is the cleanest and most elegant solution. – Genitourinary

This doesn't answer the question at all! – Piggin

Answer 5

You will have to read in all the data from the Stream object into a byte[] buffer and then pass that into the MemoryStream via its constructor. It may be better to be more specific about the type of stream object you are using. Stream is very generic and may not implement the Length attribute, which is rather useful when reading in data.

Here's some code for you:

public MyClass(Stream inputStream) {
    byte[] inputBuffer = new byte[inputStream.Length];
    inputStream.Read(inputBuffer, 0, inputBuffer.Length);

    _ms = new MemoryStream(inputBuffer);
}

If the Stream object doesn't implement the Length attribute, you will have to implement something like this:

public MyClass(Stream inputStream) {
    MemoryStream outputStream = new MemoryStream();

    byte[] inputBuffer = new byte[65535];
    int readAmount;
    while((readAmount = inputStream.Read(inputBuffer, 0, inputBuffer.Length)) > 0)
        outputStream.Write(inputBuffer, 0, readAmount);

    _ms = outputStream;
}

Mcneese

Answer 6

I use this combination of extension methods:

    public static Stream Copy(this Stream source)
    {
        if (source == null)
            return null;

        long originalPosition = -1;

        if (source.CanSeek)
            originalPosition = source.Position;

        MemoryStream ms = new MemoryStream();

        try
        {
            Copy(source, ms);

            if (originalPosition > -1)
                ms.Seek(originalPosition, SeekOrigin.Begin);
            else
                ms.Seek(0, SeekOrigin.Begin);

            return ms;
        }
        catch
        {
            ms.Dispose();
            throw;
        }
    }

    public static void Copy(this Stream source, Stream target)
    {
        if (source == null)
            throw new ArgumentNullException("source");
        if (target == null)
            throw new ArgumentNullException("target");

        long originalSourcePosition = -1;
        int count = 0;
        byte[] buffer = new byte[0x1000];

        if (source.CanSeek)
        {
            originalSourcePosition = source.Position;
            source.Seek(0, SeekOrigin.Begin);
        }

        while ((count = source.Read(buffer, 0, buffer.Length)) > 0)
            target.Write(buffer, 0, count);

        if (originalSourcePosition > -1)
        {
            source.Seek(originalSourcePosition, SeekOrigin.Begin);
        }
    }

Blanchette

Answer 7

How do I copy the contents of one stream to another?

see that. accept a stream and copy to memory. you should not use .Length for just Stream because it is not necessarily implemented in every concrete Stream.

Burnedout

Answer 8

public static void Do(Stream in)
{
    _ms = new MemoryStream();
    byte[] buffer = new byte[65536];
    while ((int read = input.Read(buffer, 0, buffer.Length))>=0)
        _ms.Write (buffer, 0, read);
}

Irrational

Answer 9

byte[] fileData = null;
using (var binaryReader = new BinaryReader(Request.Files[0].InputStream))
{
    fileData = binaryReader.ReadBytes(Request.Files[0].ContentLength);
}

Shaff