Spectty

A fast, native SSH & Mosh terminal for iOS — Metal-rendered, inspired by Ghostty, with a clean-room Mosh implementation.

Features

• SSH & Mosh — connect over SSH or Mosh with automatic reconnection and network roaming
• Metal renderer — GPU-accelerated terminal rendering with CoreText glyph atlas
• Session persistence — Mosh sessions survive app backgrounding and network switches
• 8 themes — Default, Catppuccin Mocha, Catppuccin Latte, Tokyo Night, Gruvbox Dark, Dracula, Nord, Monokai
• Secure — passwords and keys stored in the iOS Keychain; Secure Enclave support for key generation
• No tracking — no accounts, no analytics, no data collection
• Swift 6 — strict concurrency with async/await throughout

Architecture

┌──────────────────────────────────────────────────────┐
│  SwiftUI App Shell                                   │
│  ConnectionList → SessionManager → TerminalSession   │
│  MoshSessionStore (Keychain persistence)             │
└──────────────┬───────────────────────────────────────┘
               │
┌──────────────▼───────────────────────────────────────┐
│  SpecttyUI                                           │
│  TerminalMetalView (MTKView) + Metal glyph atlas     │
│  TerminalView (UIViewRepresentable)                  │
│  InputAccessory, GestureHandler                      │
└──────────────┬───────────────────────────────────────┘
               │ reads state from
┌──────────────▼───────────────────────────────────────┐
│  SpecttyTerminal                                     │
│  VTStateMachine (CSI/SGR/OSC parser)                 │
│  TerminalState (grid, cursor, modes, scrollback)     │
│  KeyEncoder (xterm key sequences)                    │
│  CGhosttyVT (C stubs, swappable for libghostty-vt)  │
└──────────────┬───────────────────────────────────────┘
               │ TerminalEmulator protocol
┌──────────────▼───────────────────────────────────────┐
│  SpecttyTransport                                    │
│  SSHTransport (SwiftNIO SSH)                         │
│  MoshTransport (clean-room Swift)                    │
│    MoshBootstrap (SSH exec → mosh-server)            │
│    MoshSSP (State Synchronization Protocol)          │
│    MoshNetwork (UDP via Network.framework)            │
│    MoshCrypto (AES-128-OCB3 via CommonCrypto)        │
│    STUNClient (NAT traversal diagnostics)            │
│  TerminalTransport / ResumableTransport protocols    │
└──────────────┬───────────────────────────────────────┘
               │
┌──────────────▼───────────────────────────────────────┐
│  SpecttyKeychain                                     │
│  iOS Keychain storage, Ed25519/ECDSA generation,     │
│  Secure Enclave, OpenSSH key import                  │
└──────────────────────────────────────────────────────┘

Data flow:

Keyboard → KeyEncoder → Transport → Remote Server
                                         │
 TerminalMetalView ← TerminalState ← VTStateMachine ← Transport

Packages

Package	Purpose
SpecttyTerminal	VT100/xterm state machine, cell model, scrollback buffer, key encoder
SpecttyTransport	SSH (SwiftNIO SSH) and Mosh transports behind TerminalTransport protocol
SpecttyUI	Metal renderer with CoreText glyph atlas, SwiftUI wrapper, input accessory bar, gestures
SpecttyKeychain	iOS Keychain key storage, Ed25519/ECDSA/Secure Enclave generation, OpenSSH PEM import

Mosh Implementation

Clean-room Swift implementation — no GPL code. Key components:

• MoshBootstrap: SSH exec → mosh-server new → parse MOSH CONNECT <port> <key> → close SSH
• MoshCrypto: AES-128-OCB3 (RFC 7253) using CommonCrypto's AES-ECB as the block cipher
• MoshNetwork: UDP transport via Network.framework with connection replacement for roaming
• MoshSSP: State Synchronization Protocol — sequence-numbered diffs with heartbeat/retransmit
• Session resumption: Credentials + SSP sequence numbers persisted to Keychain; reconnect skips SSH bootstrap entirely since mosh-server is daemonized
• STUNClient: Minimal RFC 5389 Binding Request for NAT type diagnostics

libghostty Integration

The architecture is designed so libghostty components can be swapped in incrementally:

• VT parsing: Replace VTStateMachine with libghostty-vt's terminal state C API — TerminalEmulator protocol insulates everything else
• Rendering: Replace TerminalMetalRenderer with libghostty's Metal rendering C API — TerminalRenderer protocol insulates everything else

Each swap is independent. No big-bang migration needed.

Build

Requires Xcode 26.2+, iOS 18+ deployment target.

xcodebuild build -scheme Spectty -destination 'generic/platform=iOS'