I have just tested some code on Perl 5.24.2 which was running happily on 5.16.0 and got a warning of "sysread() is deprecated on :utf8 handles". Now I'm wondering how to fix it and I'm a little confused by the discussion at RFC remove strange behaviour of sysread()/syswrite() on UTF-8 streams.

The file handle in question is a unidirectional pipe created before a fork and the parent is writing XML down the pipe (which has :encoding(UTF-8)) layer and the child is using sysread on the read end of the pipe which also has encoding(UTF-8). The child then sends the data down a socket which also has encoding(UTF-8) layer on it.

I'm slightly confused by the :utf8 and encoding("UTF-8"). I'm doing the latter but the RFC seems to indicate there is a difference between :utf8 and encoding("UTF-8") and that sysread works with :utf8 but not encoding(something else)? So why do I get the deprecated warning?

Is the solution simply to leave the encoding on the write end of the pipe which uses print to send messages down the pipe, but leave it off the read end of the pipe and decode the read message as UTF8 before sending it down the onwards socket?

CORRECTION: the connection between the parent and child is a socket although I don't think it makes any difference

UPDATE1: It appears I can't just use :raw on the socket read end and decode to UTF-8 as I might have read part of a UTF-8 sequence. Still searching for an answer.

UPDATE2: The code was originally using readline but that was switched to sysread because the code already uses IO::Select and you cannot mix buffered reading with IO::Select

UPDATE3: This link explains why you cannot use buffered IO and IO::Select https://stackoverflow.com/questions/7349124/is-it-ever-safe-to-combine-select2-and-buffered-io-for-file-handles#7352605