#! /bin/sh

set -e

### This script performs the passive side of a dynamic association.  It is
### intended to be set as the forced command in an `.ssh/authorized_keys'
### file.  Specifically, for each dynamic peer, add a line to
### `.ssh/authorized_keys' of the form
###
###	environment="TRIPE_USER=PEER" ssh-rsa ...
###
### There's an additional wrinkle.  Suppose that the passive TrIPE endpoint
### is behind a NAT, and the SSH gateway is on a different machine.  The
### gateway should have its own `tripe' user, and this script should again be
### its shell.  On the gateway, add a `.ssh/authorized_keys' entry
###
###	environment="TRIPE_USER=tripe@SERVER:PEER" ssh-rsa ...
###
### for the dynamic endpoint.  On the passive endpoint itself, you need an
### entry for the gateway's `tripe' user's key, with `TRIPE_GATEWAY' set to
### any value, like
###
###	environment="TRIPE_GATEWAY=t" ssh-rsa ...
###
### For backwards compatibility, it can also be set as the `tripe' user's
### shell, with the `[tripe@SERVER:]PEER' indicator set as the forced
### command.  If there are no forced command or `TRIPE_*' environment
### variables then it is assumed that a gateway is calling.

: ${prefix=@prefix@} ${exec_prefix=@exec_prefix@}
: ${bindir=@bindir@}
: ${TRIPEDIR=@configdir@} ${TRIPESOCK=@socketdir@/tripesock}
: ${tripectl=$bindir/tripectl}
export TRIPEDIR TRIPESOCK

## Make sure we're being called properly, and figure out the peer identity.
case "${TRIPE_USER+t},${TRIPE_GATEWAY+t},$#,$1" in
  t,,0,) set -- "$TRIPE_USER" ;;
  ,t,0,) set -- $SSH_ORIGINAL_COMMAND; unset SSH_ORIGINAL_COMMAND ;;
  ,,2,-c) ;;
  *)
    echo >&2 "usage: $0 -c [SERVER:]PEER [ACTION]"
    exit 1
    ;;
esac

## Examine the peer identifier and work out how to proceed.
case "$#,$1" in
  0,*) echo >&2 "missing peer identifier"; exit 1 ;;
  *:*) mode=proxy server=${1%:*} user=${1##*:} ;;
  *) mode=local user=$1 ;;
esac
shift

## Fetch the optional command from where SSH stashed it.
case "$#" in 0) set -- $SSH_ORIGINAL_COMMAND ;; esac
case "$#,$1" in
  0, | 1,hello) act=hello ;;
  1,goodbye) act=goodbye ;;
  *) echo >&2 "$0: unknown action spec \`$*'"; exit 1 ;;
esac

## Now actually do something.
case "$mode,$act" in
  proxy,*)
    exec ssh "$server" "$user" "$act"
    ;;
  local,hello)
    exec $tripectl SVCSUBMIT connect passive "$user"
    ;;
  local,goodbye)
    peer=$($tripectl SVCSUBMIT connect userpeer "$user")
    exec $tripectl KILL "$peer"
    ;;
  *)
    echo >&2 "$0: unknown mode/action $mode/$act"
    exit 1
    ;;
esac