sshc — Agent-Native SSH Multiplexing

Pure C daemon architecture (cross-platform: Unix + Windows). System deps only (python3 + nc + ssh). Single-file distributable. SSH ControlMaster persistent multiplexing eliminates repeated auth delay.

Execution Rules

1. Ensure daemon is alive before any exec: ./sshc health > /dev/null 2>&1 || ./sshc daemon &
2. All remote commands go through: ./sshc exec <profile> "<command>"
3. Independent commands can run in parallel
4. Config contains secrets — ensure chmod 600 ~/.sshc/profiles.json
5. Config changes are picked up automatically (hot reload via mtime detection — no daemon restart needed)

Quick Start

# 1. Compile daemon
cc -O2 -o sshc-daemon sshc-daemon.c       # Unix
# x86_64-w64-mingw32-gcc -O2 -o sshc-daemon.exe sshc-daemon.c -lws2_32  # Windows cross-compile

# 2. Ensure executable
chmod +x sshc sshc-daemon sshc-web

# 3. Create config
mkdir -p ~/.sshc
cat > ~/.sshc/profiles.json << 'EOF'
{
  "default": "my-server",
  "servers": {
    "my-server": {
      "host": "1.2.3.4",
      "user": "root",
      "key": "~/.ssh/id_ed25519",
      "port": 22
    }
  }
}
EOF

# 4. Start daemon
./sshc daemon

# 5. Health check
./sshc health

# 6. Execute remote command
./sshc exec my-server "uptime"

# 7. (Optional) Launch web UI for visual management
./sshc web
# Open http://127.0.0.1:17375

Commands

sshc daemon                              # Start daemon
sshc health [profile]                    # Health check (omit for all, "*" = all)
sshc exec <profile> <cmd> [timeout]      # Execute command (default timeout: 30s)
sshc profiles                            # List all servers and status
sshc add <name> <user@host> -i <key> [-p port] [--proxy <cmd>] [--allow <re>] [--deny <re>]  # Add server
sshc remove <name>                       # Remove server
sshc default <name>                      # Set default server
sshc reconnect <profile>                 # Force reconnect (kill + re-establish ControlMaster)
sshc upload <profile> <local> <remote>   # Upload file via SFTP (dirs auto tar-pipe)
sshc download <profile> <remote> <local> # Download file via SFTP (dirs auto tar-pipe)
sshc web [port]                          # Start web UI (default :17375)

Add server examples

# Key auth
./sshc add prod [email protected] -i ~/.ssh/id_rsa

# Key auth with custom port + proxy + command safety
./sshc add prod [email protected] -i ~/.ssh/id_rsa -p 2222 \
  --proxy "nc -X 5 -x 127.0.0.1:1080 %h %p" \
  --allow "^(ls|df|uptime|systemctl|apt|docker).*" \
  --deny ".*rm -rf.*|.*mkfs.*"

# Password auth (server must be added via Web UI or direct JSON edit for password)

Web UI & REST API

./sshc web starts a management dashboard at http://127.0.0.1:17375. Features:

• Drag-and-drop key upload — drag private key file onto drop zone, auto base64-encodes and stores to ~/.sshc/keys/<profile>/<filename>
• Proxy modal — per-server proxy config with type dropdown (HTTP / SOCKS5 / SOCKS4 / custom ProxyCommand), accessible via "代理" button in server list
• Async health checks — table renders instantly, health status streams in via parallel background checks (pulsing gray dot = checking)
• Live status — click "测试" to re-check individual server, status dot updates in real-time

API Endpoints

# ── List all servers (instant, no health check — alive: null) ──────────
curl http://127.0.0.1:17375/api/profiles
# Response: {"default":"prod","profiles":{"prod":{"host":"1.2.3.4","user":"root","port":22,"alive":null,"has_key":true,"has_password":false,"proxy":"nc -X 5 -x ..."}}}

# ── Add server (key path) ──────────────────────────────────────────────
curl -X POST http://127.0.0.1:17375/api/profiles \
  -H 'Content-Type: application/json' \
  -d '{"name":"prod","host":"1.2.3.4","user":"root","key":"~/.ssh/id_rsa"}'

# ── Add server (key content — base64, from file upload) ─────────────────
curl -X POST http://127.0.0.1:17375/api/profiles \
  -H 'Content-Type: application/json' \
  -d '{"name":"prod","host":"1.2.3.4","user":"root","key_content":"<base64>","key_filename":"id_rsa"}'

# ── Add server (password auth) ─────────────────────────────────────────
curl -X POST http://127.0.0.1:17375/api/profiles \
  -H 'Content-Type: application/json' \
  -d '{"name":"staging","host":"5.6.7.8","user":"admin","password":"mypass","port":2222}'

