Question

Can anyone explain the difference between calling GetPreamble() on a newly instantiated utf8 encoding as opposed to the public ones available from the Encoding class?

byte[] p1 = Encoding.UTF8.GetPreamble();
byte[] p2 = new UTF8Encoding().GetPreamble();

p1 is the normal 3 byte utf-8 preamble, but p2 ends up being empty, which seems very wrong.

Answer 1

The difference is that the UTF8 property of Enconding is created this way

new UTF8Encoding(true)

this indicates that encoderShouldEmitUTF8Identifier = true so the 3 byte preamble is there

and your call to the default constructor

new UTF8Encoding() 

that is equivalent to

new UTF8Encoding(false)

To get same results:

byte[] p1 = Encoding.UTF8.GetPreamble();
byte[] p2 = new UTF8Encoding(true).GetPreamble();