ssh_connector

#!/bin/sh

# SSH Connector
# Detects if there is a direct connection to host and if not tries to use proxy.

# Usage:
# 1. place the file in ~/bin/ssh_connector
# 2. Edit your ~/.ssh/config and add:
# Host example.com
#   ProxyCommand ~/bin/ssh_connector %h %p

netcat=/bin/nc
timeout=4

desthost=$1
destport=$2

detect_proxy() {
  # TODO: use multiple proxies
  proxyhost=`echo ${http_proxy} | cut -d "/" -f 3 | cut -d ":" -f 1`
  proxyport=`echo ${http_proxy} | cut -d "/" -f 3 | cut -d ":" -f 2`
  proxymeth=`echo ${http_proxy} | cut -d ":" -f 1`
  [ "x${proxymeth}" = "xhttp"   ] && proxymeth=connect
  [ "x${proxymeth}" = "xsocks*" ] && proxymeth=5
  [ "x${proxymeth}" = "xsocks4" ] && proxymeth=4
  [ -n "$debug" ] && echo "Detected proxy:" >&2
  [ -n "$debug" ] && echo " - host: ${proxyhost}" >&2
  [ -n "$debug" ] && echo " - port: ${proxyport}" >&2
  [ -n "$debug" ] && echo " - method: ${proxymeth}" >&2
}

direct_connection() {
  if ${netcat} -w ${timeout} -z ${desthost} ${destport}
  then
    [ -n "$debug" ] && echo "Using direct connection." >&2
    return 0
  fi
    [ -n "$debug" ] && echo "Direct connection failed, trying proxy." >&2
  return 1
}

if direct_connection
then
  # use direct connection if possible (via netcat)
  exec ${netcat} ${desthost} ${destport}
else
  # use netcat with proxy when direct connection is not possible
  detect_proxy
  exec ${netcat} ${desthost} ${destport} -X ${proxymeth} -x ${proxyhost}:${proxyport}
fi