[Bug 2478] New: Escape sequences (starting with ~) don't work when remote shell is BusyBox ash

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=2478

            Bug ID: 2478
           Summary: Escape sequences (starting with ~) don't work when
                    remote shell is BusyBox ash
           Product: Portable OpenSSH
           Version: 7.1p1
          Hardware: ix86
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: alexinbeijing at gmail.com

Created attachment 2725
  --> https://bugzilla.mindrot.org/attachment.cgi?id=2725&action=edit
Fix

This was originally send directly to the mailing list, but I am also
posting it here as requested by Damien Miller.

This patch was prompted by the observation that SSH escapes (using ~)
don't work at all when the remote shell is BusyBox ash (used by Alpine
Linux and some other minimalist and/or embedded Linux distributions).

This is because the BusyBox shell *always* sends a "query cursor
position" terminal control escape sequence each time you press the
<ENTER> key. Quick as a flash, as your pinky finger is descending
towards the tilda key, the terminal sends back a "report cursor
position" sequence. The result is that the SSH client *never* sees your
tilda as immediately following the newline.

Those ANSI terminal control sequences always begin with "<ESC>[" and
end
with an alphabetic character. Hence the call to isalpha() in my code.

Can someone confirm that isalpha() *always* treats a-z and A-Z as
alphabetic, no matter what the locale is?

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