PuTTY bug window-title-utf8-early-termination

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summary: Window title escape sequence terminated early by UTF-8 continuation byte 0x9C
class: bug: This is clearly an actual problem we want fixed.
difficulty: fun: Just needs tuits, and not many of them.
priority: medium: This should be fixed one day.
fixed-in: 4f41bc04ab27953cce112070b796b52a8d0de52d (0.77)

The OSC escape sequence family, e.g. used to set the window title, includes a string of arbitrary text terminated by (among other things) the control sequence ST (String Terminator). ST comes in multiple forms: one form is ESC \, and another is the C1 control character 0x9C.

In UTF-8 mode, the C1 control character 0x9C should be interpreted as the Unicode code point U+009C, encoded in UTF-8 as the bytes 0xC2 0x9C.

However, in PuTTY 0.76 and before, the byte 0x9C had the effect of terminating the OSC sequence, whenever it appeared as a continuation byte in any UTF-8 character encoding. So, for example, sending U+00DC LATIN CAPITAL LETTER U WITH DIAERESIS (Ü) in the middle of a window title would cause the OSC sequence to be prematurely terminated, simply because 0x9C is one of the bytes of that character's UTF-8 encoding. The rest of the text intended for the window title would be processed as normal terminal output, corrupting your display.

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(last revision of this bug record was at 2021-12-29 16:30:25 +0000)