PuTTY bug empty-answerback-tight-loop

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summary: Sending an empty ^E answerback causes a tight loop on the next keypress
class: bug: This is clearly an actual problem we want fixed.
present-in: 0.82
fixed-in: 19798515df5db3151370e331ca1312bb39fadf16 6ffb0e067f74962ce7fa34e0317c61cefd36edc6 (0.83)

Terminals historically send an "answerback" string if they receive the query character with ASCII code 5 (i.e. Ctrl-E), indicating something about what kind of terminal they are. PuTTY's answerback string defaults to just "PuTTY", but it's also configurable, via the "Answerback to ^E" configuration setting, in the Terminal configuration pane.

In PuTTY 0.82, if you set the answerback string to be completely empty, then PuTTY can go into a tight loop, becoming unresponsive and consuming CPU, on the first keypress after it's asked to send that string.

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Audit trail for this bug.
(last revision of this bug record was at 2025-01-16 12:54:30 +0000)