This continues the programme of UTF-8 support in authentication, begun
in commit f4519b6533 which arranged for console userpass prompts
to function in UTF-8 when the prompts_t asked them to. Since the new
line editing setup works properly when it _is_ in UTF-8 mode, I can
now also arrange that it puts the terminal into UTF-8 mode in the
right circumstances.
I've extended the applicability of the '-legacy-charset-handling' flag
introduced by the commit mentioned above, so that now it's not
specific to the console front end. Now you can give it to GUI PuTTY as
well, which restores the previous (wrong) behaviour of accepting
username and password prompt input in the main session's configured
character set. So if this change breaks someone's workflow, they
should be able to have it back.
This allows you to set a flag in conio_setup() which causes the
returned ConsoleIO object to interpret all its output as UTF-8, by
translating it to UTF-16 and using WriteConsoleW to write it in
Unicode. Similarly, input is read using ReadConsoleW and decoded from
UTF-16 to UTF-8.
This flag is set to false in most places, to avoid making sudden
breaking changes. But when we're about to present a prompts_t to the
user, it's set from the new 'utf8' flag in that prompt, which in turn
is set by the userauth layer in any case where the prompts are going
to the server.
The idea is that this should be the start of a fix for the long-
standing character-set handling bug that strings transmitted during
SSH userauth (usernames, passwords, k-i prompts and responses) are all
supposed to be in UTF-8, but we've always encoded them in whatever our
input system happens to be using, and not done any tidying up on them.
We get occasional complaints about this from users whose passwords
contain characters that are encoded differently between UTF-8 and
their local encoding, but I've never got round to fixing it because
it's a large piece of engineering.
Indeed, this isn't nearly the end of it. The next step is to add UTF-8
support to all the _other_ ways of presenting a prompts_t, as best we
can.
Like the previous change to console handling, it seems very likely
that this will break someone's workflow. So there's a fallback
command-line option '-legacy-charset-handling' to revert to PuTTY's
previous behaviour.
Until now, the command-line PuTTY tools (PSCP, PSFTP and Plink) have
presented all the kinds of interactive prompt (password/passphrase,
host key, the assorted weak-crypto warnings, 'append to log file?') on
standard error, and read the responses from standard input.
This is unfortunate because if you're redirecting their standard
input (especially likely with Plink) then the prompt responses will
consume some of the intended session data. It would be better to
present the prompts _on the console_, even if that's not where stdin
or stderr point.
On Unix, we've been doing this for ages, by opening /dev/tty directly.
On Windows, we didn't, because I didn't know how. But I've recently
found out: you can open the magic file names CONIN$ and CONOUT$, which
will point at your actual console, if one is available.
So now, if it's possible, the command-line tools will do that. But if
the attempt to open CONIN$ and CONOUT$ fails, they'll fall back to the
old behaviour (in particular, if no console is available at all).
In order to make this happen consistently across all the prompt types,
I've introduced a new object called ConsoleIO, which holds whatever
file handles are necessary, knows whether to close them
afterwards (yes if they were obtained by opening CONFOO$, no if
they're the standard I/O handles), and presents a BinarySink API to
write to them and a custom API to read a line of text.
This seems likely to break _someone's_ workflow. So I've added an
option '-legacy-stdio-prompts' to restore the old behaviour.
This removes one case from several of the individual tools'
command-line parsers, and moves it into a central place where it will
automatically be supported by any tool containing console.c.
In order to make that not cause a link failure, there's now a
stubs/no-console.c which GUI clients of cmdline.c must include.
