michal-ruzicka/TCOfficeView v2.0.0

Release v2.0.0

on GitHub

[v2.0.0] – 2026-05-22

Added

• Full render mode for Word, Excel and PowerPoint via a new
  [Mode] INI section. Four values are accepted per application:
  quick (Preview Handler, no button), quick-switchable (Preview
  Handler with overlay button — new default), full (OLE
  Automation, no button), full-switchable (OLE Automation with
  overlay button). When a full-mode value is set, the plugin launches
  a real Word / Excel / PowerPoint instance, opens the file
  read-only, and embeds its window into the Lister pane, giving the
  full Print Layout / grid / slide rendering instead of the
  simplified Preview Handler pipeline. Cold start is ~2–4 s;
  memory ~100–300 MB per instance. On any failure the plugin
  transparently falls back to quick mode.
• Mode-switch overlay button in the top-right of every Word /
  Excel / PowerPoint preview (shown when the configured mode is
  quick-switchable or full-switchable). One click toggles the
  current preview between quick and full mode without changing the
  INI default; the switch is per-preview only — the next file (or
  re-opening the same one) starts at the configured default. Button
  size and font scale with the monitor's DPI. Always hidden for file
  types with no full-mode handler (.msg, .vsdx) regardless of
  the setting.
• Per-app preview niceties in full mode:
  • Word — Print Layout view, page-width zoom that auto-refits
    on Lister resize, rulers hidden, runtime read-only enforcement
    so typing in the preview is blocked.
  • Excel — zoom locked to 100% on load; initial frame size
    matches the Lister pane. Two intrinsic limitations of embedding
    Excel as a child window via OLE Automation, which no combination
    of style edits, window-message synthesis or activation tricks
    convinced Excel to overcome:
    1. Excel does not relayout when the pane is later resized;
       reopening the Lister at the desired size triggers a fresh
       correct layout.
    2. Interactive mouse input (cell selection, sheet-tab clicks,
       most ribbon buttons) is unreliable, because Excel gates much
       of that processing on being the foreground top-level window —
       and a reparented child of a foreign process never is. Quick
       mode is unaffected; for interactive work, use quick mode.
       Full Excel mode is best treated as a read-only viewer.
  • PowerPoint — slide zoom auto-refits to the Lister pane on
    every resize. PowerPoint's main window appears briefly on
    screen before being embedded (a short visible flash) because
    PowerPoint cannot be told to run invisibly; Word and Excel
    embed silently.

Changed

• Moved the AppKind enum declaration before HostState so that
  HostState::currentFileApp can be initialised at compile time without
  relying on a forward-declaration hack.

