wraith/docs/architecture/client.md

status, last_updated

status	last_updated
draft	2026-06-01

Client

What

The wraith client establishes an SSH session to a server (via pluggable transport) and exposes local interfaces for routing traffic through that session: SOCKS5 proxy, port forwarding, and eventually TUN.

Why

Users need a way to route traffic through the SSH tunnel. SOCKS5 is the primary interface — it's standard, well-supported by browsers and CLI tools, and needs no privileges. Port forwarding (-L / -R style) covers specific service access like Postgres or Redis. TUN covers full-system VPN-like behavior.

Architecture

Client Components

┌────────────────────────────────────────────────────────┐
│                     wraith connect                      │
│                                                        │
│  ┌──────────┐ ┌──────────┐ ┌──────────┐ ┌──────────┐ │
│  │ SOCKS5   │ │ Port     │ │ Remote   │ │ (TUN     │ │
│  │ Server   │ │ Forward  │ │ Forward  │ │  shim)   │ │
│  │ :1080    │ │ -L spec  │ │ -R spec  │ │ separate │ │
│  └────┬─────┘ └────┬─────┘ └────┬─────┘ └──────────┘ │
│       │             │             │                     │
│       ▼             ▼             ▼                     │
│  ┌─────────────────────────────────┐                   │
│  │        Channel Manager          │                   │
│  │  (opens direct-tcpip,           │                   │
│  │   forwarded-tcpip streams)      │                   │
│  └──────────────┬──────────────────┘                   │
│                  │                                      │
│  ┌──────────────▼──────────────────┐                   │
│  │       SSH Client (russh)        │                   │
│  │   Handle<ClientHandler>         │                   │
│  └──────────────┬──────────────────┘                   │
│                  │                                      │
│  ┌──────────────▼──────────────────┐                   │
│  │         Transport                │                   │
│  │   (Tcp / Tls / Iroh)            │                   │
│  └──────────────────────────────────┘                   │
└────────────────────────────────────────────────────────┘

SOCKS5 Server

The primary client interface. Listens on a local port (default 127.0.0.1:1080), accepts SOCKS5 connections, and for each connection:

1. Reads the SOCKS5 handshake (auth method negotiation, target address)
2. Opens a channel_open_direct_tcpip(target_host, target_port, originator_addr, originator_port) on the SSH session
3. Converts the SSH channel to a stream via channel.into_stream()
4. Runs tokio::io::copy_bidirectional(&mut local_socket, &mut ssh_stream) to proxy data

Supports SOCKS5h (domain names resolved server-side) by default. This prevents DNS leaks.

Port Forwarding

Local port forwards (-L local_addr:local_port:remote_host:remote_port):

1. Bind TcpListener on local_addr:local_port
2. For each accepted connection, open channel_open_direct_tcpip(remote_host, remote_port, ...)
3. Proxy bytes bidirectionally via copy_bidirectional

Remote port forwards (-R remote_addr:remote_port:local_host:local_port):

1. Send tcpip_forward(remote_addr, remote_port) to request the server listen on a port
2. When the handler receives server_channel_open_forwarded_tcpip, connect to local_host:local_port
3. Proxy bytes bidirectionally

Channel Manager

The channel manager owns the Arc<client::Handle<ClientHandler>> and provides methods:

• open_direct_tcpip(host, port) — open a tunnel channel to a remote host
• open_streamlocal(socket_path) — open a tunnel to a Unix socket
• request_tcpip_forward(addr, port) — request remote listening
• cancel_tcpip_forward(addr, port) — cancel remote listening

It also handles reconnection: if handle.is_closed() returns true, attempt reconnection with exponential backoff.

Reconnection

On transport failure:

1. Detect via handle.is_closed() or transport read error
2. Exponential backoff reconnect (1s, 2s, 4s, ... max 30s)
3. Re-establish transport connection
4. Re-authenticate SSH session
5. Notify SOCKS5 server and port forwards (in-flight connections fail, new connections work)

Existing TCP connections through the tunnel are lost on reconnect. This is acceptable — same as any VPN.

CLI Interface

# Basic connection (TCP, default port 22)
wraith connect --server example.com --identity ~/.ssh/id_ed25519

# With TLS
wraith connect --server example.com:443 --transport tls --identity ~/.ssh/id_ed25519

# With iroh (no public IP needed)
wraith connect --peer <endpoint-id> --transport iroh --identity ~/.ssh/id_ed25519

# SOCKS5 on custom port
wraith connect --server example.com --socks5 127.0.0.1:1080 --identity ~/.ssh/id_ed25519

# With port forwards
wraith connect --server example.com --forward 5432:db.internal:5432 --forward 6379:redis.internal:6379

# All options
wraith connect \
  --server <addr> \          # TCP server address (required for tcp/tls)
  --peer <endpoint-id> \    # iroh peer ID (required for iroh)
  --transport tcp|tls|iroh \ # Transport mode
  --identity <path> \       # SSH private key path
  --socks5 <addr:port> \    # SOCKS5 listen address (default: 127.0.0.1:1080)
  --forward <spec> \        # Port forward spec (repeatable)
  --remote-forward <spec> \ # Remote port forward spec (repeatable)
  --proxy <url>              # Upstream proxy (SOCKS5/HTTP CONNECT)

Constraints

• SOCKS5 is always enabled when wraith connect runs (it's the primary interface). Port forwards are optional.
• The client does not know or log what destinations are accessed. The SOCKS5 server connects and proxies — no logging of SOCKS5 request targets.
• Authentication is Ed25519 public key only by default. Password auth supported but not recommended. (OQ-04)
• Only one SSH session per wraith connect process. Multiple sessions = multiple processes (or a future multiplexer).

Open Questions

• OQ-04: Authentication beyond Ed25519 keys
• OQ-06: Whether to support SSH config file parsing (~/.ssh/config) for default host/key/port settings

Design Decisions

ADR	Decision	Summary
005	SOCKS5 first	SOCKS5 is the primary interface, TUN forwards to it