[API Proposal]: BinaryReader.ReadExactly

[terrajobst]

Background and motivation

When reading custom binary formats one very often needs a specific number of bytes. The existing Read() method doesn't read a specific number of bytes, it reads as many bytes are currently available. Calling code has to handle this.

We had the same issue on Stream and solved this by exposing Stream.ReadExactly and Stream.ReadAtLeast.

API Proposal

namespace System.IO;

public partial class BinaryReader
{
    public virtual void ReadExactly(Span<byte> buffer);
}

API Usage

BinaryReader binaryReader = GetReader();

Span<byte> guidBytes = (Span<byte>)stackalloc byte[16];
reader.ReadExactly(guidBytes);

Guid guid = new Guid(guidBytes);

Alternative Designs

No response

Risks

No response

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[PaulusParssinen]

This would be equivalent to calling ReadExactly(Span<byte>) on the BinaryReader.BaseStream property, right? This method would be much nicer/accessible though.

[terrajobst]

Logically yes, but practically the challenge is that the reader has its own buffer. By passing that would be problematic.

[adamsitnik]

The proposal LGTM, I've marked it as ready for review.

[terrajobst]

Video

• Looks good as proposed

namespace System.IO;

public partial class BinaryReader
{
    public virtual void ReadExactly(Span<byte> buffer);
}