# ── Add server (with proxy) ────────────────────────────────────────────
curl -X POST http://127.0.0.1:17375/api/profiles \
  -H 'Content-Type: application/json' \
  -d '{"name":"hidden","host":"10.0.0.5","user":"root","key":"~/.ssh/id_rsa","proxy":"nc -X 5 -x 127.0.0.1:1080 %h %p"}'

# ── Update proxy ───────────────────────────────────────────────────────
curl -X PUT http://127.0.0.1:17375/api/profiles/hidden \
  -H 'Content-Type: application/json' \
  -d '{"proxy":"nc -X connect -x proxy.internal:3128 %h %p"}'

# ── Clear proxy ────────────────────────────────────────────────────────
curl -X PUT http://127.0.0.1:17375/api/profiles/hidden \
  -H 'Content-Type: application/json' \
  -d '{"proxy":null}'

# ── Set default server ─────────────────────────────────────────────────
curl -X PUT http://127.0.0.1:17375/api/profiles/prod -d '{"default":true}'

# ── Test connection (blocking — calls daemon health check) ─────────────
curl -X POST http://127.0.0.1:17375/api/test/prod
# Response: {"ok":true,"name":"prod","alive":true}

# ── Delete server ──────────────────────────────────────────────────────
curl -X DELETE http://127.0.0.1:17375/api/profiles/staging

Proxy Types (Web UI modal generates these automatically)

For agents adding servers programmatically, use the proxy field directly with any valid OpenSSH ProxyCommand string.

Configuration

~/.sshc/profiles.json:

{
  "default": "prod",
  "servers": {
    "prod": {
      "host": "10.0.0.1",
      "user": "root",
      "key": "~/.ssh/prod.key",
      "port": 22
    },
    "staging": {
      "host": "10.0.0.2",
      "user": "admin",
      "password": "secret",
      "port": 2222
    },
    "hidden": {
      "host": "10.0.0.5",
      "user": "root",
      "key": "~/.ssh/id_rsa",
      "port": 22,
      "proxy": "nc -X 5 -x 127.0.0.1:1080 %h %p"
    },
    "safe-prod": {
      "host": "10.0.0.1",
      "user": "root",
      "key": "~/.ssh/id_rsa",
      "port": 22,
      "allow": "^(ls|df|uptime|systemctl|apt|docker).*",
      "deny": ".*rm -rf.*|.*mkfs.*|.*dd if=.*"
    }
  }
}

• default — default server name (used when profile omitted in exec)
• servers.<name>.host — IP or domain (required)
• servers.<name>.user — SSH user (default: root)
• servers.<name>.key — SSH private key path on disk (mutually exclusive with password)
• servers.<name>.password — plaintext password (mutually exclusive with key)
• servers.<name>.port — SSH port (default: 22)
• servers.<name>.proxy — OpenSSH ProxyCommand string (optional, default: none / direct connect)
• servers.<name>.allow — POSIX regex for allowed commands (optional, default: allow all)
• servers.<name>.deny — POSIX regex for denied commands (optional, default: deny none)

Command Safety

Per-server command validation via POSIX extended regex (Unix) / glob matching (Windows). Rules are evaluated as: deny takes priority. If deny matches → rejected. If allow is set but doesn't match → rejected.

# Add with command restrictions
./sshc add safe-prod [email protected] -i ~/.ssh/id_rsa \
  --allow "^(ls|df|uptime|systemctl).*" \
  --deny ".*rm -rf.*"

# Update via API
curl -X PUT http://127.0.0.1:17375/api/profiles/safe-prod \
  -H 'Content-Type: application/json' \
  -d '{"allow":"^(ls|df|uptime|systemctl|apt).*"}'

Validation happens in the C daemon before any command reaches SSH — no way to bypass at the CLI or Web UI level.

SFTP File Transfer

File upload/download via OpenSSH sftp reusing the existing ControlMaster connection (no extra auth). Directories are auto-detected and transferred via tar pipe for efficiency.

