CODEWITHSUNDEEP
c#
PieterV
PieterV

Reputation: 593

How to copy Memory<byte> to a specific offset in byte[]

I am using async network IO, my read buffer is in Memory, I am trying to copy the Memory into a byte[] at a specific offset.

public bool Append(Memory<byte> buffer)
{
    // Verify input data
    if (buffer.Length <= 0 ||
        buffer.Length > PacketSize - Received)
    {
        // Debug.Assert(false);
        return false;
    }

    // Copy received data into packet at current offset
    // TODO : Avoid heap array allocation or iteration
    //Buffer.BlockCopy(buffer.ToArray(), 0, Packet, Received, buffer.Length);
    //private readonly byte[] Packet;
    for (int i = 0; i < buffer.Length; i ++)
    {
        Packet[Received + i] = buffer.Span[i];
    }
    Received += buffer.Length;

    // If we have a header it must match
    if (HasHeader() && !DoesHeaderMatch())
    {
        // Debug.Assert(false);
        return false;
    }

    return true;
}

I am looking for an equivalent of Buffer.BlockCopy(), but the memory source should be of type Memory<> or derived Span<> type. I do not want to create temporary stack or heap buffers.

Any ideas?

Solution:

// Copy received data into packet at current offset
Span<byte> destination = Packet.AsSpan().Slice(Received, buffer.Length);
Span<byte> source = buffer.Span;
source.CopyTo(destination);
Received += buffer.Length;

Upvotes: 1

Views: 2653

Answers (1)

Caius Jard
Caius Jard

Reputation: 74605

Hopefully I'm getting what you're saying..

So you have a buffer, Packet, and you're happy to make it a span. And it has some data in like Hello World:

byte[] buf = Encoding.ASCII.GetBytes("Hello World");

var bufSpan = buf.AsSpan();

And you have some other data as another span:

byte[] otherSpan = Encoding.ASCII.GetBytes("rr").AsSpan();

And you want to write that data into the buffer at a certain location. You have to slice the buffer first and copy the new data into the Span created by the slice

otherSpan.CopyTo(bufSpan.Slice(2)); //replace the ll with rr

Console.WriteLine(Encoding.ASCII.GetString(bufSpan.ToArray())); prints "Herro World"

Upvotes: 3

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