Implements RFB (RFC 6143) directly against QTcpSocket. No permissively
licensed VNC client library exists to vendor the way FreeRDP was for RDP:
LibVNCClient is GPLv2, gtk-vnc is LGPL but GTK-tied, and vendoring either
would force a licensing decision on the whole (MIT) project. This is
from-scratch protocol code instead, threaded like SshSessionBackend (a
QObject on its own QThread driven by Qt's own async socket signals)
rather than RdpSessionBackend's manual worker-thread/blocking-loop
pattern, since QTcpSocket is already async.
Scope, matching SessionTab's existing SSH/RDP dispatch pattern
(session_backend_factory.cpp, session_tab.cpp's widget construction and
signal wiring) and VncDisplayWidget mirroring RdpDisplayWidget's
scale-to-fit rendering:
- Protocol handshake: RFB 3.3/3.7/3.8 negotiated explicitly (the
SecurityResult message only exists in 3.8; pre-3.8 servers signal auth
failure by closing the socket, which the disconnect handler accounts
for)
- VNC Authentication (DES challenge-response, via OpenSSL's classic DES
API) and no-auth security types
- Raw + CopyRect framebuffer decoding into a persistent QImage, requesting
a fixed 32bpp format whose byte layout matches QImage::Format_RGB32
directly (same zero-conversion trick RdpSessionBackend uses for
FreeRDP's GDI buffer)
- Keyboard (Qt key -> X11 keysym, including the Unicode-beyond-Latin-1
keysym convention) and mouse/wheel input forwarding
Explicit non-goals for this pass (see docs/PROGRESS.md for the full
list): Apple's Screen Sharing auth (so this can't yet reach macOS's
built-in VNC server), compression encodings beyond Raw/CopyRect, dynamic
resize, remote cursor shape sync, clipboard sync.
19 unit tests (tests/test_vnc_session_backend.cpp): pure-function
coverage (DES key prep verified against an independently documented test
vector for password "COW", X11 keysym mapping, socket-error mapping) plus
state-machine coverage against a scripted in-process fake RFB server
covering all three protocol-version handshake shapes, auth success/
failure, unsupported security types, and pixel-accurate Raw decoding.
That harness caught a real re-entrancy bug: QAbstractSocket::abort()
synchronously re-emits disconnected() before returning, so
failConnection() calling it was silently letting a second, generic
disconnected-socket handler overwrite an already-correct, specific error
message.
Also verified live against a real, independently implemented VNC server
(TightVNC on Windows): connect with VNC Authentication, correct
framebuffer dimensions and pixel data, clean disconnect, reconnect.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Linux, macOS, and Windows have all been validated against the current
feature set (SSH, RDP display/keyboard/clipboard/cursor, Tab forwarding,
key repeat, profile dialog, single-window UI), with the platform-specific
bugs found along the way fixed and tracked individually on the issue
tracker (#8-#16). VNC validation remains out of scope while Milestone 6
stays deferred.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
ksmithandClaude Sonnet 5