No need to copy data around here. Add a comment explaining the purpose of this method. Copied from the Java client.

Author: lukebakken

projects/RabbitMQ.Client/client/impl/Frame.cs

@@ -221,22 +221,24 @@ private InboundFrame(FrameType type, int channel, ReadOnlyMemory<byte> payload,
 
         private static void ProcessProtocolHeader(ReadOnlySequence<byte> buffer)
         {
+            // Probably an AMQP.... header indicating a version mismatch.
+            // Otherwise meaningless, so try to read the version and throw an exception, whether we
+            // read the version correctly or not.
             try
             {
                 if (buffer.Length < 8)
                 {
                     throw new EndOfStreamException();
                 }
 
-                Span<byte> tempSpan = stackalloc byte[8];
-                buffer.Slice(0, 8).CopyTo(tempSpan);
+                var bufferSpan = buffer.First.Span;
 
-                if (tempSpan[1] != 'M' || tempSpan[2] != 'Q' || tempSpan[3] != 'P')
+                if (bufferSpan[1] != 'M' || bufferSpan[2] != 'Q' || bufferSpan[3] != 'P')
                 {
                     throw new MalformedFrameException("Invalid AMQP protocol header from server");
                 }
 
-                throw new PacketNotRecognizedException(tempSpan[4], tempSpan[5], tempSpan[6], tempSpan[7]);
+                throw new PacketNotRecognizedException(bufferSpan[4], bufferSpan[5], bufferSpan[6], bufferSpan[7]);
             }
             catch (EndOfStreamException)
             {