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

Regression vs legacy conhost: different behavior from ReadConsoleOutputCharacterW when surrogate pair(s) are present. #21415

New Issue
Open
opened 2026-01-31 07:44:04 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 07:44:04 +00:00
Owner
Copy Link

Originally created by @chrisant996 on GitHub (Mar 18, 2024).

Originally assigned to: @lhecker on GitHub.

Windows Terminal version

1.19.10573.0

Windows build number

10.0.19045.4046

Other Software

This is an API issue, and affects any software that calls ReadConsoleOutputCharacterW.
The API issue only repros with Windows Terminal, not with legacy conhost (nor with ConEmu, ConsoleZ, etc).

For example clink was affected by this when also using eza or dirx (see here for details of how this was encountered during real world usage).

Steps to reproduce

When a line of text in the console screen buffer contains one or more surrogate pairs, then the behavior ReadConsoleOutputCharacterW API does not match the documented contract, and is different from the behavior with legacy conhost.

The attached repro program demonstrates the behavior:

  • It works as expected in legacy conhost (and ConEmu, ConsoleZ, etc).
  • It malfunctions in Windows Terminal.

repro_surrogate_pairs_issue.zip

Repro:

  • Use WriteConsoleW to print a line of text that includes one or more surrogate pairs.
  • Use ReadConsoleOutputCharacterW to read back the same line.

Easy demonstration program:

  1. Create a folder and extract the files from the .zip file linked above.
  2. Optional: run the signed Repro.exe file.
  3. Or, you can build the source files and run a locally built copy of the Repro.exe program.

Expected Behavior

ReadConsoleOutputCharacterW should:

  1. Fill the out param lpNumberOfCharsRead with the number of characters read (e.g. the width of the console).
  2. Fill the out param lpCharacter with characters read from the console.
  3. Return true (success).

The demo program should first write 4 lines, then verify that reading the lines back matches what was originally written.
Each line contains Unicode codepoints that correspond to certain nerdfonts icons.

Sample expected output:

OUTPUT:

-a--- 17k 13 Mar 14:38  Aaa.cpp
-a--- 11k 13 Mar 14:44 󱗀 Bbb.xml
-a--- 10k 13 Mar 14:43 󰅲 Ccc.lisp
-a--- 11k 13 Mar 14:44  Ddd.zip

RESULTS:

Line 1 len 120 matches : -a--- 17k 13 Mar 14:38  Aaa.cpp
Line 2 len 120 matches : -a--- 11k 13 Mar 14:44 󱗀 Bbb.xml
Line 3 len 120 matches : -a--- 10k 13 Mar 14:43 󰅲 Ccc.lisp
Line 4 len 120 matches : -a--- 11k 13 Mar 14:44  Ddd.zip

Actual Behavior

Only in Windows Terminal (all versions; 1.19, 1.20, 1.20 canary):

  1. Fills the out param lpNumberOfCharsRead with 0.
  2. Does not fill the out param lpCharacter.
  3. Returns true (success).

Problem 1: It reads nothing; it should read text successfully, the same as in legacy conhost.
Problem 2: It reports success; that's inaccurate since it failed to read the text that was present.

Sample actual output:

OUTPUT:

-a--- 17k 13 Mar 14:38  Aaa.cpp
-a--- 11k 13 Mar 14:44 󱗀 Bbb.xml
-a--- 10k 13 Mar 14:43 󰅲 Ccc.lisp
-a--- 11k 13 Mar 14:44  Ddd.zip

RESULTS:

