starred/terminal
1
0
Fork 0
mirror of https://github.com/microsoft/terminal.git synced 2026-02-04 05:35:20 +00:00
Code Issues 19.0k Packages Projects Releases 20 Wiki Activity

[PR #11690] Disable the acceptance of C1 control codes by default #28710

New Issue
Open
opened 2026-01-31 09:30:17 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:30:17 +00:00
Owner
Copy Link

Original Pull Request: https://github.com/microsoft/terminal/pull/11690

State: closed
Merged: Yes

There are some code pages with "unmapped" code points in the C1 range,
which results in them being translated into Unicode C1 control codes,
even though that is not their intended use. To avoid having these
characters triggering unintentional escape sequences, this PR now
disables C1 controls by default.

Switching to ISO-2022 encoding will re-enable them, though, since that
is the most likely scenario in which they would be required. They can
also be explicitly enabled, even in UTF-8 mode, with the DECAC1 escape
sequence.

What I've done is add a new mode to the StateMachine class that
controls whether C1 code points are interpreted as control characters or
not. When disabled, these code points are simply dropped from the
output, similar to the way a NUL is interpreted.

This isn't exactly the way they were handled in the v1 console (which I
think replaces them with the font notdef glyph), but it matches the
XTerm behavior, which seems more appropriate considering this is in VT
mode. And it's worth noting that Windows Explorer seems to work the same
way.

As mentioned above, the mode can be enabled by designating the ISO-2022
coding system with a DOCS sequence, and it will be disabled again when
UTF-8 is designated. You can also enable it explicitly with a DECAC1
sequence (originally this was actually a DEC printer sequence, but it
doesn't seem unreasonable to use it in a terminal).

I've also extended the operations that save and restore "cursor state"
(e.g. DECSC and DECRC) to include the state of the C1 parser mode,
since it's closely tied to the code page and character sets which are
also saved there. Similarly, when a DECSTR sequence resets the code
page and character sets, I've now made it reset the C1 mode as well.

I should note that the new StateMachine mode is controlled via a
generic SetParserMode method (with a matching API in the ConGetSet
interface) to allow for easier addition of other modes in the future.
And I've reimplemented the existing ANSI/VT52 mode in terms of these
generic methods instead of it having to have its own separate APIs.

Validation Steps Performed

Some of the unit tests for OSC sequences were using a C1 0x9C for the
string terminator, which doesn't work by default anymore. Since that's
not a good practice anyway, I thought it best to change those to a
standard 7-bit terminator. However, in tests that were explicitly
validating the C1 controls, I've just enabled the C1 parser mode at the
start of the tests in order to get them working again.

There were also some ANSI mode adapter tests that had to be updated to
account for the fact that it has now been reimplemented in terms of the
SetParserMode API.

I've added a new state machine test to validate the changes in behavior
when the C1 parser mode is enabled or disabled. And I've added an
adapter test to verify that the DesignateCodingSystems and
AcceptC1Controls methods toggle the C1 parser mode as expected.

I've manually verified the test cases in #10069 and #10310 to confirm
that they're no longer triggering control sequences by default.
Although, as I explained above, the C1 code points are completely
dropped from the output rather than displayed as notdef glyphs. I
think this is a reasonable compromise though.