Fixed

• Preview handlers were activated in-process, which violates the
  IPreviewHandler contract. LoadHandlerSta used
  CLSCTX_LOCAL_SERVER | CLSCTX_INPROC_SERVER, so COM happily loaded any
  handler that registered an InProcServer32 (the Windows built-in MAPI
  Mail Previewer for .msg, in particular) directly into our process.
  Such handlers complete activation, initialisation and SetWindow, then
  fail DoPreview with E_FAIL because Microsoft's IPreviewHandler
  documentation states a handler must be hosted in its own background
  process. Activation is now CLSCTX_LOCAL_SERVER only, matching the
  reference preview-host sample and Windows Explorer's preview pane —
  COM now routes through the AppID's DllSurrogate (typically
  prevhost.exe), and MSG previews finally render.
• CoInitializeSecurity is now established at host start-up. Handlers
  that run in Windows' low-integrity prevhost.exe surrogate (notably the
  Outlook MSG preview handler) need an explicit process-wide COM security
  blanket to perform cross-process calls back to the host; without it
  DoPreview returns E_FAIL. The new call matches the settings used by
  Windows Explorer's own preview pane (RPC_C_AUTHN_LEVEL_DEFAULT,
  RPC_C_IMP_LEVEL_IMPERSONATE).
• Preview handlers requiring an IPreviewHandlerFrame site failed DoPreview.
  Outlook's MSG preview handler (and other handlers hosted in prevhost.exe)
  ask the host for IPreviewHandlerFrame and IOleWindow via a site object
  installed through IObjectWithSite::SetSite; without it DoPreview returns
  E_FAIL and the preview never renders. A new PreviewHostSite class
  implements IPreviewHandlerFrame (no-op accelerator translation),
  IServiceProvider (routing IPreviewHandlerFrame / IOleWindow lookups
  back to itself) and IOleWindow (returning the render window's HWND).
  The site is installed before any IInitializeWith*::Initialize call —
  Outlook's MSG handler queries the site from inside Initialize and aborts
  the load if it isn't ready yet — and cleared again on unload. The call
  order in LoadHandlerSta now matches Microsoft's recommended sequence:
  CoCreateInstance → QI IPreviewHandler → SetSite → Initialize → SetWindow
  → DoPreview.
• Preview handlers initialised only via IInitializeWithItem could not load.
  LoadHandlerSta previously tried only IInitializeWithFile and
  IInitializeWithStream. Outlook's MSG preview handler rejects both
  (E_NOINTERFACE) and supports exclusively the modern Shell-item-based
  IInitializeWithItem, which the loader now tries as a third fallback
  (SHCreateItemFromParsingName → IInitializeWithItem::Initialize).
• Preview handlers missed when registered outside the direct extension key.
  FindPreviewHandlerClsid previously looked for the preview handler CLSID
  only directly on the extension key and via the extension's default ProgID.
  This missed handlers registered in any of the other places Windows
  Explorer's preview pane consults — notably the MSG handler, which Outlook
  registers under a versioned ProgID in HKCR\.msg\OpenWithProgids
  (e.g. Outlook.File.msg.16) rather than as the default ProgID. The
  lookup now follows the full Shell association chain that Explorer uses:
  direct shellex key → default ProgID → each ProgID in OpenWithProgids →
  HKCR\SystemFileAssociations\<ext> → HKCR\SystemFileAssociations\<PerceivedType>.
  MSG and similar previews now work on systems where Windows Explorer already
  shows them.
• Plugin deadlock on Lister close / TC exit. TerminateSession used an
  infinite timeout when writing CLOSE to the host pipe. If the host's pipe
  reader thread had already died (e.g. access violation), the write would
  block forever, freezing Total Commander. The write now uses a 3-second
  timeout and cancels the pending I/O if it expires.
• Race condition in plugin ChildWndProc (use-after-free). The resize
  timer handler looked up the session under g_sessionsMutex, released the
  lock, and then wrote to session->hPipe. Between releasing the lock and
  the write, ListCloseWindow on another thread could erase and delete
  the session. The mutex is now held for the entire pipe write.
• Race condition in host HostLog critical-section initialisation.
  InitializeCriticalSection was called lazily on the first HostLog
  invocation without any synchronisation. Two threads (STA + pipe reader)
  could race and initialise the same CRITICAL_SECTION twice, corrupting
  it. The CS is now initialised once in wmain before the pipe reader
  thread is created.
• Pipe buffer exhaustion after many file switches. The host sends
  OK\n / ERR …\n replies for every LOAD and CLOSE, but the plugin
  never read them. After roughly 5 000 ListLoadNextW calls in a single
  Lister session the 64 KB pipe buffer filled up and subsequent writes
  blocked indefinitely. A background drain thread now continuously reads
  and discards host responses.
• Handle leaks in the host process. The log file handle, the logging
  CRITICAL_SECTION, and the Office JobObject handle were never closed
  or destroyed before process exit. They are now cleaned up in wmain
  after the message loop terminates.
• Potential CreateProcessW command-line mutation. CreateProcessW
  requires a writable command-line buffer. cmdLine.data() returns
  const wchar_t* in pre-C++17 standards, which is undefined behaviour.
  Changed to &cmdLine[0], which is writable in all C++ versions.
• Missing null check in ListLoadNextW. Added an explicit guard against
  a nullptr FileToLoad argument.
• Re-entrancy crash when switching modes rapidly (PowerPoint). The retry
  loops inside LoadWordFullSta, LoadExcelFullSta and
  LoadPowerPointFullSta contained PeekMessage dispatch loops that pumped
  the STA message queue. While a load was still in progress, a second
  WM_HOST_SWITCH_MODE message could be dispatched recursively, causing
  re-entrant COM calls and eventual heap corruption or access violation. The
  PeekMessage loops have been replaced with plain Sleep, and a
  loadingInProgress guard now serialises LoadFileWithModeSta calls so
  that a second switch is deferred until the first one finishes.
• Document not closed before quick-mode fallback detach. When full-mode
  loading failed and the host fell back to quick mode, the Office document
  was left open in the background while the window was detached. The
  appropriate close routine (CloseWordDocumentSta,
  CloseExcelWorkbookSta, ClosePptPresentationSta) is now called before
  detaching the window in the fallback path.
• Crash when clicking the embedded Office window's close button.
  EmbedOfficeWindowSta strips Win32 caption styles, but Office apps
  (Word, Excel, PowerPoint) render their own close button inside the
  ribbon / title bar. Clicking it sent WM_SYSCOMMAND(SC_CLOSE) or
  WM_CLOSE to the embedded HWND, which caused the Office app to destroy
  its own window while it was still a child of our render pane — leading
  to a crash or unexpected TC window closure. SetWindowSubclass cannot
  be used because Office runs out-of-process. Instead, a visible light
  grey overlay bar (hwndCloseGuard) is created as a child of the render
  pane, stretched across the full width and covering the top ~40 px
  (HiDPI-scaled) where the Office ribbon / title bar lives. The guard is
  forced to HWND_TOP so it sits above the Office window, painted with
  LTGRAY_BRUSH, and returns HTCLIENT from WM_NCHITTEST so all mouse
  clicks in that area are swallowed. This also blocks the context menu
  that appears on a right-click in the title area. The guard is destroyed
  when the Office window is detached or the render pane is torn down.

Notes

• Full mode deliberately changes no Office Application-wide settings
  (status bar, ribbon state, default zoom, …) because Office
  persists those into the user's profile on Quit. Only per-window /
  per-document settings are touched, so your standalone Word, Excel
  and PowerPoint will start up exactly as you left them.
• Every Office process spawned by the plugin is assigned to a Job
  Object with JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE. When the host
  process exits for any reason (clean shutdown, plugin-side
  TerminateProcess after the host failed to honour CLOSE within
  2 seconds, Windows shutdown), the kernel kills any still-alive
  Office processes with it — so Excel in particular can no longer
  be left orphaned and reported as a "hung application" at the next
  system restart.