bug#10919: emacs-mule/utf-8 difference

[Tiphaine Turpin]

Hi,

I have a problem regarding coding systems:

I'm using process-send-string to send substrings of a buffer through a 
socket, after setting the process encoding and decoding systems to 
emacs-mule.
I expect the number of bytes written to match the byte-length of the 
substring as obtained by position-bytes, since the specification of 
position-bytes in emacs-devel is to always work with the emacs-mule 
encoding. From emacs-devel:

"The byte sequence of a buffer after decoded is always in emacs-mule (in 
emacs-unicode-2 branch, it's utf-8).  So, changing 
buffer-file-coding-system or any other coding-system-related variables 
doesn't affects position-bytes."

However, this is not the case with 3bytes utf8 characters: 
position-bytes counts them as 3 bytes, but process-send-string wirtes 4 
bytes.

Setting the process coding systems for the socket to utf-8 solves the 
problem, but I don't think it will with other coding systems, even if I 
used buffer-file-coding-system instead, since position-bytes does not 
use it.

What is the real expected behavior of these things, and how to make this 
correct ?

Regards,

Tiphaine Turpin