CodeVetter · Repo Unpack · Data flow
microsoft/terminal
The core data path is bidirectional ConPTY pipes. Outbound: keystrokes travel XAML -> TermControl/ControlCore -> ITerminalConnection::WriteInput (UTF-16 to UTF-8, overlapped WriteFile on the ConPTY input pipe). Inbound: ConptyConnection's dedicated _OutputThread ReadFile's the output pipe and raises the TerminalOutput event; ControlCore::_connectionOutputHandler takes the terminal write lock and calls Terminal::Write -> StateMachine::ProcessString -> OutputStateMachineEngine -> ITermDispatch handlers that mutate TextBuffer rows; the Atlas renderer then paints the buffer. Settings flow from settings.json + inbox defaults.json + dynamic generators + fragments through SettingsLoader's layered ParsedSettings into CascadiaSettings, with a directory watcher triggering throttled reloads. Command lines flow through CLI11 parsing into ActionAndArgs vectors executed by ShortcutActionDispatch; between processes, whole invocations are serialized into WM_COPYDATA blobs.
- Input path: key presses reach the WindowEmperor message loop (which pre-filters F7, Alt keyup, and Alt+Space because XAML cannot suppress them), then XAML -> TermControl key handlers -> ControlCore::_sendInputToConnection -> ITerminalConnection::WriteInput.
- ConptyConnection::WriteInput serializes writers with a first-come-first-served ticket lock, drains any pending overlapped write via GetOverlappedResult, converts UTF-16 to UTF-8 into _writeBuffer, and issues an overlapped WriteFile on the ConPTY pipe; ERROR_BROKEN_PIPE tears the connection down.
- Output path: ConptyConnection::Start creates an overlapped 128KB pipe pair and ConPTY, then spawns 'ConptyConnection Output Thread' running _OutputThread which ReadFile's the pipe and raises the TerminalOutput event; ConPTY size/show/reparent changes go through ConptyResizePseudoConsole/ConptyShowHidePseudoConsole/ConptyReparentPseudoConsole.
- ControlCore::_connectionOutputHandler receives the connection's TerminalOutput string, takes _terminal->LockForWriting() (a til::recursive_ticket_lock in TerminalCore), calls Terminal::Write, then flushes any _pendingResponses (e.g. DA/DSR replies) back to the connection.
- Terminal::Write feeds the VT StateMachine::ProcessString; OutputStateMachineEngine translates C0/C1/ESC/CSI/OSC sequences into ITermDispatch calls (Print, PrintString, LineFeed, CursorBackward, DeviceAttributes...) that land on the TextBuffer (src/buffer/out/textBuffer.cpp) via the adapter layer.
- Rendering: ControlCore owns an AtlasEngine (Direct2D/DirectWrite text rasterization with optional D3D backend and custom shaders) created lazily in TermControl; EnablePainting/size changes flow TermControl::_InitializeTerminal -> _core.Initialize/SizeOrScaleChanged.
- Settings flow: CascadiaSettings::LoadAll reads settings.json via til::io::read_file_as_utf8_string_if_exists, falls back to a Release-channel copy on Preview/Canary first-run, seeds from embedded resources IDR_USER_DEFAULTS + IDR_DEFAULTS, then runs SettingsLoader steps in fixed order: GenerateProfiles -> ApplyRuntimeInitialSettings -> MergeInboxIntoUserSettings -> FindFragmentsAndMergeIntoUserSettings -> FinalizeLayering -> DisableDeletedProfiles/FixupUserSettings/AddDynamicProfileFolders.
- Settings location: GetBaseSettingsPath returns the packaged LocalState folder, or %LOCALAPPDATA%\Microsoft\Windows Terminal for unpackaged builds, or the exe directory when a '.portable' marker file exists (portable mode).
- Write-back: LoadAll only writes settings.json when it was a first-time setup or when fixups/new dynamic profiles require persistence; otherwise it just caches a hash of file content+timestamp used by AppLogic::_ProcessLazySettingsChanges to skip redundant Jumplist rebuilds.
- Command-line data flow: GetCommandLineW -> commandlineToArgArray -> CommandlineArgs -> AppCommandlineArgs (CLI11) producing std::vector<ActionAndArgs> -> TerminalPage::ProcessStartupActions which feeds each entry to _actionDispatch->DoAction, suspending to the dispatcher between panes/tabs so WinUI can lay out controls (GH#13136).
- Cross-process handoff serializes GetCommandLineW + full environment block + CWD + nCmdShow into a length-prefixed byte blob delivered by WM_COPYDATA with TERMINAL_HANDOFF_MAGIC ('TERMINAL'), retried with exponential backoff for ~30s until the owner finishes creating its message window.
- Environment synthesis for each session: ConptyConnection injects WT_SESSION (plain GUID) and WT_PROFILE_ID (braced GUID), merges user 'environment' overrides, and maintains WSLENV so those variables propagate into WSL; initial env comes from til::env::from_current_environment or a serialized block for handoffs.
- Defterm/inbound handoff: when _pipe is already set (connection received via CTerminalHandoff), Start() skips CreatePseudoConsole/_LaunchAttachedClient and only resizes/reparents/shows the existing HPCON, logging 'ConPtyConnectedToDefterm' instead of launching a client.