[API Proposal]: Span<byte> constructor for MemoryStream

[RedIODev]

Background and motivation

A memory stream should work with a span of bytes. When you have a span of bytes as your data and need a MemoryStream for another api you shouldn't need to copy the data from the span to a new byte array to get a "view" in form of a memory stream to it. This conversion from one type of memory view to another should be seamlessly possible.

API Proposal

namespace System.IO;

public class MemoryStream : Stream
{
    public MemoryStream(Span<byte> buffer) 
    {
        ...
    }
    ...
}

API Usage

Span<byte> someData = ...;
using MemoryStream ms = new MemoryStream(someData);
//The FromImage is just an example for an API that uses a stream and doesn't take a span. I don't propose a change to the creation of an Image from bytes.
Image imgFromData = Image.FromStream(ms);

Alternative Designs

Alternatively the byte array constructor of MemoryStream could be changed to a Span with likely braking no code since a byte array can implicitly be converted to a Span.

Risks

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-memory
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

A memory stream should work with a span of bytes. When you have a span of bytes as your data and need a MemoryStream for another api you shouldn't need to copy the data from the span to a new byte array to get a "view" in form of a memory stream to it. This conversion from one type of memory view to another should be seamlessly possible.

API Proposal

namespace System.IO;

public class MemoryStream : Stream
{
    public MemoryStream(Span<byte> buffer) 
    {
        ...
    }
    ...
}

API Usage

Span<byte> someData = ...;
using MemoryStream ms = new MemoryStream(someData);
//The FromImage is just an example for an API that uses a stream and doesn't take a span. I don't propose a change to the creation of an Image from bytes.
Image imgFromData = Image.FromStream(ms);

Alternative Designs

Alternatively the byte array constructor of MemoryStream could be changed to a Span with likely braking no code since a byte array can implicitly be converted to a Span.

Risks

No response

Author:	RedIODev
Assignees:	-
Labels:	api-suggestion, area-System.Memory
Milestone:	-

[EgorBo]

MemoryStream has to copy your data to its field on the heap so you can't avoid it.
In your case you can do new MemoryStream(someData.ToArray()) - there won't be a redundant copy we can avoid here.

[tfenise]

If you really need a Stream backed by a Span<byte>, you may pin the Span<byte>, get a byte*, and create an UnmanagedMemoryStream. A more hacky solution is maybe to somehow get a pointer to the Span<byte> and use that pointer to access the Span<byte> in your own implementation of Stream. However, I don't recommend these solutions, as extra attention is needed to preserve memory safety.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

A memory stream should work with a span of bytes. When you have a span of bytes as your data and need a MemoryStream for another api you shouldn't need to copy the data from the span to a new byte array to get a "view" in form of a memory stream to it. This conversion from one type of memory view to another should be seamlessly possible.

API Proposal

namespace System.IO;

public class MemoryStream : Stream
{
    public MemoryStream(Span<byte> buffer) 
    {
        ...
    }
    ...
}

API Usage

Span<byte> someData = ...;
using MemoryStream ms = new MemoryStream(someData);
//The FromImage is just an example for an API that uses a stream and doesn't take a span. I don't propose a change to the creation of an Image from bytes.
Image imgFromData = Image.FromStream(ms);

Alternative Designs

Alternatively the byte array constructor of MemoryStream could be changed to a Span with likely braking no code since a byte array can implicitly be converted to a Span.

Risks

No response

Author:	RedIODev
Assignees:	-
Labels:	api-suggestion, area-System.IO, untriaged
Milestone:	-

[teo-tsirpanis]

A MemoryStream constructor that takes a span and does not copy the data is simply impossible to have due to ref struct restrictions.

A stream that reads a Memory<byte> is possible and has been proposed in #22838.