# CLI upload (single file)
./sshc upload prod ./app.tar.gz /opt/app.tar.gz

# CLI upload (directory → auto tar pipe)
./sshc upload prod ./my-project/ /opt/my-project/

# CLI download
./sshc download prod /var/log/syslog ./syslog
./sshc download prod /opt/data/ ./data-backup/

# Web UI: click "上传" / "下载" buttons in server list

Web UI upload API:

# Upload file (base64 content in JSON)
curl -X POST http://127.0.0.1:17375/api/upload/prod \
  -H 'Content-Type: application/json' \
  -d '{"content":"<base64>","remote_path":"/opt/app.tar.gz","filename":"app.tar.gz"}'
# Response: {"ok":true,"name":"prod","size":12345,"remote":"/opt/app.tar.gz"}

Web UI download API:

# Download file (streaming binary response)
curl -o app.tar.gz 'http://127.0.0.1:17375/api/download/prod?path=/opt/app.tar.gz'

Config Hot Reload

The C daemon automatically detects config file changes via mtime (last-modified timestamp). No daemon restart needed — any changes to ~/.sshc/profiles.json take effect on the next request. This includes adding/removing servers, changing proxies, and updating allow/deny rules.

Architecture

sshc (bash) ──nc──> daemon.sock (Unix) / 127.0.0.1:{port} (Windows TCP)
                           │
                      sshc-daemon (C, fork/thread-per-request)
                           │
                      posix_spawnp/vfork+execvp("ssh") / CreateProcess + pipes
                           │
                      ControlMaster ──> Remote Server
                      (~/.sshc/mux/ssh-<name>, persist 300s)

Web UI (python3) ──socket──> daemon IPC ──> health/exec requests
         │
         └── profiles.json (read/write directly, atomic replace + chmod 600)

• Daemon overhead ~15ms, end-to-end latency ≈ raw SSH
• ControlMaster auto-warmup on first health check or exec
• Master socket persists 300s idle, auto-reconnect on failure
• Health checks: ensure_master + ssh exec "echo ok" — also serves as connection warmup
• Unix: AF_UNIX socket at ~/.sshc/daemon.sock, fork() per request, posix_spawnp for master, vfork for exec
• Windows: TCP localhost (port written to ~/.sshc/daemon.port), CreateThread per request, CreateProcess for all SSH calls
• Command validation: POSIX regex (Unix) / glob matching (Windows) evaluated in daemon before SSH execution
• SFTP: sftp -b - with ControlPath reuse for file transfer; tar pipe for directories
• Config hot reload: stat()-based mtime detection at start of each request handler, no polling loop
• Key upload: browser FileReader.readAsDataURL() → base64 → ~/.sshc/keys/<profile>/<filename> (chmod 600, basename-sanitized)
• Proxy: stored as raw ProxyCommand string, injected via -o ProxyCommand="..." into all SSH invocations

Platform Notes

Dependencies

Agent Workflow Guide

Adding a new server behind a proxy

# Via CLI
./sshc add hidden [email protected] -i ~/.ssh/id_rsa --proxy "nc -X 5 -x 127.0.0.1:1080 %h %p"

# Via REST API (when daemon+web are running)
curl -X POST http://127.0.0.1:17375/api/profiles \
  -H 'Content-Type: application/json' \
  -d '{"name":"hidden","host":"10.0.0.5","user":"root","key":"~/.ssh/id_rsa","proxy":"nc -X 5 -x 127.0.0.1:1080 %h %p"}'

Running commands on multiple servers in parallel

./sshc exec prod "uptime" &
./sshc exec staging "df -h" &
./sshc exec db "systemctl status postgresql" &
wait

Checking all server status

./sshc health          # all profiles
./sshc health prod     # single profile
./sshc profiles        # table format with status

Uploading and downloading files

# Upload
./sshc upload prod ./app.tar.gz /opt/app.tar.gz
./sshc upload prod ./my-project/ /opt/my-project/   # directory → tar pipe

# Download
./sshc download prod /var/log/syslog ./syslog
./sshc download prod /opt/data/ ./data-backup/

# Via Web UI: click "上传" / "下载" buttons in server list

Restricting commands with allow/deny patterns

# Add server with command safety
./sshc add safe-prod [email protected] -i ~/.ssh/id_rsa \
  --allow "^(ls|df|uptime|systemctl|apt|docker).*" \
  --deny ".*rm -rf.*|.*mkfs.*|.*dd if=.*"

# Update via REST API
curl -X PUT http://127.0.0.1:17375/api/profiles/safe-prod \
  -H 'Content-Type: application/json' \
  -d '{"allow":"^(ls|df|uptime|systemctl|apt|docker).*"}'

# Validation happens in daemon — bypassing impossible

Setting up via Web UI (when human needs visual management)

./sshc web
# Human opens http://127.0.0.1:17375
# - Drag key file onto drop zone
# - Fill host/user/port
# - Click "代理" in server list to configure proxy via modal
# - Click "测试" to verify connectivity

Troubleshooting

# Daemon not responding
./sshc daemon          # restart

# Master connection stale
./sshc reconnect prod  # force re-establish

# Check if daemon is alive
./sshc health > /dev/null 2>&1 && echo "alive" || echo "dead"