Make :bytes actually pop off non-byte layers

Author: Leont

lib/PerlIO.pm

@@ -175,17 +175,10 @@ between valid UTF-8 bytes and valid Unicode characters.
 
 =item :bytes
 
-This is the inverse of the C<:utf8> pseudo-layer.  It turns off the flag
-on the layer below so that data read from it is considered to
-be Perl's internal downgraded encoding, thus interpreted as the native
-single-byte encoding of Latin-1 or EBCDIC.  Likewise on output Perl will
-warn if a "wide" character (a codepoint not in the range 0..255) is
-written to a such a stream.
-
-This is very dangerous to push on a handle using an C<:encoding> layer,
-as such a layer assumes to be working with Perl's internal upgraded
-encoding, so you will likely get a mangled result.  Instead use C<:raw> or
-C<:pop> to remove encoding layers.
+This removes all layers that do unicode IO, such as C<:utf8> and
+C<:encoding>. It ensures that data read from it is considered to be
+"octets" i.e. characters in the range 0..255 only.  Likewise on output perl
+will warn if a "wide" character is written to a such a stream.
 
 =item :raw
 
@@ -203,9 +196,9 @@ to add C<:perlio> to the PERLIO environment variable, or open the handle
 explicitly with that layer, to replace the platform default of C<:crlf>.
 
 The implementation of C<:raw> is as a pseudo-layer which when "pushed"
-pops itself and then any layers which would modify the binary data stream.
-(Undoing C<:utf8> and C<:crlf> may be implemented by clearing flags
-rather than popping layers but that is an implementation detail.)
+pops itself and then any layers which do not declare themselves as suitable
+for binary data. (Undoing :crlf is implemented by clearing a flag rather
+than popping the layer but that is an implementation detail.)
 
 As a consequence of the fact that C<:raw> normally pops layers,
 it usually only makes sense to have it as the only or first element in

perlio.c

@@ -2270,12 +2270,33 @@ PERLIO_FUNCS_DECL(PerlIO_utf8) = {
     NULL,                       /* set_ptrcnt */
 };
 
+IV
+PerlIOBytes_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
+{
+    PERL_UNUSED_CONTEXT;
+    PERL_UNUSED_ARG(mode);
+    PERL_UNUSED_ARG(arg);
+    PERL_UNUSED_ARG(tab);
+    if (PerlIOValid(f)) {
+	PerlIO* current = f;
+	while(!(PerlIOBase(current)->tab->kind & PERLIO_K_RAW)) {
+	    /*PerlIO* next = PerlIONext(current);*/
+	    PerlIO_flush(current);
+	    PerlIO_pop(aTHX_ current);
+	    /*current = next; */
+	}
+	PerlIOBase(f)->flags &= ~PERLIO_F_UTF8;
+	return 0;
+    }
+    return -1;
+}
+
 PERLIO_FUNCS_DECL(PerlIO_byte) = {
     sizeof(PerlIO_funcs),
     "bytes",
     0,
     PERLIO_K_MULTIARG,
-    PerlIOUtf8_pushed,
+    PerlIOBytes_pushed,
     NULL,
     PerlIOBase_open,
     NULL,