troubles in Viewer with utf8 and widechars

[egmont]

• floating wrapping: if you scroll through long CJK text

(meaning - nearly no spaces, almost whole double-width),
you'll see line break of the first line is moving as you scroll
(bad description, see yourself); IIRC, it was that way even before regression

• 4096 bytes break: every 4096 bytes there's a chance it happens in the middle

of an utf8 char (I'm not sure if this can happen on non-double-width and
don't know yet where does this number come from), leading to a valid char(s)
treated as unprintable

[mnk]

Just a little note:
I suspect that some of those problems can be reproduces in any utf8
text outside of ASCII range (so cyrillic may be affected too).

[mnk]

FYI: this problem affects ANY utf8 text.
While in single byte locales it's OK to break
file content into arbitrary sized blocks, that's
a wrong thing to do with utf8.

As long as a more than one byte sized utf8 char is put on
the block border, you'll get the second problem.

It looks like there's already a thing that could help with
fixing that (g_utf8_get_char_validated returns -2 on a still valid,
but not yet complete sequence), but I can't figure out yet
the loading part.

[egmont]

Friendly ping :-) Now that I see work going on again, I'm wondering if anyone feels like taking it.

I was just recently bitten by the bug that UTF-8 characters crossing a 4kB boundary are handled incorrectly in mcview.

Try:
{ for i in seq 1 4095; do echo -n x ; done ; echo -e '\0303\0241x\n' ; } > /tmp/x
mcview /tmp/x
enable line wrapping

Expected: see an "á" near the end of the file.
Actual: something else, or two dots.

[slavazanko]

Friendly ping :-)

Friendly pong :)

Now that I see work going on again, I'm wondering if anyone feels like taking it.

Yep, sorry for very long answer - all our forces was in VFS restructurization...

Expected: see an "á" near the end of the file.
Actual: something else, or two dots.

Thanks for detailed test case.

[sergem]

fix, based on patch from #2372

[angel_il]

branch: ​1730_mcview_utf8_fix (parent: master)

Please review

[angel_il]

fixed: 16d1abf99c09257c9e43cc4ff44428c7f5ea75c8

[angel_il]

cherry-picked to 4.7.5-stable:
commit 03a2c310ac969826bc64f31355692521d554047c (fixup)
commit 0b8409aa85893613aac4c82e0b85f41ec66fc99c (const UTF8_CHAR_LEN)