Line 1 len 120 matches : -a--- 17k 13 Mar 14:38 ��� Aaa.cpp
Line 2 len 0   DIFFERS :
Line 3 len 0   DIFFERS :
Line 4 len 120 matches : -a--- 11k 13 Mar 14:44  Ddd.zip
Originally created by @chrisant996 on GitHub (Mar 18, 2024). Originally assigned to: @lhecker on GitHub. ### Windows Terminal version 1.19.10573.0 ### Windows build number 10.0.19045.4046 ### Other Software This is an API issue, and affects any software that calls `ReadConsoleOutputCharacterW`. The API issue only repros with Windows Terminal, not with legacy conhost (nor with ConEmu, ConsoleZ, etc). For example [clink](https://github.com/chrisant996/clink) was affected by this when also using [eza](https://github.com/eza-community/eza) or [dirx](https://github.com/chrisant996/dirx) (see [here](https://github.com/chrisant996/clink/issues/574#issuecomment-1996293488) for details of how this was encountered during real world usage). ### Steps to reproduce When a line of text in the console screen buffer contains one or more surrogate pairs, then the behavior `ReadConsoleOutputCharacterW` API does not match the documented contract, and is different from the behavior with legacy conhost. The attached repro program demonstrates the behavior: - It works as expected in legacy conhost (and ConEmu, ConsoleZ, etc). - It malfunctions in Windows Terminal. [repro_surrogate_pairs_issue.zip](https://github.com/microsoft/terminal/files/14640769/repro_surrogate_pairs_issue.zip) Repro: - Use `WriteConsoleW` to print a line of text that includes one or more surrogate pairs. - Use `ReadConsoleOutputCharacterW` to read back the same line. ### Easy demonstration program: 1. Create a folder and extract the files from the .zip file linked above. 2. Optional: run the signed Repro.exe file. 3. Or, you can build the source files and run a locally built copy of the Repro.exe program. ### Expected Behavior `ReadConsoleOutputCharacterW` should: 1. Fill the out param `lpNumberOfCharsRead` with the number of characters read (e.g. the width of the console). 2. Fill the out param `lpCharacter` with characters read from the console. 3. Return true (success). The demo program should first write 4 lines, then verify that reading the lines back matches what was originally written. Each line contains Unicode codepoints that correspond to certain [nerdfonts](https://nerdfonts.com) icons. ### Sample expected output: ```plain OUTPUT: -a--- 17k 13 Mar 14:38  Aaa.cpp -a--- 11k 13 Mar 14:44 󱗀 Bbb.xml -a--- 10k 13 Mar 14:43 󰅲 Ccc.lisp -a--- 11k 13 Mar 14:44  Ddd.zip RESULTS: Line 1 len 120 matches : -a--- 17k 13 Mar 14:38  Aaa.cpp Line 2 len 120 matches : -a--- 11k 13 Mar 14:44 󱗀 Bbb.xml Line 3 len 120 matches : -a--- 10k 13 Mar 14:43 󰅲 Ccc.lisp Line 4 len 120 matches : -a--- 11k 13 Mar 14:44  Ddd.zip ``` ### Actual Behavior Only in Windows Terminal (all versions; 1.19, 1.20, 1.20 canary): 1. Fills the out param `lpNumberOfCharsRead` with 0. 2. Does not fill the out param `lpCharacter`. 3. Returns true (success). **Problem 1:** It reads nothing; it should read text successfully, the same as in legacy conhost. **Problem 2:** It reports success; that's inaccurate since it failed to read the text that was present. ### Sample actual output: ```plain OUTPUT: -a--- 17k 13 Mar 14:38  Aaa.cpp -a--- 11k 13 Mar 14:44 󱗀 Bbb.xml -a--- 10k 13 Mar 14:43 󰅲 Ccc.lisp -a--- 11k 13 Mar 14:44  Ddd.zip RESULTS: Line 1 len 120 matches : -a--- 17k 13 Mar 14:38 ��� Aaa.cpp Line 2 len 0 DIFFERS : Line 3 len 0 DIFFERS : Line 4 len 120 matches : -a--- 11k 13 Mar 14:44  Ddd.zip ```
claunia added the Product-ConhostArea-OutputNeeds-TriageIssue-BugPriority-1 labels 2026-01-31 07:44:04 +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 Area-Output Issue-Bug Needs-Triage Priority-1 Product-Conhost
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#21415
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?