Closes #10069
Closes #10310

**Original Pull Request:** https://github.com/microsoft/terminal/pull/11690 **State:** closed **Merged:** Yes --- There are some code pages with "unmapped" code points in the C1 range, which results in them being translated into Unicode C1 control codes, even though that is not their intended use. To avoid having these characters triggering unintentional escape sequences, this PR now disables C1 controls by default. Switching to ISO-2022 encoding will re-enable them, though, since that is the most likely scenario in which they would be required. They can also be explicitly enabled, even in UTF-8 mode, with the `DECAC1` escape sequence. What I've done is add a new mode to the `StateMachine` class that controls whether C1 code points are interpreted as control characters or not. When disabled, these code points are simply dropped from the output, similar to the way a `NUL` is interpreted. This isn't exactly the way they were handled in the v1 console (which I think replaces them with the font _notdef_ glyph), but it matches the XTerm behavior, which seems more appropriate considering this is in VT mode. And it's worth noting that Windows Explorer seems to work the same way. As mentioned above, the mode can be enabled by designating the ISO-2022 coding system with a `DOCS` sequence, and it will be disabled again when UTF-8 is designated. You can also enable it explicitly with a `DECAC1` sequence (originally this was actually a DEC printer sequence, but it doesn't seem unreasonable to use it in a terminal). I've also extended the operations that save and restore "cursor state" (e.g. `DECSC` and `DECRC`) to include the state of the C1 parser mode, since it's closely tied to the code page and character sets which are also saved there. Similarly, when a `DECSTR` sequence resets the code page and character sets, I've now made it reset the C1 mode as well. I should note that the new `StateMachine` mode is controlled via a generic `SetParserMode` method (with a matching API in the `ConGetSet` interface) to allow for easier addition of other modes in the future. And I've reimplemented the existing ANSI/VT52 mode in terms of these generic methods instead of it having to have its own separate APIs. ## Validation Steps Performed Some of the unit tests for OSC sequences were using a C1 `0x9C` for the string terminator, which doesn't work by default anymore. Since that's not a good practice anyway, I thought it best to change those to a standard 7-bit terminator. However, in tests that were explicitly validating the C1 controls, I've just enabled the C1 parser mode at the start of the tests in order to get them working again. There were also some ANSI mode adapter tests that had to be updated to account for the fact that it has now been reimplemented in terms of the `SetParserMode` API. I've added a new state machine test to validate the changes in behavior when the C1 parser mode is enabled or disabled. And I've added an adapter test to verify that the `DesignateCodingSystems` and `AcceptC1Controls` methods toggle the C1 parser mode as expected. I've manually verified the test cases in #10069 and #10310 to confirm that they're no longer triggering control sequences by default. Although, as I explained above, the C1 code points are completely dropped from the output rather than displayed as _notdef_ glyphs. I think this is a reasonable compromise though. Closes #10069 Closes #10310
claunia added the pull-request label 2026-01-31 09:30:17 +00:00
Sign in to join this conversation.
No Branch/Tag Specified
Branches Tags
Labels
Clear labels
⛺ Reserved
A11yCO
A11yMAS
A11ySev1
A11ySev2
A11ySev3
A11yTTValidated
A11yUsable
A11yVoiceAccess
A11yWCAG
Area-Accessibility
Area-AtlasEngine
Area-AzureShell
Area-Build
Area-Build
Area-Chat
Area-CmdPal
Area-CodeHealth
Area-Commandline
Area-CookedRead
Area-DefApp
Area-Extensibility
Area-Fonts
Area-GroupPolicy
Area-i18n
Area-Input
Area-Interaction
Area-Interop
Area-Localization
Area-Output
Area-Performance
Area-Portable
Area-Quality
Area-Remoting
Area-Rendering
Area-Schema
Area-Server
Area-Settings
Area-SettingsUI
Area-ShellExtension
Area-ShellExtension
Area-ShellExtension
Area-Suggestions
Area-Suggestions
Area-TerminalConnection
Area-TerminalControl
Area-Theming
Area-UserInterface
Area-VT
Area-Windowing
Area-WPFControl
AutoMerge
Blocking-Ingestion
Culprit-Centennial
Culprit-WinUI
Disability-All
Disability-Blind
Disability-LowVision
Disability-Mobility
External-Blocked-WinUI3
Fixed
Gathering-Data
good first issue
HCL-E+D
HCL-WindowsTerminal
Help Wanted
Impact-Compatibility
Impact-Compliance
Impact-Correctness
Impact-Visual
In-PR
InclusionBacklog
InclusionBacklog-Windows TerminalWin32
InclusionCommitted-202206
Issue-Bug
Issue-Docs
Issue-Feature
Issue-Feature
Issue-Question
Issue-Samples
Issue-Scenario
Issue-Task
Needs-Attention
Needs-Author-Feedback
Needs-Bisect
Needs-Discussion
Needs-Repro
Needs-Tag-Fix
Needs-Tag-Fix
Needs-Triage
No-Recent-Activity
Priority-0
Priority-1
Priority-2
Priority-3
Product-Cmd.exe
Product-Colortool
Product-Colortool
Product-Colortool
Product-Conhost
Product-Conpty
Product-Meta
Product-Powershell
Product-Terminal
Product-WSL
pull-request
Mirrored from GitHub Pull Request
 Resolution-Answered
Resolution-By-Design
Resolution-Duplicate
Resolution-External
Resolution-Fix-Available
Resolution-Fix-Committed
Resolution-No-Repro
Resolution-Won't-Fix
Severity-Blocking
Severity-Crash
Severity-DataLoss
spam
this-will-be-a-breaking-change
Tracking-External
WindowsTerminal_Win32
Work-Item
zAskModeBug
zInbox-Bug
No Label pull-request
Milestone
No items
No Milestone
Projects
Clear projects
No project
Assignees
Clear assignees
claunia
No Assignees
1 Participants
Notifications
Due Date
No due date set.
Dependencies

No dependencies set.

Reference: starred/terminal#28710
Delete Branch "%!s()"

Deleting a branch is permanent. Although the deleted branch may continue to exist for a short time before it actually gets removed, it CANNOT be undone in most cases. Continue?