VTTest

A cross-platform console application for exploring raw ANSI/VT escape sequences and investigating how stdin behaves differently across Windows and Unix platforms.

Why This Exists

Terminal input is surprisingly inconsistent across platforms. On Windows, ReadFile and Console.OpenStandardInput behave differently (e.g., Ctrl+Z triggers an EOF on streams but not on ReadFile). On Unix, .NET's Console.OpenStandardInput() adds buffering that requires a newline before returning data, even with stty raw — so VTTest reads fd 0 directly to get true raw input. This tool makes all of that visible.

What It Does

VTTest puts the console into raw/VT input mode and reads input directly. Every keypress, mouse click, or mouse move is displayed as:

• A human-readable interpretation (e.g., [Ctrl+A], [Up], [Alt+X], [Mouse Left press @10,5])
• The raw hex bytes of the escape sequence

Read Modes

VTTest supports three input-reading strategies, each in its own file with independent logic. Press s to cycle between them at runtime.

Mode	Label	File	Description
Native ReadFile	RdFl	NativeInputReader.cs	Win32 ReadFile P/Invoke. Windows only.
Stream	Strm	StreamInputReader.cs	Synchronous Stream.Read — Console.OpenStandardInput() on Windows, raw fd 0 FileStream on Unix.
Async Stream	Async	AsyncStreamInputReader.cs	Background Task calling Stream.ReadAsync in a loop, buffering into a BlockingCollection. Consumer blocks on Take(). Demonstrates the pattern used by Terminal.Gui's WindowsVTInputHelper.

Cycling order:

• Windows: Native → Stream → Async → Native → …
• Unix: Stream → Async → Stream → …

Platform-Specific Behavior

Windows:

• Uses Win32 Console API via P/Invoke (ReadFile), .NET streams (Console.OpenStandardInput), or async streams
• Cycle between read modes with s to compare behavior (e.g., Ctrl+Z returns 0 bytes on streams but 0x1A via ReadFile)
• Console mode flags (ENABLE_VIRTUAL_TERMINAL_INPUT, ENABLE_PROCESSED_INPUT) control how input is delivered

Unix (macOS/Linux/WSL):

• Uses stty raw -echo -icanon for raw terminal mode
• Reads stdin fd 0 directly (not Console.OpenStandardInput(), which buffers line-by-line even in raw mode)
• Signal handling (isig) can be toggled at runtime to test Ctrl+Z suspend/resume and Ctrl+C behavior
• SIGCONT handler restores raw mode and redraws UI after fg resume
• SIGINT handler performs terminal cleanup (reset scroll region, disable mouse tracking, restore stty) before exiting

Supported Input

• Keyboard: Arrow keys, Home/End, Page Up/Down, F1-F12, Tab, Enter, Backspace, Escape
• Modifiers: Ctrl, Alt, Shift, and combinations thereof
• Mouse: Left/Middle/Right click, scroll wheel, motion tracking (SGR encoding)
• Control characters: Ctrl+A through Ctrl+Z and others

Controls

Key	Action
q	Quit
s	Cycle read mode: Native → Stream → Async (Windows) or Stream → Async (Unix)
z	Toggle signal handling — when ON, Ctrl+Z suspends and Ctrl+C exits cleanly; when OFF, they appear as raw input
c	Clear the output area

Architecture

Program.cs                  – Main loop, console setup, signal handlers, reader cycling
IInputReader.cs             – Interface: Label, DisplayName, Read(byte[])
NativeInputReader.cs        – Win32 ReadFile P/Invoke (Windows only)
StreamInputReader.cs        – Synchronous Stream.Read
AsyncStreamInputReader.cs   – Background ReadAsync + BlockingCollection
AnsiSequenceParser.cs       – Parses raw bytes into human-readable descriptions
TerminalUI.cs               – VT output helpers (header, scroll region, mouse tracking)
NativeConsole.cs            – Win32 Console P/Invoke declarations

Each IInputReader implementation is fully self-contained — changes to one have no impact on the others.

Requirements

• .NET 10
• Windows (Win32 Console API via P/Invoke) or Unix-like (macOS, Linux, WSL via stty)

Building and Running

dotnet build
dotnet run